HLA Compatibility and Cardiac Transplant Recipient Survival

Transcription

1 HLA Compatibility and Cardiac Transplant Recipient Survival William H. Frist, M.D., Philip E. Oyer, M.D., Ph.D., John C. Baldwin, M.D., Edward B. Stinson, M.D., and Norman E. Shumway, M.D., Ph.D. ABSTRACT Although the major histocompatibility complex has been linked with the control and expression of immune response in mammalian species, its importance for heart transplantation has not been demonstrated. The relationship of patient survival to human lymphocyte antigen (HLA) (A and B loci) compatibility was studied in 164 consecutive cyclosporine-treated patients who underwent orthotopic heart transplantation between 1980 and 1986 at Stanford University Medical Center. All patients receiving a transplant within this time frame were included except those for whom HLA typing was unavailable. A mismatched antigen was defined as an antigen present in the donor but not in the recipient. The actuarial four-year survival (Cutler-Ederer) for the 19 patients with 0 or 1 mismatch was 88 * 8%; for the 39 patients with 2 mismatches, 70? 12%; for the 73 patients with 3 mismatches, 59 r 7%; and for the 33 patients with 4 mismatches, 54? 14%. Both actuarial and linear rate analyses revealed no significant correlation between HLA mismatching and rejection rate, likelihood of death from rejection, or length of time to first episode of rejection. Patients with 3 or 4 mismatches had significantly (p < 0.05) more infections than those with fewer mismatches. By actuarial analysis, a trend toward a higher number of deaths from rejection and infection was observed in the groups with 3 and 4 mismatches, but it did not achieve statistical significance. The data demonstrate that wellmatched HLA grafts are associated with better long-term survival and fewer infections in cardiac transplant patients. The human lymphocyte antigen (HLA) system is the major histocompatibility complex in human beings. Analogous systems have been found in all mammalian species studied. Class I (HLA-A, HLA-B, HLA-C) antigens are highly polymorphic glycoproteins encoded by the genes of the major histocompatibility complex localized on the short arm of chromosome 6 in human beings [l]. Cytotoxic T lymphocytes lyse target cells bearing appropriate antigen and Class I HLA gene products [2]. From the Department of Cardiovascular Surgery, Stanford University Medical Center, Stanford, CA. Presented at the Thirty-third Annual Meeting of the Southern Thoracic Surgical Association, White Sulphur Springs, WV, Oct 30-Nov 1, Address reprint requests to Dr. Frist, Vanderbilt University Medical Center, st Ave S, Suite 338, Nashville, TN Since the discovery of HLA, worldwide attention has focused on the influence of these antigens on graft survival in renal transplant recipients and large multicenter trials have contributed to an understanding of this influence [3]. In contrast, the relationship between patient survival and HLA matching in heart transplantation has not been well analyzed. The purpose of this study was to examine the association between long-term survival and HLA compatibility in cardiac transplant recipients who were maintained on a cyclosporine-based immunosuppressive regimen. Material and Methods In December, 1980, cyclosporine was introduced into the clinical program of heart transplantation at Stanford University Medical Center. Between December, 1980, and May, 1986, 179 orthotopic heart transplantations were performed. Recipients and donors were selected on the basis of ABO blood group compatibility and a negative lymphocyte crossmatch. No attempt was made to match prospectively for HLA-A and HLA-B antigens. All patients were treated with a triple immunotherapy regimen consisting of cyclosporine, azathioprine, and corticosteroids. The study group included 164 consecutive (124 male, 40 female) heart transplant patients for whom HLA data were available for both donor and recipient. The mean recipient age was 36? 12 years with a range of 3 to 59 years (Table 1). Follow-up on all patients was obtained at least quarterly, and current data, including laboratory values, episodes of rejection and infection, current medicines and dosages, results of annual coronary angiography, and clinical status, are maintained in the Stanford cardiac transplant data base. Matching Grades For the analysis of HLA matching, transplant procedures were considered only if both recipient and donor had at least one antigen defined at each HLA-A and HLA-B locus; DR typing was not performed. All donors and recipients were typed prior to transplantation for HLA-A and HLA-B antigens as defined by the international histocompatibility workshops. Assays were conducted for all specificities recognized by the World Health Organization, as well as for locally designated antigens. The two-stage National Institutes of Health technique was used for HLA-A and HLA-B typing [4]. The HLA specificities are depicted in Table 2. The original broad specificities have given rise to more specific antigens over time, the latter designated splits. For the purposes of evaluating the degree of mismatch 242 Ann Thorac Surg 44: , Sep 1987

