Treatment of Resistant Leukemia by rIL-2 Activated NK Cells in Recipients of HLA Matched and Haploidentically Mismatched Stem Cell Allografts while Avoiding GVHD.

Although allogenenic stem cell transplantation may provide a cure for a growing number of patients with hematologic malignancies and several metastatic solid tumors, several problems remain to be solved. In routine medical practice transplant can be offered for patients with a matched donor available whereas the large majority of patients in need have no matched donor available. Although alloreactive lymphocytes may eliminate residual malignant cells, such an effect is accompanied by acute and chronic GVHD which may be hazardous even in recipients with perfectly matched allografts, and prohibitive in recipients treated with haploidentically mismatched allografts. On the other hand immunotherapy with intentionally mismatched allografts could provide a much more effective tool for eradication of tumor cells resistant to chemotherapy. We have pioneered a new approach for treatment of patients with resistant hematological malignancies (AML/MDS 5; ALL 1; Biphenotype 2; NHL 3; HD 1) using matched siblings (n=4), matched unrelated donor (n=1) or haploidentically mismatched donors (n=7). Prevention of rejection of mismatched allografts was accomplished by combination of fludarabine and deletion of donor reactive host lymphocytes by infusion of donor mononuclear blood cells and elimination of alloreactive lymphocytes susceptible to high-dose cyclosphosphamide (60mg/kgx3) one day later. Prevention of GVHD following infusion of G-CSF mobilized, haploidentically mismatched blood stem cells was accomplished using Miltenyi’s immunomagentic beads coupled with anti-AC133 (n=6) or using anti-CD3 (n=1). No other anti-GVHD prophylaxis was used. Following transplantation, patients were treated with rIL-2 activated donor peripheral blood lymphocytes activated for 4 days at 37°C in 5% C02 in air incubator with rIL-2 6,000 IU/ml. T cell depletion was accomplished either by positive selection of CD56+ (n=10) or negative selection of CD3 (n=2) for optimal induction of graft vs leukemia (GVL) effects by mismatched and fully activated NK cells. One patient with resistant leukemia became disease free for 8 months but died of resistant aspergilosis which was evident prior to transplantation. Five out of 12 patients with intractable and fully resistant leukemia are alive with no GVHD and no evidence of disease 1–18 (median 13) months post transplantation. Based on our ongoing preliminary study we conclude that patients with resistant hematological malignancies may benefit from cell therapy mediated by rIL-2 activated donor lymphocytes, and most likely from intentionally mismatched haploidentical allografts following elimination of host anti-donor alloreactive lymphocytes and prevention of GVHD by positively or negatively selected stem cells, followed by immunotherapy with rIL-2 activated CD3 depleted NK cells. Intentionally mismatched rIL-2 activated NK cells represents a safe approach for elimination of residual tumor cells, aiming for induction of GVL while avoiding GVHD.