Rabbit Antithymocyte Globulin (Thymoglobulin Ò )

Transcription

1 REVIEW ARTICLE Drugs 2010; 70 (6): /10/ /$55.55/0 ª 2010 Adis Data Information BV. All rights reserved. Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 25 Years and New Frontiers in Solid Organ Transplantation and Haematology A. Osama Gaber, 1 Anthony P. Monaco, 2 James A. Russell, 3 Yvon Lebranchu 4 and Mohamad Mohty 5 1 Department of Surgery, The Methodist Hospital, Houston, Texas, USA 2 Department of Transplantation, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA 3 Department of Medicine and Oncology, Tom Baker Cancer Centre, Calgary, Alberta, Canada 4 Service de Néphrologie et d Immunologie Clinique, CHU de Tours, Tours, France 5 Service d Hématologie Clinique, CHU Hôtel Dieu, Université de Nantes, Nantes, France Contents Abstract History of Antithymocyte Globulins Clinical Pharmacology of Rabbit Antithymocyte Globulin (ratg) History of ratg in Solid Organ Transplantation (SOT) Treatment of Acute Rejection Induction of Immunosuppression ratg in Corticosteroid-Minimization Regimens ratg in Calcineurin Inhibitor-Minimization Regimens Refining ratg Dosing Regimens in Kidney Transplantation Safety of ratg Summary of ratg in SOT History of ratg in Haematopoietic Stem Cell Transplantation (HSCT) ratg in Myeloablative Conditioning Regimens ratg in Non-Myeloablative or Reduced-Intensity Conditioning Regimens ratg and Total Lymphoid Irradiation Conditioning Refining ratg Dosage Regimens in HSCT History of ratg for Immunosuppressive Treatment of Immune-Mediated Bone Marrow Failure What Has Been Learned During the Past 25 Years? Future of ratg Conclusions Abstract The more than 25 years of clinical experience with rabbit antithymocyte globulin (ratg), specifically Thymoglobulin Ò, has transformed immunosuppression in solid organ transplantation and haematology. The utility of ratg has evolved from the treatment of allograft rejection and graft-versushost disease to the prevention of various complications that limit the success of solid organ and stem cell transplantation. Today, ratg is being successfully incorporated into novel therapeutic regimens that seek to reduce overall

2 692 Gaber et al. toxicity and improve long-term outcomes. Clinical trials have demonstrated the efficacy and safety of ratg in recipients of various types of solid organ allografts, recipients of allogeneic stem cell transplants who are conditioned with both conventional and nonconventional regimens, and patients with aplastic anaemia. Over time, clinicians have learnt how to better balance the benefits and risks associated with ratg. Advances in the understanding of the multifaceted mechanism of action will guide research into new therapeutic areas and future applications. The global clinical experience of rabbit antithymocyte globulin (ratg), specifically Thymoglobulin Ò (Genzyme Corporation, Cambridge, MA, USA), began more than 25 years ago and today extends across various therapeutic areas. The clinical efficacy, safety and wide-ranging effects of ratg on the immune system have driven its clinical development and approval for organ transplant and haematology indications in more than 50 countries throughout the world. ratg was first approved in France in 1984 for the treatment of acute rejection in renal and heart transplantation, acute graft-versus-host disease (GVHD) and severe aplastic anaemia. Subsequently, regulatory approvals were granted in many other countries, including the US, Canada and the UK. Over time, clinical experience with ratg has grown, and much has been learnt regarding its diverse mechanisms of action, therapeutic potential and long-term safety. This paper reviews the evolution of ratg (Thymoglobulin Ò ) in clinical immunosuppression, its therapeutic applications and future directions. A review of the literature was conducted by searching PubMed and Ovid databases for the keywords Thymoglobulin, anti-thymocyte globulin and ATG. Well designed clinical studies reporting the efficacy and/or safety of ratg therapy in the areas of solid organ transplantation (SOT) [kidney, liver, pancreas, heart and lung], allogeneic haematopoietic stem cell transplantation (HSCT) and aplastic anaemia were analysed. Key therapeutic areas of interest included prevention of rejection in organ transplantation and prevention of GVHD. There was no limit to the dates searched, but only articles in English were retrieved and reviewed. The published medical literature was also searched for papers of historical significance related to the clinical development of antithymocyte globulin (ATG). Abstracts, posters and online sources (e.g. were researched for information about investigational uses of ratg and novel applications. 1. History of Antithymocyte Globulins The lymphocyte-depleting activity of heterologous antilymphocyte serum (ALS) was first described by Metchnikoff in [1] Immunosuppressive activity would be validated more than 50 years later when, in 1963, Woodruff and Anderson [2] discovered that rabbit-derived antirat ALS reduced lymphocyte counts and prolonged skin allograft survival in rats. Soon after, Monaco and colleagues [3] intensified the interest in the clinical application of ALS after experiments in mice demonstrated that ALS suppressed antibody response and graft rejection, consistent with central failure of the immune response. These studies and their finding that polyclonal anti-canine lymphocyte serum dramatically prolonged whole organ renal allografts [4] set the stage for clinical investigations. Experimentation with different ALS preparations followed. Antilymphocyte globulin (ALG) generally refers to any ALS generated against various types of human lymphocytes. [5] The term ATG usually refers to ALG generated specifically against human thymocytes. Monaco and colleagues [6] were the first to demonstrate the immunosuppressive activity of ALG in humans. In volunteers, purified rabbit ALG produced lymphopenia, suppressed delayed hypersensitivity reactions to intradermal antigens and delayed rejection of skin allografts. In 1967, just 5 years

3 Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 693 after the first deceased donor kidney transplantation was deemed successful, [7] the initial clinical experience with ALG in human kidney transplantation was reported by Starzl et al. [8] Eight patients with endstage renal failure began treatment with equine ALG 5 or 6 days preoperatively (one patient began 35 days preoperatively), and then continued postoperative ALG treatment for an indefinite period in combination with azathioprine and, if needed, prednisone. All patients survived and had excellent renal function up to 14 weeks postoperatively. A few years later, Mathe and colleagues [9] evaluated immunosuppression with equine ALS alone as an alternative to total body irradiation (TBI) or cyclophosphamide conditioning before allogeneic bone marrow transplantation (BMT) for patients with leukaemia and other haematological disorders. Although in this early work only seven of 16 patients experienced successful haematopoietic engraftment, none of the patients developed acute GVHD. Based on these ground-breaking studies, the expansion of biological drug therapy with ATG would soon begin. Throughout the late 1960s and early 1970s, various ALG or ATG preparations with different animal sources, potencies, doses and routes of administration were studied at several institutions. Investigators explored these preparations for the treatment [10-12] and prevention [13,14] of renal allograft rejection, the treatment [15,16] and prevention [17,18] of GVHD, bone marrow transplant conditioning, [9] and the treatment of aplastic anaemia [19,20] and other forms of bone marrow failure such as pure red cell aplasia. [21,22] In the US, Minnesota ALG (i.e. MALG), an equine antibody, was used as induction therapy in renal transplantation as early as [23,24] During the 1980s, the Upjohn Company s equine ATG (eatg) product, ATGAM Ò (Pfizer Inc., New York, NY, USA), became the first commercially available ATG in Europe and the US. Thymoglobulin Ò, the first commercial ratg, became available in Europe in 1984 and in the US in Later, an ATG preparation generated from rabbits immunized with cultured Jurkat cells (ATG-Fresenius S Ò, Fresenius Biotech, Munich, Germany) was introduced in Europe. Although most of these products are currently available, ratg as Thymoglobulin Ò remains the most commonly used ATG preparation in clinical practice throughout the US and Europe. This is the result of reports from clinicians throughout the world that reinforced the clinical efficacy and safety of this ratg in SOT, [25,26] HSCT [27] and aplastic anaemia. [28] 2. Clinical Pharmacology of Rabbit Antithymocyte Globulin (ratg) ratg is the purified IgG fraction of sera from rabbits that are immunized with human thymocytes. [29] ratg is a polyclonal antibody that contains a wide variety of antibody specificities: immune response antigens, adhesion and cell trafficking molecules, and molecules involved in heterogeneous pathways (table I). [30-34] Although ratg has been shown to deplete a variety of immune cells, the primary mechanism of action is T-cell depletion. [32,33] ratg also modulates cellsurface expression of adhesion molecules and chemokine receptors, thus interfering with leukocyte-endothelial interactions that play a role in ischaemia/reperfusion injury (IRI). [34] Readers Table I. Rabbit antithymocyte globulin antibody specificities [30-34] Immune response antigens Adhesion and cell trafficking Heterogeneous pathways CD1, a CD3/TCR, CD4, CD6, CD7, CD8, CD16, CD19, CD20, a CD25, a CD28, a CD30, CD32, CD40, CD80, a CD86, CD152 (CTLA-4), HLA class I, HLA class II DR, b2-m CD6, CD11a/CD18 (LFA-1), CD44, CD49/CD29 (VLA-4), CD50 (ICAM-3), CD51/61, CD54 (ICAM-1), CD56, a CD58 (LFA-3), LPAM-1 (a4b7), CD102 (ICAM-2), CD195 (CCR5), CD197 (CCR7), CD184 (CXCR4) CD2, CD5, CD11b, CD29, CD38, CD40, CD45, CD52, CD95, CD128, CD138 a Results differ between laboratories because of inconsistencies in monoclonal competition assays. CCR/CXCR = chemokine receptor; CTLA = cytotoxic T lymphocyte antigen; HLA = human leukocyte antigen; ICAM = intercellular adhesion molecule; LFA = lymphocyte function-associated antigen; LPAM = lymphocyte Peyer s patch adhesion molecule; VLA = very late antigen.

