The effect of HLA mismatch on highly sensitized renal allograft recipients

Association of human leukocyte antigen mismatches between donor-recipient and donor-donor in pancreas after kidney transplant recipients

The effects of HLA mismatching on pancreas outcomes among pancreas after kidney (PAK) recipients are undefined. Outcomes might potentially differ depending on whether there is a mismatch between pancreas donor and recipient (PD-R) or pancreas donor and kidney donor(PD-KD). All primary PAK at our centre were included in this study. Patients were divided into two groups based on the degree of HLA mismatching: low (L-MM) as 0-4 and high (H-MM) as 5-6. We analysed all (N = 73) PAK for PD-R mismatch and the subset of PAK for PD-KD mismatch (N = 71). Comparing PD-R L-MM (n = 39) and H-MM (n = 34) PAKs, we observed no difference in the rate of pancreas graft failure. There was also no difference in the rate of rejection (L-MM 33% vs. H-MM 41%) or the severity of rejection. However, we observed a significantly (P < 0.01) shorter time to acute pancreas rejection in the H-MM group (6.8 ± 8.7 mo) versus the L-MM cohort (29.0 ± 36.2 mo) (P < 0.001). Similar to the PD-R mismatched cohort, we did not observe a detrimental effect of HLA mismatching on graft outcomes in the PD-KD cohort; time to rejection was again shorter in the H-MM subset. In this study, we found no impact of HLA mismatch on either pancreas graft survival or rejection rates, though rejection occurred earlier in high mismatched PAK transplants.

The impact of HLA-DR mismatch status on retransplant-free survival and bronchiolitis obliterans syndrome‒free survival among sensitized lung transplant recipients

INTRODUCTION

Donor‒recipient HLA-DR locus matching may be protective against bronchiolitis obliterans syndrome (BOS) in lung transplant recipients. It is unknown whether this benefit is more significant among sensitized (calculated panel reactive antibodies (CPRAs) of >0%) and highly sensitized (CPRAs of ≥80%) recipients who may be at a higher risk for BOS.

METHODS

This was a retrospective cohort study of adults in the Scientific Registry of Transplant Recipients who underwent lung transplantation between May 5, 2005 and May 31, 2019. Retransplant-free survival and BOS-free survival were compared among recipients with 0 vs ≥1 DR mismatches, grouped according to sensitization.

RESULTS

Among all 20,355 included recipients, 0 DR mismatch status was associated with improved retransplant-free survival (hazard ratio [HR] = 0.83, 95% CI = 0.74-0.93, p = 0.002) and BOS-free survival (HR = 0.86, 95% CI = 0.77-0.96, p = 0.007). Among sensitized recipients, 0 DR mismatch status was also associated with improved retransplant-free survival (HR = 0.79, 95% CI = 0.65-0.97, p = 0.02) and BOS-free survival (HR = 0.82, 95% CI = 0.67-1.00, p = 0.04). There was however no difference in retransplant-free or BOS-free survival between sensitized and non-sensitized recipients with 0 DR mismatches. Among highly sensitized recipients, 0 DR mismatch status was not associated with retransplant-free or BOS-free survival. Among sensitized and highly sensitized recipients, 0 DR mismatch status was not associated with reduced use of plasmapheresis or reduced biopsy-proven, treated acute cellular rejection compared with non-sensitized recipients.

CONCLUSIONS

HLA-DR matching is associated with a similar improvement in retransplant-free and BOS-free survival among non-sensitized and sensitized lung transplant recipients. DR matching does not confer a more substantial retransplant-free or BOS-free survival benefit to highly sensitized recipients than to non-sensitized recipients.

HLA testing in the molecular diagnostic laboratory

The human leukocyte antigen (HLA) system is a highly polymorphic family of genes involved in immunity and responsible for identifying self versus non-self. HLA typing is essential for solid organ and bone marrow transplantation as well as in non-transplant settings such as disease association and pharmacogenomics. Typing of HLA genes differs from most molecular testing as, rather than evaluating differences from an accepted "wild-type" gene, it must distinguish between thousands of similar, but distinct alleles. This article will describe the HLA system and nomenclature. We will then discuss clinical uses of HLA typing including solid organ transplantation, hematopoietic stem cell transplantation, evaluation of platelet refractory patients, disease association, and pharmacogenetics. Finally, we describe common molecular methods of HLA typing.

Intravenous Immunoglobulin and Rituximab in HLA Highly Sensitized Kidney Transplant Recipients

INTRODUCTION

HLA-sensitized patients are penalized both in the access to kidney transplantation (KT) and, once transplanted, in the incidence of rejections and long-term allograft survival despite aggressive induction and maintenance therapy.

METHODS

This study retrospectively evaluates the impact of combining T- and B-cell-depleting agents and intravenous immunoglobulin for induction therapy in 45 highly sensitized KT patients (anti-panel reactive antibodies >60%, positive flow cytometry crossmatch or donor specific antibodies at the time of transplantation). The outcome data included the occurrence of biopsy-proven acute rejection, new-onset proteinuria, development of leukopenia, incidence of poliomavirus infection (BK or JC virus), fungal or bacterial infection after KT, de novo neoplasia, graft function, graft loss, or death with functioning KT.

