Abstract 2549: Defective STAT1 activation associated with impaired IFN-γ production in lymphocytes from metastatic melanoma patients treated with HD IL-2

High dose (HD) IL-2 therapy is one of the most effective immunotherapies against melanoma, but clinical responses occur only in a fraction (10-15%) of patients. HD IL-2 is known to activate and promote the proliferation of various lymphocyte subsets including T and NK cell subsets via STAT signaling. However, evidence on how different lymphocyte subsets from metastatic melanoma patients respond to HD IL-2 treatment and whether any defects exist in different lymphocyte subsets from metastatic melanoma patients that could possibly reduce the efficacy of treatment are still lacking. To address this question, we investigated the extent of HD IL-2 induced STAT 1, 3, and 5 tyrosine phosphorylation (activation) in different T cell and NK cell subsets from the melanoma patients during the IL-2 exposure in comparison to normal donors (ND). Phosphoflow cytometry analysis revealed that HD IL-2 treatment induced a dramatic activation of STAT5 in all T-cell and NK cell subsets when PBMCs were stimulated with HD IL-2 in vitro or after the first bolus of HD IL-2 infusion. In all cases, STAT3 activation by IL-2 was never detected. Similar levels of STAT5 activation was observed in the T and NK cell compartments in both ND and patients. Furthermore, HD IL-2 treatment induced a substantial increase in the proportion of Ki67-expressing cells in CD4+, Tregs, CD8+ T-cells, CD56 hi and CD56 low NK cell subsets in both melanoma patients and ND. No apparent defects in the proliferation capacity of all T and NK cell subsets was noted when comparing the proportion of Ki67+ cells between melanoma patients and ND. In contrast to STAT5, STAT1 activation was found to be defective in all lymphocyte subsets after HD IL-2 exposure and showed a dramatic age-related decline not found in ND. This blunted STAT1 activation was associated with a reduced IFN-γ production by PBMCs from melanoma patients, while TNF-α, IL-1β, IL-8, IL-6 and GM-CSF release was unaffected. Intracellular cytokine staining found that the aberrant IFN-γ response was mainly in the CD56 hi and CD56 low NK cell subsets, which were the major IFN-γ producers in response to HD IL-2. The aberrant IL-2-induced IFN-γ secretion by NK cell subsets not only reduced STAT1 activation in these NK cell populations but also led to a defective STAT1 activation in CD4 + T and CD8 + T cells. Taken together, these findings indicate that metastatic melanoma patients have a defective IFN-γ secretion by NK cells and STAT1 activation in response to HD IL-2 that may reflect a generalized suppression of this pathway that may be involved in the lack of therapeutic benefit of IL-2 in most patients. Citation Format: Geok Choo Sim, Sheng Wu, Lei Jin, Patrick Hwu, Laszlo Radvanyi. Defective STAT1 activation associated with impaired IFN-γ production in lymphocytes from metastatic melanoma patients treated with HD IL-2. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2549. doi:10.1158/1538-7445.AM2014-2549