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Rationale: There is significant variation in approach to pre-lung transplant donor-specific antibodies (DSA), with some centers declining to cross any DSA. We implemented a protocol for transplantation for candidates with pretransplant DSA so long as a prospective complement-dependent cytotoxicity crossmatch was negative, regardless of number, specificity, class, or mean fluorescence intensity.Objectives: To compare post-transplant outcomes including overall survival, chronic lung allograft dysfunction-free survival, antibody-mediated rejection, and acute cellular rejection in lung transplant recipients where pretransplant DSA was and was not present.Methods: This was a single-center retrospective cohort study. For recipients with pretransplant DSA, if the prospective complement-dependent cytotoxicity crossmatch was negative, the donor offer was accepted and plasmapheresis was performed within 24 hours of transplantation and continued until retrospective crossmatch results returned. Immunosuppression and post-transplant management were not otherwise modified.Results: Of the 203 included recipients, 18 (8.9%) had pretransplant DSA. The median DSA mean fluorescence intensity was 4,000 (interquartile range, 2,975-5,625; total range, 2,100-17,000). The median number of DSA present per patient was one (interquartile range, 1-2). The presence of pretransplant DSA was not associated with increased mortality (hazard ratio, 1.2; 95% confidence interval [CI], 0.4-3.4) or decreased chronic lung allograft dysfunction-free survival (hazard ratio, 1.1; 95% CI, 0.6-2.1). Recipients with pretransplant DSA were more likely to require prolonged mechanical ventilation (adjusted odds ratio, 7.0; 95% CI, 2.3-21.6) and to have antibody-mediated rejection requiring treatment (adjusted odds ratio, 7.5; 95% CI, 1.0-55.8).Conclusions: A protocol of accepting donor offers for lung transplant candidates with preformed, complement-dependent cytotoxicity crossmatch-negative DSA is associated with increased need for prolonged mechanical ventilation and antibody-mediated rejection without affecting short-term overall or chronic lung allograft dysfunction-free survival.

Supplemental Digital Content is available in the text., Background. Many kidney transplant centers in the United States report both HLA class I and II antibodies detected by sensitive solid-phase assays (SPAs) to United Network for Organ Sharing as unacceptable antigens, significantly reducing the compatible donor organ pool and prolonging waiting time for highly sensitized patients. However, the clinical relevance of all detected donor-specific antibodies (DSAs) by SPA is not unequivocal, because fluorescence intensity does not always accurately reflect antibody pathogenicity. Our center does not exclude patients from transplantation based on DSA class II. Methods. We performed a retrospective analysis in 179 deceased-donor kidney transplant recipients with solely DSA class II before transplant and patients without DSA and compared graft survival, rejection, and clinical outcomes. Patient survival was also compared with matched controls on the waiting list. Results. Patients transplanted with DSA class II showed a clear survival benefit compared with matched patients who remained on dialysis or were waitlisted on dialysis/transplanted at 5 years (100%, 34%, and 73%, respectively). After a mean follow-up of 5.5 years, there was no significant difference in death-censored graft survival between transplanted patients without DSA and those with preformed DSA class II (adjusted HR 1.10; 95% confidence interval, 0.41–2.97), although the incidence of rejection was higher in recipients with DSA class II (adjusted HR 5.84; 95% confidence interval, 2.58–13.23; P < 0.001). Serum creatinine levels at 1, 3, and 5 years posttransplant did not differ between groups. No predictors of rejection were found, although patients who received basiliximab induction therapy had higher incidence of rejection (100%) compared with those who received antithymocyte globulin (52%). Conclusions. We conclude that for highly sensitized patients, deceased-donor kidney transplantation with DSA class II yields a survival benefit over prolonged waiting time on dialysis. Instead of listing DSA class II as unacceptable antigens, an individual approach with further immunologic risk assessment is recommended.

