Poster Presentation NSW State Cancer Conference 2023

Gut microbiome alteration is linked to changes in splenic T cell populations in colorectal cancer (#157)

Miguel Q Castaneda 1 2 , Reem A Elnour 3 4 , Rebecca C Simpson 1 4 , Mirei C Okada 3 4 , Zhen Bao 3 4 , Alexander Engel 2 5 , Stephen Clarke 2 5 , Andrew Holmes 3 4 , Kellie Charles 6 , Erin R Shanahan 3 4 , Mark P Molloy 1 2
  1. School of Medical Sciences, The University of Sydney, Sydney, New South Wales, Australia
  2. Kolling Institute, The University of Sydney, Sydney, New South Wales, Australia
  3. School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales, Australia
  4. Charles Perkins Centre, The University of Sydney, Sydney, New South Wales, Australia
  5. Northern Clinical School, The University of Sydney, Sydney, New South Wales, Australia
  6. Sydney Pharmacy School, The University of Sydney, Sydney, New South Wales, Australia

Background: Interactions between the immune system and gut microbiome are key factors in the development of colorectal cancer (CRC). Certain microbes have protective effects against CRC during gut homeostasis, but their roles in developing tumours are not as well understood. Understanding microbiome-immune interactions in CRC could inform therapeutic strategies for immune modulation to improve prognosis and treatment outcomes in CRC patients.

Aim: Our investigation aimed to identify potential interactions and associations between the microbiome and immune system following disruption of gut mucosal homeostasis and gut microbiome alteration through antibiotic treatment.

Methods: Colorectal dysplasia was induced in BALB/c mice (n = 12 per group) using azoxymethane and dextran sodium sulfate. Mice were then given modified drinking water for 2 weeks, containing either metronidazole, neomycin, or vancomycin. Microbiomes were profiled using 16S rRNA gene sequencing of distal colon contents and splenic immune cell populations were analysed with spectral flow cytometry.

Results: Following induction of dysplasia, antibiotic treatments produced distinct microbiome compositions in each experimental group. Treatment with neomycin and vancomycin reduced frequency of splenic TH1 cells and TReg cells (p < 0.001, 0.01), while metronidazole reduced Tregs only (p < 0.01). Vancomycin treatment also reduced splenic cell counts of TH1, TH2 and TReg cells (p < 0.001, 0.05, 0.001) while neomycin reduced counts of TH1 cells only (p < 0.01). Spearman’s correlation analysis between T cell subpopulations and differentially abundant microbes revealed numerous correlations across the dataset. Notably, Firmicutes species predominantly correlated with the TH1 population, a positive prognostic factor in CRC, while Bacteroidota species mainly correlated with TH2 and TReg populations which are negative prognostic factors in CRC.

Discussion and Conclusion: The substantial shift in microbiome profiles and immune cell frequencies in response to antibiotic-mediated microbiome alteration suggest potential microbiome-immune interactions. Further studies are required to confirm these microbe-immune interactions and their roles in CRC.