Application of HER2 peptide vaccines in patients with breast cancer: a systematic review and meta-analysis

Background The E75 and GP2 vaccines are the few therapeutic vaccines targeting HER2 currently under clinical research for patients with breast cancer. Methods Databases, including the Cochrane Library, PubMed, Medline, Embase, and Web of Science, were used to retrieve clinical studies on E75 and GP2 vaccines. Retrieval time was from the beginning of database construction until May 31st, 2021. Results A total of 24 clinical studies were included in this analysis, including 1704 patients in the vaccinated group and 1248 patients in the control group. For the E75 vaccine, there were significant differences between the vaccinated group and the control group in the delayed-type hypersensitivity reaction (SMD = 0.685 95% CI 0.52-0.85, P.sub.Heterogeneity = 0.186, P.sub.DTH < 0.05) and the change in CD8.sup.+ T-cell numbers (SMD = - 0.864, 95% CI - 1.02 to - 0.709, P.sub.Heterogeneity = 0.085, P.sub.CD8+ T cell < 0.05) before and after injection. For the GP2 vaccine, there was a significant difference between the vaccinated group and the control group in the change in CD8.sup.+ T-cell numbers (SMD = - 0.584, 95% CI - 0.803 to - 0.294, P.sub.Heterogeneity = 0.397, P.sub.CD8+ T cell < 0.05) before and after injection. In addition, the clinical outcomes, including recurrence rate (RR = 0.568, 95% CI 0.444-0.727, P.sub.Heterogeneity = 0.955, P.sub.Recurrence < 0.05) and disease-free survival rate (RR = 1.149, 95% CI 1.050-1.256, P.sub.Heterogeneity = 0.003, P.sub.DFS < 0.05), of the E75-vaccinated group were different from those of the control group. However, we found that the overall survival rate with the E75 vaccine (RR = 1.032, 95% CI 0.998-1.067, P.sub.Heterogeneity = 0.476, P.sub.OS > 0.05) was not different between the two groups. Local and systemic toxicity assessments of the two vaccines showed minimal side effects. Conclusions The E75 vaccine was effective and safe in patients with breast cancer. The GP2 vaccine could elicit a strong immune response, but more trials are needed to confirm its clinical efficacy. Keywords: HER2, Breast cancer, Vaccine, Systematic review, Meta-analysis