The hybrid AE37 vaccine seems safe and well tolerated with minimal toxicity if properly dosed. AE37 is capable of eliciting HER-2/neu-specific immune responses, even without the use of an adjuvant. This trial represents the first human experience with the Ii-Key modification, and to our knowledge, AE37 is the first peptide vaccine to show potency in the absence of an immunoadjuvant.

BACKGROUND: HER-2/neu, overexpressed in breast cancer, is a source of immunogenic peptides that include GP2 and E75. Phase 2 testing of E75 as an adjuvant vaccine has suggested a clinical benefit. GP2, derived from the transmembrane portion of HER-2/neu, has differing binding characteristics and may be more immunogenic than E75. Results of the first phase 1 trial of GP2 peptide vaccine are presented. METHODS: Disease-free, lymph node-negative, human leukocyte antigen (HLA)-A2 þ breast cancer patients were enrolled. This dose escalation trial included 4 groups to determine safety and optimal GP2 peptide/granulocyte-macrophage colony-stimulating factor (GM-CSF) dose. Toxicities were monitored. Immunologic response was assessed ex vivo via the HLA-A2:immunoglobulin dimer assay to detect GP2-specific CD8 þ T cells (and E75-specific CD8 þ T cells to assess epitope spreading) and in vivo via delayed type hypersensitivity (DTH) reaction (medians/ranges). RESULTS: Eighteen patients were enrolled. All toxicities were grade 2. Eight (88.9%) of 9 patients in the first 3 dose groups required GM-CSF dose reductions for local reactions !100 mm or grade !2 systemic toxicity. GM-CSF dose was reduced to 125 lg for the final dose group. All patients responded immunologically ex vivo (GP2-specific CD8 þ T cells from prevaccination to maximum, 0.4% [0.0%-2.0%] to 1.1% [0.4%-3.6%], P < .001) and in vivo (GP2 pre-to postvaccination DTH, 0 mm [0.0-19.5 mm] to 27.5 mm [0.0-114.5 mm, P < .001). E75-specific CD8 þ T cells also increased in response to GP2 from prevaccination to maximum (0.8% [0.0%-2.41%] to 1.6% [0.86%-3.72%], P < .001). CONCLUSIONS: The GP2 peptide vaccine appears safe and well tolerated with minimal local/systemic toxicity. GP2 elicited HER-2/neu-specific immune responses, including epitope spreading, in high-risk, lymph node-negative breast cancer patients. These findings support further investigation of the GP2 vaccine for the prevention of breast cancer recurrence. Cancer 2010;116:292-301. V C 2010 American Cancer Society.KEYWORDS: breast cancer, GP2, HER-2/neu, peptide, vaccine.Breast cancer is the most common malignancy in women (excluding cancers of the skin), and is the second leading cause of cancer mortality among women. 1 HER-2/neu is a tumor-associated antigen that is overexpressed in approximately 25% to 30% of breast cancer patients and correlates with more aggressive tumor behavior. 2,3 Immunogenic peptides derived from HER-2/neu can induce peptide-specific cytotoxic T lymphocytes (CTLs) that recognize tumor cells expressing these peptides complexed with major histocompatibility complex class I molecules. 4 Two such peptides include E75 and GP2. Our group has previously tested and reported on the E75 peptide used as a preventive clinical vaccine in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF) and found it to be safe and effective in raising HER-2/neu immunity. Furthermore, this immunity may confer a clinical benefit in the adjuvant setting. 5

Purpose: HER2/neu, a source of immunogenic peptides, is expressed in >75% of breast cancer patients. We have conducted clinical trials with the HER2/neu E75 peptide vaccine in breast cancer patients with varying levels of HER2/neu expression. Vaccine response based on HER2/neu expression level was analyzed. Experimental Design: Patients were stratified by HER2/neu expression. Low expressors (n = 100) were defined as HER2/neu immunohistochemistry (IHC) 1 + to 2 + or fluorescence in situ hybridization < 2.0. Overexpressors (n = 51) were defined as IHC 3