IL6 and neoplasm: One study on RCC patients demonstrated a correlation between CAR-T persistence and IFN-γ and IL-6, whereas the same correlation was not shown in relation to CAR-T toxicities (29); (d) CAR-T destruction mediated by the hostile tumor microenvironment (30); and (e) absence of a cancer-specific antigen in several tumor types that is suitable for inclusion in the CAR structure (31).