Allogeneic stem cell transplantation (allo-HSCT) to treat hematological malignancies can induce life-threatening complications, such as graft-versus-host disease (GvHD). Increasing evidences strongly suggest that gut microbiota composition and the activity of regulatory T cells (Tregs) could be involved in GvHD prevention. We have recently identified a novel FoxP3-negative IL-10-secreting Treg subset, named DP8a, which displays a TCR-specificity for the gut commensal Faecalibacterium prausnitzii. Sizable fractions of these cells also expressed the membrane-bound ectonucleotidases CD39 and CD73, which are directly involved in their suppressive activity in vitro. Altogether, these data prompted us to hypothesize that F. prausnitzii-reactive DP8a Tregs could bridge microbiota dysbiosis and GvHD incidence in allo-HSCT patients.

We quantified circulating DP8a Tregs and their CD39 and CD73 expression in allo-HSCT patients. A striking deficiency of CD73-expressing DP8a Tregs was strongly associated with acute GvHD (aGvHD) development at 1-month post-transplant, as compared to aGvHD-free patients or patients before transplantation. These data suggest that a CD73-dependent functional alteration of DP8a Tregs could, at least in part, be involved in aGvHD occurrence and/or development. We next evaluated the therapeutic efficacy of CD73+ DP8a Tregs in a pre-clinical NSG mouse model of acute xeno-GvHD. Injected CD73+ DP8a Treg  drastically protected mice against xeno-GvHD without preventing the development of human chimerism. Accordingly, serum inflammatory human cytokines and tissue infiltration by human cells were significantly lower in mice treated with CD73+ DP8a Tregs, as compared to untreated mice. In addition, the colon was rapidly populated with the injected DP8a Tregs and well-preserved in treated mice, while severly damaged in untreated mice.

Altogether, these results strongly support a role for CD73+ DP8a Tregs in aGVHD prevention and advocate for the use of these cells to both predict aGvHD risks and give rise to the development of innovative therapeutic strategies to preclude GvHD-related inflammation.