The cytokines expressed in tumor microenvironments are thought to be important mediators of both the host immune response and tumor survival. The source of these cytokines includes tumor cells, infiltrating leukocytes, fibroblasts, and other stromal elements. We previously reported that tumor-infiltrating lymphocytes (TIL) from human non-small cell lung cancer (NSCLC) express predominantly type 1 cytokines, which are known to enhance cell-mediated immunity. The purpose of this study is to assess the cytokine mRNA expression of human NSCLC primary cell lines and the capacity of the tumor-associated cytokines to modulate the development of TIL cytolytic activity against the autologous tumor. Cytokine mRNA expression was determined by RT-PCR and the capacity of TIL to kill autologous lung tumor cells was measured by the chromium-51 (51Cr) release assay. All NSCLC primary cell lines expressed mRNA for IL-4, IL-6, and transforming growth factor-beta1 (TGFbeta1), whereas IL-10 was expressed in only 1/7 cell lines. When added to TIL cultures stimulated with anti-CD3+IL-2, IL-4 and IL-10 enhanced and TGF-beta1 suppressed the development of TIL cytolytic activity against autologous tumor cells. The effects of IL-6 were inconsistent and for the group, were not statistically significant. These results demonstrate that human NSCLC cells express cytokines with the capacity to regulate the in situ anti-tumor immune response. However, the effects of tumor-derived cytokines varied qualitatively and quantitatively suggesting the balance between specific type 2 cytokines or TGF-beta1 within tumor microenvironments may influence prognosis or response to immunotherapy.