IL15 and neoplasm: As a result, pre-clinical models suggest that tumor antigen-specific T-cells engineered to express IL-12, survive longer in the tumor milieu and are more effective at tumor clearance than CAR transgenic T-cells alone (93) As lack of CAR-T cell persistence in vivo is another recurring obstacle in both pre-clinical and clinical studies, researchers have engineered CAR-T cells to express the pro-T cell survival cytokine IL-15 in an activation-dependent manner.