Single-cell T-cell receptor-β analysis of HLA-A*2402-restricted CMV- pp65-specific cytotoxic T-cells in allogeneic hematopoietic SCT.

Cellular immunity is important for the control of CMV infection after allogeneic hematopoietic cell transplantation (Allo-HCT). However, the actual in vivo dynamics of CMV-specific cytotoxic T cell (CMV-CTL) clones are still unclear. We conducted clone monitoring of tetramer(+) CMV-CTLs in HLA-A*2402-positive donor-patient pairs, using a direct single-cell analysis that enabled the simultaneous identification and quantification of CTL clones. Clone dynamics were assessed in three cases with or without CMV reactivation. In Case-1 without CMV reactivation, despite the long-term use of systemic steroid, dominant clones of Donor-1 persisted and remained dominant. The CMV-CTLs at 1 year after Allo-HCT included a high proportion of CD45RA(+)CCR7(-) effector and CD27(-)CD57(+)mature T cells. On the other hand, in Cases-2 and -3 with CMV reactivation, novel clones appeared and became dominant during the follow-up. Their CMV-CTLs included more CD27(+) immature T cells at 1 year after Allo-HCT. With regard to clonotypes, HLA-A*2402-restricted CMV-CTLs tended to select BV7 and BJ1-1 genes for complementarity-determining region 3 (CDR3) of T-cell receptor (TCR)-β. Specific amino-acid sequences of CDR3 of TCR-β were found in each case. Patterns of clone reconstitution and phenotype would be different according to CMV reactivation. In vivo clone monitoring of CMV-CTLs could provide insight into the mechanism of immunological reconstitution following Allo-HCT.