It is well known that approved CAR‐T cell products, which target the same tumor antigen, exhibit variations in the origin of the hinge region (CD28, CD8α, or IgG4), transmembrane domain (CD28 or CD8α), or costimulatory domain (CD28 or 4‐1BB).[13, 34] Amongst, the influence of costimulatory domains on the function of CAR‐T cells is particularly intriguing. The gene discussed is CD8A; the disease is neoplasm.