Role of minor histocompatibility antigens in renal transplantation

NFAT-dependent and -independent exhaustion circuits program maternal CD8 T cell hypofunction in pregnancy

Pregnancy is a common immunization event, but the molecular mechanisms and immunological consequences provoked by pregnancy remain largely unknown. We used mouse models and human transplant registry data to reveal that pregnancy induced exhausted CD8 T cells (Preg-TEX), which associated with prolonged allograft survival. Maternal CD8 T cells shared features of exhaustion with CD8 T cells from cancer and chronic infection, including transcriptional down-regulation of ribosomal proteins and up-regulation of TOX and inhibitory receptors. Similar to other models of T cell exhaustion, NFAT-dependent elements of the exhaustion program were induced by fetal antigen in pregnancy, whereas NFAT-independent elements did not require fetal antigen. Despite using conserved molecular circuitry, Preg-TEX cells differed from TEX cells in chronic viral infection with respect to magnitude and dependency of T cell hypofunction on NFAT-independent signals. Altogether, these data reveal the molecular mechanisms and clinical consequences of maternal CD8 T cell hypofunction and identify pregnancy as a previously unappreciated context in which T cell exhaustion may occur.

Genome-wide association studies in kidney transplantation: Advantages and constraints

Since the discovery of the human leukocyte antigen (HLA) system, the role of HLA molecules in the field of transplantation has been appreciated: better matching leads to better graft function. Since then, the association of other genetic polymorphisms with clinical outcome has been investigated in many studies. Genome-wide association studies (GWAS) represent a powerful tool to identify causal genetic variants, by simultaneously analyzing millions of single nucleotide polymorphisms scattered across the genome. GWAS in transplantation may indeed be useful to reveal novel markers that may potentially be involved in the mechanism of allograft rejection and graft failure. However, the relevance of GWAS for risk stratification or donor selection for an individual patient is limited as is already reflected by the fact that many parameters, significant in one study, cannot be confirmed in another one.

Minor Antigen Disparities Impede Induction of Long Lasting Chimerism and Tolerance through Bone Marrow Transplantation with Costimulation Blockade

Mixed chimerism and tolerance can be successfully induced in rodents through allogeneic bone marrow transplantation (BMT) with costimulation blockade (CB), but varying success rates have been reported with distinct models and protocols. We therefore investigated the impact of minor antigen disparities on the induction of mixed chimerism and tolerance. C57BL/6 (H2^b) mice received nonmyeloablative total body irradiation (3 Gy), costimulation blockade (anti-CD40L mAb and CTLA4Ig), and 2 × 10⁷ bone marrow cells (BMC) from either of three donor strains: Balb/c (H2^d) (MHC plus multiple minor histocompatibility antigen (mHAg) mismatched), B10.D2 (H2^d) or B10.A (H2^a) (both MHC mismatched, but mHAg matched). Macrochimerism was followed over time by flow cytometry and tolerance was tested by skin grafting. 20 of 21 recipients of B10.D2 BMC but only 13 of 18 of Balb/c BMC and 13 of 20 of B10.A BMC developed stable long-term multilineage chimerism (p < 0.05 for each donor strain versus B10.D2). Significantly superior donor skin graft survival was observed in successfully established long-term chimeras after mHAg matched BMT compared to mHAg mismatched BMT (p < 0.05). Both minor and major antigen disparities pose a substantial barrier for the induction of chimerism while the maintenance of tolerance after nonmyeloablative BMT and costimulation blockade is negatively influenced by minor antigen disparities.        

Minor histocompatibility antigens: past, present, and future

Minor histocompatibility (H) antigens are key molecules driving allo-immune responses in both graft-versus-host-disease (GvHD) and in graft-versus-leukemia (GvL) reactivity in human leukocyte antigen (HLA)-matched hematopoietic stem-cell transplantation (HSCT). Dissection of the dual function of minor H antigens became evident through their different modes of tissue and cell expression, i.e. hematopoietic system-restricted or broad. Broadly expressed minor H antigens can cause both GvHD and GvL effects, while hematopoietic system-restricted minor H antigens are more prone to induce GvL responses. This phenomenon renders the latter group of minor H antigens as curative tools for HSCT-based immunotherapy of hematological malignancies and disorders, in which minor H antigen-specific responses are enhanced in order to eradicate the malignant cells. This article describes the immunogenetics of minor H antigens and methods that have been developed to identify them. Moreover, it summarizes the clinical relevance of minor H antigens in transplantation, with special regards to allogeneic HSCT and solid-organ transplantation.

