A. E. Felsted1, A. L. Pepple1, A. A. Kevelin1, S. Qu1,4, B. Bredbeck1, T. Worlikar3, R. Hubbard3, A. Ganguly1,2, Z. Xu3, C. S. Cho1,2 4Xijing Hospital, Fourth Military Medical University,Department Of Hepatobiliary Surgery,Xi’an, , China 1University Of Michigan,Department Of Surgery,Ann Arbor, MI, USA 2VA Ann Arbor Healthcare System,Ann Arbor, MI, USA 3University Of Michigan,Department Of Biomedical Engineering,Ann Arbor, MI, USA
Introduction:
Despite its revolutionary successes, many patients with poorly immunogenic cancers do not reap the benefits of immunotherapy. Attempts have been made to sensitize the immune system to otherwise non-immunogenic tumors using hyperthermic techniques. However, systemic responses to hyperthermia have been modest and transient. This may be due in part to the destruction of subcellular integrity that occurs during hyperthermia. Histotripsy (HT) is a novel non-invasive ablation modality which uses acoustic cavitation to mechanically disrupt cells while preserving the integrity of potential subcellular tumor neoantigens. Previous work has shown that HT can induce immune responses strong enough to impact distant tumor growth (abscopal effect). Thus, we hypothesized that HT may be capable of stimulating a stronger and more enduring anti-tumor immune response than hyperthermia.
Methods:
Immunocompetent C57BL/6 mice bearing unilateral or bilateral B16 melanoma tumors underwent unilateral tumor ablation with HT, hyperthermia, or sham therapy. Tumors were serially measured, and ten days after ablation the tumors, tumor-draining lymph nodes, and spleens were harvested and analyzed by flow cytometry. To assess the specificity of the immune response to ablation, tumor antigen-specific CD8+ splenocytes were cocultured with the lysate of ablated tumors and subsequently assayed for IFN-γ and IL-2 production.
Results:
HT suppressed both ablated and abscopal tumor growth better than hyperthermia. Further, when cocultured with mouse splenocytes, only the lysate of HT ablated tumors induced IFN-γ and IL-2 release from tumor antigen-specific CD8+ T cells. Interestingly, the nonablated tumors of mice that received HT had greater infiltration of natural killer cells, dendritic cells, B cells, CD4+ T cells, and CD8+ T cells compared to mice treated with hyperthermia. Regionally (within tumor draining lymph nodes) and systemically (within the spleen), HT treated mice also demonstrated a higher ratio of CD8+ T cells to regulatory T cells.
Conclusion:
These findings suggest that HT ablation induces a more potent tumor-specific immune response than hyperthermia through activation of both innate and adaptive immune responses. The potency and persistence of the immune responses to HT ablation may be sufficient to produce clinically relevant responses in previously immunoresistant tumors. The strength of HT-mediated immune stimulation is likely due to its unique ability to generate immunogenically-intact tumor neoantigens.
