Anti-CD47 drug interference in pre-transfusion testing can be overcome by antigen masking

Background: Overexpression of CD47, a "don't eat me" signal for macrophages, in various malignancies has prompted the development of anti-CD47 therapies. Although the first-in-class anti-CD47 antibody magrolimab was abandoned due to its ineffectiveness in improving survival in acute myeloid leukemia, multiple anti-CD47 drugs remain in clinical trials. These agents can pose significant challenges in pre-transfusion diagnostics by inducing agglutination and interfering with serological testing due to CD47 expression on red blood cells.

Study design and methods: This study aims to evaluate the interference caused by several anti-CD47 antibodies-ligufalimab, lemzoparlimab, and letaplimab-and the SIRPα IgG1 Fc fusion protein ontorpacept in pre-transfusion testing and to compare their effects with magrolimab. We are also testing the mitigation of the anti-CD47 drug interference by antigen masking.

Results: Our results show that all drugs tested significantly interfered at clinically relevant concentrations, affecting the indirect antiglobulin test and partially also card tests without anti-human globulin and Werfen's Capture-R assay. Notably, a soluble recombinant SIRPα variant, MagroEx, demonstrated efficacy in mitigating this interference in all assays tested.

Discussion: These findings emphasize the need for awareness and adaptation in immunohematology practices as anti-CD47 drugs continue to advance in clinical development, and highlight the utility of antigen masking strategies to enhance the safe administration of blood products to treated patients.