Abstract: Despite increased nanoresearch, the influence of nanoparticles on the immune system is still poorly understood. Recently we demonstrated ex vivo modulation of T lymphocytes from aged mice post exposure to a mixture of nanodiamond (ND) and nanoplatinum (NP) coated material (DPV576-C). Here, we extend our study to examine the direct effect of a dispersed aqueous mixture of ND/NP (DPV576) in modulating human T lymphocytes in vitro. Venous blood drawn from 12 healthy volunteers was diluted 1:4 with AIM V medium, cultured with a polyclonal T cell mitogen, PHA, (10 µg/ml), and then exposed to DPV576 at various concentrations (1.25, 2.5 and 5%v/v) for 3 days. T cell proliferation was examined by thymidine uptake assay. CD4+ and CD8+ T cells proliferation and expression of activation markers (CD69 and CD25) was studied by CFSE dye dilution technique and dual color flow cytometry. Interleukin-2 (IL-2) production was determined by ELISA. DPV576 treatment resulted in a significant increase in T cell proliferation in a dose-dependent manner that was maximized at 5%v/v (p<0.001). DPV576 was effective in enhancing proliferation of both CD4+ and CD8+ T cells. This was associated with an increase in the percentages of cells expressing CD69 (an early activation marker) and CD25, as well as a significant increase in IL-2 production. We conclude that DPV576, a solution containing ND/NP, activates human T cell proliferation and enhances IL-2 production, indicating its possible usefulness in the treatment of immune-compromised patients with T cell defects.