2 243 Frist et al: HLA Compatibility and Cardiac Transplant Recipient Survival Table 1. Population Profilea No. of Mismatches Variable 0, (N = 19) (N = 39) (N = 73) (N = 33) Age (yr) 35 t Sex (WF) /10 52/ Donor age (yr) 24? ? Length of stay (d) t t f 16 Ischemic time (min) Dosages at one year (mg/kg/d) t f 50 Cyclosporine 5.5 t ? f 2.4 Azathioprine 1.5 t t k 0.9 Prednisone t c 0.09 Freedom from death from infection at ? 5 one year (actuarial %) Freedom from death from rejection at one year (actuarial %) Freedom from coronary atherosclerosis 88 f ? 8 at one year (actuarial %) "Where applicable, data are shown as the mean -C the standard deviation. for the HLA-A and HLA-B antigens between heart donor and recipient, the splits were grouped into the broader specifiaties. In a similar fashion, cross-reacting antigens were grouped into the broad specificities with which they cross-react. The match grade was defined by the number of mismatched antigens between the donor and the recipient. An antigen present in the donor but not in the recipient constituted a mismatch. In calculations of the number of mismatches, those patients with only one antigen identified at a given locus were presumed to be homozygous for that antigen. Thus, the study population was stratified into groups of either 0,1,2,3, or 4 mismatches. Because of the small number of patients with 0 mismatches (5 patients) and 1 mismatch (14 patients), these patients were combined into a single group for analysis. Analysis Patient survival and other time-related events were calculated by the Cutler-Ederer actuarial method. Actuarial curves were compared by the methods of Gehan [5]. The correlation of discrete variables with HLA mismatch grade was examined by unpaired t test. All deaths were included in the study. Actuarial values are expressed as the mean 2 the standard error. Linearized rates are expressed as the number of events per 100 patient-days (* standard deviation) during a selected postoperative interval. Results Figure 1 depicts actuarial patient survival according to HLA-A and HLA-8 mismatch grades. The figure indicates that during the first four and one-half years postoperatively, patients with fewer mismatches exhibited superior actuarial survival. At one year, survival for the 19 patients with 0 or 1 mismatch was 100% and for the 33 patients with 4 mismatches, 79 f 8%. At four years, the respective survival data were 88? 8% and 54 * 14%. Survival for the 39 pqtients in the 2-mismatch group was intermediate compared with the best and worst match grades; the one-year survival was 86 f 6%, and the four-year survival was 70 12%. All actuarial survival curves were statistically different (p < 0.05) from one another except for the 3- versus 4-mismatch grades and the 1- versus 2-mismatch grades. In addition to the joint analysis, compatibility at the A locus alone and at the B locus alone was studied. The results are shown in Table 3. Although the trends are similar for both the A locus and the B locus, with fewer mismatches associated with improved survival, statistical significance ( p < 0.05) for the observed differences in actuarial survival is reached only within the A locus (0 versus 1 mismatch and 0 versus 2 mismatches). The primary causes of death for each of the match grades are listed in Table 4. The most common cause of death in the series was infection (15 patients), followed by atherosclerosis (8 patients) and rejection (6 patients). Actuarial rejection rates for each mismatch group were determined over the entire follow-up. The findings showed no statistically significant difference in rejection rate between groups; data obtained during the first year after transplantation are shown in Table 5. Moreover, the linearized rejection rates for the first three months after operation were almost identical for all grades of HLA mismatch (Table 6). Freedom from death from rejection was also analyzed for each group on an actuarial basis (see Table 1). Once again, there was no significant difference among grades of mismatch over the five-year period, although a trend toward fewer deaths due to rejection was observed.

