Roseburia intestinalis generated butyrate boosts anti-PD-1 efficacy in colorectal cancer by activating cytotoxic CD8⁺ T cells

Objective: Roseburia intestinalis is a probiotic species that can suppress intestinal inflammation by producing metabolites. We aimed to study the role of R. intestinalis in colorectal tumourigenesis and immunotherapy.

Design: R. intestinalis abundance was evaluated in stools of patients with colorectal cancer (CRC) (n=444) and healthy controls (n=575). The effects of R. intestinalis were studied in Apc^Min/+ or azoxymethane (AOM)-induced CRC mouse models, and in syngeneic mouse xenograft models of CT26 (microsatellite instability (MSI)-low) or MC38 (MSI-high). The change of immune landscape was evaluated by multicolour flow cytometry and immunohistochemistry staining. Metabolites were profiled by metabolomic profiling.

Results: R. intestinalis was significantly depleted in stools of patients with CRC compared with healthy controls. R. intestinalis administration significantly inhibited tumour formation in Apc^Min/+ mice, which was confirmed in mice with AOM-induced CRC. R. intestinalis restored gut barrier function as indicated by improved intestinal permeability and enhanced expression of tight junction proteins. Butyrate was identified as the functional metabolite generated by R. intestinalis. R. intestinalis or butyrate suppressed tumour growth by inducing cytotoxic granzyme B⁺, interferon (IFN)-γ⁺ and tumour necrosis factor (TNF)-α⁺ CD8⁺ T cells in orthotopic mouse models of MC38 or CT26. R. intestinalis or butyrate also significantly improved antiprogrammed cell death protein 1 (anti-PD-1) efficacy in mice bearing MSI-low CT26 tumours. Mechanistically, butyrate directly bound to toll-like receptor 5 (TLR5) receptor on CD8⁺ T cells to induce its activity through activating nuclear factor kappa B (NF-κB) signalling.

Conclusion: R. intestinalis protects against colorectal tumourigenesis by producing butyrate, which could also improve anti-PD-1 efficacy by inducing functional CD8⁺ T cells. R. intestinalis is a potential adjuvant to augment anti-PD-1 efficacy against CRC.