Investigating the Combination of Trastuzumab and HER2/neu Peptide Vaccines for the Treatment of Breast Cancer
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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.
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.
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.
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.
KeywordsBreast cancer HER2/neu Immunotherapy Trastuzumab Peptide vaccine
Supported by funds from the Department of Defense to the Henry M. Jackson Foundation for the Advancement of Military Medicine (Rockville, MD) for the Clinical Breast Care Project, by the United States Army Medical Research and Materiel Command, and by the Department of Clinical Investigation at the Walter Reed Army Medical Center. The authors thank Diane Papay and Stacy O’Neill of the Clinical Breast Care Project, who provided excellent patient care and administration of the clinical trial. We also thank the staff of the Clinical Breast Care Project Immunology & Research Center for their clinical and administrative assistance.
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