4 694 Gaber et al. may refer to recently published reviews that address the mechanisms of action in more detail. [32,33] 3. History of ratg in Solid Organ Transplantation (SOT) 3.1 Treatment of Acute Rejection The first randomized, double-blind, multicentre, comparative clinical trial with ratg was conducted by Gaber and colleagues [35] in the setting of acute rejection after kidney transplantation. Patients with biopsy-proven acute rejection received either ratg (1.5 mg/kg/day) or eatg (15 mg/kg/day) for 7 14 days. The rejection reversal rate was significantly higher in patients treated with ratg than with eatg (88% vs 76%; p= 0.027). In addition, fewer ratg-treated patients experienced recurrent rejection episodes in the 3 months after therapy. Although the depletion of T cells was more profound and more prolonged with ratg than with eatg, the overall incidences of infectious complications and malignancies were similar between groups. Graft survival at 1 year after therapy was also similar. The findings from this pivotal study supported the US approval of ratg in A randomized, single-centre clinical trial compared ratg with muromonab-cd3 (OKT3) for the treatment of corticosteroid-resistant acute rejection after kidney transplantation. [36] Patients were treated with a 10-day course of either ratg (mean 0.75 mg/kg/day) or muromonab-cd3 (mean 0.05 mg/kg/day). Although not statistically significant, reversal of rejection results favoured ratg over muromonab-cd3 (overall graft failures 13% vs 21%, respectively), as did recurrent rejection rates within 3 months of treatment (28% vs 38%, respectively). One-year graft survivals and incidences of infection and malignancy were similar between groups. ratg was better tolerated than muromonab-cd3. More patients experienced fever and first-dose syndrome, also known as cytokine release syndrome (i.e. fever, chills, headache, myalgia and tremor), in the muromonab-cd3 group than in the ratg group (52% vs 6%; p= 0.001). Other nonrandomized clinical experiences with ratg also showed that it was effective for treating episodes of acute rejection after kidney transplantation. [37-39] Over-immunosuppression and infection were a concern at the time. In some studies, ratg was given in fixed daily dosages of 2.5 5mg/kg/day for days (total cumulative doses of mg/kg) [37,39] and anti-infective prophylaxis was not usually given. Subsequently, compassionate use data from the US showed that ratg (mean 1.5 mg/kg/day for nine doses) was highly effective (85%) for reversing acute rejection that was resistant to other therapies. [40] Notably, 90% of patients had no infectious complications 3 months after therapy. Clinical studies demonstrated successful treatment of acute rejection with the use of ratg, and some studies showed significant differences in efficacy and tolerability between ratg and other antibodies. [35,36] Better precautions against infection and greater international clinical experience paved the way for additional applications. 3.2 Induction of Immunosuppression While the safety and efficacy of ratg for treating rejection were being established, clinicians were also using ratg for the prevention of rejection or as induction therapy. Evidence was accumulating that induction therapy with ratg could prevent or delay early acute rejection, thus potentially improving long-term outcomes. Studies were conducted first in kidney transplantation, [41] then in pancreas, [42,43] liver, [44] heart [45,46] and lung [47] transplantation (table II). [25,26,43,48-55] Brennan and colleagues [25] conducted the first large randomized double-blind trial of ratg induction therapy in kidney transplant recipients. The trial compared ratg (1.5 mg/kg/day) with eatg (15 mg/kg/day); both drugs were administered intraoperatively and then daily for at least 6 days. Most patients received triple-drug maintenance therapy (ciclosporin, azathioprine and prednisone), and oral ganciclovir was given prophylactically when either the donor or recipient tested positive for cytomegalovirus (CMV). ratg was significantly more effective than eatg in preventing rejection. The incidence of

5 Table II. Prospective (p), randomized (r), comparative studies of rabbit antithymocyte globulin (ratg) induction therapy in solid organ transplantation Study (year) Study design No. of Drug and dosage regimen Efficacy (%) Safety and additional comments patients patient survival graft survival incidence of AR Kidney transplantation Brennan et al. [25] (1999) Hardinger et al. [48] (2004) Hardinger et al. [49] (2008) Brennan et al. [26] (2006) Ciancio et al. [50] (2008) p, r, db, sc (mean followup, 17.2 mo) 5 y follow-up of Brennan et al. [25] 10 y follow-up of Brennan et al. [25] p, r, ol, mc p, r, ol (median followup, 37 mo) ratg 1.5 mg/kg od 7d a,b 98 * (1 y) eatg 15 mg/kg od 7d a,b 96 (1 y) 98 ** (1 y) 83 (1 y) ~88 (5 y) c* 77 (5 y) - ~72 (5 y) c 54 (5 y) 75 * * 50 4 ** (1 y) 25 (1 y) 8(5y) (5 y) ratg 1.5 mg/kg od 5d a,d 16 ** BAS 20 mg on d 0 and 4 a,d 26 ratg 1 mg/kg 1 postop, then qd 6 doses e ATB 0.3 mg/kg on d 0 and 4 f DAC 1 mg/kg 1 dose preop, then qow 4 doses e 85 z z z EFS at 1 y: 94% (ratg) vs 63% (eatg) [p = ] No difference between groups in the incidence of infections CMV disease at 1 y: 12.5% (ratg) vs 33.3% (eatg) [p = 0.056] EFS at 5 y: 73% (ratg) vs 33% (eatg) [p < 0.001] CMV disease at 5 y: 13% (ratg) vs 33% (eatg) [p = 0.056] Malignancy at 5 y: 6% (ratg) vs 21% (eatg) [p = 0.01] EFS at 10 y: 48% (ratg) vs 29% (eatg) [p = 0.011] CMV disease at 10 y: 13% (ratg) vs 33% (eatg) [p = 0.056] Malignancy at 10 y: 8% (ratg) vs 21% (eatg) [p = NS] Composite endpoint (AR, DGF, graft loss or death): 50.4% (ratg) vs 56.2% (BAS) [p = 0.34] Incidences of DGF, patient death and graft loss were similar in both groups Incidence of infection: 85.8% (ratg) vs 75.2% (BAS) [p = 0.03] CMV disease: 7.8% (ratg) vs 17.5% (BAS) [p = 0.02] Incidence of chronic allograft nephropathy: 14% in the ratg group, 37% in the ATB group and 11% in the DAC group (p = for ATB vs ratg and DAC groups combined) Death-censored freedom from graft failure was significantly worse in the ATB group (p = 0.01 vs ratg and DAC group combined) Continued next page Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 695

6 Table II. Contd Study (year) Study design No. of Drug and dosage regimen Efficacy (%) Safety and additional comments patients patient survival graft survival incidence of AR Noel et al. [51] (2009) Goggins et al. [52] (2003) Stevens et al. [53] (2008) p, r, ol p, r, ol (mean follow-up, 15.1 mo) p, r, ol (mean follow-up, 23.3 mo) c Pancreas transplantation Cantarovich et al. [43] (1998) p, r, ol, sc 25 SPKT 25 SPKT Heart transplantation Schnetzler et al. [54] (2002) Bonaros et al. [55] (2006) a b p, r, ol, sc p, r, ol The first dose was administered intraoperatively. ratg 1.25 mg/kg/d 7d g DAC 1 mg/kg 1 dose preop, then qow 4 doses g ratg 1 mg/kg od 3 6 d h 1st dose intraop 1st dose postop ratg 6 mg/kg 1 intraop i ratg 1.5 mg/kg 1 intraop then qd 3 doses i ratg 1.5 mg/kg/d 10 d + delayed CNI initiation j No ratg + immediate CNI initiation j 95.6 (1 y) * 96.5 (1 y) 100 (6 mo) * 100 (6 mo) 100 (3 y) c* 83 (3 y) 97 (1 y) c* 100 (1 y) c ratg 2.5 mg/kg/d 5d k 84.6 (1 y) * ATG-F 3 mg/kg/d l 5d k 87.5 (1 y) ratg 2.5 mg/kg/d 8d k 70 (10 y) * BT563/BB10 10 mg/d 8d k 50 (10 y) 82.3 (1 y) * 86.0 (1 y) 100 (6 mo) * 100 (6 mo) 100 (3 y) c* 97 (3 y) 75 (Pa 1 y) c* 75 (Pa 1 y) c 15.0 (1 y) ** 27.2 (1 y) 4 * 16 8(1y) * 12 (1 y) 36 (K 1 y) (K 1 y) Mean no. of episodes per patient: 2.46 * (ratg) vs 2.63 (ATG-F) 10 (10 y) ** 55 (10 y) Incidence of DGF: 31.5% in the ratg group vs 44.6% in the DAC group (p = 0.044) Incidence of bacterial infections was 46% in both groups Number of bacterial infections per patient was significantly higher in the ratg group (2.5) than in the DAC group (1.8) [p = 0.014] Incidence of DGF: 14.8% (intraop) vs 35.5% (postop) [p < 0.05] S CR level on d 14: 1.81 mg/dl (intraop) vs 2.81 mg/dl (postop) [p = 0.04] Mean length of stay: 7.5 d (intraop) vs 11 d (postop) [p = 0.02] CMV infection (6 mo): 3.7% (intraop) vs 6.5% (postop) [p = NS] Incidence of DGF: 10% (single dose) vs 4% (divided dose) [p = 0.2] Recovery of renal function from post-transplantation d1 4 was significantly better in the single-dose group than in the divided-dose group (p = 0.02) Incidence of leukopenia: 48% (ratg) vs 12% -- (no ratg) Incidence of infection: 58% * (ratg) vs 75% (ATG-F) FFAR (1 y): 90% (ratg) vs 45% -- (BT563/BB10) Freedom from allograft vasculopathy: 80% (ratg) vs 60% (BT563/BB10) [p = 0.031] Maintenance immunosuppression: CsA (modified) + AZA + corticosteroid; TAC was used in place of CsA in patients who had a contraindication to or could not tolerate CsA; MMF was used in place of AZA in patients receiving a second transplant, those with immunological causes for endstage renal disease, and those requiring allopurinol therapy. Continued next page 696 Gaber et al.

