P.I 6304p Protocol 118 04/06/2016 8 Appendix D Supplemental HER2 CTL Peptide -Based Booster Vaccine Study 1. INTRODUCTION Vaccinating women with HER2 overexpressed breast cancer against HER2 -specifi c antigens has been shown to improve both overall survival in metastatic breast cancer (MBC) and disease free survival (DFS) in women with locally advanced non metastatic disease.1,2 Furthermore, vaccination has been shown to both stimulate an immune response against the vaccine antigen as well epitope spreading to other antigens within the protein (intermolecular spreading) and other tumor -related proteins (intramolecular spreading). 1,2 However, immunity to the vaccines ma y wane as patients are greater than 6 months to a year from vaccination. This loss of immunity may explain progressive disease in patients with previous immune control. To improve prolonged immune response, booster vaccinations have been evaluated to re -stimulate HER2 -specific immunity after completion of a primary vaccination series. Specifically, using GMCSF and the E75 vaccine, a single booster vaccination greater than 6 months after completing the vaccination series was demonstrated to be safe and improved immune response. 3 We therefore seek to evaluate the immunogenicity of a series of 2 booster vaccinations given 6 months apart in patients who have receiv ed at least one vaccination with the HER2 cytotoxic T lymphocyte (CTL) peptide -based vaccine and have no evidence of disease, stable disease, or slowly progressive disease. Twenty -two HLA -A2 HER2 overexpressing stage IV patients were enrolled in the NCT00194714 trial of six HER2 CTL peptide -based vaccines along with concurrent trastuzumab. Twenty -one patients received vaccinations: Fourteen of 21 patients received all six immunizations, five of the patients completed at least three immunizations, and two of the patients only completed two immunizations. The vaccine series was well tolerated and had an acceptable safety profile with 99% grade 1 or 2 toxicities, four grade 3 toxicities which included injection site reaction, infection, ulceration and fainting. There was one unrelated grade 4 event of a stroke. Furthermore, the vaccine series was immunogenic with 90% of the patients developing new or increased HER2 -specific IFN -g immunity as well as epitope spreading to other tumor associated proteins. The immunized patients also had disease response with a median progression free survival (PFS) of 17.7 months at 3 years (with 33% of patients showing no evidence of disease progression) and median overall survival of 86% at 4 years. The immunity induced by the vaccine was followed for up to a year after vaccination in 11 patients. Forty- six percent of patients maintained the same level of immunity, 36% had increased immunity, and 18% had lowered immunity after a year. 1 In long term follow up, 10 patients are currently living 10 years after completion of the initial vaccine series despite having HER2+ MBC. As an example, one of the patients had 7 years of DFS on single agent trastuzumab after the vaccine series and continues to have considerable disease control despite slowly progressive disease while remaining on single agent trastuzumab. These patients’ long disease stabilization beyond expected average DFS of 12 m onths with trastuzumab alone suggests that the immunity acquired from vaccination may have contributed to disease stabilization. 4,5 We therefore want to evaluate if providing additional boosters will possibly increase the anti -HER2 immunity of these previously vaccinated patients. Additionally, we will monitor for safety of the approach. Although most cancer vaccine studies have focused on the generation of measurable immunity during active immunization, few studies have evaluated the persistence of immunity or the generation of immunologic memory. The development of immunologic memory has been shown to b e essential. Indeed, it is the development of immunologic memory to the vaccinating antigen that would be the key to the success of a tumor vaccine to protect against relapse. In this booster study, we will evaluate the persistence of HER2 peptide -based specific immunity and also the presence and magnitude of a memory T -cell response after “booster” immunization with a HER2 peptide -based vaccine in previously immunized patients. 2. BACKGROUND Immunologic memory, a hallmark of the protective immune response after immunization, is the ability to make a faster, stronger, and more effective, immune response to an antigen that has been encountered previously.6 6304p Protocol 118 04/06/2016 9 Memory T -cells are clones of antigen -specific lymphocytes that are able to be maintained in homeostasis for a long time and reactivate when stimulated by a second encounter with an antigen.6 The goal of vaccines, whether against infectious or cancer targets, is to develop these memory cells to allow for continued immune surveillance. Antigen- specific immunity can wane over time and booster vaccines can be used to reactivate the T-cells, increase memory, and trigger a more robust immune response. In infectious disease, with each antigen challenge (either an infection or booster vaccination) there is a larger increase in effector CD8+ T-cells and a higher baseline memory T -cell response.7 Therefore booster cancer vaccines would be expected to also give a second antigen challenge increasing both anti -tumor immune res ponse and specific T -cell memory. Most breast cancer vaccine trials have evaluated the immunity that is developed immediately after primary vaccination.8,9 However, long term follow up from these vaccine trials suggest that this immunity wanes and booster vaccinations may reactivate the anti -HER2 immune response and the memory T -cell population. A. HER2 dir ected immunotherapy is safe when administered concurrently with HER2 CTL peptide based vaccination. As discussed above, patients enrolled to the original HER2 vaccine study were receiving concurrent trastuzumab and the combination immunotherapy was well t olerated with no significant cardiac toxicity observed. Over the past 2 years, the first -line treatment of HER2+ MBC has been changing and now also includes other HER2 targeted agents. In 06/2012, the FDA approved the combination of pertuzumab and trastu zumab with chemotherapy for the treatment of HER2+ MBC. This was based on data from the phase III CLEOPATRA study, which showed improved PFS with the combination of docetaxel and pertuzumab/trastuzumab versus docetaxel + placebo/trastuzumab. 10 Moreover, extensive cardiac surveillance conducted in CLEOPATRA did not show increased cardiotoxicity (increased rate of left -ventricular systolic dysfunction) in patients receiving concomitant pertuzumab and trastuzumab when compared to concomitant placebo and trastuzumab. As such, it is possible that patients enrolled in the original HER2 peptide vaccine study and who are now interested in the booster vaccine study may b e receiving maintenance pertuzumab and trastuzumab. Given the acceptable toxicity data of the combined HER2 targeted therapy, we do not anticipate any increased cardiac toxicity if pertuzumab and trastuzumab are given concurrently with HER2 peptide booste r vaccination. Therefore concurrent use of either trastuzumab or pertuzmab/trastuzumab during booster vaccination will be allowed. B.