BAFF/Blys Levels Correlate with Disease Activity and Alter Peripheral B Cell Subsets in Patients with Chronic GVHD.
Authors: Sarantopoulos Stefanie , Stevenson Kristen E. , Kim Haesook T. , Bhuiya Nazmim S. , Cutler Corey S. , Soiffer Robert J. , Antin Joseph H. , Ritz Jerome 
Published: April 2020

Abstract
Patients with chronic graft versus host disease (cGVHD) after allogeneic hematopoietic stem cell transplantation (HSCT) have been found to have high titers of allo-reactive antibodies, but a role for B cells in the pathology of this disease remains undefined. B Cell Activating Factor, BAFF/Blys (BAFF), promotes differentiation and expansion of antigen-activated B cells and contributes to loss of B cell tolerance in animal models. We hypothesized that the BAFF/BAFF receptor (BAFF-R) pathway may perpetuate potentially allo- or auto-reactive antigen-experienced CD27+ B cells in patients with cGVHD after HSCT. Soluble BAFF was measured in plasma from 104 patients after HSCT. Median BAFF levels were statistically different when groups were compared using a two-sided Wilcoxon-Rank-Sum test (see Table below). Logistic regression analysis revealed that higher BAFF levels were associated with active cGVHD after adjusting for other GVHD prognostic factors (p=0.0007). Patients with ≥10ng/ml BAFF levels had ten-fold increased odds of having cGVHD compared to patients with BAFF levels of &lt;10ng/ml (OR of 10.8, p=&lt;0.0001). High dose prednisone reduced median plasma BAFF levels (3.8ng/ml in patients receiving ≥30mg daily prednisone versus 14ng/ml for those receiving &lt;30mg or no prednisone). Serial BAFF measurements revealed peak BAFF levels at 6 months post-HSCT in patients who later developed limited cGVHD. 81% of patients with BAFF levels &gt;10ng/ml at 6 months subsequently developed cGVHD (median BAFF was 20ng/ml) compared to 39% of patients with BAFF levels &lt;10ng/ml at 6 months (p=0.002). We also found that BAFF-R expression on B cells was down-regulated in vitro in the presence of BAFF. Consistent with this finding flow cytometry revealed very low BAFF-R expression on B cells in patients with active cGVHD. BAFF-R expression on peripheral B cells correlated with BAFF levels (p=0.0001), suggesting that BAFF signals via BAFF-R in cGVHD. We used 5-color FACS to characterize peripheral B cell subsets in 68 post-HSCT patients. Compared to patients without cGVHD, the proportion of antigen-experienced CD27+ B cells was increased in patients with limited cGVHD (n=20, p=0.04). The extensive cGVHD patient group was smaller (n=11) with greater variability in CD27+ B cell frequency resulting in no statistical difference (p=0.27). The proportion of CD27+ post-germinal center B cells was also increased in patients with active cGVHD (p=0.04 and p=0.03 extensive and limited cGVHD, respectively). High BAFF levels correlated with increased total numbers of CD27+ B cells (p=0.05), but not with total or naïve B cell numbers, suggesting that BAFF plays a role in perpetuation of circulating antigen-experienced and memory B cells in cGVHD patients. Our results suggest that high levels of BAFF after HSCT help break peripheral B cell tolerance and contribute to cGVHD pathobiology.
Comparison of BAFF Levels Between Extensive/Limited versus Inactive/No cGVHD Groups cGVHD Type N Median BAFF (ng/ml) p-value vs. inactive p-value vs. no Extensive 15 11.5 0.14 0.02 Limited 33 9.0 0.02 0.0004 Inactive 27 5.7 - 0.02 No 29 4.4 0.16 - Normal 26 1.9 0.0002 0.004