Introduction

EGFR and HER2 are overexpressed by human and canine malignancies and are negative prognostic indicators. Vaccinating mice with a cryptic self-peptide from the EGFR extracellular domain, also present in HER2 and HER3, induced potent humoral and cell-mediated responses specific for EGFR and HER2 on growing tumors.¹ The primary objective of this study was to determine if vaccination with the homologous canine cryptic EGFR peptide triggered comparable responses in dogs with EGFR-expressing solid tumors. Secondary objectives included monitoring adverse events and 1-year survival times.

Methods

Dogs with solid tumors (including 43 osteosarcomas) presented to a veterinary oncology practice were enrolled after owners signed informed consent, approved by the Yale University IACUC. Tumor histopathologies were confirmed by veterinary pathologists. Following standard-of-care treatment, e.g., limb amputation/carboplatin, dogs received two subcutaneous vaccinations, 3-weeks apart, with canineEGFR p527 peptide ≥3 weeks post-chemotherapy, and serial serum samples collected: Day 0—serum+vaccine #1; Day 21—serum+vaccine #2 (boost); Day 40–50—serum (convalescent); Day >50 serum (long-term). Standard immunologic assays to detect antibodies (ELISA), EGFR/HER2 expression, antibody and immune cell infiltrates (flow cytometry, immunofluorescence), intracellular signaling (Western blot), and cell proliferation (3H-thymidine incorporation) were employed. Statistical differences between in vitro conditions were analyzed using the Mann-Whitney test.

Results

Immunization with canineEGFR p527 generated canine antibodies that bound canine and human EGFR, and HER2. Antibodies inhibited EGF signaling, promoted antibody and CD8 T-cell infiltration into the tumor microenvironment, and inhibited tumor cell growth in vitro.

Conclusion

EGFR peptide vaccination overcomes immune tolerance by triggering robust humoral and cell-mediated, specific immune responses in EGFR⁺-tumor-bearing dogs.

Funding Information

1. Hester A. Doyle, Raymond A. Koski, Nathalie Bonafé, Ross A. Bruck, Stephanie M. Tagliatela, Renelle J. Gee, Mark J. Mamula. Epidermal growth factor receptor peptide vaccination induces cross-reactive immunity to human EGFR, HER2 and HER3. Cancer Immunol Immunother. 2018;67(10):1559–1569. These studies were supported by awards from the Canine Cancer Research Alliance (MJM) and The MJ and Caral G Lebworth Foundation (MJM). No conflicts of interest.