Benjamini. Ch. 19, Pgs 379-399 Page 1 of 10 TRANSPLANTATION I. KINDS OF GRAFTS II. RELATIONSHIPS BETWEEN DONOR AND RECIPIENT
Benjamini. Ch. 19, Pgs 379-399 Page 2 of 10 II.GRAFT REJECTION IS IMMUNOLOGIC PHENOMENON. A. Mouse Experiment - Graft rejection has hallmarks of immunological response - memory and specificity 1. Strains A and B differ at major histomcompatibility complex (MHC) 2. Skin grafted from strain B mouse onto strain A mouse is rejected in 14 days - first set rejection - primary response. 3. Lymphoid cells from strain A mouse that rejected strain B skin injected into a new strain A recipient. 4. New strain A recipient of lymphoid cells rejects a transplant of strain B skin in 6 days - second set rejection (rejection quicker than first set rejection) - secondary response - indication of immunologic memory a. if T-cells removed from lymphoid cells prior to injection, strain B skin rejected in 14 days - first set rejection - shows T- cells responsible for rejection. 5. Experimental Modification (not in figure) - If skin from a strain C mouse (differs from strains A and B) is transplanted to same new strain A
Benjamini. Ch. 19, Pgs 379-399 Page 3 of 10 recipient (see above) rejection occurs in 14 days - first set rejection - indicates immunologic specificity. III. TRANSPLANTATION ANTIGENS A. Vertebrates have a single highly polymorphic major histocompatibility complex (MHC) which dominates allotransplantation. 1. Transplant with MHC difference - rejection in 14 days 2. Transplant with minor transplantation antigen difference - rejection in 30 days 3. Human MHC (HLA) - status of class I and class II MHC antigens are relevant to transplantation a. MHC class I antigen expressed on most nucleated cells b. MHC class II antigen expressed on limited number of cell types: B cells, macrophages/monocytes, dendritic cells, Langerhans cells and some activated T cells. B. MHC antigens codominantly expressed. 1. maternal and paternal MHC genes are inherited and expressed C. MHC antigens inherited as one unit except in rare event of recombination. HLA haplotype - combination of HLA alleles present at linked loci on one chromosome. HLA genotype - combination of maternal and paternal HLA
Benjamini. Ch. 19, Pgs 379-399 Page 4 of 10 genes present in an individual. HLA phenotype - products of HLA genes expressed on the cells of an individual. 1. Assuming inheritance of MHC as single unit, there is a 25% chance that 2 siblings will be MHC identical; a 50% chance that 2 siblings will share 1 MHC haplotype, and a 25% chance that 2 siblings will share neither haplotype. a. chance of MHC match much greater among siblings than in general population. IV. MECHANISMS OF GRAFT REJECTION A. Immunological components of graft rejection 1. Helper T-cells (CD4+) - play critical role - self APC's process foreign MHC antigen shed from donor cells and present processed donor MHC peptide to CD4+ T helper cell - alternatively, foreign class II MHC on "passenger" donor cells contained within grafted organ (i.e. donor B-cells or dendritic cells) are recognized by recipient CD4+ T-helper cells as self MHC plus foreign peptide. a. Activated TH1 cells secrete TNFβ and IFNγ leading to macrophage activation. Activated
Benjamini. Ch. 19, Pgs 379-399 Page 5 of 10 macrophages secrete mediators which lead to inflammation within grafted tissue. b. Activated TH1 cells secrete IL-2 which leads to proliferation of CD8+ T-cytotoxic cells which have encountered foreign class I MHC antigen positive grafted cells. IFNγ secreted by TH1 cells leads to increased expression of MHC antigens on donor cells. Grafted cells are killed by CD8+ cytotoxic T lymphocytes (CTL). 2. Activated TH2 cells 1. secrete IL-4 and IL-5, which, in conjunction with IL-2 from TH1 cells, lead to increased activation and proliferation of recipient B cells specific for donor transplantation antigens. Antibody is secreted which leads to antibody-dependent
Benjamini. Ch. 19, Pgs 379-399 Page 6 of 10 cell-mediated cytotoxicity (ADCC) and, in consort with complement, to lytic damage and vascular occlusion of grafted tissue. Note: In ADCC antibody binds specifically to foreign antigen on surface of donor cell. Host cells with lytic capacity bearing Fc receptors react with Fc portion of antibody bound to donor cell leading to lysis of the donor cell. B. Clinical characteristics (kidney as prototype) 1. Hyperacute rejection - occurs within minutes to hours - caused by preformed antibodies in recipient (previous transplants, blood transfusions or pregnancies) - complement activated - blood supply to tissue cut off - no treatment - possibility of hyperacute rejection minimized by crossmatching (see below). 2. Acute rejection - begins a few days after transplant - loss of function within 10 to 14 days - intense mononuclear infiltrate found - frequently manageable by increased immunosuppressive therapy. 3. chronic rejection - occurs months or longer after graft has assumed normal function - mechanism poorly understood - both antibody and cell mediated immunity may be involved - little can be done to save graft VI. PREVENTION OF GRAFT REJECTION A. Crossmatching - test recipient serum for presence of preformed antibodies to donor tissue. Must also consider major blood group antigens, guarding against the presence of isohemmaglutinins. B. Tissue Typing Not needed in autograft. 1. HLA - Matching at HLA-A and HLA-B loci increases chances of success in grafting among related
