Antitumor immune responses are largely mediated by cytotoxic lymphocytes (CD8+ T cells) that recognize tumor-associated antigens presented in the context of a major histocompatibility complex class I molecule (MHC I). However, many tumors downregulate MHC I expression as a means of immune escape. Under these conditions, additional effector lymphocytes, such as natural killer cells (NK cells) which mediate non-MHC restricted cytotoxicity, provide antitumor defenses. Although the presence of intratumoral CD8+ T cells has been associated with an improved survival in muscle-invasive bladder cancer, the role of other effector lymphocytes including NK cells in bladder cancer (BC) is less studied. Here, a comprehensive examination of intratumoral lymphocytes in murine and human urothelial tumors revealed a relatively high proportion of macrophages, γδ T cells and NK cells and whereas macrophages were detrimental, NK cells were protective to BC growth. γδ T cells and NK cells contribute to innate effector immune responses and likely crosstalk as γδ T cells can boost NK cell cytotoxic function. Our findings suggest that γδ T cells could potentially have a role in activating NK cells function marked by increased IFN-γ and TNF-α expression. In patients undergoing cystectomy for muscle-invasive BC, a higher frequency of intratumoral NK cells was associated with an improved survival and this association was maintained in MHC I low but not MHC I high tumors. Higher stage bladder tumors had a higher proportion of intratumoral CD56dim NK cells, which exhibit less cytotoxicity and IFN-γ secretion compared to their CD56bright counterparts. Moreover, bladder infiltrating CD56bright but not CD56dim NK cells predicted improved survival for cystectomy patients. Further, older patients with BC had significantly less intratumoral NK cells compared to younger patients. Interestingly, surface expression of CD56 on NK cells decreased with increasing patient age and the proportion of CD56bright subsets decreased with increasing age whereas the proportion of CD56dim subsets slightly increased with age. Finally, because intravesical Bacillus Calmette-Guérin (BCG) activates NK cells and is commonly used to treat non-muscle invasive BC, we conducted a proof-of-concept trial of administering BCG to patients with muscle-invasive BC prior to cystectomy. While intravesical BCG was well tolerated and increased the percentage of intratumoral NK cells in this neoadjuvant setting, it had no discernable antitumor activity and did not alter CD56 expression or functional status of intratumoral NK cells. We conclude that NK cells are protective in BC and the extent of an intratumoral CD56bright NK cells is a prognostic indicator in BC. While BCG may induce NK cells, alternative approaches to improve NK cell function in BC are warranted.

Citation Format: Neelam Mukherjee, Niannian Ji, Maggie E. Tomasini, Vincent Hurez, Tyler J. Curiel, Maureen O. Montgomery, Andrew J. Braun, Marlo Nicolas, Marcela A. Flores, Qianqian Liu, Jianhua Ruan, Robert S. Svatek. Intratumoral CD56bright natural killer cells are associated with improved survival in bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3792.