A patient has become refractory to platelet transfusion. What is the most probable cause?

In cases where a patient becomes refractory to platelet transfusions, the development of antibodies to HLA (human leukocyte antigen) antigens is a common cause. This scenario generally occurs when the patient's immune system mounts a response against donor platelets, which express different HLA antigens than the patient's own cells. As these antibodies are directed against HLA class I antigens present on platelets, they can lead to the rapid destruction of transfused platelets, resulting in a lack of increase in platelet counts after transfusion. This phenomenon is particularly notable in patients who have received multiple transfusions or those with certain underlying conditions that predispose them to alloimmunization.

While other factors can affect platelet transfusion efficacy, they do not directly lead to the immunologic rejection of platelets in the same way that HLA antibodies do. For example, transfusing Rh-incompatible platelets and decreased pH can affect the quality of the transfusion or the stability of the platelets, but they do not typically lead to refractoriness. The development of an alloantibody with anti-D specificity, while it can cause reactions to red blood cells, is not directly related to platelet transfusions. Thus, the presence of anti-HLA antibodies is the