There is significant variability in lung transplant centers' approach to HLA antibodies, creating heterogeneity regarding their clinical significance. Some institutions use beads coated with multiple HLA to screen candidate sera and then use single antigen bead (SAB) to determine antibody identity if the pre-screen is positive. Other centers do not pre-screen, using SAB alone, which may detect low-level antibodies of unknown significance. The primary objective of this study was to review the current literature to identify sources of heterogeneity in the identification of pre- and post-lung transplant HLA antibodies, particularly regarding antibody-detection methods. A random effects model meta-analysis was used to evaluate the relationship between pre-transplant HLA antibodies and the development of de novo donor-specific antibodies (dnDSA) and dnDSA and chronic lung allograft dysfunction (CLAD). Each outcome was stratified by the method of antibody detection (pre-screen followed by SAB vs SAB alone). We identified 13 cohort studies with a total of 3039 patients. The use of pre-screening followed by SAB testing and the use of induction immunosuppression were associated with lower prevalence of dnDSA. Patients with pre-transplant HLA antibodies were more likely to develop dnDSA (hazard ratio [HR] = 1.49, 95% confidence interval [CI]: 1.19-1.86, P < .001). dnDSA was associated with CLAD (HR = 2.02, 95% CI = 1.37-2.97, P < .001). When considering studies using SAB alone, however, pre-transplant antibody status was no longer associated with dnDSA and dnDSA was no longer associated with CLAD. Based on the current literature, SAB-alone testing may detect less clinically relevant antibodies than pre-screening followed by SAB.

BACKGROUND Development of donor-specific antibodies (DSA) after lung transplantation is associated with antibody mediated rejection, acute cellular rejection, and bronchiolitis obliterans syndrome; however, the significance of circulating antibodies before transplant remains unclear. METHODS We performed a retrospective cohort study including recipients of primary lung transplants between 2008 and 2012. We assessed the impact of circulating HLA and noncytotoxic DSA detected before transplant on development of Chronic Lung Allograft Dysfunction (CLAD) or CLAD-related death. RESULTS 30% of subjects had circulating class I antibodies alone, 4% Class II, and 14.4% class I and class II at mean fluorescent intensity greater than 1000. Nine percent of the subjects had DSA class I, 9% class II, and 2.4% both DSA classes 1 and 2. Neither the presence of circulating antibodies (adjusted hazard ratio, 0.87; 95% confidence interval, 0.50-1.54) nor the presence of DSA (adjusted hazard ratio, 1.56; 95% confidence interval, 0.77-3.18) before transplant at mean fluorescent intensity greater than 1000 was associated with the development of CLAD or CLAD-related death. CONCLUSIONS Although in previous studies we have shown an increased incidence of antibody-mediated rejection in patients with pretransplant DSA, neither the presence of HLA antibodies nor DSA translated to an increased risk of allograft dysfunction or death if prospective crossmatch testing was negative. Prospective studies are needed to define the impact of pretransplant sensitization on lung transplant recipients.

Background Patients with short telomere syndromes and pulmonary fibrosis have increased complications after lung transplant. However, the more general impact of donor and recipient telomere length in lung transplant has not been well characterized. Methods This was an observational cohort study of patients who received lung transplant at a single center between January 1st 2012 and January 31st 2015. Relative donor lymphocyte telomere length was measured and classified into long (third tertile) and short (other tertiles). Relative recipient lung telomere length was measured and classified into short (first tertile) and long (other tertiles). Outcome data included survival, need for modification of immunosuppression, liver or kidney injury, cytomegalovirus reactivation, and acute rejection. Results Recipient lung tissue telomere lengths were measured for 54 of the 79 patients (68.3%) who underwent transplant during the study period. Donor lymphocyte telomeres were measured for 45 (83.3%) of these recipients. Neither long donor telomere length (hazard ratio [HR] = 0.58, 95% confidence interval [CI], 0.12–2.85, p = 0.50) nor short recipient telomere length (HR = 1.01, 95% CI = 0.50–2.05, p = 0.96) were associated with adjusted survival following lung transplant. Recipients with short telomeres were less likely to have acute cellular rejection (23.5% vs. 58.8%, p = 0.02) but were not more likely to have other organ dysfunction. Conclusions In this small cohort, neither long donor lymphocyte telomeres nor short recipient lung tissue telomeres were associated with adjusted survival after lung transplantation. Larger studies are needed to confirm these findings.

