IL15 and cancer: The causal role of IL-15 in tumor angiogenesis treated with H9 CAR-IL15 T cells remains unclear; as previous studies have shown that IL-15 can promote angiogenesis or the production of angiogenic factors by cancer cells (34, 35), one possibility is that IL-15 secreted by activated H9 CAR-IL15 T cells promotes angiogenesis in treated tumors at early phase that may benefit the subsequent entry of CAR-T cells and host immune cells and ultimately contributes to the increased antitumor activity.