Precision probiotic therapy enhances immune checkpoint therapy efficacy in melanoma bearing mice.

Abstract

e14195 Background: Immune checkpoint inhibitor therapy, ICT, achieves remissions in melanoma patients but factors modulating response are not well defined. Our group (Frankel et al. Neoplasia 2017) and others have identified specific gut microbiota associated with improved ICT response. Recently, we identified specific gut microbiota that induce adaptive immune responses and potentiate ICT (Tanoue et al. Nature 2019). In this study, we determined whether this predefined consortia of gut microbiota augment ICT efficacy in melanoma bearing mice. Methods: Mice (C57BL/6, 6-8wk old, female, Jackson, n = 4-12 mice) received ± antibiotic water (penicillin G 1500U/mL + streptomycin 2mg/mL) for 6 d to deplete gut microbiota. Mice were then inoculated with 105 B16F10 melanoma cells SQ. At d 4, 8, 12 post-tumor inoculation, 0.2 mg anti-mCTLA4 + anti-mPD1 antibodies (Bio X Cell) were administered IP. Precision probiotic therapies included Vedanta Bioscience VE800 (Tanoue et al., Nature 2019), VE804 (same as VE800 without R. lactatiformans and F. ulcerans), VE411 (four Clostridial firmicutes) (Narushima, 2014), and Lactobacillus acidophilus (ATCC 4356) probiotics were given via gavage (1x109 cfu) starting day +1 after tumor inoculation and 3xwkly. Loss of survival was defined as death or tumor diameters ≥ 2 cm. Tumor growth inhibition, TGI = (1- mean treated tumor volume/mean control tumor volume) x 100%. Tumor mononuclear cells were isolated for flow cytometry for murine CD4, CD8, and CD11c. Results: TGI in mice with intact gut microbiota and treated with ICT was 84 ± 4% (SEM). Pre-treatment antibiotics reduced TGI to 38 ± 11%. Groups treated with Vedanta VE800, VE804, and VE411 exhibited TGIs of 77 ± 9, 61 ± 8, and 69%, respectively, whereas treatment with Lactobacillus acidophilus achieved TGIs 57%. VE800 treated mice had significantly increased length of survival compared to mice treated with antibiotics (p = 0.0008, log-rank test). Length of survival was not significantly different between groups with intact gut microbiota and those pretreated with antibiotics and dosed with VE800 (p = 0.52, log-rank test). ICT increased tumor CD4 cells to 11% from 2% and CD8 cells to 9% from 1%., however pre-treatment with antibiotics reduced CD4 cells to 4% and CD8 cells to 1%. Conclusions: Defined consortia of gut microbiota facilitate ICT efficacy. These preclinical studies lay the foundation for optimizing the host response to ICT.