Chronic GvHD Is Characterized By Impaired B Cell Development in the Bone Marrow

Abstract Background. Chronic-graft-versus-host disease (cGvHD) continues to be a major complication following allogeneic hematopoietic stem cell transplantation (HSCT). Despite significant progress, mechanisms underlying development of the pathology are yet to be fully understood. Recent studies utilizing mouse models and patient samples have demonstrated a critical role for B cells in GvHD pathogenesis. Bone marrow (BM)-derived B cells can produce auto-reactive antibodies causing tissue fibrosis and multiorgan cGvHD. Impaired B cell homeostasis in the periphery, activation due to abnormally high levels of B cell-activating factor (BAFF), increased survival of auto-reactive B cells and aberrant BCR signaling are shown to be important for disease progression in cGvHD patients. Murine models also highlighted the critical role of germinal center reactions, particularly interactions between T follicular helper (Tfh) cells and B cells for generation of auto-antibodies which are responsible for triggering immune responses and cell-mediated toxicity. A growing body of evidence has emerged highlighting the fact that BM itself is a target organ during acute GvHD (aGvHD) with recent work suggesting a role for donor CD4+ T cells in BM specific aGvHD. Our group has shown that patients with higher numbers of BM B cell precursors were less likely to develop cGvHD after allogeneic HSCT (Fedoriw et al., 2012). These observations indicate clinical relevance of impaired BM B lymphopoiesis for cGvHD development. Methods. In order to investigate the effect of cGvHD on BM B cell development, we used the well-characterized major mismatch B6 into B10.BR model of systemic cGvHD. Recipient mice were treated with cyclophosphamide on day -3 and -2, irradiated with 700 cGy on day -1, and injected with 107 T cell depleted (TCD) BM with or without total splenic T cells (0.5-1x105). Mice were monitored for 30 days, and BM and spleen was harvested and analyzed using flow cytometry. Results. Consistent with patient data, we observed a decrease in the frequency and number of donor-derived uncommitted common lymphoid progenitors (CLP) and B cell progenitors in the BM+ allogeneic T cells group (CLP: 0.17±0.03% vs. 0.06±0.01%, p A recent study showed that activation and proliferation of conventional T cells in aGvHD model can be prevented by in vivo expansion of regulatory T cells (Tregs) using αDR3 antibody (4C12). We adopted this approach to determine whether Tregs can suppress the cytotoxic effect of donor CD4+ T cells in BM in cGvHD model. Animals that received T cells from 4C12-treated donors had an increase in survival and lower cGvHD pathology scores. These mice also had higher frequency of pro B, pre B, and immature B cells compared to the mice infused with T cells from isotype-treated donors. Conclusions. These studies demonstrate that BM development of B lymphocytes is impaired in a mouse model of systemic cGvHD. Our data suggests that donor-derived CD4+ T cells are involved in the destruction of hematopoietic niches in BM, particularly OB, which support B lymphopoiesis. Moreover, depletion of CD4+ T cells and infusion with in vivo expanded Tregs reduced the severity of cGvHD. Thus, Treg therapy in patients with cGvHD may be important for BM B cell development, and improvement of clinical outcomes. Download : Download high-res image (183KB) Download : Download full-size image Disclosures No relevant conflicts of interest to declare.