CD4 and neoplasm: To elucidate the reason for this tumour suppressive effect, mouse spleens were harvested, and subjected to immunophenotyping, which revealed a significant increase in the number of effector CD44hiCD62Llow CD8+ T cells, CD137+/CD8+ cytotoxic T cells and CD69+/CD4+ cells in Ack1 KO mice compared with WT mice (Fig. 4b–d and Supplementary Fig. 7c–e).