Tryptophan degradation by intestinal Bacteroides induces anti-tumor immunity and limits melanoma growth
(1) Olea XD (2) Beede K (3) Pereira G (4) Scott D (5) Petucci C (6) Martens E (7) Rodionov D (8) Shah A (9) Martinez MP (10) Kim H (11) Sharma AK (12) Martin A (13) Zhang T (14) Faries MB (15) Hamid O (16) Devkota S (17) Osterman A (18) Knott S (19) Voest EE (20) Ajami NJ (21) Wargo J (22) Ramer-Tait AE (23) Ronai ZA
Olea and Beede et al. identified Bacteroides rodentium and Bacteroides uniformis (found in mice and humans, respectively) as gut microbes that induced antitumor immunity and inhibited tumor growth in melanoma mouse models. These strains expressed tryptophanase A (TnaA) and aromatic aminotransferases (ArAT) that degraded tryptophan into indoles. TnaA loss in B. uniformis abrogated antitumor activity, whereas indole administration increased CD8+ T cell infiltration and restrained tumor growth, independent of AhR signaling. Elevated levels of ArAT and TnaA were found in patients with melanoma who responded to ICB.
Contributed by Shishir Pant
(1) Olea XD (2) Beede K (3) Pereira G (4) Scott D (5) Petucci C (6) Martens E (7) Rodionov D (8) Shah A (9) Martinez MP (10) Kim H (11) Sharma AK (12) Martin A (13) Zhang T (14) Faries MB (15) Hamid O (16) Devkota S (17) Osterman A (18) Knott S (19) Voest EE (20) Ajami NJ (21) Wargo J (22) Ramer-Tait AE (23) Ronai ZA
Olea and Beede et al. identified Bacteroides rodentium and Bacteroides uniformis (found in mice and humans, respectively) as gut microbes that induced antitumor immunity and inhibited tumor growth in melanoma mouse models. These strains expressed tryptophanase A (TnaA) and aromatic aminotransferases (ArAT) that degraded tryptophan into indoles. TnaA loss in B. uniformis abrogated antitumor activity, whereas indole administration increased CD8+ T cell infiltration and restrained tumor growth, independent of AhR signaling. Elevated levels of ArAT and TnaA were found in patients with melanoma who responded to ICB.
Contributed by Shishir Pant
ABSTRACT: Study of gut microbiota control of anti-tumor immunity (ATI) identifies Bacteroides rodentium and the human-related Bacteroides uniformis species to be capable of inducing ATI and limiting melanoma development in germ-free (GF), complex microbiome, or wild-type (WT) mice. Enhanced CD8(+) T cell infiltration within tumors of mice harboring B. rodentium coincides with increased expression of immune-stimulating pathways. Metabolomic analyses identify lower tryptophan levels in the cecal samples of GF mice harboring B. rodentium. In silico genomic reconstruction reveals that B. rodentium and B. uniformis harbor tryptophanase A (TnaA) and aromatic aminotransferase genes, which degrade tryptophan to indoles. Administration of B. uniformis harboring TnaA mutant fails to inhibit melanoma growth. Notably, administration of indoles effectively induces ATI and inhibits melanoma development. Correspondingly, the levels of bacterially encoded tryptophan-degrading enzymes are higher in cohorts of patients with melanoma responding to immunotherapy. These findings identify indoles as tryptophan breakdown products capable of inducing ATI resulting in melanoma inhibition.
Author Info:
(1) Translational Research Institute, Elinor and Rendall Department of Surgery, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA; Department of Biomedical Sciences, Cedars S
inai Medical Center, Los Angeles, CA 90048, USA; Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037, USA. (2) Department of Food Science and Technology, Nebraska Food for Health Center, University of Nebraska-Lincoln, Lincoln, NE 68588, USA. (3) Department of Microbiology & Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA. (4) Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037, USA. (5) Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. (6) Department of Microbiology & Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA. (7) Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037, USA. (8) Translational Research Institute, Elinor and Rendall Department of Surgery, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA. (9) Division of Molecular Oncology & Immunology, the Netherlands Cancer Institute, Amsterdam 1066 CX, the Netherlands. (10) Translational Research Institute, Elinor and Rendall Department of Surgery, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA. (11) Human Microbiome Research Institute, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA. (12) Human Microbiome Research Institute, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA. (13) Division of Cancer Epidemiology & Genetics, National Cancer Institute, Rockville, MD 20892, USA. (14) The Angeles Clinic and Research Institute, Cedars Sinai Medical Center, Los Angeles, CA 90025, USA. (15) The Angeles Clinic and Research Institute, Cedars Sinai Medical Center, Los Angeles, CA 90025, USA. (16) Department of Biomedical Sciences, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA; Human Microbiome Research Institute, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA. (17) Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037, USA. (18) Translational Research Institute, Elinor and Rendall Department of Surgery, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA. (19) Division of Molecular Oncology & Immunology, the Netherlands Cancer Institute, Amsterdam 1066 CX, the Netherlands. (20) Department of Genomic Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. (21) Department of Genomic Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. (22) Department of Food Science and Technology, Nebraska Food for Health Center, University of Nebraska-Lincoln, Lincoln, NE 68588, USA. Electronic address: aramer-tai2@unl.edu. (23) Translational Research Institute, Elinor and Rendall Department of Surgery, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA; Department of Biomedical Sciences, Cedars Sinai Medical Center, Los Angeles, CA 90048, USA. Electronic address: zeev.ronai@csmc.edu.
Citation: Cell Rep Med 2026 Jul 14 102921 Epub07/14/2026