7 Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 697 Table II. Contd c Values estimated from graph. d Maintenance immunosuppression: CsA (modified) + MMF + corticosteroid. e Maintenance immunosuppression: TAC (target trough, 8 10 ng/ml) + MMF 1 g bid + corticosteroid. f Maintenance immunosuppression: TAC (target trough, 4 7ng/mL at 1 mo and 4 6ng/mL thereafter) + MMF 500 mg bid. g Maintenance immunosuppression: TAC + MMF + corticosteroid; TAC was initiated preop in the DAC group but was delayed up to 5 d in the ratg group. h Maintenance immunosuppression: CsA or TAC + MMF + corticosteroid. i Maintenance immunosuppression: TAC + SRL (initiated when S CR <3.0 mg/dl); MMF was used in place of SRL in patients with DGF or obesity; MMF was replaced with low-dose SRL when S CR declined to <3.0 mg/dl or at 3 4 wk after transplantation in obese patients. j Maintenance immunosuppression: CsA + AZA + corticosteroid. Patients who did not receive ratg received CsA immediately after surgery. k Maintenance immunosuppression therapy: CsA + AZA + corticosteroid. l Dosage of ATG-F increased slightly by d 5; the dosage was increased in patients who had a total lymphocyte count >300/mm 3. AR = acute rejection; ATB = alemtuzumab; ATG-F = antithymocyte globulin-fresenius; AZA = azathioprine; BAS = basiliximab; bid = twice daily; CMV = cytomegalovirus; CNI = calcineurin inhibitor; CsA = ciclosporin; DAC = daclizumab; db = double-blind; DGF = delayed graft function; eatg = equine antithymocyte globulin; EFS = event-free survival; FFAR = freedom from allograft rejection; intraop = intraoperatively; K = kidney; mc = multicentre; MMF = mycophenolate mofetil; NS = not significant; od = once daily; ol = open-label; Pa = pancreas; postop = postoperatively; preop = preoperatively; qd = every other day; qow = every other week; sc = single-centre; S CR = serum creatinine; SPKT = simultaneous pancreas-kidney transplantation; SRL = sirolimus; TAC = tacrolimus; * p = NS, ** p < 0.05 vs comparator; - p = 0.046, -- p 0.01 vs comparator; z p = NS for simultaneous comparison of three groups. acute rejection at 1 year was 4% in the ratg group and 25% in the eatg group (p = 0.014). Event-free survival (composite endpoint of freedom from death, graft loss or rejection) at 1 year was also superior in the ratg group (94% vs 63%; p= ). Only one patient in the study experienced delayed graft function (DGF). As expected, lymphocyte counts were depressed to a greater degree for a longer period of time with ratg. Unexpectedly, patients in the ratg group had a lower incidence of CMV disease at 6 months (10.4% vs 33.3%; p = 0.025). Patient survival rates did not differ between treatment groups and no patient in either group developed post-transplantation lymphoproliferative disorder (PTLD). After 5 and 10 years of follow-up, event-free survival remained significantly higher in the ratg group than in the eatg group (73% vs 33% [p < 0.001] and 48% vs 29% [p = 0.011], respectively). [48,49] Through 10 years after transplantation, the incidences of CMV disease and PTLD were numerically lower in the ratg group (13% and 0%, respectively) than in the eatg group (33% and 8%, respectively). In the past, many transplant centres reserved induction therapy for recipients of deceased donor kidneys with DGF or for those patients at high risk for DGF and acute rejection. Early preclinical and clinical data suggested that ratg may mitigate DGF not only because of its T celldepleting properties, but also because it plays a role in preventing IRI via down-modulation of adhesion molecules and inhibition of chemokine receptors, [34] thereby reducing leukocyte adhesion to endothelial cells. [56,57] In a study of deceased donor kidney transplant recipients, intraoperative administration of ratg was associated with a lower incidence of DGF than was postoperative administration (14.8% vs 35.5%; p< 0.05). [52] Intraoperative ratg also resulted in better early renal function and reduced length of hospitalization after transplantation. In a small study of liver transplant recipients, ratg induction appeared to protect liver allografts from IRI. [58] In comparison with no induction therapy, ratg treatment improved early graft function and reduced the duration of hospitalization.

8 698 Gaber et al. ratg was also compared with other induction modalities, including non-t cell-depleting monoclonal antibody therapy, e.g. basiliximab, which binds to the interleukin (IL)-2 receptor on activated T cells. Results from two studies that compared ratg with basiliximab showed that both treatments were effective in immunological low-risk patients, [59,60] but results from several other retrospective studies have suggested that basiliximab might be less effective than ratg in this population. [61-64] In retrospective [65-67] and prospective [68] studies that stratified patients on the basis of risk profile, rates of acute rejection were lower among high-risk patients who received ratg than in low-risk patients who received basiliximab. A prospective randomized trial in deceased donor kidney transplant recipients who were considered to be at high risk for acute rejection or DGF, on the basis of cold ischaemia time and other donor and recipient factors, directly compared ratg (1.5 mg/kg intraoperatively and on days 1 4) with basiliximab (20 mg intraoperatively and on day 4). [26] All patients received ciclosporin, mycophenolate mofetil (MMF) and prednisone for maintenance therapy, and when either the donor or recipient was CMVpositive, patients received ganciclovir for CMV prophylaxis. At 1 year, the composite primary endpoint of acute rejection, DGF, graft loss or death was equivalent in both groups. However, the rate of acute rejection was significantly lower in the ratg group (16% vs 26%;p= 0.02). There were also fewer severe rejection episodes and a lower rate of CMV disease at 1 year in patients who received ratg. Long-term outcomes from this study were recently analysed by matching all 183 patients who were enrolled in the US with their Organ Procurement and Transplantation Network (OPTN) registry records. [69] Through 5 years, a composite endpoint of acute rejection, graft loss or death was lower in the ratg group than in the basiliximab group (37% vs 51%; p= 0.04). The rate of acute rejection also remained lower among ratg-treated patients in this US cohort (15% vs 27%; p = 0.03). The lower incidence of CMV disease in the ratg group was maintained through 5 years (7% vs 17%; p= 0.02). There was no difference between groups in the incidence of malignancy at 1 and 5 years. Evidence has mounted that supports the improved efficacy of ratg over basiliximab for preventing acute rejection in deceased donor kidney transplant recipients at high risk for DGF and acute rejection. [26,65] Now there is also evidence from a randomized comparative trial of ratg and daclizumab, another nondepleting anti-il-2 monoclonal antibody, in high-immunological-risk kidney transplant recipients. [51] In this study, high risk was defined as having a current panel reactive antibody (PRA) level 30%,a peak PRA level 50%, or one to three previous kidney transplants. For maintenance immunosuppression, patients received tacrolimus, MMF and corticosteroids. ratg (1.25 mg/kg/day for 7 days) was superior to daclizumab (1 mg/kg on days 0, 14, 28, 42 and 56) for reducing the incidence of acute rejection (15.0% vs 27.2%; p = 0.016) and the incidence of DGF (31.5% vs 44.6%; p= 0.044). Although both drugs resulted in similar patient and graft survival rates at 1 year, the relative benefit of ratg in this highrisk population was clearly demonstrated. Historically, ratg has been viewed as the induction agent of choice in patients at high immunological risk. [70] An analysis of United Network for Organ Sharing (UNOS) data found that ratg was the antibody induction agent most likely to be chosen for patients who were sensitized, were undergoing repeat transplantation or experienced DGF. [71] The conventional belief that recipients of expanded criteria donor (ECD) kidneys derive a greater benefit from ratg than do recipients of standard criteria donor (SCD) kidneys was not validated in a recent analysis. Among recipients of SCD kidneys or kidneys from normotensive donors, rejection occurred significantly less frequently in patients who were treated with ratg than in patients who were treated with basiliximab. [72] Among recipients of ECD kidneys, rejection occurred with similar frequency. Contrary to popular opinion, ratg may actually be most beneficial in recipients of SCD kidneys. Over the years, the use of ratg induction therapy has expanded from predominantly highrisk deceased donor kidney transplant recipients

