Concomitant decrease of double-positive lymphocyte population CD4CD8αα and Faecalibacterium prausnitzii in patients with colorectal cancer.

Introduction And Aims: Changes in the composition of the gut microbiota in patients with colorectal cancer (CRC) compatible with a contribution of the gut microbiota in carcinogenesis have been reported. In particular, a decrease Faecalibacterium prausnitzii has been identified. A CD4CD8αα, double-positive lymphocyte population (DP8α) has recently been demonstrated in the human colon and blood with regulatory functions and specificity for F. prausnitzii. Here, we aimed to detect dysbiosis in the fecal microbiome of patients with CRC by metagenomic analysis, and to look for changes in the levels of DP8α circulating T cells specific for F. prausnitzii in these patients.

Patients And Methods: Patients with CRC and control subjects were prospectively included. None had received antibiotics in the previous month or any anti-tumor treatment. A stool sample was collected for each participant, and analyzed by shotgun sequencing. The DP8α T cell population was identified and quantified on fresh whole blood by flow cytometry with anti-CD45, anti-CD3, anti-CD4 and anti-CD8α co-labeling.

Results: Twenty-one patients with CRC and 20 controls subjects were included. We found that mean relative abundance of five species was significantly decreased in CRC patients compared with controls, including F. prausnitzii, Barnesiella intestinihominis, Alistipes finegoldii, Bacteroides eggerthii and Eubacterium siraeum. We also found that the DP8α T cell population was significantly decreased in the blood of CRC patients compared with controls.

Conclusion: In our work, we showed that a reduced abundance of F. prausnitzii in CRC patients was associated to a significant decrease in the circulating DP8α Treg population, suggesting a potential involvement of reduced activity of DP8α T cells in colonic carcinogenesis. These findings open new diagnostic and therapeutic strategies for CRC.