Minor histocompatibility antigens

Rejection of leukemic cells requires antigen-specific T cells with high functional avidity

In a context where injection of antigen (Ag)-specific T cells probably represents the future of leukemia immunotherapy, identification of optimal target Ags is crucial. We therefore sought to discover a reliable marker for selection of the most potent Ags. To this end, (1) we immunized mice against 8 individual Ags: 4 minor histocompatibility Ags (miHAs) and 4 leukemia-associated Ags (LAAs) that were overexpressed on leukemic relative to normal thymocytes; (2) we assessed their ability to reject EL4 leukemic cells; and (3) we correlated the properties of our Ags (and their cognate T cells) with their ability to induce protective antileukemic responses. Overall, individual miHAs instigated more potent antileukemic responses than LAAs. Three features had no influence on the ability of primed T cells to reject leukemic cells: (1) MHC-peptide affinity; (2) the stability of MHC-peptide complexes; and (3) epitope density at the surface of leukemic cells, as assessed using mass spectrometry. The cardinal feature of successful Ags is that they were recognized by high-avidity CD8 T cells that proliferated extensively in vivo. Our work suggests that in vitro evaluation of functional avidity represents the best criterion for selection of Ags, which should be prioritized in clinical trials of leukemia immunotherapy.

Origin and plasticity of MHC I-associated self peptides

Endogenous peptides presented by MHC I molecules represent the essence of self for CD8 T lymphocytes. These MHC I peptides (MIPs) regulate all key events that occur during the lifetime of CD8 T cells. CD8 T cells are selected on self-MIPs, sustained by self-MIPs, and activated in the presence of self-MIPs. Recently, large-scale mass spectrometry studies have revealed that the self-MIP repertoire is more complex and plastic than previously anticipated. The composition of the self-MIP repertoire varies from one cell type to another and can be perturbed by cell-intrinsic and -extrinsic factors including dysregulation of cellular metabolism and infection. The complexity and plasticity of the self-MIP repertoire represent a major challenge for the maintenance of self tolerance and can have pervasive effects on the global functioning of the immune system.

Prediction of graft-versus-host disease in humans by donor gene-expression profiling

BACKGROUND

Graft-versus-host disease (GVHD) results from recognition of host antigens by donor T cells following allogeneic hematopoietic cell transplantation (AHCT). Notably, histoincompatibility between donor and recipient is necessary but not sufficient to elicit GVHD. Therefore, we tested the hypothesis that some donors may be "stronger alloresponders" than others, and consequently more likely to elicit GVHD.

METHODS AND FINDINGS

To this end, we measured the gene-expression profiles of CD4(+) and CD8(+) T cells from 50 AHCT donors with microarrays. We report that pre-AHCT gene-expression profiling segregates donors whose recipient suffered from GVHD or not. Using quantitative PCR, established statistical tests, and analysis of multiple independent training-test datasets, we found that for chronic GVHD the "dangerous donor" trait (occurrence of GVHD in the recipient) is under polygenic control and is shaped by the activity of genes that regulate transforming growth factor-beta signaling and cell proliferation.

CONCLUSIONS

These findings strongly suggest that the donor gene-expression profile has a dominant influence on the occurrence of GVHD in the recipient. The ability to discriminate strong and weak alloresponders using gene-expression profiling could pave the way to personalized transplantation medicine.

The H4b minor histocompatibility antigen is caused by a combination of genetically determined and posttranslational modifications

Minor histocompatibility (H) Ag disparities result in graft-vs-host disease and chronic solid allograft rejection in MHC-identical donor-recipient combinations. Minor H Ags are self protein-derived peptides presented by MHC class I molecules. Most arise as a consequence of allelic variation in the bound peptide (p) that results in TCR recognizing the p/MHC as foreign. We used a combinational peptide screening approach to identify the immune dominant H2K(b)-restricted epitope defining the mouse H4(b) minor H Ag. H4(b) is a consequence of a P3 threonine to isoleucine change in the MHC-bound peptide derived from epithelial membrane protein-3. This allelic variation also leads to phosphorylation of the H4(b) but not the H4(a) epitope. Further, ex vivo CD8(+) T lymphocytes bind phosphorylated Ag tetramers with high efficiency. Although we document the above process in the minor H Ag system, posttranslational modifications made possible by subtle amino acid changes could also contribute to immunogenicity and immune dominance in tumor immunotherapeutic settings.

