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

Abstract

ObjectiveGut microbiota is a key player in dictating immunotherapy response. We aimed to explore the immunomodulatory effect of probioticLactobacillus gallinarumand its role in improving anti-programmed cell death protein 1 (PD1) efficacy against colorectal cancer (CRC).DesignThe effects ofL. gallinarumin 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.ResultsL. gallinarumsignificantly 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. gallinarumsynergised 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 phenocopiedL. gallinarumeffect and significantly improved anti-PD1 efficacy in vivo, which could be reversed by Kyn supplementation.ConclusionL. 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. gallinarumis a potential adjuvant to augment anti-PD1 efficacy against CRC.

Modulating gut microbiome in cancer immunotherapy: Harnessing microbes to enhance treatment efficacy

“… 27 Moreover, indole-3-carboxylic acid (ICA) derived from Lactobacillus gallinarum also enhanced anti-PD-1 efficacy in mouse models with distinct MSI statuses. 28 …”

“…For instance, indoleamine 2,3-dioxygenase 1 (IDO1) was able to initiate the transformation of tryptophan into the immunosuppressive metabolite kynurenine (Kyn), while other microbial metabolites such as ICA inhibit IDO2 expression, potentially serving as therapeutic agents in cancer treatment. 28 , 72 …”

“…gallinarum improved the efficacy of anti-PD-1 therapy by inhibiting IDO1 expression and Kyn production within tumors, competing with Kyn for binding to the aryl hydrocarbon receptor (AhR) and antagonizing Kyn binding on CD4 + T cells. 28 These events inhibit the differentiation of Tregs to enhance the efficacy of anti-PD-1 therapy. 28 Daily administration of Lactobacillus reuteri also led to the translocation of gut microbes to B16-F0 melanoma tumors in mice, triggering antitumor IFN-γ + CD8 + T cell-mediated immunity in the TME through the metabolism of dietary tryptophan to indole-3-aldehyde (I3A) by intratumoral L .…”

Probiotics intervention in colorectal cancer: From traditional approaches to novel strategies

“…Increased anti-PD-1 ef cacy Reduced Treg function by IDO1/Kyn/AHR axis [56] VSL#3 DMH-induced CRC mouse models…”

Modulating commensal bacteria to intervene in cancer immunotherapy

“…A growing number of specific gut strains have been shown to play a role in immunotherapy, but they act with different components, some through their own bacterial components and others through secreted metabolites. 3 , 4 , 5 There is a lack of specific means and standardized procedures to reveal the exact components of bacterial action. We used different treatments to investigate the active components of L. johnsonii .…”