Regulatory B10 cells display an altered homoeostasis in acute graft-versus-host disease

Objective: The role of B cells and the subgroup of IL-10 producing B cells, known to have a regulatory function, in patients following a haematopoietic stem cell transplant (alloSCT) has not been clearly understood to date. Methods: We prospectively recruited 95 patients following an alloSCT and studied the B-cell reconstitution on days 30, 90 and 150. Regulatory B10 cells could be analysed in 22 consecutively recruited patients on day 30 post-transplant. Results: The total B-cell percentages in transplant recipients (median 0.33; range 0.01-5.9) were significantly reduced than the controls (P = 0.0001) and constituted predominantly of transitional CD24(high) CD38(high) B cells. Regulatory B10 cells could be analysed in 22 consecutively recruited patients on day 30 post-transplant. The percentages of B10 cells (median 1.35; 0.0-4.5) were significantly reduced in the transplant recipients in comparison with the control cohort (P < 0.0001). Interestingly, the percentages of B10 cells in patients with acute GvHD (median 1.7; 0.33-4.5) were significantly higher than those without GvHD (median 0.7; 0-1.9) (P = 0.0003). Conclusion: This is the first report demonstrating B10 cells in stem cell transplant recipients in the early post-alloSCT (30 d) period. Our data suggest a possible role for B10 cells in the pathophysiology of acute GvHD. Further longitudinal studies are warranted to understand the implications of our findings.