3 244 The Annals of Thoracic Surgery Vol 44 No 3 September 1987 Table 2. HLA Specificities Broad Specificities A LOCUS A1 A2 A3 A9 A10 Awl9 B LOCUS 85 B7 88 B B B21 Bw Bw41 Bw46 Bw67 Bw70 Bw71 Bw72 8w73 Splits or Cross-reacting Antigens Aw36 A28, Aw68, Aw69 All A23, A24 A25, A26, Aw34, Aw43, Aw66 A29, A30, A31, A32, Aw33 851, Bw52 Bw73 Bw59 844, B45 Bw64, Bw65 Bw62, Bw63, B38, 839 Bw57, Bw58 B49, Bw50 Bw42, Bw54, Bw55, Bw56 Bw53 Bw60, Bw61 Bw47, Bw48 Bw71, Bw72 Actuarial analysis was also performed for combined bacterial, fungous, protozoan, and nocardial infections. As shown in Figure 2, the actuarial infection rate is associated with the degree of HLA compatibility. Although mismatch groups 3 and 4 were not significantly different from one another, they were both different (p < 0.05) from groups 0, 1 and 2. This relationship between infection rate and HLA compatibility is also reflected in the linearized rate for the first three months after transplantation. The patients with 4 mismatches had double the rate of infection of those with 0 or 1 mismatch ( p < 0.05) (see Table 6). Although the differences in actuarial calculations of freedom from death due to infection between match groups did not reach statistical significance, the trend at one year, as shown in Table 1, indicates that more deaths due to infection occurred in the poorly matched groups. The pathogenesis of coronary atherosclerosis that oc- 0.1 (N = 19) 2 (N = 39) PERCENT 3 (N = 73) SURVIVAL 6o 4 (N = 33) I I I I I I I I I I YEARS Fig 1. Actuarial survivul according to nurnber of rnismutchcs. Table 3. Actuarial Survival One-Year Four-Year No. of No. of Survival Survival Mismatches Patients (%) ( /.I A Locus f 4 87? f 4 64? f 6 55? 11 B Locus ? f f 4 61, 7 For statistical significance, see text. Table 4. Primary Cause of Death No. of Mismatches Cause 0, Rejection Infection Atherosclerosis Nonspecific graft failure Lymphoproliferative disease Nonlymphoma malignancy Cerebrovascular accident Other Total Table 5. Actuarial Rejection Rate No. of Months Postop Mismatches , Tt 11 11? 7 11 r ? ? 6 18? f 9 16 f 7 0 Data are shown as cumulative event-free probability (%).

4 245 Frist et al: HLA Compatibility and Cardiac Transplant Recipient Survival Table 6. Linearized Rates for First 90 Postoperative Daysa No. of Mismatches Rejection Infectionb 0, t t k t t 0.16 "Data are shown as events per 100 patient-days. bthis excludes viral infections. 80 k FREE FROM,L \" Od" 1 ' 2 I ' 3 I ' I YEARS POSTOP (N= 19) (N=39) (Ne73) =33) Fig 2. Actuarial rate of infection according to number of mismatches. Data include bacterial, fungous, protozoan, and nocardial infections. Viral infections are excluded. curs in some patients after cardiac transplantation is poorly understood. It may be a manifestation of subacute, chronic, or recurrent rejection and therefore might in some fashion reflect the quality of HLA matching. All surviving patients were studied at annual intervals by coronary arteriography. Graft atherosclerosis was defined as any coronary lesion producing greater than 30% luminal narrowing. Actuarial analysis of arteriographic results over the entire follow-up revealed no significant differences between the HLA mismatch groups. At one year, % of all recipients were free from disease, and at four years, 74 * 6% were free from disease (see Table 1). Indeed 2 of the 3 deaths that occurred in the 0-mismatch group were due to accelerated graft atherosclerosis. Thus, a "full-house" match is not indicative of freedom from accelerated graft atherosclerosis. Other variables that were examined for correlation with HLA mismatch groups included age, sex, donor age, ischemic time, pathology of native heart, dosages of immunosuppressive agents, length of hospital stay, and interval between transplantation and first episode of rejection (see Table 1). None showed a significant association. Comment The introduction of cyclosporine has led to a substantial improvement in the outcome after heart transplantation. At Stanford University Medical Center, the current overall one-year survival is 83 * 2%. In this era of improved survival with cyclosporine, the value of HLA matching for heart transplantation has not been clarified. The data in this study demonstrate that the degree of mismatching for Class I HLA antigens at the A and B loci does correlate with long-term survival in cardiac transplant patients. A proposed explanation for the poorer survival in the populations with more mismatches might be that more rejection episodes occurred in the poorly matched groups and contributed to shorter graft survival and potentially higher doses of immunosuppressive drugs, each with well-known deleterious side effects. Somewhat surprising was the finding that HLA compatibility was not significantly associated with any measure of early or late rejection analyzed, including actuarial rate over five years, linearized rate during the first three months after operation, or time to first episode of rejection. However, the grade of mismatch was strongly associated with rate of infections: the better the match, the fewer the infections. This observation obtained even though maintenance immunosuppressive dosages (see Table l), as well as number of rejection episodes treated with steroid augmentation, were similar for the various mismatch groups. The major histocompatibility complex has been linked with the control of immune response in all mammalian species studied [6]. These genes affect the breadth and strength of immune responsiveness to a wide variety of antigens. Although the HLA system is the major histocompatibility system in human beings, other histocompatibility systems do exist. Their role in transplantation, however, is less clearly defined. In addition, a multitude of other host factors, including age and nutritional status, play an important role in determining acceptance or rejection of the graft as well as susceptibility or