9 Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 699 to also include living donor kidney transplant recipients. In 2006, approximately 36% of living donor kidney transplant recipients received ratg induction therapy. [73] The TAILOR (Thymoglobulin Ò Antibody Immunosuppression in Living Donor Recipients) registry provides evidence that ratg is safe and effective in living donor kidney transplantation. [74] After 1 year of follow-up, excellent clinical outcomes were observed among the 2243 patients studied, the majority of whom were maintained on triple-drug therapy. The low incidences of adverse events and infections further reinforce the safety profile of ratg in living donor kidney transplant recipients. At one transplant centre, the introduction of ratg induction therapy in living unrelated donor kidney transplant recipients resulted in significantly fewer episodes of acute rejection than did the use of no induction (2% vs 48%; p < 0.001), without an increase in the incidence of CMV disease, malignancy or mortality at 1 year. [75] Ten years of clinical experience with ratg induction therapy in heart transplantation was retrospectively analysed by researchers at the Montreal Heart Institute (Montreal, QC, Canada). [45] A previous protocol consisting of no induction, ciclosporin, azathioprine and corticosteroids was compared with ratg induction (125 mg/day for 3 days), azathioprine or MMF, and corticosteroids. Ciclosporin was initiated on the day of transplantation in the former protocol, whereas ciclosporin was initiated postoperatively on day 2 to day 5 in the ratg protocol. The patient survival rates at 5 and 10 years were comparable, but the rate of freedom from acute rejection at 1 year was significantly higher among patients who received the ratg protocol (43% vs 30%; p = 0.03). The rates of freedom from infection and freedom from cancer were similar, indicating that the reduction in rejection was not accompanied by any rise in infection or cancer. An interesting finding was that freedom from graft coronary artery disease was higher in patients treated with the ratg protocol than in patients treated with the earlier regimen, at both 5 and 10 years (68% and 50% vs 58% and 30%, respectively; p = 0.1). ratg induction therapy has evolved from specific use in high-risk recipients to routine use in SOT across the spectrum of immunological risk. Currently, ratg is the antibody most commonly used for induction therapy in kidney, pancreas, liver and heart transplantation. [76] 3.3 ratg in Corticosteroid-Minimization Regimens Even though corticosteroids have long been a mainstay of immunosuppression in SOT, they are associated with long-term adverse effects such as diabetes mellitus, hypertension, hyperlipidaemia, weight gain, osteoporosis and cataracts. [77] As a result, clinicians have sought effective ways to minimize these complications to improve longterm patient well-being. Studies conducted in the early era of immunosuppression that examined corticosteroid discontinuation in the late posttransplantation period had variable results. A large Canadian, multicentre, randomized double-blind study of corticosteroid withdrawal 3 months after transplantation with ciclosporin monotherapy revealed an unacceptably high rate of graft loss at 5 years. [78] Subsequently, the use of ratg induction therapy and the addition of MMF to ciclosporin maintenance therapy, with corticosteroid withdrawal at 3 months, produced very good outcomes at 1 year. [79] Over time, research efforts continued, and protocols focused on early corticosteroid withdrawal (usually within the first week after transplantation) with the use of antibody induction and newer immunosuppressants. ratg has been incorporated into many corticosteroid-minimization maintenance strategies in kidney, pancreas, liver and heart transplantation, with excellent outcomes (table III). [80-91] Successful corticosteroid discontinuation (after 6 days) in combination with ratg induction therapy was initially reported in a study of simultaneous pancreas-kidney transplant recipients. [86] Patient, kidney and pancreas survivals at 1 year were all 100%. In an historical control group treated with long-term corticosteroids, patient, kidney and pancreas survivals were 96.5%, 93.0% and 91.9%, respectively. The feasibility of rapid

10 Table III. Selected studies of rabbit antithymocyte globulin (ratg) in corticosteroid-minimization immunosuppression regimens Study (year) Study design No. of patients Drug and dosage regimen Efficacy (%) Safety and additional comments Kidney transplantation Birkeland [80] (2001) p, sc (4.5 y of follow-up) Khwaja et al. [81] (2004) Matas et al. [82] (2005) Kandaswamy et al. [83] (2005) Woodle et al. [84] (2008) Retro, sc Retro, sc (5 y of follow-up) p, r, sc (mean follow-up, 16 mo) patient survival graft survival incidence of AR 100 ratg 1.25 mg/kg od 10 d a (4 y) 13 Infections: CMV infection (n = 36), CMV disease (n = 0), EBV reactivation (n = 18) Malignancy: nonmelanoma skin cancer (n = 4), lymphoma (n = 0) 79 (high immuno risk) ratg 1.25 mg/kg od 5d b,c 95 (3 y) d 94 (3 y) d Actuarial AR-free rate at 3 y: 95% 589 ratg mg/kg od 5d b,c 97 (1 y) d 91 (5 y) d 95 (1 y) d p, r, db, mc ratg mg/kg od 5d b CsA + MMF Low TAC + high SRL High TAC + low SRL ratg 1.5 mg/kg 4 doses or BAS or DAC + ESW e,f ratg 1.5 mg/kg 4 doses or BAS or DAC + long-term corticosteroid e 98 (1 y) * 97 (1 y) * 97 (1 y) * Death-censored graft survival at 1 and 84 (5 y) d 5y:98% and 92%, respectively Compared with historical controls who did not discontinue corticosteroids, study patients had significantly lower rates of cataracts (p < 0.001), diabetes mellitus (p < 0.001), avascular necrosis (p 0.001) and fractures (p = 0.04) 96 (1 y) * 96 (1 y) * 94 (1 y) * 7(1y) 7(1y) 5(1y) 17.8 (5 y) ** 10.8 (5 y) There were no significant differences between groups in AR-free survival, chronic rejection-free survival or mean serum creatinine levels at 24 mo Wound complications were significantly more frequent in the SRL groups than in the MMF group (p = 0.02) Composite endpoint of death, graft loss or moderate/severe AR (primary endpoint): 15.7% in the ESW group vs 14.4% in the long-term corticosteroid group (p = 0.691) The proportions of patients who required initiation and maintenance of lipid-lowering therapy, and the Continued next page 700 Gaber et al.

11 Table III. Contd Study (year) Study design No. of patients Drug and dosage regimen Efficacy (%) Safety and additional comments Woodle et al. [85] (2009) Pancreas transplantation Kaufman et al. [86] p, sc (2002) Freise et al. [87] (2004) Fridell et al. [88] (2006) p, r, ol, mc 103 LDKT 48 LDKT 20 SPKT 20 SPKT 86 HxCx ratg 1.25 or 1.5 mg/kg 4 doses + ESW e,g,h Long-term corticosteroid e ratg 1.0 mg/kg intraop and on d 1, then qd 7d+ ESW h protocol: TAC + MMF TAC + SRL Induction + MMF + TAC + corticosteroids patient survival 100 (1 y) d* 100 (1 y) d 96 (1 y) d graft survival 100 (Pa 1 y) d* 100 (Pa 1 y) d 92 (Pa 1 y) d incidence of AR 13.9 (1 y) * 19.4 (1 y) Retro, sc 44 SPKT ratg 1.5 mg/kg 1 intraop, then 1mg/kg/d 6d i (Pa 6 mo); 5 (K 6 mo) Retro, sc 29 PAKT ratg 1 mg/kg/dose 5 doses j Long-term corticosteroid ESW 100 (1 y) * (1 y) * 89 proportion of patients with new-onset diabetes who required insulin, were significantly higher in the long-term corticosteroid group than in the ESW group (p < 0.05) Composite endpoint of freedom from biopsy-proven AR, death and graft loss at 1 y: 84.4% in the ESW group vs 74.4% in the long-term corticosteroid group (p = NS) Total cholesterol level at 12 mo was significantly lower in the ESW group than in the long-term corticosteroid group (159.7 vs mg/dl) [p = 0.012]. There were trends toward lower triglycerides and less weight gain in the ESW group Rejection-free survival: 97.5% in the ESW groups vs 80.2% in the historical control group (p = 0.034) 1 case of PTLD, 4 cases of CMV/polyoma virus infection Incidence of infectious complications: 40% (chronic corticosteroid) vs 39% (ESW) [p = 0.77] Continued next page Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 701

12 Table III. Contd Study (year) Study design No. of patients Drug and dosage regimen Efficacy (%) Safety and additional comments Liver transplantation Eason et al. [89] (2001) Eason et al. [90] (2003) Heart transplantation Yamani et al. [91] (2008) p, r, sc p, r, sc patient survival ratg k 1.5 mg/kg/dose 2 doses e 91 No ratg + MP l 91 ratg k 1.5 mg/kg/dose 2 doses e No ratg + MP l p, r, ol, sc 16 ratg 1.5 mg/kg/d 1, then 0.9mg/kg/d 5d+ corticosteroid avoidance e 85/82 (1 y/2y) * 85/83 (1 y/2y) graft survival (1 y) * 80 (1 y) incidence of AR 20 * * 31 Incidence of CMV and incidence of recurrent HCV: 8.8% vs 20.6% * and 50% vs 71% * in ratg and no ratg groups, respectively Incidence of bacterial/fungal complications requiring hospitalization: 22% (ratg) vs 25% * (no ratg) Incidence of CMV: 5% (ratg) vs 23% - (no ratg) 50 (1 y) * ratg patients had significant improvements in muscle strength and had less bone loss 16 ratg 1.5mg/kg intraop + long-term 69 (1 y) corticosteroid e a Maintenance immunosuppression: CsA + MMF; no corticosteroids were administered. b The first dose was administered intraoperatively; corticosteroids were discontinued on postoperative d 6. c Maintenance immunosuppression: CsA + MMF. d Actuarial results. e Maintenance immunosuppression: TAC + MMF. f Corticosteroids discontinued on postoperative d 8. g Patients weighing 100 kg received a total ratg dose of 6 mg/kg divided over 4 d, and patients weighing >100 kg received 5 mg/kg divided over 4 d. h Corticosteroids discontinued on postoperative d 7. i Maintenance immunosuppression included MMF + TAC + SRL; corticosteroid was utilized during ratg treatment and was discontinued 1 wk postoperatively. j Maintenance immunosuppression included TAC + SRL; MMF was added to the ESW group to reduce the dosages of the other medications. k Patients in the ratg group received one dose in the anhepatic phase and one dose postoperatively. l Patients in the control group were given 1000 mg MP in the anhepatic phase, and the corticosteroid was gradually tapered. AR = acute rejection; BAS = basiliximab; CMV = cytomegalovirus; CsA = ciclosporin; DAC = daclizumab; db = double-blind;ebv = Epstein-Barr virus; ESW = early steroid withdrawal; HCV = hepatitis C virus; HxCx = historical controls; immuno = immunological; intraop = intraoperatively; K = kidney; LDKT = living donor kidney transplantation; mc = multicentre; MMF = mycophenolate mofetil; MP = methylprednisolone; NS = not significant; od = once daily; ol = open-label; p = prospective; Pa = pancreas; PAKT = pancreas after kidney transplantation; PTLD = post-transplantation lymphoproliferative disorder; qd = every other day; r = randomized; Retro = retrospective; sc= single-centre; SPKT = simultaneous pancreas-kidney transplantation; SRL = sirolimus; TAC = tacrolimus; * p = NS, ** p = 0.058, p = 0.04 by Kaplan Meier analysis; - p < 0.05 vs comparator. 702 Gaber et al.

