Changes in the phenotypic characteristics of eosinophils from patients receiving recombinant human interleukin-2 (rhIL-2) therapy.

We have studied the properties of eosinophils from 26 patients with malignant melanoma and 16 patients with renal cell carcinoma (RCC) who were entered into a phase II clinical trial using various schedules of low-dose rhIL-2 immunotherapy. Eosinophilia was observed in 65% of melanoma patients and 100% of renal patients when receiving rhIL-2 therapy. The eosinophil count increased up to 20-fold approximately 5 d after the appearance of lymphocyte activation markers. This would be consistent with eosinophil kinetics and the release of soluble mediators, for example IL-5, from lymphocytes. Eosinophils from eosinophilic patients became hypodense compared to their pre-treatment levels as demonstrated by sedimentation through a discontinuous metrizamide density gradient; they also showed an increased expression of CD4, CD25 and CD11b cell surface activation markers. Eosinophil count could not be correlated to either patient survival or response to therapy in melanoma patients; however, patients with renal cell carcinoma demonstrated a significant correlation (P < or = 0.05) between eosinophil count and survival but not with clinical response. Therefore the maximum eosinophil count achieved during rhIL-2 therapy is of prognostic significance in patients with renal cell carcinoma.