Benjamini. Ch. 19, Pgs 379-399 Page 7 of 10 donor/recipient pairs since MHC is usually inherited as single unit (haplotype). HLA matching in cadaver transplants is of lesser value, and rejection is managed through immunosuppressive therapy. HLA-A, B, C, DR and DQ antigens determined using typing sera (antibodies). Monoclonal antibodies directed to individual HLA antigens are used. Assay can be done in hours. 2. HLA-DP antigens detected by capacity to stimulate proliferation of T cells in a one way mixed lymphocyte reaction (MLR) - Assay is in vitro correlate of in vivo CD4+ T cell proliferation - Assay requires 5 days or more. Cannot be used in cadaver transplants where results are needed quickly. 3. As time goes on more and more HLA typing is being done with molecular techniques and not by typing sera and MLR techniques. a. allowed for serologically defined alleles to be further subdivided - (i.e. HLA-B3 can be subdivided into several subtypes) - permits more accurate MHC typing in allotransplantation. 4. Minor histocompatiblity transplantation loci - Differences at multiple loci have additive effects. Grafts among siblings lessen likelihood of such differences. C. Prolongation of allograft survival - general problem with most agents is suppression of CMI leading to increased infections with opportunistic organisms - viral infections such as with cytomegalovirus - selected malignancies are increased (B-cell lymphomas, Kaposi's sarcoma, squamous cell carcinoma) 1. Anti-inflammatory agents - andrenocortical steroids such as prednisone - stabilize lysosomal membranes of inflammatory cells inhibiting release
Benjamini. Ch. 19, Pgs 379-399 Page 8 of 10 of lysosomal enzymes - block cytokine gene transcription and cytokine secretion from mononuclear phagocytes 2. Antimetabolites and alkylating agents - azathioprine, mercaptopurine, chlorambucil and cyclophosphamide - alter RNA and DNA synthesis 3. Lymphoid cell ablation a. Anti-lymphocyte globulin, total lymphoid irradiation 4. Cyclosporin A - fungal metabolite which selectively enters antigen sensitive T cells entering the G1 phase of cell cycle. Resting memory cells spared. Decreases deleterious effects to pool of memory T cells able to respond to microorganisms. Inhibits production of IL-2 and interferon γ by T-cells. Nephrotoxicity is severe problem. 5. Other fungal metabolite, such as FK506, are proving to be quite effective. 6. Monoclonal antibodies to - CD3, IL-2 receptor, class II MHC, or CD4 are immunosuppressive. 7. Experimental procedures: Anti-cytokine antibodies (IL2, IFNγ, TNFα); Blockage of adhesion molecules (ICAM-1, LFA-1); Blockage of costimulation leading to anergy. V. BONE MARROW TRANSPLANT(BMT) AND GRAFT VERSUS HOST DISEASE (GVH) A. In BMT the goal is transplant of stem cells to an immuno incompetent individual such that reconstitution of the hemopoietic and immune systems occurs. B. When GVH occurs, immunocompetent cells are injected into immuno incompetent recipient. The donor and recipient differ from each other in transplantation antigens. Donor T cells activated by antigenic differences with host tissues proliferate and synthesize
Benjamini. Ch. 19, Pgs 379-399 Page 9 of 10 lymphokines. Host inflammatory cells recruited to site by donor lymphokines are responsible for most pathology. C. Scenarios in which GVH could occur 1. bone marrow transplantation into immunodeficiency (SCID) patient (reconstitution). 2. bone marrow transplantation into lethally irradiated patient with lymphoma or acute leukemia (ablation of radiosensitive tumor cells followed by reconstitution). D. Symptoms - Fever, anemia, diarrhea, weight loss, rash and splenomegaly - can be fatal. E. Severity and time-course of GVH affected by: 1. strength (minor versus major H differences) or number of H differences determine intensity of GVH. 2. presensitization of injected lymphocytes F. Purging of mature T-cells from donor bone marrow lessens chance of GVH but seems to decrease chances of engraftment and the "graft versus leukemia (GVL)" effect. GVL occurs when cells activated in a GVH reaction develop cytotoxicicty toward malignant lymphoid cells. Study Questions 1. A kidney transplant patient develops signs of rejection 10 days after transplant. Needle biopsy of the kidney indicates an intense mononuclear infiltrate. The episode is managed by increasing doses of immunosuppressive drugs. This patient most likely experienced an episode of A. chronic rejection B. delayed type hypersenstivity to immunosuppressive drug C. hyperacute rejection D. immunologic enhancement
Benjamini. Ch. 19, Pgs 379-399 Page 10 of 10 E. acute rejection Answer E 2. Which one of the following statements are true A. a transplant between siblings provides the highest probability of a match B. a transplant between a child and one of its parents provides the highest probability of a match C. a transplant using a cadaver donor provides the highest probability of a match D. the probability of a match is identical whether a sibling or a parent is used as a transplant donor for a child E. the risk of GVH is negligible in allogeneic bone marrow transplantation. Answer A 3. The best indicator of little or no risk of hyperacute rejection in kidney transplantation is A. a lack of proliferation by recipient lymphocytes in response to donor cells in a mixed lymphocyte response (MLR). B. a lack of proliferation by donor lymphocytes in response to recipient cells in an MLR. C. cross matching showing the absence of antibody to donor cells in the serum of the recipient D. cross matching showing the absence of antibody to recipient cells in the serum of the donor E. tissue typing showing a match of class II MHC antigens between the donor and the recipient Answer C