Abstract P2-11-03: Phase I/II randomized study of combination immunotherapy with or without polysaccharide krestin (PSK) concurrently with a HER2 ICD peptide-based vaccine in patients with stage IV breast cancer receiving HER2-targeted monoclonal antibody therapy

Natural killer (NK) cell defects, commonly seen in metastatic breast cancer (MBC) lead to decrease in dendritic cell (DC) maturation, proinflammatory cytokine production, and tumor infiltrating T-cells (TILs). This results in a protumorigenic Th2 immune microenvironment with low response rates to immunotherapy (i.e., immune checkpoint blockade) and standard chemotherapy. PSK, a potent TLR-2 agonist, activates NK cells to produce IFN-γ and IL-12 and promote DC maturation/differentiation toward a Th1 profile in the tumor microenvironment which results in antigen specific TIL that can eradicate tumor. The combination immunotherapy of PSK and HER2 directed therapy described here, aims at inducing Th1 immunity and tumor specific T-cells. This proposed regimen could eradicate microscopic residual disease and prevent recurrence in optimally treated HER2+ MBC patients. Moreover, the regimen could result in enhanced trafficking of TILs to the site of tumor and improve the efficacy of checkpoint inhibitors and other therapies. A phase I/II randomized 2 arm study of combination immunotherapy with oral PSK (or placebo) given with a HER2 peptide vaccine and HER2 mAb therapy (trastuzumab (TZ) +/- pertuzumab (PZ)) was initiated to assess the safety of the approach and evaluate the effect of PSK on NK cell activity, pro-inflammatory cytokine/chemokine profile; and HER2 vaccine-induced T cell immunity.

Methods: Up to 30 patients with HER2+ MBC who are without evidence of disease after definitive therapy and currently on maintenance TZ +/- PZ are enrolled and randomly assigned in equal numbers to 1 of 2 arms (15 patients/arm): Arm 1: HER2 ICD vaccine + placebo or Arm 2: HER2 ICD vaccine + PSK. All patients receive concomitant treatment with 4 months of daily oral PSK or placebo, 3 monthly intradermal HER2 ICD vaccinations and continued TZ +/- PZ. Toxicity is evaluated per CTEP CTCAE 4.0, during and post vaccination. Serial blood draws for immunologic evaluation of NK cell activity and antigen-specific T cell immunity via flow cytometry and IFN-γ ELISPOT, respectively; and pro-inflammatory cytokines/chemokines.

Results: 24 subjects have been enrolled and 60 vaccines have been given. 16 subjects have completed all 3 vaccines and PSK/placebo; and 6 subjects are currently in progress. 2 subjects received < 3 vaccines and were taken off study. Of 144 reported adverse events (AEs), 97% were Grade 1-2; 66 (46%) were possibly, probably, or definitely related to study treatment. Most common AEs are injection site reaction and flu-like symptoms. There have been a total of four Grade 3 AEs, 1 episode of self-limited nausea/vomiting attributed to study treatment; and cognitive disturbance, fatigue, and lymphopenia all in 1 subject and attributed to disease progression. There have been no Grade 4 AEs. Immunologic analyses are ongoing and will be presented along with completed clinical data on all patients.

Conclusion: Combination immunotherapy with PSK/placebo and concurrent HER2 directed therapy is safe and well-tolerated. Further ongoing immunologic studies will help define the immunogenicity of the approach.

Citation Format: Salazar LG, Higgins D, Childs J, Coveler AL, Liao J, Stanton S, Gooley T, Standish LJ, Sasagawa M, DISIS ML. Phase I/II randomized study of combination immunotherapy with or without polysaccharide krestin (PSK) concurrently with a HER2 ICD peptide-based vaccine in patients with stage IV breast cancer receiving HER2-targeted monoclonal antibody therapy. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-11-03.

