In this context, we assessed the therapeutic efficiency of IL-15 to boost the therapeutic activity of trastuzumab in HTM, which were generated by the cotransplantation of HSCs and HER2-positive BT474 and SK-BR-3 BC cells into neonatal immunodeficient NSG mice which resulted in two different HTM models: The transplantation of only moderately trastuzumab sensitive SK-BR-3 cells results in an ascitis with greater incidence of metastases in different organs including the brain. This evidence concerns the gene IL15 and breast cancer.