Inosine monophosphate dehydrogenase polymorphisms and renal allograft outcome

BACKGROUND

Interindividual variation in inosine monophosphate dehydrogenase (IMPDH) enzyme activity and adverse effects caused by mycophenolate mofetil (MMF) inhibition may be genetically determined, and if so, transplant recipients should receive personalized dosing regimens of MMF, which would maximize efficacy and minimize toxicity. Some studies have demonstrated a relationship between the single nucleotide polymorphism and the risk of acute rejection with IMPDH I variants rs2278293 and rs2278294 and IMPDH II variant rs11706052, whereas others have failed to exhibit an effect. The aim of this work was to investigate the influence of these polymorphisms on acute rejection rates, graft survival and function, and MMF doses in a large cohort of patients.

METHODS

A random sample of 1040 recipients from the Collaborative Transplant Study DNA bank was genotyped for the variants IMPDH I rs2278293 and rs2278294 and IMPDH II rs11706052.

RESULTS

The presence of the T (rs2278293) and G alleles (rs2278294) in the IMPDH I variants and carriage of the G allele (rs11706052) in the IMPDH II variant did not increase the risk of rejection or affect graft function by 1 year after transplantation. There was no association with MMF dose tolerated at 1 year. Furthermore, these polymorphisms did not impact graft or patient survival at 5 years.

CONCLUSION

This study represents the largest cohort of patients with the longest follow-up to date and does not support previous evidence for an association between these IMPDH variants and renal allograft rejection and graft survival.

Frequencies of 10 autosomal minor histocompatibility antigens in Korean population and estimated disparities in unrelated hematopoietic stem cell transplantation

Disparity of minor histocompatibility antigens (mHAs) is known to induce graft-versus-tumor and graft-versus-host disease reactions in stem cell transplantation. Not much information is available on genotypic and phenotypic distributions of the currently identified mHAs, especially in Korean population. Therefore, we report genotype and phenotype frequency analyses of 10 autosomal mHAs in 329 unrelated healthy Koreans using the Sequenom MassARRAY matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) system and polymerase chain reaction-sequence specific primers (PCR-SSP). Estimates of the probability of immunogenic mismatches between donor/recipient pairs were made from observed phenotypic frequencies. HA-1 was the most favorable mHA for clinical application with the highest disparity of 7.0%. Similar results were obtained in ACC-1. The Korean population can benefit the most in a setting of matched major histocompatibility complex (MHC)-restricted mHAs-mismatched unrelated hematopoietic stem cell transplantations with the disparity rate of 27.5% with eight hematopoietic mHAs. This is the first comprehensive report on the genotypic and phenotypic frequency distributions of human mHAs in the Korean population. It can contribute to not only donor selection before transplantation but also therapeutic approaches after transplantation. It is expected that mHA-based immunotherapy will lead to a new treatment modality tailored for patients at high risk of relapse following allogeneic hematopoietic cell transplantation.

Genetic polymorphisms of adhesion molecules and kidney transplant survival

BACKGROUND.: Adhesion molecules play a key role in the recruitment of leukocytes to sites of inflammation. Genetic polymorphisms of adhesion molecules may alter their expression or function and may thereby influence the process of leukocyte infiltration in the transplanted organ. It has also been suggested that polymorphic adhesion molecules may act as minor histocompatibility antigens. METHODS.: In two randomly selected cohorts (954 and 1002 kidney transplants), the effect of L-selectin/CD62L (codon 206 and 213), platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31; codon 125, 563, and 670), and activated leukocyte cell adhesion molecule (ALCAM/CD166; codon 258) single nucleotide polymorphisms on 5-yr allograft survival was investigated. DNA samples and clinical data were provided by the Collaborative Transplant Study. Recipients and donors were genotyped by polymerase chain reaction sequence-specific primer. A multivariate analysis was performed using a Cox regression model. RESULTS.: Incompatibility for L-selectin at codon 213 was significantly associated with better graft survival in the first cohort, but the effect could not be replicated in the second cohort. Polymorphisms of PECAM-1 and ALCAM had no impact on graft outcome. CONCLUSIONS.: This is the first comprehensive and large-scale study on the relevance of L-selectin, PECAM-1, and ALCAM genetic polymorphisms in kidney transplantation, showing no significant associations of recipient or donor genotypes with allograft survival. Because the effect of L-selectin mismatch was not reproducible, a putative role of adhesion molecules as minor histocompatibility antigens cannot be confirmed. Our results demonstrate the importance of testing large sample sizes and of performing confirmation studies to validate genetic associations.

