Induction of two distinct natural killer-cell populations, activated T cells and antineoplastic cytokines, by interleukin-2 therapy in children with solid tumors

Children with poor prognoses regarding solid tumors have benefited from autologous bone marrow transplantation as a treatment modality. Posttransplantation adjuvant interleukin-2 (IL-2) therapy has previously been shown to improve prognosis in adults with neoplastic disease. The improved survival probability has been attributed to IL-2-mediated stimulation of the immune system and its antineoplastic activity. In this study, 10 pediatric patients with solid tumors in complete remission after autologous stem cell transplantation were treated with recombinant IL-2, which was administered in three 5-day cycles of continuous intravenous infusions with a 2-week rest in between cycles. We demonstrated that IL-2 therapy enhanced transplantation-related stimulation of the immune system, on both the cellular and humoral levels. Peripheral blood T and natural killer (NK) cells increased by the factors four and 14, respectively. Activation of the immune system was demonstrated by significantly elevated levels of soluble IL-2 receptor (IL-2R) and increased CD25 surface expression on T lymphocytes. IL-2 also induced significant proliferation of the CD56(bright) NK-cell subpopulation that appears post-bone marrow transplant (BMT) and is found only in minimal amounts in normal controls. In vivo and in vitro production of tumor cytotoxic cytokines tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) was significantly stimulated following IL-2 therapy, further indicating IL-2-mediated stimulation of the antineoplastic activity of the immune system.