Tumors skew endothelial cells to disrupt NK cell, T-cell and macrophage functions

Patients and mice with solid tumors, such as Lewis lung carcinoma (LLC), have defects in functions of immune effector cells. Endothelial cells, a component of the tumor vasculature, are potential regulators of immune cell functions. Therefore, these studies examined the impact of exposure to LLC tumor on the ability of endothelial cells to modulate immune cell functions.

Endothelial cells were pre-treated with LLC tumor-conditioned medium (Endo^T-sup) for 24 h. Control endothelial cells that were exposed to medium (Endo^Media) or epithelial cell-conditioned medium (Endo^Epi-sup). After the initial 24 h incubation, endothelial cells were washed and fresh media was added. Cells were allowed to incubate for an additional 24 h. Supernatants from Endo^Media, Endo^Epi-sup or Endo^T-sup were collected and assayed for immune modulatory products and for immune modulatory activity.

Supernatant from Endo^T-sup contained increased levels of PGE₂, IL-6 and VEGF as compared to Endo^Media and Endo^Epi-sup controls. NK cell activity, as measured by TNF-α and IFN-γ secretion, was increased following exposure to media conditioned by Endo^Media and Endo^Epi-sup. Exposure of NK cells to supernatants of Endo^T-sup, also increases TNF-α and IFN-γ secretion, but to a lesser extent than by Endo^Media and Endo^Epi-sup. Examination of macrophage functions demonstrated that supernatant from Endo^T-sup decreased microbead phagocytosis and increased production of the immune suppressive mediators, IL-10 and PGE₂. Lastly, T-cell responses to stimulation with anti-CD3 in the presence of supernatants from Endo^T-sup were examined. IFN-γ production by CD8⁺ T-cells was reduced after exposure to Endo^T-sup-conditioned medium, as compared to cells treatments with medium or control conditioned medium. Production of IFN-γ by CD4⁺ T-cells exposed to Endo^T-sup was not altered.

Taken together, these studies demonstrate that tumors skew endothelial cells to disrupt NK cell, T-cell and macrophages functions, and represents a novel mechanism of tumor-induced immune suppression.