Progression of natural immunity during one-year treatment of residual disease in neuroblastoma patients with high doses of interleukin-2 after autologous bone marrow transplantation

The aim of this work was to monitor the functional and phenotypic variations of natural killer (NK) cells in seven children with stage IV neuroblastoma (NB) treated with recurrent 5-day cycles of interleukin-2 (IL-2) at a dose of 18 x 10⁶ IU/m²/d by continuous intravenous infusion. All patients who entered the study had no detectable disease after hematologic recovery from intensive chemotherapy and autologous bone marrow transplantation (ABMT). To evaluate the effect of this treatment on tumor relapse, IL-2 immunotherapy was adjusted to maintain levels of NK activity above those of age-matched controls (threshold of 40 lytic units [LU]/10⁹ mononuclear cells) during a 1-year period since hematologic recovery of ABMT. The levels of NK and endogenous lymphokine-activated killer (eLAK) cell cytotoxic activities, as well as phenotype-differentiated lymphocyte counts, were determined from patients' freshly isolated peripheral blood mononuclear cells (MNC). Data were analyzed at different points between each cycle of IL-2, and before and 36 hours after each infusion. NK and eLAK activities significantly increased in response to IL-2. Both cytotoxic parameters correlated with the serum levels of the soluble IL-2 receptor (sIL-2R). IL-2 increased the amounts of NK and T cell subsets but not of B cells. The effects of IL-2 were time-dependent. Early cycles of IL-2 preferentially increased cell numbers, especially of cells bearing a CD3^-/CD16^-/CD56⁺(bright) and CD8⁺(dim) phenotype. Conversely, late courses promoted higher cytotoxic effects but with a smaller increase in NK and T cell counts; the main NK subset became CD16⁺, and CD8⁺(dim) cells remained a minor subset. It is worthy to note that the patient who relapsed after completing immunotherapy showed only a slight increase of the NK subset in response to IL-2. These results show the feasibility of sustaining an increased NK activity during 1 year after ABMT in children with advanced neuroblastoma and suggest the occurrence of changes in the functional and phenotypic characteristics of the NK cells generated throughout the 1-year treatment.