Prevention and Therapy of Metastatic HER-2+ Mammary Carcinoma with a Human Candidate HER-2 Virus-like Particle Vaccine

Vaccines are a promising therapeutic alternative to monoclonal antibodies against HER 2+ breast cancer. We present the preclinical activity of an ES2B-C001, a VLP-based vaccine being
developed for human breast cancer therapy. FVB mice challenged with HER-2+ mammary carci noma cells QD developed progressive tumors, whereas all mice vaccinated with ES2B-C001+Mon tanide ISA 51, and 70% of mice vaccinated without adjuvant, remained tumor-free. ES2B-C001 com pletely inhibited lung metastases in mice challenged intravenously. HER-2 transgenic Delta16 mice
developed mammary carcinomas by 4–8 months of age; two administrations of ES2B-C001+Monta nide prevented tumor onset for >1 year. Young Delta16 mice challenged intravenously with QD
cells developed a mean of 68 lung nodules in 13 weeks, whereas all mice vaccinated with ES2B C001+Montanide, and 73% of mice vaccinated without adjuvant, remained metastasis-free. ES2B C001 in adjuvant elicited strong anti-HER-2 antibody responses comprising all Ig isotypes; titers
ranging from 1–10 mg/mL persisted for many months. Antibodies inhibited the 3D growth of hu man HER-2+ trastuzumab-sensitive and -resistant breast cancer cells. Vaccination did not induce
cytokine storms; however, it increased the ELISpot frequency of IFN-γ secreting HER-2-specific
splenocytes. ES2B-C001 is a promising candidate vaccine for the therapy of tumors expressing HER 2. Preclinical results warrant further development towards human clinical studies.