RESULTS

The average panel reactive antibody was 62.5%; 41 patients (91.1%) had ≥3 HLA mismatches with the donor and 91.1% of patients had class I or II anti-HLA antibodies. Fourteen patients (31.1%) presented pre-KT donor-specific antibodies and 6 patients (13.3%) had a positive flow cytometry cross-match at the time of transplantation. The incidence of acute rejection in the first 6 months was 24.4% and the cumulative incidence was 37.8%. Two patients were diagnosed with leukopenia in the first 6 months after KT. Two patients (4.5%) had cytomegalovirus disease, 17 patients (37.8%) were diagnosed with bacterial infections. Cutaneous neoplasms were identified in 5 patients (11.1%) and solid tumors in 4 (8.9%). The death-censored graft survival was 100% in the first 6 months and 93.5% at the last evaluation. Patient survival in the same periods was 97.8% and 93.3%, respectively.

CONCLUSIONS

Induction immunosuppressive therapy with intravenous immunoglobulin and rituximab is effective; outcomes demonstrate an excellent patient and allograft survival and allograft function over the follow-up period.

Risk Factors for Acute Rejection After Deceased Donor Kidney Transplantation in China

OBJECTIVES

This study aimed to identify the potential risk factors of acute rejection after deceased donor kidney transplantation in China.

METHODS

Adult kidney transplantations from deceased donors in our center from February 2004 to December 2015 were enrolled for retrospective analysis. All deceased donations complied with China's Organ Donation Program. No organs from executed prisoners were used. The incidence of clinical and biopsy-proved acute rejection was assessed with the Kaplan-Meier method, and the Cox proportional hazard model was used for multivariate analysis.

RESULTS

One-year, 2-year, 3-year and 5-year incidences of acute rejection were 12.4%, 14.2%, 14.8%, and 17.1%, respectively. Multivariate analysis demonstrated that longer pre-transplant dialysis duration (hazard ratio [HR] 1.009 per month; 95% confidence interval, 1.003-1.015; P = .003), positive pre-transplant panel reactive antibody (PRA) (positive vs negative HR 3.266; 1.570-6.793; P = .023), and increasing HLA mismatches (≥4 vs < 4 HR 2.136; 1.022-4.465; P = .044) increased the risk of acute rejection, while tacrolimus decreased acute rejection risk compared to cyclosporine (HR 0.317; 0.111-0.906; P = .032).

CONCLUSION

Longer pre-transplant dialysis duration, HLA mismatch, and positive pre-transplant PRA increase the risk of acute rejection, while tacrolimus helps prevent acute rejection compared to cyclosporine in deceased donor kidney transplantation.

HLA Mismatching Strategies for Solid Organ Transplantation - A Balancing Act

HLA matching provides numerous benefits in organ transplantation including better graft function, fewer rejection episodes, longer graft survival, and the possibility of reduced immunosuppression. Mismatches are attended by more frequent rejection episodes that require increased immunosuppression that, in turn, can increase the risk of infection and malignancy. HLA mismatches also incur the risk of sensitization, which can reduce the opportunity and increase waiting time for a subsequent transplant. However, other factors such as donor age, donor type, and immunosuppression protocol, can affect the benefit derived from matching. Furthermore, finding a well-matched donor may not be possible for all patients and usually prolongs waiting time. Strategies to optimize transplantation for patients without a well-matched donor should take into account the immunologic barrier represented by different mismatches: what are the least immunogenic mismatches considering the patient’s HLA phenotype; should repeated mismatches be avoided; is the patient sensitized to HLA and, if so, what are the strengths of the patient’s antibodies? This information can then be used to define the HLA type of an immunologically optimal donor and the probability of such a donor occurring. A probability that is considered to be too low may require expanding the donor population through paired donation or modifying what is acceptable, which may require employing treatment to overcome immunologic barriers such as increased immunosuppression or desensitization. Thus, transplantation must strike a balance between the risk associated with waiting for the optimal donor and the risk associated with a less than optimal donor.

Pretransplantation monitoring of HLA antibodies by complement dependent cytotoxicity and Luminex-based assays

BACKGROUND

The introduction of more sensitive techniques, such as Luminex® for HLA antibody screening of patients awaiting organ transplantation has resulted in a better understanding of transplantation immunology and improvements in clinical practice.

OBJECTIVE

The interpretation of the results obtained only by Luminex® can lead to inaccurate evaluation of a patient's antibody status and unjustified rejection of a potential organ donor. The aim of this study was to demonstrate the benefits of performing HLA antibody screening in the sera of patients on the waiting list for organ transplantation by two different assays, complement dependent cytotoxicity (CDC) and Luminex®.

METHODS

A retrospective analysis was performed on 563 pretransplant serum samples from 141 patients on the kidney transplantation waiting list in Rijeka, tested from March 2012 until March 2015. All samples were tested in parallel by the CDC assay and the Luminex®-based assay.

