Human cytomegalovirus-specific cytotoxic T lymphocytes: requirements for in vitro generation and specificity

The nature of any virus-specific T cells involved in controlling human cytomegalovirus (HCMV) infection in normal subjects harboring latent virus is unknown. As an approach to this problem, peripheral blood mononuclear cells (PBM) from normal seropositive subjects were cocultured with HCMV and responding T cells expanded in interleukin 2 (IL2)-dependent culture, determining in particular whether HCMV-specific cytotoxic T cells (Tc) were generated. Coculture of PBM with free HCMV resulted in the generation of short-term T cell lines of predominantly helper phenotype (Leu 3a+), expressing no cytotoxicity. However, when PBM were cocultured on HCMV-infected fibroblasts (autologous to the donor in these experiments) predominantly Leu 2a+ lines were generated, which lysed HCMV-infected cells. The cytotoxicity of these short-term IL 2-dependent lines was HCMV-specific and human HLA-restricted; HCMV-infected target cells expressing only early viral antigens were lysed. It is concluded that HCMV-specific Tc precursors are present in peripheral blood of latently infected individuals without preceding overt infection and that effector Tc may be capable of lysing infected cells prior to viral replication.