Ibrutinib suppresses alloantibody responses in a mouse model of allosensitization

Ibrutinib is a Bruton's tyrosine Kinase (BTK) antagonist that inhibits B cell receptor (BCR) signaling. Complete BTK deficiency is associated with absence of B-cells. Ibrutinb is currently approved by FDA for treatment of B-cell malignancies, including Waldenström macroglobulinaemia. We recently carried out studies to determine if ibrutinib could modify alloantibody responses. A mouse model of allogenic sensitization using a C57BL/6 mouse as the recipient of a skin allograft from an HLA-A2 transgenic mouse was utilized to examine the effects of ibrutinib on alloantibody responses and B cell effector functions. Donor-specific antibody (DSA) levels were measured in a flow-cytometric antibody binding assay. Splenic T and B cell subsets and plasma cells were analyzed in flow cytometry. Control mice developed peak levels of DSA IgM at day 14 PTx while the ibrutinib treated mice had significantly lower levels of DSA IgM (p = 0.0047). Control mice developed HLA.A2-specific IgG antibodies at day 14 (230 ± 60 MFI) and reached peak levels at day 21 (426 ± 61 MFI). In contrast, mice in the treatment group had low levels of HLA.A2-specific IgG at day 14 (109 ± 59 MFI, p = 0.004) and day 21 (241 ± 86 MFI, p = 0.003). FACS analysis found a reduction of B220+ or CD19+ B cell population (p < 0.05). In addition, ibrutinib attenuated recall DSA IgG responses to re-sensitization (p < 0.05) and reduced CD38+ CD138+ plasma cells (p < 0.05) in the spleens. Ibrutinib is effective in suppressing alloantibody responses through blocking BTK-mediated BCR signaling, leading to reduction of B cells and short-lived plasma cells in the spleens. Use of ibrutinib may provide benefits to HLA-sensitized transplant patients for alloantibody suppression.