RESULTS

Out of the 563 samples tested 302 (53.7%) tested negative for HLA antibodies and 88 (15.6%) positive by both assays. From 173 (30.7%) samples with discordant results 149 (26.5%) were CDC negative and Luminex® positive, while 24 (4.3%) were CDC positive and Luminex® negative. Among the Luminex positive patients seven did not experience any immunizing events.

CONCLUSION

Evaluation of the HLA antibody status in patients on a waiting list for organ transplantation should be based on the results of the both CDC and Luminex® (or other sensitive) assays in accordance to information about patient's clinical status and exposure to immunizing events.

A candidate gene approach of the calcineurin pathway to identify variants associated with clinical outcomes in renal transplantation

AIM

To investigate the potential influence of variants in genes involved in the calcineurin pathway on the efficacy and toxicity of calcineurin inhibitors in renal transplantation.

MATERIALS & METHODS

Twenty-three polymorphisms in thirteen genes were tested in 381 renal transplant recipients receiving ciclosporin (n = 221) or tacrolimus (n = 160) and mycophenolate mofetil. Data were collected prospectively over the first year post-transplantation.

RESULTS

Multivariate survival analyses revealed no genetic associations with biopsy proven acute graft rejection and serious infections. Donor-recipient Cytomegalovirus mismatch was the only variable associated with serious infection.

CONCLUSION

This large exploratory study casts doubts on the potential interest of genetic biomarkers related to CNI pharmacodynamics but associations with other phenotypes in transplantation deserve further studies.

Combined induction therapy with rabbit antithymocyte globulin and rituximab in highly sensitized renal recipients

Compared to non-sensitized renal transplant recipients, patients with preformed alloantibodies are at greater risk of cellular and humoral rejection and premature graft failure. We explored the effects of adding B-cell depleting agent (rituximab) to standard rabbit anti-thymocyte globulin (rATG) induction regimen for patients with panel reactive antibody levels >50%. Following induction therapy, 14 recipients were given two doses of rituximab (375 mg/m(2)) within the first month post-transplantation. Their long-term outcomes were compared to a historical control group of 23 recipients who received rATG alone. Graft survival at 5 years was superior with combination therapy compared to induction therapy alone (92.9 versus 48.3%, respectively, p = 0.02). While 30% of the rATG alone group experienced cellular rejection and 26% humoral rejection, none of rituximab plus rATG renal transplant recipients group had rejection. Thus, addition of rituximab to rATG provided superior outcomes to rATG alone. This combination induction therapy should be considered for a high-risk population.

Efficacy and safety of thymoglobulin and basiliximab in kidney transplant patients at high risk for acute rejection and delayed graft function

OBJECTIVES

To compare the efficacy and safety of thymoglobulin compared with basiliximab in patients who had kidney transplants and are at high risk for acute rejection and delayed graft function.

MATERIALS AND METHODS

A retrospective review of patients who had 1 or more risk factors for acute rejection and delayed graft function and who were given either thymoglobulin or basiliximab for induction therapy. Incidences of acute rejection, antibody-treated acute rejection, delayed graft function, chronic rejection, cancer, infection, leucopenia, and thrombocytopenia were compared between thymoglobulin and basiliximab groups. Serum creatinine levels within 1 year and long-term graft and patient survival also were compared.

RESULTS

A total of 327 patients were included. Incidences of acute rejection, antibody-treated acute rejection, delayed graft function, and chronic rejection were significantly lower in the thymoglobulin group than in the basiliximab group (P < .05). Serum creatinine levels were lower in the thymoglobulin group on postoperative days 7, 14, and 30 (P < .05). There were no statistically significant differences regarding long-term graft and patient survival, cancer, or total infection rate between the groups. Incidences of Cytomegalovirus infection, leucopenia, and thrombocytopenia were significantly higher in the thymoglobulin group (P < .05).

CONCLUSIONS

Thymoglobulin may improve short-term outcomes, compared with basiliximab, in patients who had kidney transplants and are at high risk for acute rejection and delayed graft function. However, long-term outcomes are similar with thymoglobulin and basiliximab.

Treatment options and strategies for antibody mediated rejection after renal transplantation

Antibody mediated rejection is a significant clinical problem encountered in a subset of renal transplant recipients. This type of rejection has a variable pathogenesis from the presence of donor specific antibodies with no overt disease to immediate hyperacute rejection and many variations between. Antibody mediated rejection is more common in human leukocyte antigen sensitized patients. In general, transplant graft survival after antibody mediated rejection is jeopardized, with less than 50% graft survival 5 years after this diagnosis. A variety of agents have been utilized singly and in combinations to treat antibody mediated rejection with differing results and significant research efforts are being placed on developing new targets for intervention. These same agents have been used in desensitization protocols with some success. In this review, we describe the biology of antibody mediated rejection, review the available agents to treat this form of rejection, and highlight areas of ongoing and future research into this difficult clinical problem.