Strategies to Inhibit Alloantibody Production in Alloprimed Murine Recipients of Hematopoietic Stem Cell Grafts

Alloantibody, not primed T cells, is the major barrier to bone marrow (BM) engraftment in allosensitized mice. We have shown that a single intravenous injection of donor splenocytes, to mimic a blood transfusion, results in high, sustained levels of serum alloantibody sufficient to eliminate donor BM within 3 h, resulting in uniform mortality in lethally irradiated allogeneic recipients. Current studies focused preventing and treating allopriming. Blockade of B cell survival signals with mTACI‐Ig pre‐ and postpriming was ineffective, as was the B cell but not plasma cell depleting anti‐CD20 mAb. Germinal center formation inhibition by lymphotoxin‐beta receptor‐Ig (LβR‐Ig) diminished allosensitization, although conditional Prmd1 (Blimp‐1) deletion in CD19+ cells was highly effective. By combining anti‐CD20 mAb to reduce B cells and LTβR‐Ig to diminish the frequency of B cells that could form germinal centers pre‐ and postpriming, allosensitization was precluded, permitting long‐term survival in T‐ and NK‐depleted, irradiated allogeneic recipients, whereas combined therapy postpriming alone was ineffective. As evidence of the critical role of B cells, the proteosomal inhibitor, bortezomib, given unencapsulated or encapsulated, proved ineffective in influencing allosensitization. These data extend our understanding of allopriming and provide a potential therapy for patients at risk for allosensitization and BM graft rejection. The authors show that alloantibody production resulting in lethal donor allogeneic bone marrow graft rejection in pre‐sensitized recipients can be blocked by several novel strategies. See editorial by Ramaswami and Chalasani on page 857.