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

Abstract

<i>Roseburia intestinalis</i> is a probiotic species that can suppress intestinal inflammation by producing metabolites. We aimed to study the role of <i>R. intestinalis</i> in colorectal tumourigenesis and immunotherapy. <i>R. intestinalis</i> abundance was evaluated in stools of patients with colorectal cancer (CRC) (n=444) and healthy controls (n=575). The effects of <i>R. intestinalis</i> were studied in <i>Apc^Min/+</i> 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. <i>R. intestinalis</i> was significantly depleted in stools of patients with CRC compared with healthy controls. <i>R. intestinalis</i> administration significantly inhibited tumour formation in <i>Apc^Min/+</i> mice, which was confirmed in mice with AOM-induced CRC. <i>R. intestinalis</i> 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 <i>R. intestinalis. R. intestinalis</i> 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. <i>R. intestinalis</i> 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. <i>R. intestinalis</i> protects against colorectal tumourigenesis by producing butyrate, which could also improve anti-PD-1 efficacy by inducing functional CD8⁺ T cells. <i>R. intestinalis</i> is a potential adjuvant to augment anti-PD-1 efficacy against CRC.