Oral Administration of Ibrutinib Is Ineffective at Preventing Scleroderma in Chronic Gvhd in Two Preclinical Mouse Models

We have established two mouse models of chronic graft versus host disease (cGVHD): one is an MHC-matched DBA/2 donor to BALB/c recipient, and this model amplifies the role of CD4⁺ T and B cells in transplants; the other model is an MHC-mismatched C57BL/6 donor to BALB/c recipient, and this model amplifies the role of de novo-developed CD4⁺ T and B cells. BALB/c recipients in both models started to develop scleroderma ~35 days after transplantation of donor spleen and bone marrow cells and this peaked ~50 days after transplantation. BALB/c recipients given DBA/2 transplants also developed proteinuria due to IgG anti-dsDNA autoantibody deposition in the glomeruli. We have reported that donor CD4⁺ T and B cells play critical roles in the pathogenesis of chronic GVHD (J. Immunol 2012 and 2013). Administration by I.V. injection of depleting anti-CD20 prevented induction of chronic GVHD in both models (Biol. Blood and Marrow Transplant 2014). In the current studies, using these two models, we tested whether oral administration of Ibrutinib could prevent induction of cGVHD. Ibrutinib was gavaged at 12.5 mg/kg/day from day 0 to day 30 or given in drinking water at 35 mg/kg/day (0.16 mg/ml) from day 0 to day 50. We found that administration of Ibrutinib significantly delayed the onset of proteinuria in the model of DBA/2 donor to BALB/c recipient, but accelerated the onset and increased the severity of scleroderma in 20/20 recipients given DBA/2 transplants and 9/9 recipients given C57BL/6 transplants as measured by a clinical score system. Administration of Ibrutinib significantly reduced CD138⁺B220^lo plasma cells but not CD138^-B220⁺ B cells in the spleen and peripheral lymph nodes of both recipients. Administration of Ibrutinib slightly reduced CD4⁺ T cell numbers in the spleen but significantly increased CD4⁺ T cell numbers in the peripheral lymph nodes, although there was no significant impact on CD4⁺ T cell expression of IFN-g and TNF-α in both recipients. These results indicate that, although oral administration of Ibrutinib is able to reduce B cell activation and differentiation into plasma cells, it is ineffective at inhibiting the CD4⁺ T cell expansion that mediates scleroderma in the models of DBA/2 donor to MHC-matched BALB/c recipient and C57BL/6 donor to MHC-mismatched BALB/c recipient. Our result is in contrast to a previous report showing that oral administration of Ibrutinib prevented induction of chronic GVHD with bronchiolitis obliterans in a mouse model and reversed scleroderma in another mouse model (Poster 2591, AACR 2014, San Diego). Further discussion about the differences is warranted. (This work was supported by Nesvig Lymphoma Foundation).