Gut Microbiota and Antitumor Immunity: Potential Mechanisms for Clinical Effect

Mechanisms of immune modulation by the gut microbiota. The gut microbiota may affect immune cells playing key roles in antitumoral immunity. The microbiota may affect maturation processes, either in the bone marrow [for dendritic cells (DC)] or in the thymus (for T cells). Microbiota may also affect the activity of mature immune cells within the tumor microenvironment or in the surrounding lymph nodes. The microbiota-derived effect is mediated by three potential pathways: activation of pathogen recognition receptors such as TLRs and NODs; molecular mimicry initiating immune responses against cancer antigens that are similar to bacterial ones; and metabolic modulation using vitamins, short-chain fatty acids, bile salt, or amino acids that promote favorable intracellular processes among host cells. LN, lymph node; NOD, nucleotide-binding oligomerization domain-containing proteins; TCR, T-cell receptor; TLR, Toll-like receptor.