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Effects of the Administration of High-Dose Interleukin-2 on Immunoregulatory Cell Subsets in Patients with Advanced Melanoma and Renal Cell Cancer

Purpose: High-dose recombinant human interleukin-2 (IL-2) therapy is of clinical benefit in a subset of patients with advanced melanoma and renal cell cancer. Although IL-2 is well known as a T-cell growth factor, its potential in vivo effects on human immunoregulatory cell subsets are largely unexplored. Experimental Design: Here, we studied the effects of high-dose IL-2 therapy on circulating dendritic cell subsets (DC), CD1d-reactive invariant natural killer T cells (iNKT), and CD4+CD25+ regulatory-type T cells. Results: The frequency of both circulating myeloid DC1 and plasmacytoid DC decreased during high-dose IL-2 treatment. Of these, only a significant fraction of myeloid DC expressed CD1d. Although the proportion of Th1-type CD4− iNKT increased, similarly to DC subsets, the total frequency of iNKT decreased during high-dose IL-2 treatment. In contrast, the frequency of CD4+CD25+ T cells, including CD4+Foxp3+ T cells, which have been reported to suppress antitumor immune responses, increased during high-dose IL-2 therapy. However, there was little, if any, change of expression of GITR, CD30, or CTLA-4 on CD4+CD25+ T cells in response to IL-2. Functionally, patient CD25+ T cells at their peak level (immediately after the first cycle of high-dose IL-2) were less suppressive than healthy donor CD25+ T cells and mostly failed to Th2 polarize iNKT. Conclusions: Our data show that there are reciprocal quantitative and qualitative alterations of immunoregulatory cell subsets with opposing functions during treatment with high-dose IL-2, some of which may compromise the establishment of effective antitumor immune responses.