Cancer patients receiving targeted immunotherapy may face an unexpected challenge beyond tumor treatment: their therapeutic antibodies can trigger destruction of their own red blood cells, potentially complicating blood transfusions and worsening treatment-related anemia.
Laboratory analysis of blood samples from patients receiving magrolimab, an IgG4 monoclonal antibody targeting the CD47 protein for cancer therapy, revealed significant erythrophagocytosis—the process where immune cells consume red blood cells. Five of six patient samples showed phagocytosis indices between 20-60, well above the clinically significant threshold of 5. The mechanism involves specific Fcγ receptors (FcγRI and FcγRIIa) on immune cells recognizing the antibody-coated red blood cells, while natural killer cell pathways remained uninvolved. Blocking the CD47 pathway amplified this destruction 1.7 to 3.9-fold.
This finding illuminates a concerning mechanistic gap in cancer immunotherapy. While magrolimab shows promise against tumors by blocking CD47—a "don't eat me" signal that cancer cells exploit—the same antibody inadvertently marks healthy red blood cells for destruction. The research suggests this represents a class effect of IgG4 antibodies rather than a magrolimab-specific problem, as similar destruction occurred with other IgG4 antibodies targeting different red blood cell antigens.
For oncology practice, this mechanistic insight may explain why some patients develop severe anemia during anti-CD47 therapy and experience transfusion complications. The findings could inform dosing strategies, patient monitoring protocols, and development of next-generation CD47 inhibitors with improved selectivity. However, the study's limitation to laboratory conditions means clinical correlation remains essential for translating these mechanistic insights into patient care improvements.