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Investigating the Combination of Trastuzumab and HER2/neu Peptide Vaccines for the Treatment of Breast Cancer

¹ Clinical Breast Care Project, Department of Surgery, Walter Reed Army Medical Center, 6900 Georgia Avenue NW, Washington, DC 20307-5001
² National Naval Medical Center, Henry M. Jackson Foundation for the Advancement of Military Medicine, Clinical Breast Care Project Immunology & Research Center, Building 139, 8901 Wisconsin Avenue, Bethesda, Maryland 20889-5600

Correspondence: Address correspondence and reprint requests to: George E. Peoples, MD; E-mail: george.peoples{at}na.amedd.army.mil.

Background: Trastuzumab, an anti-HER2/neu monoclonal antibody, is thought to promote HER2/neu receptor internalization and/or turnover. This study was designed to investigate the kinetics of trastuzumab treatment on tumor cells with varying levels of HER2/neu expression and to determine the effect of trastuzumab on HER2/neu-specific cytotoxic T lymphocyte–mediated lysis.

Methods: Three cell lines with varying levels of HER2/neu expression were incubated with varying doses of trastuzumab at multiple time points. Trastuzumab binding and HER2/neu expression were determined. Peripheral blood mononuclear cells from three HLA-A2⁺ healthy donors and four E75 peptide–vaccinated patients were stimulated with HER2/neu-derived peptides and tested in standard chromium release cytotoxicity assays with HER2/neu⁺ tumor cells pretreated with trastuzumab.

Results: Treatment of tumor cells with 10 µg/mL of trastuzumab in an overnight incubation resulted in saturation of cell-surface HER2/neu receptors. At higher doses, trastuzumab staining and HER2/neu expression decreased in a time-dependent manner. Pretreatment of tumor cells with trastuzumab resulted in increases in specific cytotoxicity by peptide-stimulated cytotoxic T lymphocytes from HLA-A2⁺ donors over untreated cells by an average of 5.6% and 15.3% (P = .0002) for doses of 10 and 50 µg/mL, respectively. In similar experiments involving peripheral blood mononuclear cells obtained from immunized patients, the average specific cytotoxicity for untreated cells was 34.2% ± 1.3% vs. 40.6% ± 2.5% (P = .035) and 40.7% ± 1.6% (P = .0005) for those treated with 10 and 50 µg/mL, respectively.

Conclusions: Our data suggest that pretreatment of breast cancer cells with trastuzumab induces turnover of the HER2/neu protein and enhanced killing by HER2/neu peptide–stimulated CTLs. This increased lysis occurs regardless of the degree of HER2/neu expression and seems more pronounced in vaccinated patients. These findings support further investigation into the use of combination immunotherapy with trastuzumab and HER2/neu peptide–based vaccines.

Key Words: Breast cancer • HER2/neu • Immunotherapy • Trastuzumab • Peptide vaccine

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