HLA matching and avoidance of pre-transplant donor-specific antibodies are important in selection of donors for solid organ transplant. Solid phase testing with single antigen beads allows resolution of antibody reactivity to the level of the allele. Single antigen bead testing results at a large transplant center were reviewed to identify selective reactivity patterns of anti-HLA antibodies. Many HLA-DP antibodies were identified in the context of other HLA antibodies, but some sera had antibodies against only HLA-DP. B cell flow crossmatch testing was positive for 2 out of 9 sera with HLA-DP antibodies. Many patterns of reactivity corresponded to epitopes in hypervariable regions C and F of DPB1, but some matched epitopes in other regions or DPA1. Through analysis of single antigen bead testing from a large number of patients, we report that anti-HLA-DP antibodies predominantly recognize broadly cross-reactive epitopes. The United Network for Organ Sharing has mandated HLA-DP typing on all deceased kidney donors, and HLA-DP epitopes should be considered as the major antigens for avoidance of pre-transplant donor-specific antibodies.

Aim Currently, there are two different approaches to calculating cPRA. The first, used in USA since 2009, is the expectation maximization (EM) algorithm. The second, utilized in Europe/Canada, is to simply observe the percentage of donors with a particular antigen (“count method”). Recently, the UNOS/OPTN Histocompatibility Committee has been re-evaluating the optimal method for determining cPRA. This has been driven by the need to consider incorporating DP (and other) locus antibodies. The benefit of the EM method, based on haplotype frequencies, is to estimate population frequencies that would include unobserved, rare phenotypes. However, because DP is not in linkage disequilibrium, it may no longer be feasible to use. Here, we evaluate the use of the count method in comparison with the EM approach for determining HLA antigen frequencies in the U.S. donor population. Methods Using the UNOS/OPTN data, we evaluated HLA typings from 39,568 deceased donors from 1/2015–1/2018. We then compared the observed antigen frequencies (count method) with those derived from the UNet cPRA calculator (EM method). Results See table. Download : Download high-res image (81KB) Download : Download full-size image Conclusions There was high concordance between the two methods of calculating cPRA in antigen frequencies within the A, B, and DR loci. Instances where there were large discrepancies were primarily due to parent antigens that were subsequently split; the UNet cPRA was based upon a pool of donors from 2007–9. This suggests, at the very least, that updates to the cPRA calculator are needed. Since DPB is not in linkage disequilibrium with the other loci, thereby negating our ability to use the EM algorithm, we suggest a new updated cPRA calculator be based upon the count method of calculating antigen frequencies.

Aim Single antigen bead (SAB) assay is used to test the presence of antibodies against HLA antigens including HLA-DQ. Each SAB DQ bead is comprised of an alpha and a beta chain representative of an HLA-DQ antigen. A positive result represents reactivity to either or both chains. The aim of this report is to evaluate the frequency of HLA-DQ alpha antibodies in transplant candidates known to have Class II antibody. Methods Class II SAB data (One Lambda Inc.) was collected from 2346 transplant candidates at Brigham and Women’s Hospital from 6/9/2012 to 1/15/2014. The reactivity to HLA-DQ alpha was considered positive (MFI >3000) if all the beads containing a specific HLA-DQ alpha were reactive but the beads with corresponding HLA-DQ beta chain were negative. For example, the sera which were considered positive for HLA DQA1*03:02, had positive reaction with two beads containing DQA1*03:02, [DQA1*03:02, DQB1*03:02] and [DQA1*03:02, DQB1*03:03], but negative reaction with five beads positive for either DQB1*03:02 or DQB1*03:03 combined with DQA1 chains other than DQA1*03:02. Results Of the 29 HLA-DQ assay beads, 12 different HLA-DQ alpha chains were combined with different HLA-DQ beta chains. Sixteen (16/2346, 0.69%) sera reacted with beads specific for DQA1*03:02. These sera reacted with the alpha chain in combination with either DQB1*03:02 or DQB1*03:03. A similar pattern could be observed with sera (17/2346, 0.72%) that had specific reactivity to DQA1*02:01. Interestingly, none of the sera appeared to react selectively with DQA1*01:01, DQA1*01:02, DQA1*03:01, or DQA1*05:01. Although reactions with beads coated with DQA1*01:03, DQA1*03:03, DQA1*04:01, DQA1*05:03, DQA1*05:05, or DQA1*06:01 were present, they could not be attributed to DQA1 as the number of reactions or beads were not sufficient to rule out reactivity to DQB1. Out of the 33 patients who showed reactivity to either DQA1*03:02 or DQA1*02:01, only three (9.1%) had reactivity exclusively to the HLA-DQ alpha chain with no reactivity to any other HLA class II antigen. Conclusions The frequency of antibodies which appear to have HLA-DQ alpha specificity in transplant candidates is low (1.4%). Our results imply that a large number of sensitized patients will have to be studied in order to determine the clinical significance of antibodies to DQAlpha.

