Improved Efficiency of OX40L-Based Gene Therapy Using a Non-Viral Delivery System in Fibroblast-Enriched Mouse Tumor Models

Objective: During their development, malignant tumors are able to establish a permissive microenvironment that influences their further growth and development. Cancer-associated fibroblasts play an important role in this process. However, the role of fibroblasts in therapeutic interventions remains unclear. Methods: We used inoculation of a co-culture of cancer cells and fibroblasts to create a cell-enriched tumor microenvironment. After tumor nodule formation, a preparation containing a plasmid encoding the gene of the ligand of the activating receptors of immune checkpoints - OX40L, controlled by the CMV promoter, was administered intratumorally. For delivery to cells, the plasmid was encapsulated in a polymer shell based on PEG-PEI-TAT. Results and Discussion: We evaluated the effects of fibroblasts on tumor growth and survival of mice during immunotherapy. In the proposed model, we artificially enriched the presence of fibroblasts in tumors, which to some extent can perform the function of a developed tumor microenvironment. Fibroblast-enriched tumors had an increased proliferation rate. However, with intratumoral administration of a non-viral drug encoding OX40L, we observed a significant increase in the proportion of complete responses in these tumors, reaching up to 25%. Conclusions: By co-inoculating cancer cells and fibroblasts, tumors with an increased proliferation rate were generated in mice. Nevertheless, some of these tumors are more likely to regress under immunotherapy than tumors composed of cancer cells alone. It is possible that the introduced fibroblasts are able to play an antigen-presenting role or act as additional sources of signals to activate the immune system.