Treatment of Hepatocellular Carcinoma by Multimodal in Situ Vaccination Using Cryoablation and a Plant Virus Immunostimulant

Purpose: To test the hypothesis that cryoablation combined with intratumoral immunomodulating nanoparticles from cowpea mosaic virus (CPMV) as an in situ vaccination approach induces systemic antitumoral immunity in a murine model of hepatocellular carcinoma (HCC).Materials and Methods: Mice with bilateral, subcutaneous RIL-175 cell-derived HCCs were randomized to 4 groups: (a) phosphate-buffered saline (control), (b) cryoablation only (Cryo), (c) CPMV-treated only (CPMV), and (d) cryoablation plus CPMV-treated (Cryo + CPMV) (N = 11-14 per group). Intratumoral CPMV was administered every 3 days for 4 doses, with cryoablation performed on the third day. Contralateral tumors were monitored. Tumor growth and systemic chemokine/ cytokine levels were measured. A subset of tumors and spleens were harvested for immunohistochemistry (IHC) and flow cytometry. One-or 2-way analysis of variance was performed for statistical comparisons. A P value of <.05 was used as the threshold for statistical significance.Results: At 2 weeks after treatment, the Cryo and CPMV groups, alone or combined, outperformed the control group in the treated tumor; however, the Cryo + CPMV group showed the strongest reduction and lowest variance (1.6-fold & PLUSMN; 0.9 vs 6.3 fold & PLUSMN; 0.5, P < .0001). For the untreated tumor, only Cryo + CPMV significantly reduced tumor growth compared with control (9.2-fold & PLUSMN; 0.9 vs 17.8-fold & PLUSMN; 2.1, P = .01). The Cryo + CPMV group exhibited a transient increase in interleukin-10 and persistently decreased CXCL1. Flow cytometry revealed natural killer cell enrichment in the untreated tumor and increased PD-1 expression in the spleen. Tumor-infiltrating lymphocytes increased in Cryo + CPMV-treated tumors by IHC.Conclusions: Cryoablation and intratumoral CPMV, alone or combined, demonstrated potent efficacy against treated HCC tumors; however, only cryoablation combined with CPMV slowed the growth of untreated tumors, consistent with an abscopal effect.