Anti-human histocompatibility antigen antibodies (HLA-Ab) are deleterious after kidney transplant and may be increased after T-cell depleting agents are given. A retrospective case control study was conducted to evaluate increase in HLA-Ab in 27 kidney transplant recipients who had received antithymocyte globulin (ATG) induction compared with 27 control subjects. A greater than 10% increase in class I or class II HLA-Ab was found in 6 (22.2%) of ATG subjects versus only 1 (3.7%) of non-ATG subjects (p = 0.05). In females, 6/14 ATG subjects developed increased HLA-Abor =10% compared with none of the control subjects (p = 0.016). In sensitized subjects, 4/10 in the ATG group developed increased HLA-Abor =10% versus none of the controls (p = 0.043). There was no difference in number or severity of acute rejection episodes or estimated glomerular filtration rate 6 months after transplant between the two treatment groups. We conclude that ATG induction may result in increased posttransplant HLA-Ab, particularly in subjects at higher immunologic risk. Further studies are necessary to determine the natural history, clinical consequences, appropriate therapy, and mechanisms responsible for HLA-Ab in this setting.

BACKGROUND : TRALI is thought to be triggered by recipient-specific anti-HLA class I or antibodies against neutrophils in donor plasma. Recently, anti-HLA class II have also been implicated. The prevalence of anti-HLA class II was investigated in normal volunteer platelet donors and in two nonfatal TRALI cases utilizing a flow-based assay. Potential target antigens also were investigated. STUDY DESIGN AND METHODS : Commercial flow cytometry-based assays (FlowPRA, One Lambda, Inc.) for anti-HLA class I and II were compared with standard lymphocytotoxicity tests. Subsequently, 151 volunteer platelet donors and two clinical cases of TRALI were screened with FlowPRA. Immunohistochemical studies were performed on lung tissue from a surgical case, an autopsy case, and a fatal TRALI case. RESULTS : The FlowPRA assays showed moderate concordance for anti-HLA class I (κ = 0.448) and good concordance for class II antibodies (κ = 0.801), when compared to standard lymphocytotoxicity assays. Ten and 9 percent of female platelet donors were positive for anti-HLA class I and class II, respectively. Two nonfatal cases of TRALI showed both anti-HLA class I and anti-HLA class II. Immunohistochemical analysis of a TRALI case revealed granulocyte aggregation in alveolar capillaries with activated vascular endothelial cells. HLA class II antigen expression was not present on vascular endothelium or intravascular WBCs; however, strong expression was seen on alveolar macrophages. CONCLUSION : FlowPRA assays often detect anti-HLA class I not detected by conventional lymphocytotoxicity assays. These assays reveal anti-HLA class II in normal female donor plasma and in sera implicated in TRALI. Immunohistochemical studies failed to reveal endothelial or intravascular-WBC HLA class II antigen expression in lung tissue derived from TRALI cases or controls, but demonstrated HLA class II expression on pulmonary macrophages.

