IL2 and lung cancer: The first results of a multiplex cytotoxicity and cytokine analysis (Multiplex Cytotoxic T/NK cell kit) of the blood of lung cancer patients with a low CD4+ T cell (mean 34.3%; n = 3) and a high CD3−/CD56+ NK cell (mean 16.6%) prevalence versus high CD4+ T cells (mean 61.3%; n = 2) revealed comparatively low IL-2 concentrations (mean 5.6 pg/mL versus 268.1 pg/mL, respectively), supporting the hypothesis that the limited effectiveness of NK cells could be due to the lack of the stimulatory cytokine IL-2, despite the presence of Hsp70 in the circulation (mean 303.3 ng/mL).