Abstract P2-20-02: Increased Prevalence of HLA-DR3 among Breast Cancer Patients: Implications for Adjuvant Her2/neu Peptide Vaccine Trials
Authors: Olson MD , Clifton GT , Mittendorf EA , Ponniah S , Peoples GE , Holmes JP. 
Published: April 2011

Abstract
BACKGROUND: HER2/neu is overexpressed in approximately 25% of breast cancer (Bca) patients (pts) and the source of a number of immunogenic HLA class I and II peptides. HLA class II molecules are generally promiscuous in their peptide affinity. Previous studies have shown that HLA-DR3, which has a prevalence of 13% in the population, has a lower binding affinity to multiple HER2/neu peptides. This suggests that pts who are HLA-DR3 positive (DR3+) may respond more poorly to HER2/neu peptide vaccines than HLA-DR3 negative (DR3-). We are conducting clinical trials evaluating HER2/neu-derived peptides GP2, E75, and AE37 administered in the adjuvant setting to prevent disease recurrence in high risk pts. GP2 and E75 are class I peptides. AE37 is the Ii-Key hybrid of HER2/neu:776-790 (AE36), an HLA class II peptide. Here, we report an analysis of DR3 status and response to AE37 vaccination in our trials. METHODS: We enrolled Bca pts rendered disease-free after receiving standard adjuvant therapy. HLA-DR3 status was determined via flow cytometry performed on peripheral blood mononuclear cells. In our phase II trial, pts were randomized to six monthly inoculations of either AE37 with granulocyte-macrophage colony-stimulating factor (GM-CSF) or GM-CSF alone. In vivo immune responses were measured using a delayed-type hypersensitivity immune response (DTH). Ex vivo immune response was measured by vaccine specific proliferative activity of T-lymphocytes using standard 3H-thymidine incorporation proliferation assay and a standard ELISPOT assay measuring peptide specific interferon-γ secreting T-cells.
RESULTS: DR3 status has been determined in 131 pts; 34 (26%) are DR3+, twice the expected (13%). Demographics (age, nodal status, tumor size, HER2 expression) were similar when comparing DR3+ pts to DR3-pts, with the exception that DR3 + pts were less likely to have high grade disease (n=11, 33%) compared to DR3-pts (n=58, 60%, p=0.035). 77 pts (56 DR3-, 21 DR3+) received AE37 ± GM-CSF. Post-vaccination DTH responses were significantly larger in AE37 pts compared to their respective GM-CSF controls (DR3-pts: AE37 40 ± 7 mm, GM-CSF 1 ± 0.5 mm, P&lt;0.00001; DR3+ pts: AE37 39 ± 8 mm, GM-CSF 6 ± 3mm, p=0.002). DTH were similar comparing DR3-and DR3+ pts in both the GM (DR3+ 6 ± 3mm vs DR3-1 ± 0.5 mm, p=NS) and in the AE37 pts (DR3+ 39 ± 8 mm vs DR3-39 ± 7 mm, p =NS). There was a non-statistically significant trend toward increased post vaccination peptide-specific T-cells measured by proliferation and ELISPOT assay when comparing AE37 pts to GM-CSF pts; however, there was no difference in assays comparing DR3+ and DR3-pts.
CONCLUSIONS: We have observed DR3 phenotype in our BCa pts at twice the expected prevalence. DR3+ pts were less likely to have high grade tumors compared to DR3-pts. Despite in vitro studies demonstrating limited binding affinity of DR3 for numerous Her2/neu-derived peptides, our pts demonstrated no statistical difference in the in vivo or ex vivo immunogenic response between DR3+ and DR3-pts to vaccination with AE37 + GM-CSF, suggesting the Ii-key hybrid peptide AE37 may overcome weakly binding MHC II phenotypes. The increased prevalence of DR3 among BCa pts warrants further study.
Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-20-02.