FOXO1 and neoplasm: Notably, the reduced expression of CD39 mediated by FOXO1 was not recapitulated by the overexpression of either TCF7 or ID3 in T cell-only cultures (Extended Data Fig. 8f) or following co-culture with tumour cells (Extended Data Fig. 8g), providing further evidence for an enhanced capacity of FOXO1 to favourably modulate CAR T cell phenotype relative to these factors.