Overexpression of TNFα in colorectal cancer cell lines affects tumorigenicity, differentiation, and immune cell infiltration

The progression of cancer strongly depends on the tumor microenvironment and immune surveillance. Tumor necrosis factor alpha (TNFα), a key inflammatory cytokine, can drive both tumor elimination and promotion, depending on its dose and the type of cancer. Colorectal cancer cell lines HCT 116, HT-29, and melanoma cells A375 engineered to stably overexpress the human TNFα gene were used to induce experimental subcutaneous tumors in two immunodeficient mouse strains: athymic Balb/c-nu/nu and SCID/bg mice. In athymic mice, TNFα-overexpressing cells completely lost their tumorigenicity. In SCID/bg mice, with no mature T and B cells and defective NK cells, the TNFα-overexpressing cells formed rudimentary flat ulcerous xenografts with rapidly reduced size, with tumor penetrance of 50-85%. Histopathological analysis revealed necrotic lesions, a more differentiated phenotype of tumor cells forming pseudoglandular structures, and more abundant stromal cells. Intratumoral infiltration of immune cells increased in TNFα-secreting tumors. Positivity of cytokeratins 7 and 20 in colorectal cancer xenografts was decreased. Paradoxically, the expression of ALDH1A1 and ALDH1A3 isoforms, which are important for disease prognosis, was increased. Our study suggests that careful modulation of the tumor microenvironment to a tumor-suppressive one using cytokine TNFα and controlled stimulation of antitumor immunity can contribute to the improvement of cancer treatment.