SUMMARYTwo different subsets of CD8+, CD57+ cells have been defined, one expressing high levels (CD8W0+(CD57+)), the other expressing low levels of surface CD8 (CD81o0+(CD57+)). Increased numbers of CD8,gh+(CD57+) cells correlated with previous HCMV infection. By three-colour fluorescence analysis, the CD8high+(CD57+) population expressed T cell markers such as CD3 and CD5, and most were axf T cell receptor (afi TCR)-positive. A significant proportion also expressed CD71 (transferrin receptor) and MHC class II, although little if any CD25 (IL-2R-p55). Some ( > 40%) co-expressed CD45RA and CD45RO. The CD810,+(CD57+) population expressed classical natural killer (NK) cell markers-CD2, CD16 and CD56. The two subsets were also functionally distinct; CD8,gh+(CD57+) cells suppressed pokeweed mitogen (PWM)-driven, but not phytohaemagglutinin (PHA)-driven proliferation and immunoglobulin production; CD81,w+(CD57+) cells exhibited NK cytotoxic activity which was not increased by interferon-alpha (IFN-a). Supernatant from cultured CD8igh+(CD57+) cells suppressed PWM-driven immunoglobulin production, but not proliferation, and this effect was abrogated by physical separation with tissue culture inserts. Thus, a T cell subset expressing activation and memory T cell markers with direct non-specific suppressor activity was present in peripheral blood mononuclear cells (PBMC) of healthy subjects with asymptomatic HCMV infection.

Little is known about the nature and specificity of T-cell-mediated responses to picornaviruses in humans. In this study, the nature of the T-cell response to seven picornaviruses, including polioviruses, coxsackieviruses B3 and B4, human rhinovirus 14, and encephalomyocarditis virus, was determined. Twenty-nine individuals responded to poliovirus type 3, coxsackievirus B3, and encephalomyocarditis virus by proliferation of T cells, and from such cultures, 130 virus-specific T-cell lines were established. T-cell lines generated in response to encephalomyocarditis virus were exclusively strain specific. However, the majority of T-cell lines established in response to viruses, other than encephalomyocarditis virus, were cross-reactive to each other. Their cross-reactivity was confirmed in 2 of the 30 picornavirus-specific clonally derived T-cell lines from two subjects, but the majority of these lines were serotype specific. T-cell epitopes adjacent to each of the B-cell antigenic sites in VP1 of poliovirus type 3 were identified. The response to the region adjacent to B-cell antigenic site 1 (residues 97 to 114) was dominant between individuals. The localization of this major CD4 T-cell epitope may permit the construction of chimeric viruses utilizing the natural picornavirus T-cell response to augment production of antibody specific for inserted sequences.

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CD8+CD57+ lymphocytes from normal peripheral blood are divided into T cells expressing high levels of CD8 and NK cells expressing low levels of surface CD8. Increased numbers of CD8highCD57+ T cells correlate with previous exposure to human cytomegalovirus (HCMV) infection, but no virus-specific function or function for CD8highCD57+ cells has been recorded. We have studied the TCR repertoire and responses of the CD8highCD57+ population induced by virus-infected fibroblasts in healthy individuals. Using three-color flow cytometry of PBL, we detected restricted TCRBV usage in the CD8highCD57+ subset of 11/15 subjects, compared with 1/15 in the CD8+, CD57- subset. The results of anchored PCR and sequencing also showed oligoclonality of TCR; 40-70% of CD8highCD57+ lymphocytes (10-20% of total CD8+ T cells) were derived from single clones. Such expansions were stable with time and detected in one subject over a 2-yr period. Functionally, CD8highCD57+ lymphocytes proliferated strongly to HCMV-, but not HSV-, VZV-, or influenza-infected fibroblasts in an MHC-unrestricted manner in vitro, including preferential augmentation of particular in vivo oligoclonally expanded subpopulations. HCMV-specific MHC-restricted CTL were detected, but limiting dilution analysis showed that these were a minority (< 10%) and not the oligoclonal subsets. In contrast, depletion of oligoclonally expanded CD8highCD57+ subpopulations, resulted in the increase of HCMV-specific CTL, suggesting functional heterogeneity in these cells.