The T-cell receptor Vβ6 gene usage in alloreactive T-cell responses

To analyze the role of TCR Vβ gene elements in allorecognition, we have determined frequencies of the TCR Vβ6 elements expressed by allospecific T cells as compared to randomly activated T cells. Limiting dilution analysis was applied to estimate the usage of TCR Vβ elements in CD4 T cells polyclonally stimulated by immobilized anti-CD3 or specifically activated with HLA-DR disparate allotargets. In a focused alloresponse of HLA-DRB1^*0401⁺ responders to HLA-DRB1^*0404 ⁺ stimulator cells, Vβ6⁺ T cells were preferentially recruited. To map the functional domain of allogeneic HLA-DR molecules involved in the recruitment of Vβ6⁺ T-cell specificities, CD4⁺ T cells from HLA-DRB1*0401⁺ donors were activated with allogeneic stimulators sharing either the first and second or the third HVR of the HLA-DRB1 gene. Stimulation with allotargets sharing the sequence of the HVR3 caused a twofold to fourfold enrichment of Vβ6⁺ CD4⁺ T cells, while sequence variations in the HVR3 was sufficient to abrogate the preferential usage of Vβ6 T cells. These data suggest that sequence variations mapped to the ot-helical loop of the HLA-DRβ chain impose structural constraints that shape the alloreactive TCR Vβ repertoire.