Distribution of human CMV-specific memory T cells among the CD8pos. subsets defined by CD57, CD27, and CD45 isoforms

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Abstract
Chronic antigenic stimulation has been associated with peripheral blood expansions of CD8pos. T cells characterized by CD57 expression, loss of CD27 expression, and reversal of the CD45RObright /RAdim phenotype usually associated with immunological memory towards a CD45ROdim /RAbright phenotype. However, the relationship and functional significance of these subset(s) has remained controversial. Here, this issue was addressed using a novel flow cytometric technique that allows simultaneous detection of human cytomegalovirus (HCMV)‐specific CD8pos. memory T cells by rapid (< 6 h) HCMV peptide‐specific induction of cytokine synthesis, and their phenotypic characterization, including CD57, CD27 and CD45RA/RO. The vast majority of resting CD8pos. T cells capable of rapid induction of IFN‐γ and TNF‐α synthesis in response to HCMV peptides were found in a subset characterized by intermediate to high expression of CD57, down‐regulation/loss of CD27, and varying degrees of reversal of the classical “memory” CD45RObright /RAdim phenotype. This subpopulation likely includes the fully differentiated memory cells responsible for the long‐term immune defense against HCMV reactivation.