Immune system and intestinal microbiota determine efficacy of androgen depletion therapy against prostate cancer.

168 Background: Prostate cancer (PC) responds to androgen deprivation therapy (ADT) usually in a transient fashion, progressing from hormone-sensitive PC (HSPC) to castration-resistant PC (CRPC). While it is recognized that ADT has an immunomodulatory effect, little is known about the intestinal microbiome effect on therapeutic outcome of ADT. Methods: We investigated a mouse model of PC as well as specimens from PC patients to unravel an unsuspected contribution of thymus-derived T lymphocytes and the intestinal microbiota in the efficacy of ADT. Preclinical experiments were performed in PC-bearing mice, immunocompetent or immunodeficient. In parallel, we prospectively included 65 HSPC and CRPC patients to analyze their feces and blood specimen. Results: In PC-bearing mice, ADT increased thymic cellularity and output. PC implanted in T lymphocyte-depleted or athymic mice responded less efficiently to ADT than in immunocompetent mice. Moreover, depletion of the intestinal microbiota by oral antibiotics reduced the efficacy of ADT. PC reduced the relative abundance of Akkermansia muciniphila in the gut, and this effect was reversed by ADT. Moreover, cohousing of PC-bearing mice with tumor-free mice, or oral gavage with Akkermansia improved the efficacy of ADT. This appear to be applicable to PC patients because long-term ADT resulted in an increase of thymic output, as demonstrated by an increase in circulating recent thymic emigrant cells (sjTRECs). Moreover, as compared to HSPC controls, CRPC patients demonstrated a shift in their intestinal microbiota that significantly correlated with sjTRECs. While feces from healthy volunteers restored ADT efficacy. Conclusions: These findings suggest that reversing the intestinal dysbiosis and repairing acquired immune defects in PC patients have a potential impact on the therapeutic outcome of ADT.