Human cytomegalovirus-specific immunity following haemopoietic stem cell transplantation.

The herpesvirus Human Cytomegalovirus (HCMV) is an important opportunistic infection in recipients of allogeneic haemopoietic stem cell transplants, in whom HCMV-specific CD8+ and CD4+ T-cell responses are impaired. The nature of the HCMV-specific T-cell response in healthy virus carriers has been characterised in detail. High frequencies of circulating CD8+ T-cells that recognise defined viral peptides are maintained for years, and include individual CD8+ clones that have undergone extensive clonal expansion and phenotypic diversification in vivo. Following stem cell transplantation, the kinetics of HCMV-specific CD8+ T-cell reconstitution in the recipient are related to the presence or absence of antigen-experienced CD8+ T-cells transferred via the allograft, and to the presence of the virus in the recipient. We discuss recent progress in our understanding of HCMV-specific immunity in healthy virus carriers and in recipients after alloSCT.