Fig. 1

The intestinal microbiome may help determine outcomes of ICI therapy. Increased intestinal microbiome diversity and the presense of specific intestinal bacteria are associated with both responses and toxicity following ICI therapy. One possible group of mechanisms is antigen-independent, via induction of mucosal and systemic immune responses, especially Th1 and cytotoxic T cell responses, by the microbiome (left). Alternatively, antigen-specific mechanisms, specifically antigen mimicry between microbial and tumor antigens, could modulate anti-tumor immune responses. For example, T cell targeting an epitope SVYRYYGL (SVY) expressed in Bifidobacterium breve cross-react with a model neoantigen, SIYRYYGL (SIY) [63]. Antigen-specific T cells that can cross-react against both commensal bacterial and tumor antigens may play a role in ICI therapy (right)