S. Qu1,2, A. Kevelin1, M. Toma1, A. Pepple1, A. Felsted1, T. Worlikar3, R. Hubbard3, T. K. Luther1, Z. Xu3, C. S. Cho1,4 1University Of Michigan,Department Of Surgery,Ann Arbor, MI, USA 2Xijing Hospital, Fourth Military Medical University,Department Of Hepatobiliary Surgery,Xi’an, SHAANXI, China 3University Of Michigan,Department Of Biomedical Engineering,Ann Arbor, MI, USA 4Ann Arbor VA Healthcare System,Ann Arbor, MI, USA
Introduction: Despite its revolutionary successes, many patients with poorly immunogenic cancers have not been able to reap the benefits of immunotherapy. It has been speculated that tumor-directed therapies like radiation and thermal ablation may be able to enhance the immunogenicity of these refractory cancers to stimulate tumor-specific immune responses. Unfortunately, these therapies disrupt subcellular integrity and molecular activity while having limited effects on antitumor immune responses. A novel non-invasive, non-thermal ablation therapy termed histotripsy (HT) uses acoustic cavitation to disrupt cell membrane integrity while preserving subcellular integrity. Recent studies have shown that immunogenic cell death (ICD), characterized by the release of damage-associated molecular patterns (DAMPs) such as HMGB1, can provoke immune responses against cancer. Thus, we hypothesize that HT may be uniquely capable of stimulating a significant anti-tumor immune response.
Methods: We inoculated C57BL/6 mice with B16 melanoma cells unilaterally or bilaterally. Radiation therapy (XRT), radiofrequency ablation (RFA), or HT ablation was performed on day 10 after tumor inoculation, and tumor growth was monitored every 3 days. Tumor, spleen, inguinal tumor-draining lymph nodes (TDLN), and axillary non-tumor-draining lymph nodes (NTDLN) were harvested and processed for flow cytometry to assess the immune response on days 3 and 10 after HT treatment. Similarly, tumor and serum were harvested and processed for ELISA to measure HMGB1 on days 1 and 8 after HT treatment.
Results: HT suppressed the growth of treated tumors and resulted in significant increases in CD8+ T cells locally within tumors, but also increased the numbers of tumor-specific CD8+ T cells regionally within TDLN (but not NTDLN), and systemically within the spleen. HT also increased the ratio of CD8+GP33+ lymphocytes to Treg cells in the systemic circulation. The ability of HT to promote intratumoral CD8+ TIL was stronger than irradiation or radiofrequency ablation. Surprisingly, histotripsy also suppressed the growth of untreated, contralateral tumors. In untreated tumors, HT significantly increased CD8+ tumor infiltrating lymphocytes. HT also upregulated circulating NK cells and neutrophils. Moreover, HT resulted in significant increases of extracellular HMGB1 in tumors and serum.
Conclusion: These data suggest, for the first time, that HT is capable of stimulating potent anti-tumor immune responses. The immunostimulatory effect of HT appears to be much stronger than that of other tumor-directed therapies, and may be mediated by its ability to promote the release of tumor-associated antigen DAMPs like HMGB1.
