Biomarker correlation to clinical response in phase I/II trials of the adjuvant breast cancer vaccine neuvax (nelipepimut-S or E75).

Abstract

TPS3126 Background: We completed phase I/II clinical trials with NeuVax (nelipepimut-S), a HLA-A2/A3-restricted, HER2-derived peptide vaccine. The vaccine was administered in the adjuvant setting to prevent recurrence in breast cancer patients rendered disease-free with standard-of-care therapy. Here, we examine the relationship between in vitro immunologic response (IR) and clinical recurrence (CR) after 5-year follow-up. Methods: The phase I/II trials were performed as dose-escalation/schedule-optimization trials enrolling node positive and high-risk, node-negative patients (pts) with tumors expressing any level of HER2 (IHC 1+,2+,or 3+). HLA-A2/A3+ pts were enrolled in the vaccine group (VG) while HLA-A2/A3- pts were followed prospectively as an untreated control group (CG). The VG was given 4-6 monthly intradermal inoculations of nelipepimut-S+GMCSF (immunoadjuvant) during the primary vaccine series (PVS). In vitro IR was assessed for E75-specific, cytotoxic T lymphocyte clonal expansion by HLA-A2:IgG dimer assay and expressed as mean dimer index (mdi) at baseline, after PVS (R6), and six months after the PVS. HER2 under-expression was defined as an IHC 1/2, and a FISH < 2.2. VG and CG pts were followed for CR over 60 months. P-values were calculated using the Fisher’s exact test. Results: Of the 195 pts enrolled, 8 withdrew, leaving 187 evaluable pts; 108 in the VG and 79 in the CG. R6 dimer assays were available for 86 pts in the VG. The mean R6 dimer in the VG is 0.63 mdi+.08. Of the 30 pts with an R6 dimer above the mean, only one recurred, compared to eight of the 56 below the mean (p=.09). The difference between baseline and maximum mdi was available in 56 HER2 under-expressing VG pts. Of the 26 pts above the mean difference (1.08 mdi +.17), one recurred, compared to six CR in the 30 pts below the mean (p=.06). There were no CR in pts with HER2 under expression with a mean difference ranked in the top third. Conclusions: In prospective, completed phase I/II trials of NeuVax (nelipepimut-S), patients who exhibit robust in vitro IR have lower recurrence rates. This finding suggests that nelipepimut-specific CTL clonal expansion is a valid biomarker for CR in pts treated with NeuVax. Clinical trial information: NCT00841399.