Abstract Cowpea Mosaic Virus (CPMV) is a plant virus which infects legumes such as cowpea plants. It has been used as a powerful intratumoral immunotherapy in murine cancer models and canine veterinary clinical trials. CPMV is a multi- Toll-Like Receptor (TLR) agonist which induces a strong anti-tumor immune response both locally and systemically. While highly potent as a monotherapy, the most robust immunotherapy approaches are those which target cancer through multiple axes. In the present work, we tested the combination of intratumoral immunotherapy using CPMV with human epidermal growth factor receptor 2 (HER2) monoclonal antibody (mAb) therapy targeting HER2+ tumors. More specifically, we combined CPMV with an anti-HER2 mAb or anti-HER2 antibody-(IL-12) fusion protein (anti-HER2 antibody-(IL-12))—an anti-HER2 antibody genetically fused to the cytokine IL-12. Amplification of HER2 is known to occur in several cancers and is associated with poor prognosis as well as cancer recurrence. Mice with HER2+ tumors from colorectal cancer cell lines (MC38-HER2+ and CT26-HER2+) were treated with CPMV and HER2 mAb or anti-HER2 antibody-(IL-12). Tumor volume and overall survival were measured over the course of 8 weeks. While animals were refractory to HER2 mAb therapy alone, reduced tumor growth and increased survival was achieved using CPMV and the combination therapies- with the combination therapies outperforming CPMV therapy alone. These results indicate that CPMV can synergize with targeted antibody therapies for greater anti-tumor efficacy. This work was funded in part through NIH grants R01-CA274640 and R01-CA253615-02S1, NIH training grant T32-CA121938, the American Cancer Society Extramural Discovery Science (EDS) Accelerator Award EDS-24-1330440-01-EDS, and the American Cancer Society - F.M. Kirby Foundation Inc. - Mission Boost Grant MBGI-23-1030244-01-MBG. The authors declare the following competing financial interests: Dr. Steinmetz is a cofounder and CEO of and has equity in PlantiosX Inc. Dr. Steinmetz is a co-founder of and has equity in Mosaic Immunoengineering, Inc. Dr. Steinmetz is a cofounder and manager of Pokometz Scientific LLC, under which she is a paid consultant to Ring Therapeutics, Inc. The other authors declare no potential conflicts of interest. Citation Format: Ayumi E. Pottenger, Miguel A. Moreno Gonzalez, Manuel L. Penichet, Nicole F. Steinmetz. Cocktail immunotherapy: Plant virus immunomodulator, HER2 antibody, and co-delivered IL-12 cytokine for the treatment of HER2+ cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1572.
Pottenger et al. (Fri,) studied this question.