Aim Accurate classification of serologically-distinct antigens (Ag) is critical in organ allocation, and nowadays it is possible to define anti-HLA antibody specificity to the allelic level. We examined class I antibodies (Ab) for allelic specificities that may be serologically distinct and evaluated its impact on crossmatch (XM) results and organ allocation. Methods 6726 sera were tested for anti-HLA Ab using LABScreen Single Ag assay (One Lambda), in which 17 class I HLA Ag are represented by more than one allele. Discordance in MFI values between the two allelic beads was examined as a categorical variable to mimic clinical practice, and as a continuous variable (MFI value) to better reflect biological plausibility. To evaluate the significance of an allele-specific Ab on XM results, we examined an unbiased cohort of deceased donor-candidate testing (125,828 CDC XMs between 2014 and 2017). In our lab, all candidates within a blood group have a CDC XM performed, regardless of whether they have donor-specific antibody (DSA). This uniquely allows us to examine whether a candidate with an allele-specific DSA, who has already been excluded from the match run, would indeed have a positive XM against a donor who has a different allele. Statistical analyses were performed using JMP12Pro (SAS Institute). Results 1. The incidence of discordance between the two allelic beads varied depending on whether MFI values were considered as continuous vs categorical variables. 2. The presence of allele-specific Ab for rare alleles was out of proportion to their frequencies in the population. 3. The presence of Ab against only the rare allele was a poor predictor of a positive CDC XM, with a positive predictive value of 0–7% compared with 52.5% if the candidate had DSA against an A or B locus Ag. Conclusions 9 out of 17 Class I HLA antigens had potential allele-specific reactivity, meaning that candidates with antibody selectivity against rare alleles may be unnecessarily excluded from many organ offers based on definition of unacceptable antigens by serological equivalence. Conversely, for centers relying on virtual-XM, prematurely defining alleles as new serological splits could unfortunately allow transplants for which the recipient has DSA. Further testing is needed to rigorously confirm these allele-specific reactivity patterns.

The prevalence of anti-HLA antibodies in lung transplant candidates and their impact on waitlist and transplant outcomes is not known.We examined the prevalence of pretransplant anti-HLA antibodies at varying thresholds and evaluated their impact on outcomes before and after lung transplantation.We performed a single-center retrospective cohort study including all patients listed for lung transplantation between January 2008 and August 2012. Per protocol, transplant candidates were assessed by solid phase LABscreen mixed Class I and II and LABscreen Single Antigen assays.Among 224 patients, 34% had anti-HLA antibodies at mean fluorescent intensity (MFI) greater than or equal to 3,000 (group III), and 24% had antibodies at MFI 1,000 to 3,000 (group II). Ninety percent of the patients with pretransplant anti-HLA antibodies had class I antibodies, whereas only seven patients developed class II alone. Patients in group III were less likely to receive transplants than patients without any anti-HLA antibodies (group I) (45.5 vs. 67.7%, P = 0.005). Wait time to transplant was longer in group III than group I, although this difference did not meet statistical significance, and waitlist mortality was similar. Among transplant recipients, antibody-mediated rejection (AMR) was more frequent in group III than in group II (20% vs. 0%, P = 0.01) or group I (6.3%, P = 0.05).The presence of anti-HLA antibodies at the high MFI threshold (3,000) was associated with lower transplant rate and higher rates of AMR. Screening for anti-HLA antibodies using the 3,000 MFI threshold may be important in managing transplant candidates and recipients.