The relevance of minor histocompatibility antigens in solid organ transplantation

PURPOSE OF REVIEW

Disparities in minor histocompatibility antigens between HLA-matched organ and hematopoietic stem cell donors and recipients create the risks of graft failure and graft-versus-host disease (GvHD) respectively. A decade ago, technical advances combined with genomic information resulted in the identification of the chemical nature of the first series of minor histocompatibility antigens, facilitating their molecular typing. A new era of research had begun in exploring the role of minor histocompatibility antigens in physiological and nonphysiological settings. Here we summarize, to the best of our knowledge, human studies on the relevance of minor histocompatibility antigens in solid organ transplantation with a main focus on renal allografting.

RECENT FINDINGS

The minor histocompatibility antigen HY is associated with acute rejection, and male grafts in female recipients have reduced graft survival; both cellular and humoral responses are observed. Studies on autosomal minor histocompatibility antigens on graft rejection are less conclusive; their role in transplant tolerance, however, offers perspective.

SUMMARY

Information on the clinical relevance of minor histocompatibility antigen allo-immune responses in solid organ allografting is still scarce. The possible implications of the minor histocompatibility allo-immune responses for future clinical practice in solid organ transplantation are discussed in relation to their possible detrimental or beneficial effects on the host.

Non-HLA T-cell reactivity during the first year after HLA-identical living-related kidney transplantation

BACKGROUND

It has been reported that donor-reactive T-cell responses may decrease during the first year after HLA-mismatched organ transplantation. We wondered whether donor-reactive T-cell responses directed to minor histocompatibility antigens (mHAgs) or other non-HLA antigens also decrease after HLA-identical living-related (LR) kidney transplantation.

METHODS

We studied donor-reactive T-cell responses by IFN-gamma and granzyme B (GrB) Elispot assays in 15 HLA-identical LR kidney transplant recipients before, six months and one yr after transplantation. Third-party reactivity was used as control. Patient and donor peripheral blood mononuclear cells were typed for 11 known mHAgs.

RESULTS

During the study period, 60% and 36% of the patients demonstrated donor-reactive IFN-gamma and GrB producing cells (pc), respectively. The number of donor-reactive IFN-gamma and GrB pc was significantly lower than the number of third-party reactive IFN-gamma and GrB pc. After transplantation, donor-reactivity and third-party reactivity were comparable to pre-transplant values. No relation was found in mHAg mismatches between donor and recipient and donor-reactive T-cell response.

CONCLUSIONS

Donor-reactivity could be detected before and after HLA-identical LR kidney transplantation, but was not related with the number of mHAg mismatches, and did not decrease after transplantation.

Successful tapering of immunosuppression to low-dose monotherapy steroids after living-related human leukocyte antigen-identical renal transplantation

BACKGROUND

Living-related (LR) human leukocyte antigen (HLA)-identical renal transplant (RTx) recipients often receive standard immunosuppression, despite the absence of mismatched major HLA-antigens and the known complications of long-term use of immunosuppression. No data are available on the need for immunosuppression for these specific patients. We wondered whether their immunosuppressive load could be radically reduced.

METHOD

Between November 1982 and November 2005, 83 LR HLA-identical RTx were performed in our center. Their unadjusted graft survival was 74% at 10 years. In 29 patients (median time after transplantation 5.6 [range 1.0-21.4] years) with stable uncompromised renal function, we tapered their immunosuppression from triple or dual therapy to prednisolone 5 mg/day. Follow up on prednisolone monotherapy was at least 24 months.

