2529 Background: We have completed accrual and are in the follow up portion of phase I/II clinical trials evaluating the E75 HER2 peptide vaccine. E75 has been proven safe, capable of stimulating HER2 immunity, and effective in decreasing breast cancer recurrence rates. During the conduct of this trial, it was noted that E75-specific immunity waned after the Primary Vaccine Series (PVS) which corresponded with late recurrences. To maintain long-term immunity, a voluntary booster program was started. Here we present analysis of the booster inoculations. Methods: The trial enrolled node-positive or high-risk, node-negative breast cancer patients (pts) with tumors expressing any level of HER2 (IHC 1-3+). HLA-A2/A3+ pts comprised the vaccine group (VG), HLA-A2/A3- pts were followed as the control group (CG). The VG received 4-6 monthly inoculations of E75+GM-CSF. Volunteer booster program pts (BG) received inoculations every 6 months after the PVS. Pts were monitored for toxicities, in vivo responses by local reactions (LR) and DTH, and in vitro responses measured by enumeration of E75 specific cytotoxic T lymphocytes. Results: 53 pts received at least 1 booster, 34 received 2, 24 three, 20 four, 12 five, and 8 at least 6. 24% of pts had no local toxicity, 73% Grade 1 (G1), 3% G2. 74% had no systemic toxicity, 35% G1, 1% G2. LRs increased significantly from the initial vaccine (R1) during PVS to each booster (B) (R1: 59.5±3.1 v B1: 89.2±3.3, p<0.001; v B2: 95.15±5, p<0.001; v B3: 86.63±5.5, p<0.001; v B4: 83.26±4.6, p=<0.001; v B5: 80.67±6.7, p=0.006; v B6: 78.75±9.4, p=0.04). Dimer values increased from the end of PVS to each post-booster value (pre B1:1.29±0.25 v post B1: 1.46±0.38; post B2: 1.41±0.4; post B3: 1.84±0.35; post B4: 2.23±0.4; post B5:1.94±0.31; post B6: 2.73±0.09, p=0.02). At median 60 months, the recurrence rate for BG was 3.8% vs 18.9% in the CG (p=0.01). Conclusions: Booster inoculations are well-tolerated and appear to assist in the maintenance of long term peptide-specific immunity. Boosted pts have improved recurrence rates. Based on the success of this program, we have incorporated the practice of booster inoculations in our current cancer vaccine trials.
Final analysis of a phase I/IIa trial of the folate‐binding protein‐derived E39 peptide vaccine to prevent recurrence in ovarian and endometrial cancer patients