A 56-year-old white female presented for evaluation for kidney transplantation in November 2003. Her end-stage renal disease (ESRD) was presumed due to medullary sponge kidney associated with stones and infection and she had started haemodialysis in April 2003. Other medical history included hypertension and anaemia. She was otherwise well. She had had four pregnancies and had received blood transfusions. Examination was unremarkable. Initial tests showed blood group ABO-O. Her current panel reactive antibody (PRA) was 64% by the complement-dependent cytotoxicity (CDC) method and the peak PRA, 5 months prior to that, was 100%. Flow PRA screening confirmed IgG antibodies against class I and II human leukocyte antigens (HLA). The cause of the sensitization to HLA antigens was presumed to be the pregnancies and transfusions. Her 37-year-old son was the only potential living donor but he was ABO-A1; furthermore, she had a positive CDC crossmatch against his T and B lymphocytes. The patient’s baseline anti-A antibody titre was 1:128 (Figure 1). Because of her high sensitization to HLA antigens, the idea of a transplant across the HLA and ABO barrier was discussed with the patient. She was advised to wait several months to see if her PRA or crossmatch titres fell with rituximab therapy. She was vaccinated against pneumococcus and meningococcus in the event that a splenectomy would be included in her immunosuppressive protocol. She received rituximab 375mg/m in March and April of 2004. However, the crossmatch remained strongly positive and the PRA remained high (Table 1). After detailed discussion of the risks vs benefits, the patient and son gave informed consent to proceed with transplantation of a kidney from the son to the mother. Before 4 weeks of the transplant, she began receiving thrice-weekly plasmapheresis and daily tacrolimus plus mycophenolate mofetil (MMF). She was given 10 g of IgG intravenously after each plasmapheresis session. The anti-microbial prophylaxis was sulfamethoxazole-trimethoprim (SMX-TMP) and acyclovir. On 20 December 2004, the T-cell and B-cell crossmatch against her donor were negative and the anti-A titre (IgG titer by enhanced antiglobulin assay) was 1:2 (Figure 1). A third dose of rituximab was given, and she underwent kidney transplantation the next day. A laparoscopic handassisted splenectomy was also performed. There were no intra-operative complications and the allograft produced urine immediately. She received five more sessions of plasmapheresis in the first 10 post-operative days, to maintain anti-A titres 1 : 4. The patient was discharged 1 week after surgery with a plasma creatinine of 63 mmol/l. Immunosuppression was now tacrolimus, MMF and prednisone. After 2 weeks of the transplant, the creatinine rose to 141 mmol/l, and an urgent allograft biopsy was performed. The anti-A titre was 1 : 4 and the crossmatch was positive against donor Tand B-cells by flow cytometry. The biopsy showed mild focal neutrophil capillaritis, acute tubular injury and intraluminal calcifications. There was diffuse staining for C4d in the peritubular capillaries. Interestingly, she had started p.o. phosphate 1–2 days prior to the elevation in plasma creatinine. The possibility of acute calcium—phosphate precipitation in the allograft [1] was, therefore, entertained and the phosphate was stopped. The presumed acute antibodymediated rejection was treated with four sessions of plasmapheresis over 10 days (followed by 10 g IgG) and pulse IV methylprednisolone. The plasma creatinine fell quickly to 71 mmol/l. A repeat flow cytometry crossmatch against donor Tand B-cells was negative. The patient was continued on immunosuppression with tacrolimus, MMF and prednisone. No further Correspondence and offprint requests to: Colm C. Magee, MD, Renal Division, Brigham and Women’s Hospital, 75 Francis Street, Boston, MA 02115, USA. Email: cmagee@partners.org Nephrol Dial Transplant (2007) 22: 602–604

Aim Bw4 and Bw6 are mutually exclusive HLA Class I “public” epitopes encoded by amino acids 77–83. We sought to explore selective reactivity patterns of sera with antigens which only differed for Bw4 or Bw6. Methods We tested 6726 sera from 2953 transplant candidates using Labscreen ® Single Antigen (One Lambda, Canoga Park, CA). We focused on target alleles B∗27:05(Bw4) vs B∗27:08(Bw6) and B∗53:01(Bw4) vs B∗35:01(Bw6). Reactions were called Positive (MFI > 3000) or Negative (MFI Results Table 1 shows the excellent correlation between the two sets of allele pairs we used to detect anti-Bw4/Bw6 antibody. Fig. 1 shows that the mean MFI against Bw4 or Bw6 on the other target alleles in the kit were strongly predicted based only on the deduction from the two B27 alleles. Similar predictive value was found for the B35/B53 allele pair. Conclusion Use of selective reactivity of sera with allele targets which only differ in the Bw4 or Bw6 epitopes is a definitive method for detecting such antibodies without presence of masking antibodies against private antigens. Table 1 Bw4 Bw6 B∗53:01posB∗35:01neg B∗53:01negB∗35:01pos Bw4 B∗27:05posB∗27:08neg 79 0 Bw6 B∗27:05negB∗27:08pos 1 37