13 Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 703 corticosteroid withdrawal in patients undergoing pancreas after kidney transplantation has also recently been explored. In patients receiving corticosteroids for a previous kidney transplant at the time of pancreas transplantation, a regimen of ratg induction, tacrolimus-sirolimus maintenance therapy and corticosteroid withdrawal by day 5 was safe and did not result in any deleterious effects on patient or graft survival when compared with an historical control group of patients who continued on long-term corticosteroids. [88] Apart from its well known metabolic adverse effects, long-term corticosteroid use is also associated with an increased risk of infection, including chronic hepatitis C recurrence after liver transplantation. Eason and colleagues [89,90] were the first to report results from a prospective, randomized trial of a complete corticosteroid avoidance protocol in liver transplant recipients. Patients were assigned to receive either ratg induction (1.5 mg/kg during the anhepatic phase and another dose on day 1) or methylprednisolone (1 g during the anhepatic phase, then tapered after 3 months), followed by maintenance tacrolimus-mmf with eventual discontinuation of MMF after 3 months. After a mean follow-up of 18.5 months, patient survival, graft survival and incidence of acute rejection were similar in both treatment groups. [90] However, the incidences of CMV infection and post-transplantation diabetes were significantly higher in the corticosteroid group (p < 0.05), and there was a trend toward a lower rate and reduced severity of recurrent hepatitis C in the ratg group. This study demonstrated that with this corticosteroid-avoidance regimen both effective immunosuppression and a reduction in corticosteroid-related complications may be achieved. Enthusiasm for corticosteroid-minimization strategies in kidney transplant recipients grew, especially after positive long-term results were reported. A protocol consisting of ratg induction ( mg/kg/day for 5 days), ciclosporin- MMF or tacrolimus-sirolimus maintenance therapy, and discontinuation of corticosteroid therapy on postoperative day 6 provided favourable outcomes and reduced the incidence of adverse effects in mostly Caucasian living donor kidney transplant recipients. [82] Actuarial 5-year patient survival and graft survival rates were 91% and 84%, respectively, and significantly fewer study patients than corticosteroid-treated historical controls experienced CMV infection (p < 0.001), posttransplantation diabetes (p < 0.001), cataracts (p < 0.001), non-ptld malignancy (p = 0.02) and fractures (p = 0.04). Recently reported results from a 5-year randomized controlled trial provide assurance. [84] In deceased or living donor kidney transplant recipients treated with antibody induction therapy (ratg or an IL-2 receptor antagonist) and tacrolimus-mmf maintenance, no significant differences in long-term graft survival were observed between patients who underwent corticosteroid withdrawal at day 7 and patients who received chronic corticosteroid therapy. Cardiovascular risk factor endpoints such as triglyceride levels, weight gain and incidence of insulinrequiring diabetes favoured the corticosteroid withdrawal group. A similar randomized controlled trial in living donor kidney transplantation is also encouraging. [85] At 1 year, a composite endpoint of freedom from biopsy-proven acute rejection, graft loss and death was no different between patients who received ratg induction with corticosteroid withdrawal at day 7 and patients who did not receive induction but continued corticosteroid therapy (84.4% vs 74.4%; p= not significant). All patients received tacrolimus-mmf maintenance. After 1 year, total cholesterol levels were significantly lower in the early corticosteroid withdrawal group than in the long-term corticosteroid group (159.7 vs mg/dl; p = 0.012). Beneficial trends in other metabolic parameters were also noted in favour of early corticosteroid discontinuation. Corticosteroid cessation incorporating antibody induction and tacrolimus maintenance appears to be a feasible method that does not appear to increase late graft loss. In low-risk heart transplant recipients, ratg and corticosteroid-free maintenance immunosuppression were investigated in a recent randomized prospective study. [91] Patients were randomly assigned to receive either ratg (total dose of 6mg/kg) and a corticosteroid-avoidance regimen

14 704 Gaber et al. or no induction and long-term corticosteroid therapy (all patients received ratg 1.5 mg/kg intraoperatively). At 1 year, the incidence of acute rejection was similar in both groups. However, at 6 months, the patients in the corticosteroidavoidance group experienced greater improvements in muscle strength, less bone loss and a lower incidence of post-transplantation diabetes than did controls. Studies have demonstrated that ratg induction therapy, in combination with modern maintenance immunosuppression, provides a level of immunosuppression that allows corticosteroids to be safely eliminated or completely avoided without compromising patient or graft survival. This strategy may reduce the metabolic and infectious complications of long-term corticosteroid use. 3.4 ratg in Calcineurin Inhibitor-Minimization Regimens The introduction of ciclosporin in the early 1980s and tacrolimus in the 1990s dramatically improved short-term outcomes after kidney transplantation. Unfortunately, with this success came the risk of calcineurin inhibitor (CNI)- induced nephrotoxicity. In an effort to reduce CNI exposure and thus reduce the potential for nephrotoxicity, without increasing the risk of rejection, ratg induction therapy was incorporated into various CNI-minimization protocols (table IV). [44,60,92-103] These protocols avoid the use of CNIs completely, delay their introduction or minimize dosing. Some early studies of ratg induction and CNI minimization in kidney transplantation focused on recipients of deceased donor kidneys, since these kidneys are associated with a higher rate of DGF and are more susceptible to CNIinduced nephrotoxicity than are living donor kidneys. Grinyo and colleagues [104,105] prospectively examined CNI avoidance in low-immunological-risk recipients of ECD kidneys or kidneys at risk for DGF because of prolonged cold ischaemia time. Patients received MMF and corticosteroids for maintenance immunosuppression after ratg induction, and ciclosporin was introduced only if moderate to severe rejection or significant MMF dose reductions occurred. Although CNI avoidance was possible in only 36% of patients after 5 years, there was a low rate of acute rejection (24%), and 5-year patient and graft survivals were acceptable (79% and 65%, respectively). Routine prophylaxis against CMV was not used and ten patients (33%) developed CMV infection. This study showed that ciclosporin could be delayed in the early post-transplantation period, and in some cases completely avoided, with good results in recipients of suboptimal allografts. The authors recommended CMV prophylaxis in future studies. Further prospective randomized studies showed that a regimen of ratg induction therapy (1.25 mg/kg/day for 10 days) and a 9-day delay in ciclosporin or tacrolimus administration, in combination with azathioprine and corticosteroids, was associated with a lower rate of biopsy-confirmed acute rejection than no induction therapy and immediate CNI administration. [92,93] Graft function improved rapidly with both induction and non-induction regimens, and serum creatinine levels were comparable between regimens at the end of the studies. CMV infection and leukopenia were more frequent in patients who received induction therapy (p < 0.05). Lo and colleagues [94] evaluated ratg (1.5 mg/kg for up to seven doses) in combination with sirolimus-based immunosuppression as part of a CNI dose-minimization (reduced dose of tacrolimus and sirolimus) or CNI-free (MMF and sirolimus) regimen in high-risk deceased donor kidney transplant recipients. Both regimens were effective: 1-year patient and graft survivals and the incidence of acute rejection were similar. At 1 year, estimated creatinine clearance was higher in the CNI-free group than in the CNI dose-minimization group (72 vs 51 ml/min; p < 0.05). One study prospectively compared sirolimusbased (CNI-free) and tacrolimus-based maintenance immunosuppression in predominantly Caucasian recipients of living donor kidney transplants; all patients received ratg induction (1.5 mg/kg/day on days 0, 1, 2, 4 and 6). [95] Although mean glomerular filtration rate (GFR) at 1 month was significantly higher in the CNI-free

15 Table IV. Selected studies of rabbit antithymocyte globulin (ratg) in calcineurin inhibitor (CNI)-minimization immunosuppression regimens Study (year) Study design No. of Drug and dosage regimen Efficacy (%) Safety and additional comments patients patient survival graft survival incidence of AR Kidney transplantation Mourad et al. [92] (2001) Lebranchu et al. [60] (2002) Charpentier et al. [93] (2003) Lo et al. [94] (2004) Larson et al. [95] (2006) Büchler et al. [96] (2007) p, ol, mc (followup, 12 mo) p, r, ol, mc (follow-up, 6 mo) p, r, ol (follow-up, 6 mo) r (mean followup, 333 d) p, r (mean follow-up, 33 mo) p, r, mc ratg 1.25 mg/kg od 10 d + delayed TAC a No ratg + immediate TAC a BAS 20 mg on d 0 and 4 + immediate CsA b ratg mg/kg od 6 10 d c + delayed CsA b No induction + TAC c ratg 1.25 mg/kg od 10 d + delayed TAC c ratg 1.25 mg/kg od 10 d + delayed mcsa c ratg 1.5 mg/kg od 3 7 doses d + reduced-dose TAC (CNI sparing) e ratg 1.5 mg/kg od 3 7 doses d + no TAC (CNI free) e ratg 1.5 mg/kg od 5d+ CNI free (SRL) f ratg 1.5 mg/kg od 5d+ no CNI free (TAC) f ratg 1.5 mg/kg od 5 doses + SRL + MMF g ratg 1.5 mg/kg od 5 doses + CsA + MMF g 97.4 (1 y) * 96.8 (1 y) 98 (1 y) * 100 (1 y) 97.0 (6 mo) * 98.4 (6 mo) 97.0 (6 mo) 98 (1 y) * 100 (1 y) 98 (1 y) * 96 (1 y) 97 (1 y) * 97 (1 y) 92.1 (1 y) * 91.1 (1 y) 94 (1 y) * 96 (1 y) 93.2 (6 mo) * 95.2 (6 mo) 90.8 (6 mo) 80 (1 y) * 89 (1 y) 94 (1 y) * 92 (1 y) 90 (1 y) * 93 (1 y) 15.2 (1 y) ** 30.4 (1 y) 8.0 (1 y) * 8.0 (1 y) 25.4 (6 mo) *** 15.1 (6 mo) 21.2 (6 mo) 10 (1 y) * 7(1y) 19 (1 y) * 14 (1 y) 14.3 (1 y) * 8.6 (1 y) CMV infection: 32.5% (ratg) vs 19.0% (no ratg) [p = 0.009] Herpes simplex: 17.9% (ratg) vs 5.7% (no ratg) [p = 0.001] CMV infection: 6% (BAS) vs 19% (ratg) [p = 0.005] Symptomatic CMV infection: 6% (BAS) vs 12% * (ratg) No malignancies or PTLD in either group CMV infection: 15.7% (no induction), 24.2% (ratg + TAC), and 28.3% (ratg + CsA) [p = 0.012] No significant differences between groups in bacterial, fungal or protozoal infections Malignancies: 1 (no induction), 2 (ratg + TAC) and 4 (ratg + CsA) patients Estimated creatinine clearance (1 y): 50.5 (CNI sparing) vs 72.4 ml/min (CNI free) [p < 0.01] Overall infection: 41% (CNI sparing) vs 45% * (CNI free) 3 cases of polyoma virus interstitial nephritis in the CNIsparing group No CMV viraemia, infection or disease in either group Iothalamate clearance was significantly higher in the SRL group than in the TAC group at 1 mo (67 vs 58 ml/min, p = 0.002); differences were not significant at 1 or 2 y Estimated GFR (primary endpoint): ITT population, 60 ml/min (SRL) vs 57 ml/min (CsA) [p = 0.45]; on treatment, 69 ml/min (SRL) vs 60 ml/min (CsA) [p = 0.013] Discontinuation of study medication: 28.2% (SRL) vs 14.9% (CsA) Liver transplantation Eason et al. [97] (2007) p, sc 100 h ratg i 1.5 mg/kg od 2 doses j TAC was delayed by a mean of 4 d Continued next page Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 705

