Hsp90 is critical for the regulation of human T lymphocytes and NK cell phenotype and function.

Hsp90 inhibitor has shown promising anti-tumor activity through the destabilization and eventual degradation of Hsp90 client proteins critical for cell survival. In this study, we examined the in vitro effects of Hsp90 inhibitor on the phenotype and function of human T lymphocytes and NK cells. We observed no significant effects of Hsp90 inhibitor treatment on cell survivals. However, Hsp90 inhibitor treatment for 24 hours led to irreversible down-regulation of expression of critical T-cell surface antigens including CD3, CD4, CD8, CD28, CD154 (CD40L) and TCRab. Among the antigens evaluated, expression of CD4 antigen was most significantly downregulated (untrt vs. trt = 326 vs. 88 in Mean Fluorescence Intensity) following Hsp90 inhibitor treatment. Decreased CD3 + T lymphocytes proliferation (untrt vs. trt = 222839 cpm vs. 111102 cpm, 3 [H]-thymidine incorporation) and reduced IFN-g secretion (untrt vs. trt = 77 vs. 48 pg/ml) was observed upon stimulation with allogeneic dendritic cells following 24 hrs treatments of T cells with Hsp90 inhibitor. Furthermore, CD3 + T-cell proliferation in response to mitogen stimulation, as measured by flow cytometry using CFSE was decreased following Hsp90 inhibitor treatment (untrt vs. trt = 41% vs. 3%, CFSE). Specifically, the CD4 + CD28 + (untrt vs. trt = 32% vs. 1%) and CD8 + CD28 + (untrt vs. trt = 27% vs. 17%) activated T-cell subpopulations displayed a significant decrease in proliferation in response to mitogen. Similarly, NK cells displayed decreased activation receptor expression including CD2, CD11a, CD94, NKp30, NKp44, NKp46, and KARp50.3 and reduced cytotoxic activity against multiple myeloma cells (untrt vs. trt = 49% vs. 11% against MM1S cells, 65% vs. 8% against ARP cells) following Hsp90 inhibitor treatment. These studies demonstrate that Hsp90 inhibitor treatment significantly affects phenotype and function of human T-lymphocytes as well as NK cells, and suggest the need to monitor immune functions in patients being treated with Hsp90 inhibitor in our future studies.