Activation of human peripheral blood immune cells in vitro by sodium stibogluconate (SSG) and SSG/IL-2 combination

Abstract

2557 Background: SSG, an inhibitor of SHP-1 and SHP2 which are negative regulatory signaling tyrosine phosphatases, suppressed the growth of murine renal carcinoma (Renca) in combination with IL-2 via an interferon (IFN)-γ+ T cell-dependent mechanism (J Immunol 175:7003–8, 2005). Activation of primary human immune cells by SSG or SSG/IL-2 would provide additional supporting evidence for SSG clinical evaluation in combination with IL-2. Methods: Peripheral blood of healthy and melanoma donors were treated in vitro with SSG or SSG/IL-2 and then subjected to ELISPOT assays and FACS analysis for quantification of TH1 (IFN-γ+) and TH2 (IL-5+) cells. Results: Characterization by ELISPOT assays of peripheral blood identified IFN-γ+ cells with marked increase (9.1x) following SSG/IL-2 treatment in contrast to the modest increases induced by SSG alone (2.1x) at its clinically achievable dose (20 μg/ml) or by IL-2 (3.1x) at its Cmax of low-dose schedule (30 IU/ml). SSG at an even higher dose (100 μg/ml) was less effective alone (1.5x) or in combination with IL-2 (7.8x). IL-5+ cells were not induced by the agents individually or in combination. Induction of peripheral IFN-γ+ cells by SSG/IL-2 was detectable after 4 and 16 h. Increased effectiveness of the SSG/IL-2 combination vs. the individual agents in inducing IFN-γ+ cells in vitro was detected by ELISPOT assays in the peripheral blood from 7 healthy donors and 6 melanoma patients. FACS analysis showed that the combination induced IFN-γ+ cells in the CD4+ and CD8+ lymphocytes and also increased lymphocytes expressing the activation marker CD69 in both CD4+ (2–5x) and CD4− populations (∼ 3x). Conclusion: SSG, a compound used clinically for treatment of leishmaniasis, can interact with IL-2 in vitro to activate immune cells in peripheral blood of healthy and melanoma donors. Results provide further rationale, in addition to the mouse tumor data, for proof of concept clinical trials for effecting augmentation of IL-2 through inhibition of negative regulatory signaling phosphatases. No significant financial relationships to disclose.