Two monoclonal antibodies, anti-2H4 and anti-4B4, reciprocally divide the T4+ (CD4+) and T8+ (CD8+) lymphocytes into T4+2H4+, T4+4B4+, T8+2H4+ and T8+4B4+ subsets. The T4+2H4+, T4+4B4+ and T8+2H4+ subsets possess suppressor-inducer, helper-inducer, and suppressor-effector function, respectively, as previously defined in a system of B cell immunoglobulin production. Using monoclonal antibodies, including anti-2H4 and anti-4B4, and flow cytometry, we monitored lymphocyte subpopulations in 66 renal allograft recipients. We found that patients with stable allograft function have a decrease in the percentage of total T4+ lymphocytes from 41.9 +/- 9.5% pretransplant (pre-Tx) to 36.3 +/- 13.9% posttransplant (post-Tx) (P less than 0.05). This decrease was seen mainly in the T4+4B4+ or helper-inducer subset from 20.8 +/- 4.7% (pre-Tx) to 16.0 +/- 6.3% (post-Tx) (P less than 0.005). Patients with stable function were also noted to have an increase in the percentage of total T8+ lymphocytes from 21.3 +/- 10.7% (pre-Tx) to 30.9 +/- 15.4% (post-Tx) (P less than 0.02). Examination of T8 subsets revealed that a statistically significant increase was seen in the T8+2H4+ or suppressor effector subset from 15.5 +/- 9.2% (pre-Tx) to 21.5 +/- 10.2% (post-Tx) (P less than 0.01). Additionally, serial studies on 14 patients revealed an increase in the %T4+2H4+ suppressor-inducer subset from 9.31 +/- 3.64% (pre-Tx) to 15.71 +/- 6.41% (post-Tx) (P less than 0.0025). Since the role of these subsets has not been established in alloimmunity, in vitro allogeneic studies of 2H4-enriched (2H4+) and 2H4-depleted (2H4-) lymphocytes from normal peripheral blood were performed. In the mixed lymphocyte reaction, 2H4+ cells proliferated less than 2H4- cells (cpm ratio 2H4+/2H4-: 0.63-0.84), but 2H4+ cells generated twice as much suppressor activity as 2H4- cells (ratio % suppression 2H4+/2H4-: 1.9-2.3). These results suggest that 2H4+ cells play a role in the suppressor limb of the alloimmune response and that the increase in cells of this phenotype in our transplant population may be responsible for the maintenance of stable allograft function.

Patients were entered into a randomized trial of prophylaxis for renal allograft rejection by the administration of an anti-human IL-2 receptor antibody, anti-Tac, during the first ten days posttransplant. Interleukin-2 receptor (IL-2 R) expression was measured using two anti-IL-2 R monoclonal antibodies (moAbs), anti-Tac and 1HT4-4H3. These two antibodies recognize closely spaced epitopes on the 55 kD chain of the IL-2 R. IL-2 R expression was examined on peripheral blood small lymphocytes in three groups of patients who received: (A) cyclosporine CsA and prednisone for baseline immunosuppression (n = 9); (B) anti-Tac with CsA and prednisone as baseline immunosuppression (n = 12); and (C) anti-Tac with azathioprine and prednisone as baseline immunosuppression (n = 5). We found that large numbers of T cells express IL-2 receptors despite the presence of anti-Tac (average of IL-2 R-positive cells at day of peak IL-2 R expression 56.0 +/- 20.8% in group A, 65.2 +/- 26.6% in group B, 21.0 +/- 7.4% in group C). IL-2 R expression did not correlate with clinical activity, and the presence or accessibility of epitopes on the same 55 kD chain varied dramatically from patient to patient.