Efficient Expansion of Human Granzyme B–Expressing B Cells with Potent Regulatory Properties
Mélanie Chesneau, Hoa Le, Richard Danger, Sabine Le Bot, Thi‐Van‐Ha Nguyen, Josselin Bernard, Cyrielle Poullaouec, Pierrick Guerrif, Sophie Conchon, Magali Giral, Béatrice Charreau, Nicolas Degauque, Sophie Brouard
Abstract
Abstract Granzyme B–expressing B cells have been shown to be an important regulatory B cell subset in humans. However, it is unclear which subpopulations of B cells express GZMB under normal conditions and which protocols effectively induce ex vivo expansion of GZMB+ B cells. We found that in the peripheral blood of normal individuals, plasmablasts were the major B cell subpopulation that expressed GZMB. However, when using an in vitro plasmablast differentiation protocol, we obtained only 2% GZMB+ B cells. Nevertheless, using an expansion mixture containing IL-21, anti-BCR, CpG oligodeoxynucleotide, CD40L, and IL-2, we were able to obtain more than 90% GZMB+ B cells after 3 d culture. GZMB+ B cells obtained through this protocol suppressed the proliferation of autologous and allogenic CD4+CD25− effector T cells. The suppressive effect of GZMB+ B cells was partially GZMB dependent and totally contact dependent but was not associated with an increase in effector T cell apoptosis or uptake of GZMB by effector T cells. Interestingly, we showed that GZMB produced by B cells promoted GZMB+ B cell proliferation in ERK1/2-dependent manner, facilitating GZMB+ B cell expansion. However, GZMB+ B cells tended to undergo apoptosis after prolonged stimulation, which may be considered a negative feedback mechanism to limit their uncontrolled expansion. Finally, we found that expanded GZMB+ B cells exhibited a regulatory phenotype and were enriched in CD307bhi, CD258hiCD72hi, and CD21loPD-1hi B cell subpopulations. Our study, to our knowledge, provides new insight into biology of GZMB+ B cells and an efficient method to expand GZMB+ B cells for future cell therapy applications.