Reactivations of cytomegalovirus (CMV), Epstein Barr virus (EBV) and adenovirus (AdV) occur frequently in immune compromised patients after allogeneic stem cell transplantation (alloSCT) and cause high morbidity and mortality. T-cell immunity is essential for anti-viral protection, but a fully competent T-cell repertoire generally does not develop until 3-6 months after transplantation. Especially patients transplanted with a graft from a virus non-experienced donor are at risk. Adoptive transfer of partially HLA-matched virus-specific T cells from healthy third party donors is a potential strategy to temporarily provide anti-viral immunity to these patients. However, such T cells harbor a risk of mediating off-target toxicity due to allo-HLA cross-reactivity. It is not currently known whether the degree of allo-HLA cross-reactivity is random or whether rules exist that might allow prediction of specific T-cell populations. Here, we investigated whether virus specificity, HLA type of the donor or HLA restriction of the virus-specific T cells influence the risk of allo-HLA cross-reactivity.
Through cell sorting using tetramers for various peptides from CMV, EBV and AdV, 164 CD8 T-cell populations (21 specificities) were isolated from peripheral blood of 24 healthy donors, homozygous for HLA-A*01:01/B*08:01 and HLA-A*02:01/B*07:02. Allo-HLA cross-reactivity was tested using an allogeneic EBV-LCL panel covering 116 different HLA molecules and confirmed using K562 cells retrovirally transduced with single HLA alleles of interest.
Forty percent of all virus-specific T-cell populations exerted allo-HLA cross-reactivity. Similar frequencies were found for the various viral specificities showing 33% of the CMV, 43% of the EBV and 38% of the AdV-specific T-cell populations to be allo-HLA cross-reactive. Surprisingly, a much larger fraction of the HLA-B*08:01-restricted virus-specific T-cell populations exhibited allo-HLA cross-reactivity (77%) than from those restricted by the other HLAs (32% of HLA-A*01:01, 38% of HLA-A*02:01 and 26% of HLA-B*07:02-restricted virus-specific T-cell populations). HLA-B*08:01-restricted virus-specific T cells also exhibited the broadest allo-HLA reactivity, reacting to a median of 5 different allogeneic EBV-LCLs (range 1-17). In contrast, HLA-A*01:01, HLA-A*02:01 and HLA-B*07:02-restricted virus-specific T cells reacted to a median of 1, 2 and 3 (range 1-7) different allogeneic EBV-LCLs, respectively. Dissection of the diversity/specificity of the allo-HLA reactivities using a panel of 40 different single HLA-A, B, or C-transduced K562 cells further illustrated recurrent recognition of a restricted group of allogeneic HLA-B molecules by HLA-B*08:01-restricted T-cell populations, mediated by single T-cell clones. Heterozygosity for recurrently recognized allo-HLA-B molecules led to a significant decrease in the broadness of allo-HLA cross-reactivity by HLA-B*08:01-restricted T-cell populations, presumably due to negative thymic selection. In contrast, heterozygosity HLA-B molecules that were not part of the restricted group of cross-recognized alleles did not significantly decrease allo-HLA cross-reactivity.
These data show that allo-HLA cross-reactivity by virus-specific T cells is highly influenced by their HLA restriction and the HLA background of the donors, but not by their virus specificity. Of the HLA-A*01, A*02, B*07 and B*08-restricted virus-specific T-cell populations isolated from homozygous donors, HLA-B*08:01-restricted virus-specific T cells showed the highest frequency and diversity of allo-HLA cross-reactivity with recurrent recognition of groups of specific mismatched allogeneic HLA-B alleles. Our results indicate that selection of virus-specific T cells with specific HLA restrictions and HLA backgrounds may decrease the risk of off-target toxicity after infusion of third-party virus-specific T cells to patients with uncontrolled viral reactivation after alloSCT.
No relevant conflicts of interest to declare.
Author notes
Asterisk with author names denotes non-ASH members.
