Immune Adjuvant Activity of Pre-Resectional Radiofrequency Ablation Protects against Local and Systemic Recurrence in Aggressive Murine Colorectal Cancer

Abstract

PurposeWhile surgical resection is a cornerstone of cancer treatment, local and distant recurrences continue to adversely affect outcome in a significant proportion of patients. Evidence that an alternative debulking strategy involving radiofrequency ablation (RFA) induces antitumor immunity prompted the current investigation of the efficacy of performing RFA prior to surgical resection (pre-resectional RFA) in a preclinical mouse model.Experimental DesignTherapeutic efficacy and systemic immune responses were assessed following pre-resectional RFA treatment of murine CT26 colon adenocarcinoma.ResultsTreatment with pre-resectional RFA significantly delayed tumor growth and improved overall survival compared to sham surgery, RFA, or resection alone. Mice in the pre-resectional RFA group that achieved a complete response demonstrated durable antitumor immunity upon tumor re-challenge. Failure to achieve a therapeutic benefit in immunodeficient mice confirmed that tumor control by pre-resectional RFA depends on an intact adaptive immune response rather than changes in physical parameters that make ablated tumors more amenable to a complete surgical excision. RFA causes a marked increase in intratumoral CD8+ T lymphocyte infiltration, thus substantially enhancing the ratio of CD8+ effector T cells: FoxP3+ regulatory T cells. Importantly, pre-resectional RFA significantly increases the number of antigen-specific CD8+ T cells within the tumor microenvironment and tumor-draining lymph node but had no impact on infiltration by myeloid-derived suppressor cells, M1 macrophages or M2 macrophages at tumor sites or in peripheral lymphoid organs (i.e., spleen). Finally, pre-resectional RFA of primary tumors delayed growth of distant tumors through a mechanism that depends on systemic CD8+ T cell-mediated antitumor immunity.ConclusionImproved survival and antitumor systemic immunity elicited by pre-resectional RFA support the translational potential of this neoadjuvant treatment for cancer patients with high-risk of local and systemic recurrence.

Tumor-induced MDSC act via remote control to inhibit L-selectin-dependent adaptive immunity in lymph nodes

“…Compared to the 4T1 system, MDSC expansion was delayed in C57BL/6 mice implanted with AT-3 mammary tumor cells derived from genetically-engineered MMTV-PyMT/B6 transgenic mice (MTAG) (Waight et al, 2013), corresponding with moderate but significant L-selectin downregulation on naïve T cell subsets at ≥21 days post-tumor implantation (Figure 1—figure supplement 3A and B). L-selectin downregulation also occurred on splenic T cells in other tumor models including B16 melanoma and CT26 colorectal tumor, but only in rare individual mice with abundant MDSC (Figure 1—figure supplement 4), consistent with observations that these tumors do not typically induce MDSC expansion (Youn et al, 2008; Fisher et al, 2011; Ito et al, 2015). …”

Pre-resectional Radiofrequency Ablation as a Neoadjuvant in situ Tumor Vaccine

“…Evidence for the immunostimulatory activities of RFA inspired us to evaluate the potential oncological benefits of RFA as a neoadjuvant procedure [18]. For these studies we reasoned that the immunomodulatory activity of RFA could be exploited for therapeutic benefit by performing RFA prior to surgical resection (pre-resectional RFA).…”

“…We tested this hypothesis in preclinical solid tumor models that represent highly immunogenic tumors (i.e., CT26 murine colon adenocarcinoma) versus poorly immunogenic tumors (B16.F10 melanoma) [19]. Of note, both these tumor systems are characterized by minimal infiltration by activated CD8 + T cell populations under baseline conditions [18–20]. In our proof-of-principle study [18], CT26 and B16.F10 tumor-bearing mice were treated by neoadjuvant RFA 7 days prior to resection to allow sufficient time for an adaptive immune response to be generated (Figure 1).…”

“…Of note, both these tumor systems are characterized by minimal infiltration by activated CD8 + T cell populations under baseline conditions [18–20]. In our proof-of-principle study [18], CT26 and B16.F10 tumor-bearing mice were treated by neoadjuvant RFA 7 days prior to resection to allow sufficient time for an adaptive immune response to be generated (Figure 1). Experimental procedures were performed so that there was a high incidence (≥ 75%) of local recurrence with either monotherapy [18].…”

Case report on the role of radiofrequency-assisted spleen-preserving surgery for splenic metastasis in the era of check-point inhibitors

“…Together with that, post RF ablative changes in the immune system have been considered as evidence for both a systemic and local immunomodulatory effect. [13][14][15] Furthermore, the immunomodulatory effects of RF could be potentially beneficial in the augmentation of therapeutic effects of checkpoint inhibitors. [16,17] Immunologically, splenectomy is associated with loss of memory B cells which are preserved in the case of a partial splenectomy, where the number of T and B lymphocytes increase as do the number of monocytes in the red pulp.…”