CD47 blockade augments anti-GD2 driven phagocytosis in vitro but fails to improve in vivo efficacy in immunocompetent, chemoresistant neuroblastoma preclinical models

CD47 delivers a dominant "Don't Eat Me" signal that inhibits macrophage‑mediated clearance of tumour cells. Using immunocompetent, chemoresistant neuroblastoma (NB) models, we tested a Fc‑silent CD47 blocker (ALX301) with anti‑GD2 antibody alone and in combination with a clinically aligned temozolomide/irinotecan chemoimmunotherapy backbone. Tumours expressed GD2 and CD47, and bound ALX301. In macrophage coculture assays, anti-GD2 antibody induced dose-dependent phagocytosis, whereas ALX301 or an anti-CD47 antibody alone did not. CD47 blockade in combination with a suboptimal concentration of anti-GD2 antibody showed an additive effect on phagocytosis in vitro. In vivo, however, ALX301 failed to improve tumour control or survival when added to anti‑GD2 or to chemoimmunotherapy in the dosing regimens and two independent models tested. Toxicity was acceptable, showing only mild, expected red‑cell changes without overt organ injury. This form of CD47 inhibition is therefore mechanistically active in vitro but insufficient to enhance anti‑GD2 antibody-based therapy in immunocompetent mice bearing a chemoresistant NB, highlighting the potential need for myeloid‑reprogramming partners.