Allorecognition of HLA-C Mismatches by CD8+ T Cells in Hematopoietic Stem Cell Transplantation Is a Complex Interplay between Mismatched Peptide-Binding Region Residues, HLA-C Expression, and HLA-DPB1 Disparities

Abstract

HLA-C locus mismatches (MMs) are the most frequent class I disparities in unrelated hematopoietic stem cell transplantation (HSCT) and have a detrimental impact on clinical outcome. Recently, a few retrospective clinical studies have reported some variability in the immunogenicity of HLA-C incompatibilities. To get better insight into presumably permissive HLA-C MMs, we have developed a one-way in vitro mixed lymphocyte reaction (MLR) assay allowing to quantify activated CD56−CD137+CD8+ lymphocytes in HLA-C incompatible combinations. T cell-mediated alloresponses were correlated with genetic markers such as HLA-C mRNA expression and the number of amino acid (aa) MMs in the α1/α2 domains (peptide-binding region). Because of the high rate of HLA-DPB1 incompatibilities in HLA-A-, B-, C-, DRB1-, and DQB1-matched unrelated HSCT patient/donor pairs, the impact of HLA-DPB1 mismatching, a potential bystander of CD4+ T cell activation, was also considered. Heterogeneous alloresponses were measured in 63 HLA-C-mismatched pairs with a positive assay in 52% of the combinations (2.3–18.6% activated CTLs), representing 24 different HLA-A~B~DRB1~DQB1 haplotypes. There was no correlation between measured alloresponses and mRNA expression of the mismatched HLA-C alleles. The HLA-C*03:03/03:04 MM did not induce any positive alloresponse in five MLRs. We also identified HLA-C*02:02 and HLA-C*06:02 as mismatched alleles with lower immunogenicity, and HLA-C*14:02 as a more immunogenic MM. A difference of at least 10 aa residues known to impact peptide/T cell receptor (TCR) binding and a bystander HLA-DPB1 incompatibility had a significant impact on CTL alloreactivity (p = 0.021). The same HLA-C MM, when recognized by two different responders with the same HLA haplotypes, was recognized differently, emphasizing the role of the T-cell repertoire of responding cells. In conclusion, mismatched HLA-C alleles differing by 10 or more aas in the peptide/TCR-binding region, when occurring together with HLA-DPB1 incompatibilities, should be considered as high-risk MMs in unrelated HSCT.

Stability and Expression Levels of HLA-C on the Cell Membrane Modulate HIV-1 Infectivity

“…HLA-C*01 and -*04, highly expressed alleles according to Vince et al ( 9 ), show lower β 2 m/peptide binding stability according to Sibilio et al ( 28 ). Vince et al did not report HLA-C mRNA expression for these alleles, while other studies ( 22 – 25 ) did not report any particular increase in their mRNA expression. Similarly, HLA-C*01 and -*04 were reported to have a high surface reactivity to MAb DT9 ( 21 ), but since they are also less stably bound to β 2 m/peptide, it is possible that DT9 staining underestimates the real amounts of HLA-C molecules on the cell surface.…”

“…Adding complexity to this matter, other studies failed to confirm the association between HLA-C expression and these genetic markers ( 22 – 25 ). Furthermore, a study of a very specific population in Nairobi, Kenya ( 26 ), found that the same HLA-C allotype, HLA-C*07, could be associated with either a low (HLA-C*07:01) or an increased (HLA-C*07:02) rate of seroconversion.…”

HLA-B57 micropolymorphism defines the sequence and conformational breadth of the immunopeptidome

“…Vigorous T-cell alloresponses can be generated by a high degree of HLA class I mismatching between allogeneic individuals or as little as a single amino acid mismatch (e.g. across HLA-B44 allotypes) 28 , 35 – 37 . Here we examined whether the closely related alleles HLA-B*57:01 and HLA-B*58:01 are capable of eliciting either anti-HLA-B*58:01 (B*57:01 responder vs B*58:01 stimulator) or anti-HLA-B*57:01 (B*58:01 responder vs B*57:01 stimulator) CD8 + T-cell alloreactivity, which would support distinct presentation of the immunopeptidome.…”

CD8+ T-Cell Repertoire in Human Leukocyte Antigen Class I-Mismatched Alloreactive Immune Response

“…HLA class I molecules have extremely high allelic polymorphism ( ) ( 13 ), potentially influencing direct alloreactivity in HLA mismatched situations. Indeed, we and others ( 14 – 16 ) have previously shown that HLA alloantigens can induce variable strengths of alloreactive T-cell response in cellular in vitro assays and in vivo , emphasizing the potential role of the TCR repertoire of the alloreactive responder T-cell population.…”

“…One way MLRs were performed as previously described ( 14 , 24 ). Briefly, responder PBMC cells (2x10 6 ) were stimulated at a ratio of 1:1 with 30Gy irradiated stimulator PBMC cells in RPMI 1640 medium (Gibco) supplemented with 10 mM l -glutamine, 100 units/ml penicillin/streptomycin (Gibco) and 10% human AB serum (own preparation).…”