RESULTS

In 27 of 29 patients reduction of immunosuppression to prednisolone monotherapy was uneventful. One patient, using dual therapy, developed JC-virus nephropathy resulting in graft loss. One refused further discontinuation of his medication. Four (15%) of the 27 patients on monotherapy developed biopsy-proven recurrence of their original disease. Only one of them showed a transient decline in renal function. One additional patient developed minor proteinuria and a rise in serum creatinine level, as a result of chronic urinary tract infections. The remaining 23 of 27 patients (85%) had an uneventful follow up during 24 months prednisolone monotherapy.

CONCLUSION

We conclude that HLA-identical LR RTx recipients who are at least 1 year after transplantation might be treated with low-dose steroid monotherapy. Close surveillance of patients for recurrence of their original disease is recommended to allow for potential early therapeutic intervention.

T-cell reactivity during tapering of immunosuppression to low-dose monotherapy prednisolone in HLA-identical living-related renal transplant recipients

BACKGROUND

In many transplant centers, human leukocyte antigen (HLA)-identical living-related (LR) renal transplant recipients receive standard maintenance immunosuppression from 1 year after transplantation. We questioned whether discontinuation of azathioprine (AZA) or mycophenolate mofetil (MMF) influenced T-cell reactivity, circulating dendritic cell (DC) subsets numbers and their maturation status.

METHODS

Twenty-nine HLA-identical LR renal transplant recipients were withdrawn from AZA or MMF. Thereafter, the patients received only prednisolone. T-cell reactivity was determined by interferon-gamma (n=23), interleukin (IL)-10 (n=16), and granzyme B (n=10) Elispot assays. Circulating DC subset numbers and their maturation status determined by CCR2, CCR5, CCR7, and CD83 expression were measured by flow cytometry (n=12).

RESULTS

The number of donor, third-party, and tetanus toxoid-reactive interferon-gamma and granzyme-B producing cells was not affected after withdrawal of immunosuppression. Discontinuation of AZA or MMF resulted in significant increased numbers of third-party (P=0.003) and tetanus toxoid-reactive (P=0.008) IL-10 producing cells, and a trend in higher numbers of donor-reactive IL-10 producing cells (P=0.06). No effect was found on the number of circulating DC subsets, but DC was shifted toward a more mature phenotype.

CONCLUSIONS

In HLA-identical LR renal transplant recipients, therapy with AZA and MMF suppress the IL-10 production and the maturation of DC. This suggests that these immunosuppressants may hinder suppression of immune responses in general, including allogeneic responses.

C3 polymorphisms and allograft outcome in renal transplantation

BACKGROUND

Complement activation plays a role in the development of chronic allograft nephropathy, a common cause of late allograft loss. The role of two complement component 3 (C3) allotypes, called C3F (fast) and C3S (slow) on the basis of their electrophoretic motility, in the long-term outcome of renal allografts remains controversial.

METHODS

We selected a random sample of 1147 donor and recipient pairs from the Collaborative Transplant Study DNA bank, and their DNA specimens were genotyped for the C3F and C3S alleles. The genotyping results were analyzed according to allograft outcome. Transplants were divided into four groups, according to the recipient and donor genotypes: SS recipient and FS or FF donor (the standard for comparison, since this combination has been reported to have the best outcome), SS recipient and donor, FS or FF recipient and SS donor, and FS or FF recipient and donor.

RESULTS

Baseline characteristics of the four transplant groups were similar. The hazard ratios for allograft survival in the SS recipient and FS or FF donor group as compared with the other three groups (SS recipient and donor, FS or FF recipient and SS donor, and FS or FF recipient and donor) were not significant: 0.90 (95% confidence interval [CI], 0.7 to 1.14; P=0.33), 0.87 (95% CI, 0.65 to 1.16; P=0.33), and 0.89 (95% CI, 0.65 to 1.23; P=0.48), respectively. The four groups had similar patient-survival rates and similar cumulative rates of acute rejection and allograft dysfunction, as assessed by means of serum creatinine levels.

CONCLUSIONS

Our results suggest that transplantation of FS or FF kidneys to SS recipients is not advantageous, possibly because chronic allograft nephropathy is a multifaceted disease involving the interplay of many biologic pathways.