Low dose gemcitabine increases the cytotoxicity of human Vγ9Vδ2 T cells in bladder cancer cells in vitro and in an orthotopic xenograft model.

Human γδT cell immunotherapy is well tolerated and has shown promising results in clinical trials; however, its antitumor efficacy is limited, including results in solid tumors. Ex-vivo expanded γδT cell stimulated by zoledronic acid (ZOL) activates the γδT cell subpopulation of so called Vγ9Vδ2 T cells. To improve the clinical outcomes of Vγ9Vδ2 T cell (abbreviated as γδT cell here) immunotherapy, we aimed to increase the cytotoxicity of γδT cells by focusing on two issues: recognition of tumor cells by γδT cells and the effector (γδT cell)-to-target (tumor cell) (E/T) ratio. Ex vivo-expanded γδT cells showed potent cytotoxicity against urinary bladder cancer (UBC) cells in in vitro assays. Combination treatment with standard anticancer agents showed that low dose gemcitabine pretreatment significantly enhanced the cytotoxicity of γδT cells by upregulating the expression of MICA and MICB (MICA/B), which are tumor-associated antigens recognized by γδT cells. These effects were abrogated by small interfering RNA-mediated knockdown of MICA/B in UBC cells, suggesting that pre-exposing cancer cells to anticancer agents could be a promising strategy. A bladder instillation approach was used to increase the E/T ratio. The efficacy of ex vivo-expanded γδT cell immunotherapy was examined in an orthotopic xenograft model. In Vivo Imaging System analysis revealed the potent cytotoxicity of weekly intravesical administration of γδT cells, and weekly gemcitabine pretreatment enhanced the cytotoxicity of γδT cells in vivo. In conclusion, intravesical γδT cell immunotherapy and combination therapy with low dose gemcitabine may be a promising strategy in UBC.