Quantitative analysis of melanoma-induced cytokine-mediated immunosuppression in melanoma sentinel nodes

Melanoma sentinel nodes (SN) show evidence of immunosuppression prior to tumor metastasis. Interleukin (IL)-10 and IFN-gamma can induce dendritic cells (DC) that express immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO). The goals of this study are to evaluate the role of melanoma in SN immunosuppression and to assess reversibility of SN immunosuppression by a cytokine therapy.

Fifty-seven clinical stage I/II melanoma patients underwent wide local excision and sentinel lymphadenectomy (WLE/SL), with removal of non-SN. In 21 patients, nodal RNA was analyzed by quantitative real-time PCR for expression levels of IL-2, IL-10, IL-12, IFN-gamma, and IDO genes. Among the remaining 36 patients, 15 received peritumoral injection of recombinant human granulocyte macrophage colony-stimulating factor (rhGM-CSF) 2 to 5 days prior to WLE/SL. Lymph nodes (LN) from these 36 patients were assessed for T-cell area, DC area, and DC density.

Of 21 patients whose nodal RNA was analyzed, 13 had residual melanoma at the primary site or a tumor-positive SN. In these patients, expression levels of IL-10 (P = 0.05), IFN-gamma (P < 0.05), and IDO (P = 0.06) were dramatically higher in SNs than non-SNs. This difference was not evident in the 8 patients without residual melanoma or SN metastasis. Of the 36 patients whose LNs were examined for histologic features, the 15 patients who received rhGM-CSF had significantly higher SN values of T-cell area, DC area, and DC density than those who did not receive rhGM-CSF.

Our data provide molecular evidence of cytokine-mediated SN immunosuppression that is associated with presence of melanoma. Furthermore, SN immunosuppression can potentially be reversed by a cytokine therapy.