Primary analysis of a prospective, randomized, single-blinded phase II trial evaluating the HER2 peptide AE37 vaccine in breast cancer patients to prevent recurrence

Abstract

Background: AE37 is the Ii-Key hybrid of the MHC class II peptide, AE36 (HER2 aa:776-790). Phase I studies showed AE37 administered with granulocyte macrophage colony-stimulating factor (GM-CSF) to be safe and highly immunogenic. A prospective, randomized, multicenter phase II adjuvant trial was conducted to evaluate the vaccine's efficacy.

Methods: Clinically disease-free node-positive and high-risk node-negative breast cancer patients with tumors expressing any degree of HER2 [immunohistochemistry (IHC) 1-3+] were enrolled. Patients were randomized to AE37 + GM-CSF versus GM-CSF alone. Toxicity was monitored. Clinical recurrences were documented and disease-free survival (DFS) analyzed.

Results: The trial enrolled 298 patients; 153 received AE37 + GM-CSF and 145 received GM-CSF alone. The groups were well matched for clinicopathologic characteristics. Toxicities have been minimal. At the time of the primary analysis, the recurrence rate in the vaccinated group was 12.4% versus 13.8% in the control group [relative risk reduction 12%, HR 0.885, 95% confidence interval (CI) 0.472-1.659, P = 0.70]. The Kaplan-Meier estimated 5-year DFS rate was 80.8% in vaccinated versus 79.5% in control patients. In planned subset analyses of patients with IHC 1+/2+ HER2-expressing tumors, 5-year DFS was 77.2% in vaccinated patients (n = 76) versus 65.7% in control patients (n = 78) (P = 0.21). In patients with triple-negative breast cancer (HER2 IHC 1+/2+ and hormone receptor negative) DFS was 77.7% in vaccinated patients (n = 25) versus 49.0% in control patients (n = 25) (P = 0.12).

Conclusion: The overall intention-to-treat analysis demonstrates no benefit to vaccination. However, the results confirm that the vaccine is safe and suggest that vaccination may have clinical benefit in patients with low HER2-expressing tumors, specifically TNBC. Further evaluation in a randomized trial enrolling TNBC patients is warranted.

Keywords: HER2; breast cancer; immunotherapy; triple-negative breast cancer; vaccine.

Figure 1.

Consort diagram. Flow of patients through the study. Asterisk indicates that one of three patients with a second malignancy in the control arm withdrew and is included in the seven withdrawals. Circumfex symbol indicates that the number of patients that did not complete the primary vaccination series (PVS) includes patients that withdrew, met the primary end point (recurrence, second malignancy, or death from any cause), or chose not to continue on study before completing the PVS.

Figure 2.

Maximum toxicity. The maximum local and systemic toxicity experienced by patients administered the AE37 + GM-CSF vaccine were comparable with those experienced by patients receiving GM-CSF alone.

Figure 3.

Immunologic response to vaccination. (A) In vivo immune responses were determined in all patients using a delayed-type hypersensitivity (DTH) reaction. Patients who were vaccinated with AE37 + GM-CSF had a significant increase in their DTH reaction to both the immunizing peptide, AE37, and the wild-type peptide, AE36, postvaccination compared with prevaccination. In vaccinated patients, the average (± standard error) orthogonal mean to AE36 before vaccination was 2.0 ± 0.4 versus 16.0 ± 1.2 mm postvaccination (P < 0.001). The average induration to AE37 before vaccination was 2.6 ± 0.6 versus 28.7 ± 1.9 mm postvaccination (P < 0.001). In addition, the postvaccination response was significantly greater in vaccinated patients than in control patients (AE36: 16.0 ± 1.2 versus 4.0 ± 0.7 mm, P < 0.001; AE37: 28.7 ± 1.9 versus 5.6 ± 1.2 mm, P < 0.001). (B) Ex vivo immune responses were determined in all patients using a ³H-thymidine incorporation assay to measure peptide-specific T-cell proliferation in response to the native peptide AE36. Patients vaccinated with AE37 + GM-CSF demonstrated robust T-cell proliferation at all time points assessed after the initiation of vaccination. (C) T-cell proliferation in response to the vaccinating peptide AE37 was also determined using a ³H-thymidine incorporation assay and vaccinated patients demonstrated robust T-cell proliferation at all time points assessed. *P < 0.001.

Figure 4.

Additional immunological responses. (A) IFN-γ ELISPOT assays were performed in a subset of the patients (n = 97) comparing AE37 + GM-CSF vaccinated patients (n = 53) with GM-CSF-only control patients (n = 44) at baseline (prevaccine) and multiple postvaccine time points. Results are expressed as specific spots (subtracting background) per 10⁶ PBMC for both AE36 (top row) and AE37 (bottom row). Results are presented as medians, range, and 50% quartiles. *P < 0.01. (B) Regulatory T cells (Treg) were assessed by flow cytometry (CD4 + CD25hiCD127low/neg) in the same subset and at the same time points. Results are expressed as the %Treg per all CD4+ cells and compared within each treatment group at the given time points as well as between groups. *P < 0.02.

Figure 5.

Disease-free survival is shown on an intention-to-treat basis for (A) all patients, (B) patients with HER2-overexpressing breast cancer, (C) patients with HER2 1+ and 2+ tumors regardless of hormone receptor status, and (D) triple-negative breast cancer patients (HER2 1+ and 2+ and hormone receptor-negative tumors).