16 Table IV. Contd Study (year) Study design No. of Drug and dosage regimen Efficacy (%) Safety and additional comments patients patient survival graft survival incidence of AR Tchervenkov et al. [44] (1997) Tchervenkov et al. [98] (2004) Tector et al. [99] (2004) Soliman et al. [100] (2007) Bajjoka et al. [101] (2008) Cantarovich et al. [102] (2007) Retro, sc Retro, sc ratg k given every 2nd or 3rd d No ratg ratg l mean 1.5 mg/kg od mean 8 d No ratg (1 y) * 80 (1 y) (1 y) * 76 (1 y) CsA was delayed for up to 2 and sometimes 3 wk after transplantation Incidence of infectious complications: 56% (ratg) vs 69% (no ratg) RFGS at 1 y: 50.9% - (ratg) vs 39.2% (no ratg) Freedom from rejection at 6 mo and 1 y: 75.1% -- vs 52.4% and 71.6% -- vs 50% for ratg and no ratg groups, respectively p, sc 112 ratg m 2mg/kg/dose n 96 (1 y) 94 (1 y) 4 (2 mo) Incidence of CMV: 46% Incidence of recurrent HCV: 32% Retro, sc Retro, sc Retro 112 with RD 209 without RD 58 without RD ratg 2.5 mg/kg od 3d o No ratg + immediate CNI use o 74.3 * (5 y) 70.1 (5 y) ratg p 0.5 1mg/kg od + delayed CNI use q No ratg + immediate CNI use ratg every 3 5d r + low-dose delayed CNI ratg od r + low-dose delayed CNI No ratg + standard-dose delayed CNI 90 (1 y) * 89 (1 y) 46 (7 y) 63 (7 y) (7 y) * (5 y) 68% (5 y) 88 (1 y) * 86 (1 y) 36 (1 y) 28 (1 y) z 43 (1 y) There were no statistically significant differences between groups in recurrent or de novo malignancies or in PTLD Mean time to CNI: 4.6 d -- (ratg) vs 1.9 d (no ratg) Incidence of CMV: 2.5% ** (ratg) vs 11.3% (no ratg) Incidence of infection: 38% - (ratg) vs 51% (no ratg) Cumulative incidence of chronic kidney disease requiring dialysis at 7 y: 9.8% (ratg every 3 5 d), 2.0% (ratg od), and 3.3% (no ratg) Creatinine clearance at 7 y: 63 ml/min (ratg every 3 5 d), 64 ml/min (ratg od),and 60 ml/min (no ratg) a Maintenance immunosuppression: AZA + corticosteroid. b Maintenance immunosuppression: MMF + corticosteroid. c ratg dosage was adjusted to maintain CD2+ or CD3+ counts below 20 cells/mm 3. The mean cumulative dose was mg and the mean duration of therapy was 8.7 d. d Patients with immediate graft function received 3 doses and patients with delayed graft function received up to 7 doses of ratg. e Patients in the CNI-sparing group received full-dose SRL (targettrough level, 10 15ng/mL) andreduced-dose TAC (target troughlevel, 3 6ng/mL). Patients in the CNI-free group received full-dose SRL (target trough, ng/ml) and MMF 2 g/d. All patients received corticosteroids. f All patients received ratg + MMF + corticosteroid; patients in the CNI-free protocol group received SRL and other patients received TAC (both initiated on postoperative d 4). Continued next page 706 Gaber et al.

17 Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 707 Table IV. Contd g Corticosteroids were discontinued at 6 mo post-transplantation. h 100 patients underwent consecutive liver and simultaneous kidney/liver transplantation. i One dose of ratg was administered in the anhepatic phase, and one dose was given on post-transplantation d 2. j Maintenance immunosuppression: TAC + MMF; TAC therapy was delayed 2 d and was started at low doses. k Maintenance immunosuppression: CsA + AZA + prednisone; CsA was started when patients had good renal function and was adjusted on the basis of trough whole blood levels of ng/ml. l Maintenance immunosuppression: TAC or CsA. m ratg was given every other day starting on d 1 postoperatively up to d 3. n Maintenance immunosuppression: MP + TAC; TAC was targeted to a trough level of 8 12 ng/ml and was started postoperatively on d 3 or 4. o Maintenance immunosuppression: CsA (on d 3) in the ratg group and CsA or TAC in the immediate CNI group; corticosteroids were usually withdrawn after 3 6 mo. p ratg was started d 1 postoperatively and was continued until either serum creatinine had decreased to 1.2 mg/dl or a total of five doses were given. q Maintenance immunosuppression: MMF + TAC/CsA; TAC or CsA was started either 1 d before the last of the five ratg doses or when S CR decreased to 1.2 mg/dl. r Maximum dose: 6 mg/kg. AR = acute rejection; AZA = azathioprine; BAS = basiliximab; CMV = cytomegalovirus; CsA = ciclosporin; GFR = glomerular filtration rate; HCV = hepatitis C virus; ITT = intent to treat; mc= multicentre; mcsa = modified ciclosporin; MMF = mycophenolate mofetil; od = once daily; ol = open-label; p = prospective; PTLD = post-transplantation lymphoproliferative disorder; qd = once daily; r = randomized; RD = renal dysfunction; Retro = retrospective; RFGS = rejection-free graft survival; sc = single-centre; SRL = sirolimus; TAC = tacrolimus; * p = not significant, ** p vs comparator; *** p = vs ratg + delayed TAC group; - p < 0.05, -- p 0.01, --- p 0.01 vs ratg every 3 5 d group; z p < 0.05 vs both groups. group (p = 0.002), GFR did not differ between groups after 1 and 2 years. At 1 year, patient survival, graft survival and acute rejection rates were similar between groups. Another study investigated concurrent CNI and corticosteroid minimization by comparing sirolimus-mmf and ciclosporin-mmf maintenance therapy in recipients of deceased donor kidneys, all of whom received ratg induction therapy (1.5 mg/kg/day for 5 days) and had corticosteroids withdrawn 6 months after transplantation. [96] The CNI-free sirolimus-based regimen was as effective as the ciclosporin-based regimen in terms of 1-year acute rejection and patient and graft survival rates, showing that both CNI avoidance and late corticosteroid withdrawal are possible with this protocol. However, discontinuation from the study because of adverse events was more common in the sirolimus group than in the ciclosporin group, and the difference between groups in estimated GFR was significant only in those patients who continued on treatment per protocol (69 ml/min in the sirolimus group vs 60 ml/min in the ciclosporin group; p = 0.01). These studies provide some evidence that ratg induction, which can be incorporated into various immunosuppressive regimens, allows for either CNI minimization or complete CNI avoidance to be successful in deceased and living donor kidney transplant recipients, thereby potentially preventing CNIinduced nephrotoxicity without reducing graft survival. As in kidney transplantation, the use of ratg to delay introduction of, or to minimize longterm exposure to, CNIs has been investigated in liver transplantation. Renal function was compared between liver transplant recipients who received ratg induction and those who did not receive ratg. [98] In ratg-treated patients, initiation of CNI therapy was delayed (mean delay 9.5 vs 6.3 days; p < 0.001) and serum creatinine levels were significantly lower after 6 months (1.39 vs 1.56 mg/dl; p = 0.014). A larger study analysed outcomes in patients who received either immediate CNI therapy or ratg induction (2.5 mg/kg/day for 3 days) and delayed CNI administration (3 days). [100] At 1 year, mean GFR