resistance to infections; the interrelationship of so many variables makes the task of defining the importance of HLA matching difficult. Any discussion of the impact of matching or mismatching must be undertaken with the understanding that the extreme polymorphism of the HLA complex makes analysis difficult and inexact, especially with a limited patient population. Interpretation of the data must be made with the following assumptions and limitations in mind. First, the evolution of HLA serology has been associated with an increasing number of antigens that have been discovered to be recognizably distinct by international consensus. The products of the HLA loci have been defined at annual workshops. Patients studied in earlier years have not been typed as specifically as patients in later years because laboratories could not take into account those antigens subsequently defined. This ongoing refinement of classification has made the interpretation of historical HLA data a complicated process and necessitates assumptions that may or may not be correct. In this study it was elected to use the broad antigen classification rather than the more specific splits. Second, those patients with only one antigen iden-

5 246 The Annals of Thoracic Surgery Vol 44 No 3 September 1987 tified at a given locus were presumed to be homozygous for that antigen. However, there exists the possibility that some of those patients are actually heterozygous for two antigens, one of which was not identified because of limitations of the current tissue-typing procedures. Third, a central limitation of any single-center study, especially in the field of heart transplantation, is the relatively few number of patients available for analysis. In this study, the association between survival and HLA compatibility has been documented. In the future, larger multicenter studies will elucidate this relationship more specifically. Although the analyses of rejection rate and coronary atherosclerosis did not show statistically significant differences in the present study, these observations are based on a relatively small number of patients, and definitive conclusions must await future investigations. Fourth, this analysis has focused on mismatches rather than on antigens in common, or matches. This approach was adopted because the experience in renal transplantation has shown that analysis on the basis of mismatches has allowed inclusion of a larger number of evaluable recipients than analysis of matched antigens while the quality of outcome results are similar. There remains the issue of alternative or additional methods of evaluating histocompatibility matching that may provide further information predictive of transplant outcome (e.g., DR typing). The implications of this study are several. Tissue typing for cardiac transplant recipients and donors should be continued at all centers to understand further the association between the determinants of survival and HLA compatibility. Future multicenter investigations to include DR matching and analysis of matching for specific antigens at each locus are likely to contribute to our understanding of this association. From a practical standpoint, securing cardiac donor- recipient pairs who are well matched for HLA-A and HLA-B on a prospective basis, even with the potential advantages of national pools, would not be easy. The scarcity of donors and the unrelenting progression of underlying heart disease without the ready availability of temporizing life-support devices combine to make prospective matching logistically difficult. However, for those centers with long recipient waiting lists of candidates in clinically stable condition, the grade of HLA compatibility may be considered a potentially important factor in the choice of an appropriate recipient for an available donor. Supported in part by Grant HL from the National Heart, Lung, and Blood Institute. References 1. Jongsma A, Someven H, Westerwald A, et al: Localization of human chromosomes by studies of human-chinese hamster somatic cell hybrids. Hum Genet 20195, Zinkernagel RM, Doherty PC: MHC cytotoxic T cells: studies on the biological role of polymorphic major transplantation antigens determining T cell restriction-specificity, function and responsiveness. Adv Immunol2751, Opelz G: Correlation of HLA matching with kidney graft survival in patients with or without cyclosporine treatment. Transplantation 40240, Ray J, Hare D, Pederson P, Mullay D: NIAID Manual of Tissue Typing Technique. NIAIH National Institutes of Health, DHEW Publication No. NIH76545, 1976, p Gehan EA: A generalized two-sample Wilcoxon test for doubly censored data. Biometrika 52650, Benacerraf B, Katz DH: The nature and function of histocompatibility-linked immune response genes. In Benacerraf B (ed): Immunogenetics and Immunodeficiency. Baltimore, University Park Press, 1975, pp Notice from the Southern Thoracic Surgical Association The thirty-fourth Annual Meeting of the Southern Thoracic Surgical Association will be held at the Boca katon Hotel and Club, Boca Raton, FL, November 5-7, There will be a $125 registration fee for nonmember physicians except for guest speakers, authors and coauthors on the program, and residents. There will be a $50 registration fee for attendees of the Postgraduate Course on Saturday, November 7, The Postgraduate Course of the Southern Thoracic Surgical Association has been expanded to a full day and will provide in-depth coverage of thoracic surgical topics selected primarily as a means to enhance and broaden the knowledge of practicing thoracic and cardiac surgeons. The Southern Thoracic Surgical Association is accredited by the Accreditation Council for Continuing Medical Education to sponsor continuing medical education for physicians. Gordon F. Murray, M.D. Secretary-Treasurer Southern Thoracic Surgical Association Basic Science Center West Virginia University Morgantown, WV 26506