Reply: The Hepa 1–6 may not be suitable for use in hepatocellular carcinoma models to explore responses to drug therapy

To the editor,Lu et al raise excellent points regarding the Hepa1-6 model of HCC. Our study1 characterized the immune microenvironment of multiple preclinical models of HCC and showed that the Hepa1-6 model in C57BL/6J mice elicits a brisk immune infiltrate that is not representative of human HCC. This may be related to a minor major histocompatibility complex haplotype difference with the C57BL/6J mouse (H2b for C57BL/6 and H2bc for Hepa1-6), resulting in an alloreactive response. We conclude that the Hepa1-6 model should not be used for testing the effects of immunotherapy-based strategies for HCC. Lu et al expand on the limitations of the Hepa 1–6 model, proposing that the variability of this model's in vivo growth should preclude its use, even for nonimmunotherapy studies. We agree with the points raised by their letter. As discussed in their letter, we observed highly variable levels of tumor growth in the subcutaneous model of Hepa1-6, including complete regressions of some tumors without any intervention. This was observed over multiple independent experiments in our group in addition to the experiments included in our manuscript. While the Hepa1-6 model is currently among the most widely used for HCC research, we agree with Lu et al that given its highly variable tumor growth, it is a poor choice for in vivo drug discovery or testing. Moreover, there is a rapidly growing appreciation that even therapies originally thought to be nonimmunotherapeutic in mechanism in fact leverage the immune system to exert the observed antitumor responses. Given the association of the immune microenvironment with sensitivity or resistance to various treatment modalities including radiotherapy, cytotoxic chemotherapy, and targeted therapies,2–5 we seek to use models that most closely resemble human disease. We hope that our work can guide the design of future studies in HCC for the benefit of the patients suffering from this disease.