Risk factors for corneal graft failure and rejection in penetrating keratoplasty

PURPOSE

To evaluate risk factors for graft failure and allograft rejection after penetrating keratoplasty (PK).

METHODS

We retrospectively studied clinical results of PKs in terms of graft survival and rejection-free graft survival rates. PKs were done on 271 eyes between 1987 and 1997. Clinical results were analyzed by Kaplan-Meier's life table method and the log-rank test. Relative risks and adjusted survival probabilities for each value of the factor were compared with the risk for a specified reference value.

RESULTS

The overall rates of graft survival and rejection-free graft survival in 10 years after PK were 79.3% and 77.9%, respectively. Higher relative risk of graft failure was associated with corneal vascularization (relative risk for within one quadrant = 1.67, two quadrants = 2.37, three or more quadrants = 3.39), regraft (relative risk for one failed previously graft = 2.08, two or more failed previously graft = 2.65), aphakia (relative risk = 2.17) or pseudophakia (relative risk = 3.02), presence of anterior synechia (relative risk = 2.91), presence of posterior synechia (relative risk = 2.56), long (more than 85 minutes) operation time (relative risk = 2.20), and older (more than 50 years) recipient age (relative risk = 2.38). Higher relative risk of rejection was associated with corneal vascularization (relative risk for within one quadrant = 2.35, two quadrants = 2.03, three or more quadrants = 2.63), long (more than 85 minutes) operation time (relative risk = 1.47), and younger (less than 60 years) donor age (relative risk = 2.10). There was no association between graft failure or allograft rejection and graft size or suture technique, respectively.

CONCLUSION

The risk factors for graft failure after PK were corneal vascularization, regraft, aphakia or pseudophakia, presence of anterior synechia, presence of posterior synechia, long operation time, and older recipient age. The risk factors after PK for allograft rejection were corneal vascularization, long operation time, and younger donor age.

Histocompatibility Y antigen compatibility and allograft rejection in corneal transplantation

PURPOSE

To assess the effects of histocompatibility Y (H-Y) antigen matching on the rate of corneal allograft rejection after penetrating keratoplasty (PKP).

METHODS

We retrospectively investigated the graft survival rate and rejection-free graft survival rate after PKP in 396 eyes. The compatible combinations of H-Y antigen included male donors and male recipients (n = 135), female donors and male recipients (n = 107), and female donors and female recipients (n = 60). Incompatible combination was from male donors and female recipients (n = 94). The eyes were classified into two groups--high-risk (168 eyes) and low-risk (228 eyes)--depending on the degree of vascularisation in the recipient corneas or a history of previous allograft rejection. Data were analysed using the Kaplan-Meier life table method, the log-rank test and the Cox proportional hazards model.

RESULTS

In both the high-risk and low-risk groups, the graft survival and rejection-free graft survival rates were not affected by the H-Y compatibility. The graft survival (p < 0.001) and rejection-free graft survival (p < 0.001) rates were higher in the low-risk group than in the high-risk group. High-risk PKP was associated with greater risk of graft failure (risk ratio, 2.33) and rejection (risk ratio, 2.05) than low-risk PKP.

CONCLUSION

H-Y antigen matching does not influence the rate of allograft rejection after PKP.

The minor histocompatibility antigen HA-1: a diallelic gene with a single amino acid polymorphism

The minor histocompatibility antigen (mHag) HA-1 is the only known mHag for which mismatching is correlated with the development of severe graft versus host disease (GvHD) after human leukocyte antigen-identical bone marrow transplantation. HA-1 was found to be a nonapeptide derived from an allele of the KIAA0223 gene. The HA-1-negative allelic counterpart encoded by KIAA0223 had one amino acid difference from HA-1. Family analysis with HA-1 allele-specific polymerase chain reaction showed an exact correlation between this allelic polymorphism and the HA-1 phenotype. HA-1 allele typing of donor and recipient should improve donor selection and allow the determination of bone marrow transplantation recipients with high risk for HA-1-induced GvHD development.

