Background:  Natural killer (NK) cells play an important role in innate immune control of HIV infection and disease progression. To assess the contribution of NK cells as targets for immunotherapy in HIV infection, we evaluated the priming effect of interleukin-15 (IL-15) on human peripheral NK cells, from viremic and aviremic HIV-infected patients, measuring the production of interferon-g (IFN-g), CCL4 and CCL5 chemokines, and the expression of surface CD69 molecule.

Methods:  The study population consisted of 13 HAART-naīve viremic patients, 27 aviremic HAART-treated patients, and 16 healthy donors. NK cells were isolated by negative selection from peripheral blood mononuclear cells (PBMC) with a purity >90% and cultured for 24 hours with medium alone or in presence of IL-15 (100 U/mL), IL-2 (100 U/mL), IL-15+IL-12, and IL-2+IL-12. IFN-g and CC chemokines were measured in culture supernatant and cell surface CD69 expression was evaluated in CD3^-/CD16⁺/CD56⁺ gate.

Results:  The production of IFN-γ, CCL4, and CCL5 by NK cells from ART-naīve viremic patients was significantly smaller than quantity found in aviremic HAART-treated patients and healthy controls (p <0.05). IL-15 priming in vitro induced a significant increase of IFN-g, CCL4, and CCL5 production in both viremic and aviremic patients. The dose-response curve showed that increased release of INF-g and CC chemokines was found at IL-15 concentrations of 10 to 100 ng/mL. NK cells from healthy donors and aviremic HAART-treated patients stimulated with IL-15 alone or IL-15 + IL-12 showed the highest and most significant increase both in the percentage of CD69-expressing cells and in mean florescence intensity; little or no activation was observed in NK cells treated with IL-2 or IL-2 + IL-12. The greatest levels of CC chemokines were also found in supernatant cultures from NK cells treated with the combination of IL-15 + IL-12, while no effect was detected with IL-2 alone or IL-2 + IL-12.

Conclusions:  NK cells derived from HIV viremic and aviremic patients can secrete relevant amounts of IFN-g and CC chemokine after in vitro treatment with IL-15 alone or in combination with IL-12. The present study indicates that NK cells are an important target for immunotherapeutic agents and provides additional pre-clinical data supporting the great potential of IL-15 in the immune-based interventions in HIV disease.