*Purpose: Granzyme B (GZMB)+ B cells are increased in blood from transplanted patients who tolerate a kidney graft without immunosuppressive treatment. We demonstrated that these cells display regulatory properties, they prevent effector CD4+CD25-T cell proliferation by a mechanism depending from GZMB and the contact of the B cells with its target. Nevertheless, still very little is known about their phenotype in healthy individuals (HV) as well as in transplanted patients in different clinical situations.

*Methods: Because of the paucity of such cells, we showed that GZMB+ B cells may be expanded in vitro from sorted B cells after stimulation with a cocktail of IL-2, IL-21, IgG IgA IgM F(ab)’2, CpG oligodeoxynucleotides and CD40L, while keeping their immunosuppressive properties. We first used single cell RNA sequencing to characterize the profile of expanded GZMB+ Bregs vs unstimulated GZMB- B cells from the same patient in healthy volunteers and kidney transplanted recipients: tolerant patients, patients with stable kidney function and patients with chronic rejection. To further analyze the effect of GZMB+ cells on their target population, we then used single cell RNA sequencing to characterize the profile of CD3/CD28 stimulated CD4+CD25- T cells alone or in cocultures with either GZMB+Bregs or resting GZMB- B cells.

*Results: Whereas GZMB+Bregs single cell analysis did not evidence higher involvement of regulatory pathways, it reveals a high GZMB+Bregs proliferating and differenciated profile, concordant with their phenotype. Coculture with GZMB+Bregs induce an inhibition of effector T cell activity and IFN responses, with a drastic decrease of GZMB expression on T cells whereas GZMB-B cells have no effect. We used a prediction model to analyze receptor/ligand interactions based on T cell differential expression in coculture with B cells and we identified LTA and MIF overexpressed by GZMB+Bregs as potential modulators of effector T cell response.

*Conclusions: These data allow identifying specific interactions that may be instrumental in the B cell suppressive properties and B/T cell contact.

« Back to 2022 American Transplant Congress