Minors held by majors: the H13 minor histocompatibility locus defined as a peptide/MHC class I complex

The products of minor histocompatibility (H) loci are serious barriers to tissue transplantation even among major histocompatibility complex (MHC) identical individuals, frequently causing chronic graft rejection and graft versus host disease. Over 50 minor H loci map to mouse autosomal chromosomes but none are known at the molecular level. By expression cloning, we identified the H13 locus, a classical minor H locus first detected 30 years ago by the trait of graft rejection. The H13a allele is located on chromosome 2 and encodes a novel protein that yields the rare naturally processed nonapeptide SSVVGVWYL (SVL9) for presentation by the Db MHC class I molecule. The SVL9 peptide binds Db MHC despite the absence of the consensus binding motif, and a conservative methyl group substitution (Valine 4 <--> Isoleucine) explains why reciprocal T cell responses are elicited in H13a and H13b congenic strains.

Role of non-major histocompatibility complex antigens in the rejection of transplanted myoblasts

Myoblasts obtained from donors histoincompatible for several non-major histocompatibility complex antigens (i.e., including minor histocompatibility antigens) and from syngeneic donors were transplanted without any immunosuppression into the muscles of male dystrophic C57BL/10J mdx/mdx mice. Myoblasts from syngeneic mice resulted in the formation of a high percentage of dystrophin-positive fibers 16 weeks after the transplantation. There was no evidence of a cellular immune reaction against the donor myoblasts, i.e., no infiltration by CD4 or CD8 lymphocytes and no increased expression of granzyme B and interferon-gamma mRNAs. Transplantation of myoblasts obtained from donors histoincompatible only for non- major histocompatibility complex antigens produced a transient increase of dystrophin-positive fibers at 4 weeks after transplantation for some donor strains but not for others. For donor strains that did produce an increase at 4 weeks, the number of dystrophin-positive fibers was reduced 16 weeks after the transplantation. There was evidence of a cellular immune reaction-infiltration by CD4 and by CD8 lymphocytes and increased expression of granzyme B and interferon-gamma mRNAs. Transplantation of myoblasts obtained from male C57BL/10J +/+ mice into female C57BL/10J mdx/mdx mice also led to the presence of only a few dystrophin-positive fibers with the same signs of cellular immune reaction. In this later case, the cellular immune response was attributed to the H-Y minor antigens. Finally, antibodies against fetal calf serum were detected after both syngeneic and nonsyngeneic transplantations, indicating that the culture medium may also be a source of antigens. In mice, the presence of these antibodies against culture medium did not reduce the success of a first syngeneic transplantation.

Immunodominant minor histocompatibility antigens expressed by mouse leukemic cells can serve as effective targets for T cell immunotherapy

Numerous minor histocompatibility antigens (MiHAs) show tissue-specific expression and can induce vigorous T cell responses. They therefore represent attractive targets for leukemia immunotherapy mediated by adoptive transfer of T cells. The main objective of this work was to determine whether MiHAs expressed by normal hematopoietic cells were present on leukemic cells and whether they could trigger lysis by cytotoxic T lymphocytes (CTLs). CTL assays showed that mouse leukemic cells of both lymphoid and myeloid lineages were sensitive to CTLs targeted toward some but not all MiHAs. In four out of four strain combinations in which we primed CTLs against immunodominant MiHAs, effectors killed leukemic blasts, whereas no cytotoxicity was observed when CTLs were targeted toward four immunorecessive MiHAs. Testing of HPLC fractions obtained from normal and leukemic cells provided molecular evidence that leukemic blasts expressed only some of the MiHAs found on normal mouse hematopoietic cells. Decreased density of H-2 class I molecules at the surface of leukemic cells suggests that down-regulation of genes encoding either class I molecules or proteins involved in antigen processing played a role in the aberrant expression of MiHAs. In vivo resistance to the leukemic cells by various strains of mice correlated with in vitro CTL activity. These results show that leukemic cells express only some (immunodominant) MiHAs and suggest that this subset of MiHAs represent prime targets for adoptive immunotherapy.