18 708 Gaber et al. was significantly higher (81 vs 75 ml/min; p = 0.02) and the incidence of acute rejection was significantly lower (14.5% vs 31.8%; p= ) in the ratg group. Five-year patient and graft survivals were similar between groups, as were the incidences of death due to infection, tumour recurrence, de novo malignancy and PTLD. Bajjoka and colleagues [101] retrospectively evaluated the effect of ratg induction and delayed CNI initiation on renal function in liver transplant recipients with baseline renal dysfunction. Compared with historical controls, who received CNIs within 48 hours of transplantation, patients who received ratg induction and delayed CNI initiation (mean delay 4.6 days) had a significantly higher mean GFR at 1 year after transplantation (57.4 vs 43.7 ml/min/1.73 m 2 ; p < 0.001). Anti-infective prophylaxis was administered to all patients, regardless of whether they received induction therapy. The incidences of CMV disease and overall infection were significantly lower in patients who received ratg than in controls (2.5% vs 11.3% [p < 0.01] and 38% vs 51% [p < 0.05], respectively). The delayed introduction of CNIs is an important strategy for heart transplant recipients, a population who are at high risk for developing postoperative renal dysfunction. [106] ratg administration every 2 5 days at a dosage of 1.5 mg/kg allowed a mean 12-day delay in ciclosporin initiation among 15 heart transplant patients with postoperative renal dysfunction (serum creatinine 150 mmol). [103] All patients received MMF and corticosteroids for maintenance immunosuppression and had 1-year patient survival (87%) and acute rejection (27%) rates that were comparable to those of historical controls, who received ratg 1.5 mg/kg daily for 5 7 days and had ciclosporin initiated a mean of 2 days after transplant. In heart transplant patients with preoperative renal dysfunction (serum creatinine levels 200 mmol/l for 3 months), basiliximab and ratg allowed ciclosporin to be delayed by a mean of 7.3 days and 3.2 days, respectively, with sustained improvements in serum creatinine levels from baseline to 6 months. [107] Patients in both groups received MMF and corticosteroids, and had similar serum creatinine levels at the end of follow-up, but the average biopsy score was significantly lower in the ratg group than in the basiliximab group (0.65 vs 0.25; p = 0.026). Both groups experienced a similar number of infections. ratg plays an important role in CNIminimization strategies: renal function (native or allograft) can be maintained or improved without adversely affecting acute rejection or infectious complications. 3.5 Refining ratg Dosing Regimens in Kidney Transplantation In kidney transplantation clinical studies, ratg dosages have varied over time and several novel dosing strategies have been employed (figure 1a c). [25,26,41,52,53,60,61,80-84,92-96,104, ] Evidence from a single comparative study suggests that administration of ratg intraoperatively before reperfusion has greater potential to minimize IRI than does postoperative ratg administration. [52] ratg appears to inhibit leukocyte adhesion and other mechanisms of IRI that occur early after reperfusion. [56,57] Although results from several other clinical studies support the intraoperative prereperfusion administration of ratg for prevention of acute rejection, [25,26,123] additional studies are needed to confirm the optimal timing of administration for achieving specific immunological effects and minimizing early graft damage. Data derived from a non-human primate model suggest that T-cell depletion with ratg is dose dependent and that the optimal total dose required to achieve lymphocyte depletion in both peripheral blood and secondary lymphoid tissues (spleen and lymph nodes) is approximately 6.4 mg/kg. [124] Based on this study and preliminary clinical experience, some studies in kidney transplantation used total cumulative dosages between 10.5 and 15 mg/kg ( mg/kg/day for 7 10 days). [25,35,92,93] More recent literature supports a target cumulative dose of mg/kg for prevention of acute rejection, even in high-risk recipients. [26,53,108,125] A total dose of 7.5 mg/kg initiated intraoperatively and administered over the course of 5 days has successfully protected against acute rejection in patients at high risk. [26]

19 Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 709 Cumulative thymoglobulin dose (mg/kg) a b c Year of study publication Fig. 1. Rabbit antithymocyte globulin (ratg) dosage regimens in kidney transplantation (protocol dose in the ratg treatment group; the actual dose or mean value of the dose range was used when a single protocol dose was not reported): (a) standard triple maintenance immunosuppression; [25,26,41,52,53, ] (b) corticosteroid minimization regimen; [61,80-84, ] (c) calcineurin inhibitor minimization regimen. [60,92-96,105, ] Results from a number of studies suggest that a dose of mg/kg (e.g mg/kg for 5 days) is important for successful minimization of maintenance immunosuppression. [81-84,95,96,119] There is some experience with using total doses <6mg/kg in patients treated with standard maintenance immunosuppression. [52,114] Clinically, relatively short courses of ratg therapy have also been shown to be effective. A 3-day course of ratg (3 mg/kg intraoperatively followed by 1.5 mg/kg/day for 2 days [total dose 6mg/kg]) was as effective as a 7-day course (1.5 mg/kg intraoperatively followed by 1.5 mg/kg/day for 6 days [total dose 10.5 mg/kg]): 1-year patient and graft survival rates were similar, but absolute lymphocyte count was significantly lower (p < 0.05) and duration of hospital stay was significantly shorter (p = 0.002) in patients treated with the 3-day dosing regimen. [108] These effects may have been due to the higher intraoperative dose administered with the 3-day dosing regimen. Recently, a single-dose regimen of ratg (6 mg/kg infused over 24 hours) was compared with a divided-dose regimen (1.5 mg/kg every other day for 4 days [total dose 6 mg/kg]) in a prospective randomized trial. [53,126] After a mean follow-up of 16 months, there were no significant differences between regimens in terms of patient survival, graft survival, acute rejection or adverse events. Early renal allograft function was better in the single-dose group than in the divided-dose group (GFR 50 vs 41 ml/min/1.73 m 2 ;p= 0.05). The incidence of chronic allograft nephropathy in clinically indicated and protocol biopsies was also lower in the single-dose group (p = 0.045). Importantly, a positive correlation was found between the amount of ratg administered before kidney reperfusion and improved early renal function. [53] These data support the notion that the beneficial effects of ratg on early graft function may depend on both the dose and timing of administration. Data from the TAILOR registry provide some insight into ratg dosing for living donor kidney transplant recipients. Among 610 patients followed up for 1 year, the mean total dose of ratg received was 5.6 mg/kg (mean 1.5 mg/kg/day for 4 days), usually in combination with standard triple-drug immunosuppression. [127] This dosing regimen was associated with low incidences of acute rejection (6.4%) and infection (31%) at 1 year after transplantation.

20 710 Gaber et al. ratg dosing protocols often vary in clinical practice, and the optimal dosing schedule in patients at high or low immunological risk has yet to be determined. Nonetheless, total cumulative dosages between 5 and 7 mg/kg appear to be associated with excellent safety and efficacy outcomes. 3.6 Safety of ratg ratg is generally well tolerated. [29,109] The most frequently reported adverse events include fever, chills and leukopenia. [29] Lymphopenia, neutropenia and thrombocytopenia also commonly occur, but they can be easily managed with dosage adjustment. Serum sickness is a rare complication caused by deposition of immune complexes in tissues. [128] Characteristic symptoms include fever, jaw pain, arthralgia, lymphadenopathy and rash. Serum sickness can be rapidly treated with plasmapheresis and corticosteroids. [128] The most common viral infection after SOT is CMV infection, the direct and indirect effects of which can lead to considerable morbidity and mortality. [129] Two European studies in kidney transplant recipients reported a higher incidence of CMV infection in patients who received ratg than in patients who did not receive induction therapy, but the use of antiviral prophylaxis was not clearly described by the investigators. [92,93] Consequently, this finding may not be applicable to current standards of practice. In the randomized controlled trial that compared ratg with eatg, patients did receive viral prophylaxis, and CMV disease was not significantly different between the ratg group and the eatg group at 1 year (12.5% vs 33.3%, respectively; p = 0.056). [25] Less CMV disease was also observed when ratg was compared with basiliximab in a randomized trial, probably because of the use of antiviral prophylaxis and the greater efficacy of ratg in reducing rejection and in reducing the need for additional immunosuppressive therapy. [26] In addition to CMV infection, infection with Epstein-Barr virus (EBV), bacteria, fungi, BK virus or hepatitis C virus may be encountered as a result of the immunosuppression used in SOT. [130] Specific recommendations regarding monitoring and preventative therapies are available for patients being treated with ATG. [130] Patients who are at risk for CMV infection (i.e. either the donor or recipient is seropositive) should receive anti-cmv prophylaxis and be monitored for CMV load or antigenaemia for approximately 3 months after ATG induction therapy. A longer duration of surveillance is advised for patients who receive ATG for treatment of rejection. Recipients of EBV-positive organs who are EBV-negative before the transplant should be monitored monthly for at least 1 year after ATG induction. At least 6 months of screening for BK virus is recommended. Hepatitis C seropositive patients should have viral load measured every 3 months during the first year after transplantation. Although routine laboratory monitoring is not required for bacterial or fungal infections, appropriate pharmacological prophylaxis should persist for approximately 6 12 months after transplantation. Malignancy, particularly PTLD, is a serious and sometimes fatal complication of both SOT and HSCT. [131] The PTLD that occurs in these settings is, in most cases, associated with EBV infection that causes uncontrolled B-cell proliferation and tumour development. A number of risk factors for PTLD in solid organ recipients have been identified, including primary EBV infection, recipient age and type of organ transplanted. [132] The modern immunosuppressive medications that are so critical in preventing rejection in transplantation are also thought to play a role in PTLD pathogenesis; however, it appears that the overall burden of immunosuppression is of much greater importance than any specific agent or class of agents. [ ] Several registry studies have tried to determine whether ratg induction therapy is associated with a greater risk of developing PTLD, but they have provided mixed results. [ ] Analyses of the Collaborative Transplant Study and the OPTN/UNOS databases have suggested that the risk is increased with ratg induction therapy in kidney transplant recipients. [ ] One study reported a relative risk of 1.63 (95% CI 1.188, 2.235; p = 0.025) for ratg versus no induction. [135] This study also found that the use of T cell-depleting antibody was not an independent

