MAIT and Vδ2 Unconventional T Cells Predict Favorable Outcome after Allogeneic HCT and Are Supported By a Diverse Intestinal Microbiome

Microbial diversity is associated with improved outcome in patients receiving allogeneic hematopoietic cell transplantation (allo-HCT), however, the mechanism underlying this observation is unclear. Unconventional T cells recognize specific metabolites of bacterial biosynthesis and their role in the post-HCT immunity has not yet been fully clarified. Here we have performed an observational study (n = 174 patients) using 16S rRNA sequencing of early post-HCT patient stool samples (day 7-21 after HCT) paired with multiparameter flow cytometry (performed at day 30 and day 100 after HCT) to explore the relationship between the intestinal microbiome early after HCT and the unconventional T cell populations in circulation. Our data extend findings of other groups suggesting that mucosal-associated invariant T (MAIT) cells are dependent on a diverse microbiome and are also associated with favorable allo-HCT outcome. In addition, we report for the first time that the Vδ2 subset of γδ T cells is positively correlated with MAIT cells as well as independent predictors of favorable transplant outcome.