CD4 and cancer: To investigate whether the improved anti-cancer activity displayed by CEA-28ζ-I1 CAR T cells during repetitive antigen-challenge could derive from the higher frequency of CD8+ T cells, CD107a degranulation with simultaneous detection of CD8+ CAR T cells and CD4+ CAR T cells was recorded upon a short-term re-stimulation with BxPC-3 cells at the end of each round 1-3 (R1-3).