The IL-15-IL-15Ra complex has been shown to significantly stimulate CD8+ T cells, especially memory CD8+ T cells, to enhance cytotoxicity against multiple tumors, such as myeloma [31], breast cancer [32], colorectal carcinoma [33], and prolonged survival of tumor-bearing mice, establishing a long-term immune memory against tumor re-challenge [34, 35]. Here, CD8A is linked to breast cancer.