SIRPA and neoplasm: Similar to targeting CD47 [13, 31], SIRPα blockade with hAB21 improved responses to rituximab (anti-CD20) in the Raji human tumor xenograft model, indicating that a major mechanism of action of both anti-CD47 and anti-SIRPα therapies in xenograft models, which lack NK, B and T cells, is to enhance the antitumor activity of myeloid cells.