IL-7 enhancement of antigen-driven activation/expansion of HIV-1-specific cytotoxic T lymphocyte precursors (CTLp).

CD8+ cytotoxic T lymphocytes are an important component in the immunologic control of human viral diseases. IL-7, a stromal cell-derived cytokine, has been demonstrated to enhance both anti-tumour and anti-viral CTL as well as lymphokine-activated killer (LAK) activity. We studied the ability of IL-7 to support the activation and the growth of in vitro antigen-specific CTL precursors (CTLp) present in peripheral blood mononuclear cells (PBMC) from HIV-infected patients. Results from these studies demonstrate that inclusion of IL-7 in a vaccinia/HIV-1 vector-based stimulation strategy greatly augmented overall CTL reactivities, whereas addition of IL-7 to unstimulated cultures failed to induce any significant anti-viral cytolytic activity. In four of six patients, HIV-specific lytic activities were significantly higher in cultures stimulated with antigen plus IL-7 compared with in vitro stimulation (IVS) with antigen alone. Cytotoxic activity was principally mediated by CD8+ effector cells, and CD3+/CD8+ cell expansion was increased by 2.7-fold in the presence of IL-7. In PBMC from seronegative donors, IL-7 enhanced anti-vaccinia CTL activities with less effect on cell proliferation. Furthermore, anti-gag CTL frequencies determined by limiting dilution analysis were increased by 2- and 10-fold in two asymptomatic patients following IVS plus IL-7 compared with antigen stimulation alone. Cytofluorimetric analysis revealed that IL-7 preferentially expanded CD8 memory cells (CD45RO+) and CD8+ lymphocytes expressing activation molecules. IL-7 was also able to support the growth of CD4+ lymphocytes, while having no effect on natural killer (NK)/K lymphocytes. Taken together, these data suggest that IL-7 acts cooperatively with the antigen supporting in vitro maturation of CTLp into functional cytotoxic effectors. Thus IL-7 may be an important biologic entity to consider as part of future immune-based therapies in which ex vivo expansion of antigen-driven CTL is an important determinant.