21 Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 711 risk factor for PTLD. In contrast, several other registry analyses have indicated that the use of ratg for induction therapy is not associated with an increased risk of PTLD. [ ] Cherikh and colleagues [136] analysed the OPTN/UNOS database and reported a small nonsignificant relative risk of 1.29 (95% CI 0.82, 2.03; p = 0.27) for polyclonal antibody induction versus no induction. When data from the UNOS and US Renal Data System Registry were analysed by specific induction agent, ratg was also found to be not associated with a significantly increased risk of PTLD. [137,138] Although many registry studies have addressed the issue of whether ratg increases the risk of PTLD, the data are inconclusive. 3.7 Summary of ratg in SOT The initial clinical experience with ratg in the treatment of acute rejection has led to its successful use in preventing acute rejection and improving long-term outcomes in SOT. ratg has a multifaceted mechanism of action and, over time, the clinical use of ratg has expanded to patients across the spectrum of risk and to recipients of different types of organ transplants. ratg also has an established role in facilitating the minimization or complete avoidance of corticosteroids and/or CNIs, thereby reducing potential long-term toxicity from these agents. In recent studies, the efficacy and safety of ratg have been demonstrated in patients who are at low immunological risk, including living donor kidney transplant recipients. ratg is effective as part of both conventional (standard triple therapy) and corticosteroid- or CNI-minimization immunosuppression strategies, which seek to reduce long-term complications such as renal dysfunction, cardiovascular disease and osteoporosis. Studies with long-term follow-ups (up to 10 years) have demonstrated that ratg therapy is safe and is not associated with an increased risk of infection or malignancy. [45,46,49,69,82,140] Experience with novel dosing regimens is growing and may provide further evidence for improving the balance of efficacy and safety in SOT. Published data and clinical experience have established the efficacy and safety of ratg in kidney, liver, pancreas, heart and lung transplantation. A reduced risk of rejection and the ability to minimize post-transplant maintenance immunosuppression are important advantages of ratg, and consideration should be given to strategies (such as appropriate dosing, premedication and anti-infective prophylaxis) aimed at minimizing potential complications associated with its use, when determining the optimal therapy for each individual patient and for each type of organ transplanted. Extensive clinical experience and robust clinical trial data have strongly supported the use of ratg in kidney and pancreas transplantation, as reflected by its widespread use and acceptance in these areas. [76] Even though the use of ratg, as well as other induction therapies, is lower in liver transplantation, ratg seems to have established a strong foundation in this area with its ability to minimize maintenance immunosuppression. ratg appears to be the primary induction agent in heart transplantation, even though published data are more limited than in kidney, pancreas or liver transplantation. The use of ratg in lung transplantation seems to be most controversial, possibly due to the limited published evidence and clinical experience. Perceptions are likely to continue to change as the body of literature and expertise grow in this area. 4. History of ratg in Haematopoietic Stem Cell Transplantation (HSCT) The modern era of HSCT began after the Second World War, when it was learned that bone marrow was particularly sensitive to irradiation and exposure to a lethal level resulted in death from bone marrow failure. [141] Subsequently, results from experiments in mice showed that haematopoietic recovery after irradiation was possible with the infusion of allogeneic spleen cells or bone marrow. [ ] The potential application of HSCT for the treatment of haematological diseases would soon be realized. For patients with haematological malignancies, there was hope that the intensity of cytotoxic chemotherapy could be raised to new levels, possibly improving its effectiveness. The transplantation

22 712 Gaber et al. of stem cells could rescue bone marrow after intense radiation and chemotherapy. The early human studies of BMT following irradiation alone in the 1950s and early 1960s were mainly disappointing as the majority of patients failed to achieve durable haematopoietic engraftment or developed severe GVHD. [141] Further research from larger animal studies was needed to fill gaps in knowledge about histocompatibility matching and control of GVHD. In the late 1960s, high-dose conditioning regimens that consisted of TBI and/or chemotherapy (e.g. cyclophosphamide) were developed to not only eradicate malignant cells but also suppress the patient s immune system so that the bone marrow graft would not be rejected. [147] By the 1970s, advances in supportive care and post-transplantation immunosuppression for prevention of GVHD (i.e. methotrexate) allowed clinical trials of allogeneic BMT in HLA-matched siblings to once again move forward. [147] In 1977, results from a landmark study by Thomas and colleagues [148] demonstrated that some patients with endstage leukaemia could be cured, and a new era of successful HSCT began. [141] Technological advances in HSCT continued to be made in the 1980s and 1990s. [147] Conditioning regimens were further refined to reduce rejection, relapse and toxicity. Studies with ALS as preparation for BMT began in the 1970s. [9] In the mid-1990s, eatg was effectively combined with cyclophosphamide to increase immunosuppression in aplastic anaemia patients undergoing allogeneic BMT. [149] In 1983, busulfan, a myelotoxic alkylating agent, emerged as an alternative to irradiation. [150] The more recently developed intravenous formulation and pharmacological targeting of busulfan (i.e. therapeutic drug monitoring) appear to reduce drug toxicity, although target exposure ranges in different populations need to be better defined. [151] The graft-versus-leukaemia (GVL) effect of allogeneic HSCT was reported as early as 1956, when it was demonstrated that leukaemic cells could be destroyed by the injection of bone marrow from a different strain of mice; this effect was not evident when the marrow originated from the same strain of mice. [152] A negative association between relapse and GVHD was later reported in patients with leukaemia. [153] This advantageous interaction between graft and host is now a well known property of allogeneic HSCT. The GVL effect is mediated by donor T cells and natural killer cells that target host malignant tissue. [154] In the late 1990s, reduced-intensity conditioning regimens were developed on the basis of this immune reaction and the theory that optimizing immunosuppression could control both GVL and GVHD. [155,156] Achieving a balance between GVHD and the GVL effect is a goal of allogeneic HSCT. Today, HSCT is a well established and potentially life-saving treatment for a number of malignant and nonmalignant haematological diseases. The number of procedures continues to increase each year, with more than allogeneic transplantations performed worldwide annually. [157] The list of possible sources of stem cells also continues to expand, and the use of stem cells recovered from peripheral blood and cord blood is growing. [157,158] The list of possible donors also continues to expand. Recent advances have been made in unrelated and mismatched related HSCT, [159,160] providing an opportunity for the approximately 70% of patients who lack the ideal HLA-identical sibling donor. For many patients, a search for an unrelated donor is undertaken. The likelihood of finding the optimal donor depends on many factors, including the patient s clinical urgency and donor characteristics (e.g. CMV status and age). [161] Because some HLA types are more common in certain populations, the ethnic background of a patient can affect the likelihood of success. Caucasians have a greater chance of finding a potential donor within a transplant registry than do members of other ethnic groups. [160] When a suitable unrelated donor cannot be found within an acceptable period of time, other options that may be considered include reducing the match criteria, autologous transplantation, umbilical cord blood transplantation, haplo-identical transplantation or nontransplant therapy. [161] GVHD is caused by an immune response by immunocompetent cells in the graft against the host (figure 2). [162,163] Although major improvements

23 Rabbit Antithymocyte Globulin (Thymoglobulin Ò ) 713 Conditioning prior to allograft infusion leads to host tissue damage Cytokine storm (TNFα, IL-1, IL-6, LPS) Host tissue Inflammatory cytokines DC/ APC Activation of DC/APC and interaction with donor cells Naive donor cell IL-12 secretion Destruction of GVHD target tissue Differentiation of CD4+ T h 1 cells T h 1 IFNγ IL-2 T h 1 chemokines NK CD8+ CTL T h 1 MΦ Activation of donor immune effectors Fig. 2. The pathophysiology of graft-vs-host disease (GVHD). [162,163] The pathophysiology of GVHD involves a three-step process: (i) the conditioning regimen injures host tissues, which results in the release of inflammatory cytokines (i.e. cytokine storm ); (ii) antigen-presenting cells (APCs) and dendritic cells (DCs) activate donor T cells, followed by donor T-cell proliferation and differentiation; (iii) numerous immune effector cells are activated, which leads to GVHD-mediated destruction of target tissue through cytotoxic and inflammatory attacks (adapted from Mohty and Gaugler, [163] with permission from Elsevier). CTL = cytotoxic T cell; IFN = interferon; IL = interleukin; LPS = lipopolysaccharide; MU = macrophage; NK = natural killer cell; T h 1 = T helper-1 cell; TNF = tumour necrosis factor. have been made in recent years, GVHD is a major barrier to successful allogeneic HSCT. The initial phase of acute GVHD involves antigen presentation and activation of donor T cells, with subsequent clonal proliferation and differentiation. This phase is followed by cytokine release and recruitment of additional donor immune effector cells that damage recipient target tissues. HSCT from an unrelated or mismatched related donor is associated with a greater risk of GVHD than is HSCT from an HLA-identical sibling. [164] Other factors that influence the risk of GVHD are stem cell source, [165] intensity of the conditioning regimen, underlying disease and disease status. The greater anti-t cell activity of ratg in allogeneic HSCT, compared with the activity of other antibodies, [166] and the success of ratg in the treatment of corticosteroid-resistant acute rejection after renal transplantation, [39] led to its early use in the treatment of acute GVHD. One study analysed the use of ratg (2.5 mg/kg/day for 4 6daysor2.5mg/kg/day on days 1, 3, 5 and 7) in patients who developed acute corticosteroidresistant GVHD grade III IV after sibling or unrelated donor BMT. [167] Although the overall response rate of 59% was noteworthy, opportunistic infections and PTLD were significant complications. The authors suggested that more favourable results might be seen with lower doses of ratg or that ratg used as a prophylactic therapy for GVHD might be a better approach. Later, ratg became widely used for the prevention of GVHD in patients at high risk, such as recipients of unrelated donor or mismatched related donor haematopoietic stem cells. Initially, ratg was used during myeloablative conditioning. More recent evidence also supports a role for