Lactobacillus gallinarum-derived metabolites boost anti-PD1 efficacy in colorectal cancer by inhibiting regulatory T cells through modulating IDO1/Kyn/AHR axis

Gut. 2023 Nov 24;72(12):2272-2285. doi: 10.1136/gutjnl-2023-329543.

Abstract

Objective: Gut microbiota is a key player in dictating immunotherapy response. We aimed to explore the immunomodulatory effect of probiotic Lactobacillus gallinarum and its role in improving anti-programmed cell death protein 1 (PD1) efficacy against colorectal cancer (CRC).

Design: The effects of L. gallinarum in anti-PD1 response were assessed in syngeneic mouse models and azoxymethane/dextran sulfate sodium-induced CRC model. The change of immune landscape was identified by multicolour flow cytometry and validated by immunohistochemistry staining and in vitro functional assays. Liquid chromatography-mass spectrometry was performed to identify the functional metabolites.

Results: L. gallinarum significantly improved anti-PD1 efficacy in two syngeneic mouse models with different microsatellite instability (MSI) statuses (MSI-high for MC38, MSI-low for CT26). Such effect was confirmed in CRC tumourigenesis model. L. gallinarum synergised with anti-PD1 therapy by reducing Foxp3+ CD25+ regulatory T cell (Treg) intratumoural infiltration, and enhancing effector function of CD8+ T cells. L. gallinarum-derived indole-3-carboxylic acid (ICA) was identified as the functional metabolite. Mechanistically, ICA inhibited indoleamine 2,3-dioxygenase (IDO1) expression, therefore suppressing kynurenine (Kyn) production in tumours. ICA also competed with Kyn for binding site on aryl hydrocarbon receptor (AHR) and antagonised Kyn binding on CD4+ T cells, thereby inhibiting Treg differentiation in vitro. ICA phenocopied L. gallinarum effect and significantly improved anti-PD1 efficacy in vivo, which could be reversed by Kyn supplementation.

Conclusion: L. gallinarum-derived ICA improved anti-PD1 efficacy in CRC through suppressing CD4+Treg differentiation and enhancing CD8+T cell function by modulating the IDO1/Kyn/AHR axis. L. gallinarum is a potential adjuvant to augment anti-PD1 efficacy against CRC.

Keywords: colorectal cancer; immunotherapy; probiotics.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Lysates / pharmacology
  • Bacterial Lysates / therapeutic use
  • CD8-Positive T-Lymphocytes
  • Colorectal Neoplasms* / drug therapy
  • Immune Checkpoint Inhibitors* / pharmacology
  • Immune Checkpoint Inhibitors* / therapeutic use
  • Kynurenine* / metabolism
  • Lactobacillus* / chemistry
  • Mice
  • Programmed Cell Death 1 Receptor / drug effects
  • Programmed Cell Death 1 Receptor / immunology
  • Receptors, Aryl Hydrocarbon / drug effects
  • Receptors, Aryl Hydrocarbon / metabolism
  • T-Lymphocytes, Regulatory

Substances

  • Kynurenine
  • Receptors, Aryl Hydrocarbon
  • Pdcd1 protein, mouse
  • Programmed Cell Death 1 Receptor
  • Immune Checkpoint Inhibitors
  • IDO1 protein, mouse
  • Bacterial Lysates

Supplementary concepts

  • Lactobacillus gallinarum