Targeting Bruton Tyrosine Kinase with Acalabrutinib Attenuates Murine Sclerodermatous Chronic Graft Versus Host Disease

Introduction Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is deemed the only curative option for some malignant hematopoietic disorders, yet its benefits are limited by the onset of graft-versus-host disease (GVHD). Chronic GVHD (cGVHD) is often characterized by chronic inflammation and fibrosis mediated by alloreactive donor B- and T-cell involvement. Bruton tyrosine kinase (BTK) is the downstream effector in the B-cell receptor signaling pathway and has a crucial role in mast cell activation, both of which are critical in the pathogenesis of cGVHD. Selective inhibition of BTK may be beneficial in ameliorating cGVHD pathogenesis. In this study, we evaluated the efficiency of acalabrutinib, a highly selective Bruton tyrosine kinase inhibitor using a murine sclerodermatous cGVHD model. Methods Recipient BALB/c mice received the total body irradiation (800cGy), followed by infusion of bone marrow and splenocytes of either syngeneic (BALB/c) or allogeneic (B10.D2) hematopoietic cells and were subsequently treated with acalabrutinib or control from starting three weeks after HSCT until end of week 8. Mice were monitored for clinical signs of GVHD, survival, organ pathology of lung, liver, gut, skin, and inflammatory mediator expression. Results Acalabrutinib treatment showed better survival, improved clinical cGVHD scores, and reduced skin pathology (P = 0.002). Significant reductions in dermal thickness and skin fibrosis (P = 0.001) as well as mast cell numbers (P = 0.0001) were evidenced in the acalabrutinib-treated group. No differences were seen in pathology scores of gut, liver and lung among allogeneic groups. In vitro, experiments on mast cell activation show increased pro-inflammatory chemokines CCL2, CCL3, and CCL4 were effectively inhibited by acalabrutinib in a dose-dependent manner. Chemokine analysis from serum samples revealed significantly decreased levels of CXCL10, CXCL13, and CCL22 in acalbrutinib allogeneic recipients when compared to the allogeneic control group. Conclusion Our results demonstrate that specific inhibition of BTK with acalabrutinib has a potentially beneficial role in ameliorating sclerodermatous cGVHD of the skin and warrants further investigation with respect to underlying pathophysiology and why beneficial effects were seen in skin only. Our future work on transcriptomics will provide insights into the molecular transcriptional signatures and pathways associated with the regulation of cGVHD.