Long-Term Stable Expanded Human CD4~+ T Cell Clones Specific for Human Cytomegalovirus Are Distributed in Both CD45RA~(high) and CD45RO~(high) Populations

摘要

T cells play an important role in the control of human CMV (HCMV) infection.Peripheral blood CD4~+ T cell proliferative responses to the HCMV lower tegument protein pp65 have been detected in most healthy HCMV carriers.To analyze the clonal composition of the CD4~+ T cell response against HCMV pp65,we characterized three MHC class II-restricted peptide epitopes within pp65 in virus carriers.In limiting dilution analysis,we observed high frequencies of pp65 peptide-speciflc CD4~+ T cells,many of which expressed peptide-speciflc cytotoxicity in addition to IFN-gamma secretion.We analyzed the clonal composition of CD4~+ T cells specific for defined HCMV peptides by generating multiple independent peptide-specific CD4~+ clones and sequencing the TCR beta-chain.In a given carrier,most of the CD4~+ clones specific for a defined pp65 peptide had identical TCR nucleotide sequences.We used clonotype oligonucleotide probing to quantify the size of individual peptide-specific CD4~+ clones in whole PBMC and in purified subpopulations of CD45RA~(high)CD45RO~(low) and CD45RA~(low)CD45RO~(high) cells.Individual CD4~+ T cell clones could be large (0.3-1.5% of all CD4~+ T cells in PBMC) and were stable over time.Cells of a single clone were distributed in both the CD45RA~(high) and CD45RO~(high) subpopulations.In one carrier,the virus-specific clone was especially abundant in the small CD28~CD45RA~(high) CD4~+ T cell subpopulation.Our study demonstrates marked clonal expansion and phenotypic heterogeneity within daughter cells of a single virus-specific CD4~+ T cell clone,which resembles that seen in the CD8~+ T cell response against HCMV pp65.