HER2/neu (HER2) specific T-cell immunity in patients with HER2+ inflammatory breast cancer (IBC) and prognosis

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Background: IBC is rare, highly aggressive, and associated with worse prognosis when compared to non-IBC tumors. Moreover, multimodality treatment has had little impact on overall prognosis. HER2 is overexpressed in about 40% of IBC tumors and is associated with worse overall survival (OS). We have developed vaccines that elicit both HER2-specific CD4+ and CD8+ T-cell immunity in HER2+ cancer patients. Generation of HER2-specific T-cell immunity could (1) target immunogenic and biologically relevant proteins such as HER2 in IBC, (2) result in immunogenic eradication of HER2+ tumor cells, and (3) potentially prevent disease relapse when used in the adjuvant setting after standard therapy. A retrospective analysis of IBC patients immunized with HER2 vaccines was conducted to better understand the development of HER2-specific T-cell immunity and its possible impact on overall prognosis in IBC. Methods: Clinical and immunological data of IBC patients enrolled in University of Washington IRB approved HER2 vaccine trials was collected and reviewed. 27 patients immunized between 1996–2008 were identified; and 24/27 subjects who received vaccines designed to elicit both CD4+/CD8+ immunity were included in immunologic and survival analysis. The 24 subjects received either a HER2 DNA or HER2 peptide-based vaccine that were admixed with GM-CSF and given intradermally monthly for a total of 3 DNA or 6 peptide vaccines. Immune responses were assessed via IFN-γ ELISPOT at baseline and post-vaccination. Results: All 24 subjects had stage III IBC and median age was 48 (range 34–77). 10/24 (42%) patients had ER/PR+ tumors, 9/24 (37%) had received trastuzumab, and 15/24 (62%) had received multimodality treatment (chemotherapy, mastectomy, radiotherapy). 12/18 subjects (66%) evaluable for immunologic response developed HER2-specific T-cell immunity post-vaccination. Median OS for patients (n=6) not generating HER2-specific immunity was 31 months and median OS for the 12 patients who developed HER2-specific immunity has not been reached at median follow-up of 46 months, (p=0.026). Conclusions: Patients with IBC are able to generate HER2-specific T-cell immunity after HER2 vaccination, and development of HER2-specific immunity may impact survival.

No significant financial relationships to disclose.

A phase I study of a DNA plasmid based vaccine encoding the HER2/neu (HER2) intracellular domain (ICD) in subjects with HER2+ breast cancer

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Background: HER2 is overexpressed in 25% of breast cancers and plays a role in the malignant transformation of cells. Vaccine-induced immunity against the HER2 ICD correlates with antitumor responses in animal models. DNA-based vaccines offer a strategy to immunize against multiple tumor antigens and are able to elicit both CTL and T helper immune responses. Plasmid DNA can also remain at the vaccine site, providing a constant source of antigen. However, DNA vaccines have been poorly immunogenic due in part to inefficient APC transfection. Intradermal (i.d.) delivery of DNA vaccines with GM-CSF as adjuvant may enhance immunogenicity due to local influx of dermal Langerhans cells. A phase I study was conducted to evaluate the safety and immunogenicity of a DNA-based vaccine encoding the HER2 ICD. Methods: 44 subjects with stage III and IV HER2+ breast cancer in complete remission were enrolled sequentially into 2 vaccine arms (22 subjects/arm) and received 10μg pNGVL3-hICD (Arm 1) or 100μg pNGVL3-hICD (Arm 2). All vaccines were admixed with 100μg GM-CSF and given i.d. monthly for a total of 3 vaccines. Toxicity was assessed at baseline, during vaccination, and at follow-up. Immune responses were assessed with IFN-γ ELISPOT at baseline and post-vaccination. Vaccine site biopsies were analyzed for plasmid persistence via RT-PCR, 1 and 6 months after vaccination. Results: 43 subjects (21 in Arm 1; 22 in Arm 2) completed 3 vaccines. Vaccine-related toxicity in both arms was primarily grade I/II; no cardiac or grade IV toxicity was observed. 13/21 (62%) subjects in Arm 1 developed T-cell immunity, defined as HER2-specific T cell precursors:PBMC, to the HER2 protein (median 1:5,972, range 1:717–1:3,000,000) and to p776, a HER2 pan DR binding epitope (median 1:3,150, range 1:543–1:108,696). 13/19 (68%) subjects in Arm 1 had persistent plasmid DNA at the vaccine site. ELISPOT and RT-PCR analysis for Arm 2 are on-going. Conclusions: Immunization with a DNA plasmid-based HER2 vaccine is safe and immunogenic. Moreover, plasmid DNA persists at the vaccine site post-immunization and HER2+ cancer patients are able to develop immunity to the HER2 ICD.

No significant financial relationships to disclose.