Reduced alloimmunization in mice following repeated transfusion with pathogen-reduced platelets

Allogeneic transfusion can result in alloimmunization, leading to platelet (PLT) refractoriness and rejection of solid organ transplants. Previously we demonstrated that pathogen reduction using UV light and riboflavin (UV + R) eliminates the immunogenicity of white blood cells (WBCs) in vitro, blocks alloimmunization from transfusion in mice, and results in reduced ex vivo cytokine responses to subsequent untreated transfusions. We sought to determine if repeated transfusion with pathogen-reduced PLT-rich plasma (PRP) would eventually cause breakthrough alloimmunization or enhanced tolerance.

BALB/cJ mice were transfused weekly for 2, 4, or 8 weeks with C57Bl/6J PRP that was either untreated or pathogen reduced with UV + R and leukoreduced or not. Alloimmunization was determined by measuring donor antibody levels, ex vivo cytokine responses, and 24-hour donor PLT recovery. The role of donor antibodies in PLT refractoriness was also assessed by transfer of diluted immune sera into naïve recipients.

Donor antibody levels increased with the number of transfusions, but levels were significantly reduced using either UV + R or leukoreduction, and combining UV + R and leukoreduction gave the best protection. Priming of ex vivo cytokine responses required WBCs and remained suppressed with repeated UV + R-treated transfusion. PLT recovery was reduced with UV + R in naïve mice, and multiply transfused mice had poor PLT recovery even when antibody levels were relatively low. Approximately 1/100 dose of serum from a multiply transfused mouse was sufficient for complete rejection of donor PLTs.

Pathogen reduction significantly reduces alloimmunization in repeatedly transfused mice and combined with leukoreduction provides a high level of protection from alloimmunization.