Hsp90 Is Critical for the Regulation of Phenotype and Functionality of Human Dendritic Cells.

Hsp90, a molecular chaperone, plays a critical role in protein folding and transport, and thereby it modulates cellular activity. Pre-clinical data shows over-expression of Hsp90 in multiple myeloma (MM) and efficacy of Hsp90 inhibitor in myeloma has been determined in vitro. Based on these results, phase I/II trial evaluating clinical efficacy of the Hsp90 inhibitor is underway in MM. Although Hsp90 inhibitor shows significant effects on tumor cells, there is limited information concerning its effects on the immune system. The objective of this study was to evaluate the effects of Geldanamycin on activity of antigen-presenting cells. Immature and mature monocyte derived dendritic cells (DC) from normal human donors were used as the source of antigen-presenting cells in this study. Geldanamycin treatment of DC for 24 hours had no effect on cell viability (>90%), however, it led to a significant down-regulation of surface antigens associated with activation (CD86, CD80), maturation (CD83) and antigen presentation (HLA-ABC, HLA-DPQR). This decline was associated with changes in gene expression levels of these antigens, however the protein expression analyzed by % positive cells was not down-regulated with the treatment. Exposure to Hsp90 inhibitor was associated with significant decreases in IL-12 secretion (untrt vs. trt = 135 vs. 21 pg/ml), antigen uptake (MFI untrt 798 vs. MFI trt 449, Dextran-FITC), and antigen processing. These changes were associated with decline in DC function, which were demonstrated by significant decrease in Hsp90-treated DC compared to untreated DC in presentation of Tetanus Toxoid to autologous T lymphocytes (untrt vs. trt = 73 % vs. 47 %, CFSE proliferation), allogeneic T lymphocytes stimulation (untrt vs. trt = 232795 cpm vs. 116876 cpm, ³H-thymidine incorporation), and induction of IFN-g secretion from allogenic T lymphocytes (untrt vs. trt = 500 vs. 30 pg/ml). Taken together, these results show significant decline in DC function following Hsp90 inhibitor treatment. Further studies are underway using MM patient samples pre- and post-Hsp90 inhibitor treatment to understand in vivo effects on the immune system. Our pre-clinical data suggests the need to consider proper sequence of various therapeutic modalities, including immunotherapy, to optimize and improve clinical outcome.