- Primary objectives are: 1) to assess the feasibility of harvesting and expanding activated NK cells to meet escalating dose goals in Cohort A, 2) to assess the toxicity of infusing escalating doses of activated NK cells following lymphodepleting chemotherapy without rhIL15 (cohort A), and 3) to assess the toxicity of infusing NK activated cells with escalating doses of rhIL15 (cohort B) in pediatric patients with refractory malignant solid tumors.