Helper T cell-independent proliferation of CD8⁺ cytotoxic T lymphocytes transduced with an IL-1 receptor retrovirus

Although the proliferation of CD8⁺ CTL typically requires cytokine support provided by helper T cells, a subset of naturally occurring CD8⁺ CTL are capable of proliferating independently of T cell help. Such helper- independent CTL have previously been shown to possess IL-1 receptors (IL-1R) and to proliferate in response to IL-1 through endogenous production of IL- 2. In this study, we have transduced conventional helper-dependent CTL clones with a retroviral vector encoding the murine type I IL-1R. Transduced CTL selected in G418 expressed vector-derived transcripts encoding IL-1R and displayed approximately 1000 cell surface receptors with an IL-1 affinity typical for the type I IL-1R. In contrast to parental cells, transduced CTL proliferated in response to IL-1 in the presence of Ag, without a requirement for helper T cells, IL-2, or other cytokine support. Stimulation with both IL-1 and Ag was necessary for the proliferative response. No endogenous synthesis of IL-2 could be detected in the IL-1R transduced cells in response to IL-1 stimulation, in the presence or absence of Ag. The IL-1R-induced phenotype was demonstrated in two independent T cell clones, both of which retained Ag-specific cytolytic activity. No such conversion to a helper- independent phenotype was induced by a retroviral vector encoding only the neo gene. The behavior of the IL-1R-transduced CTL in proliferation assays thus resembled that of the naturally occurring helper-independent CTL.