Table 1 Major gut microbial taxa and their predominant influence on systemic immunity and response to immunotherapy.

Predominately positive influence

 Firmicutes

  Faecalibacterium prauznitzii

Boosts effector T-cells and dampens T-regs

Humans

Melanoma

  Faecalibacterium spp.

Increases efficacy of anti-CTLA-4 immunotherapy

Humans

Metastatic melanoma

  Eubacterium limosum

  Clostridiales spp.

  Ruminococcaceae spp.

  Phascolarctobacterium spp.

Boost CD8+ T-cells and enhance anti-PD-1 responses

Cell line

Colorectal Adenocarcinoma

Cell line (MC38)

 Fusobacteria

  Fusobacterium ulcerans

  Fusobacterium varium

Boost CD8+ T-cells and enhance anti-PD-1 responses

Cell line

MC38

Verrucomicrobia

  Akkermansia muciniphila

Increase in memory T-cells and decrease in T-regs in the TME

Humans

Epithelial tumors

Increases mucus layer of the gut to prevent lipopolysaccharides absorption

Humans

Epithelial tumors

Mixed influence

 Bacteroidetes

  Bacteroides fragilis

Increases efficacy of anti-CTLA-4 immunotherapy

Human/animal/cell line

Epithelial tumors

Promotion of T-regs through polysaccharide-A

Humans

Healthy humans

Higher IL-12 levels in transplant recipients

Animal/cell line

Cervical cancer

  Bacteroides thetaiotaomicron

Increases efficacy of anti-CTLA-4 and anti-PD-1 immunotherapy

Humans

Melanoma

  Bacteroides spp.

Inferior response of anti-CTLA-4 immunotherapy

Humans

Metastatic melanoma

 Actinobacteria

Bifidobacterium longum

Increases CD8+ T-cells

Animal/cell line

Melanoma

Humans

Melanoma

  Bifidobacterium bifidum

Induces naïve T-cell differentiation into T-regs and increases IL-10

Humans/in vitro

Healthy humans

Increases the integrity of epithelial barrier

Predominately negative influence

 Proteobacteria

  Enterobacteriaceae

Inferior response and survival

Humans

Pediatric cancers