Evaluation of the antiproliferative effect of Bifidobacterium longum BB-536 in solid tumor cell lines, co-cultured with murine splenocytes

Introduction: In the last decade, cancer immunotherapy has delivered impressive results in clinical settings. However, its efficacy has not been consistent probably because of several environmental and genetic factors influencing the outcome. Many studies have indicated that intestinal microbiota could affect the outcome of immune checkpoint inhibitors-based immunotherapy, both in animal models and patients. In particular, the Bifidobacterium genus seems to have a role as a positive regulator of in vivo antitumor immunity by promoting proinflammatory signals in innate immune cells. According to the considerable evidence that demonstrated its crucial role in the carcinogenesis and, overall, in the response to immunotherapy, we decided to use a commercial probiotic and grow its principal strain, the Bifidobacterium longum BB-536, in order to test its capability to affect antitumoral immune responses. Methods: Prior to in vivo studies, we carried out a feasibility evaluation study to test in vitro, antitumoral effects of the isolated probiotic strain. Tumor cell viability was used as parameter to determine Bifidobacterium longum BB-536 anti-proliferative ability before or after heat inactivation. Results: Interestingly, we found that B. longum inhibits cell growth, both in mouse melanoma B16-OVA and colorectal CT26 cells, showing a more pronounced effect on the latter ones. Conclusion: This preliminary evaluation of live and heat-inactivated probiotic in tumor cell lines indicates a potential cell growth inhibitory effect of these bacterial strains and encourage further studies in mouse models.