Intradermal Tumor Implantation as a Robust Model for Murine Cancer Intratumoral Immunotherapy Studies

Establishing reproducible murine tumor models is essential for evaluating cancer biology and immunotherapy strategies. Intratumoral immunotherapy treats established tumors with immune-stimulating reagents to reverse local immune suppression and stimulate systemic antitumor immunity. Most cancer studies in mice establish the tumors in the subcutaneous space, which has inherent challenges for experimental intratumoral immunotherapy due to the inability to visualize intratumoral injections. Intradermal injection of tumor cells provides a reliable approach to generate visualizable tumors that support accurate and reproducible intratumoral injection and monitoring of growth kinetics and therapeutic responses. Here, we present a reproducible methodology for establishing and treating intradermal tumors using the murine B16F10 melanoma model in C57BL/6 mice as our example. Tumor cell suspensions are injected intradermally, and 7-10 days after tumor implantation, once tumors reach ~60 mm³, an intratumoral injection of immune-stimulating agents or a physical treatment like electroporation or heating can be directly applied. This allows precise delivery of treatments and measurement of tumor growth with calipers and avoids the challenge of the inherent variability of multiple treatments of subcutaneous tumors that cannot be visualized. By providing detailed insight into this technique, this article aims to support reproducibility and advance pre-clinical research in intratumoral immunotherapy.