T- cell populations essential for immune efficacy after vaccination . T-cells go through three stages in response to anti gen, acute expansion in the lymph node when exposed to antigen, contraction after an acute inflammatory response where the antigen -specific T -cell populations decrease, and then development of memory T -cells in case of any further exposure to antigen. Naï ve T-cells localized in the lymph node are either CD4 + or CD8+ T-cells and, on association with antigen presented in association with MHC class I or II receptors, are able to clonally expand into effector T -cells (either CD4+ helper T -cells or CD8+ cytotox ic T- cells).6 How these T -cells clonally expand is controlled by the cytokine milieu, immune environment, and secondary signals from the antigen pr esenting cell.11,12 After antigen clearance, the number of antigen specific CD4+ and CD8+ T-cells r apidly decline believed to be due to decreasing pro -inflammatory cytokines and decreased antigen stimulation.6 After contraction of the antigen -specific T -cell populations, a small population of memory T -cells remain and these T -cells are called central memory T -cells which can persist for decades despite the average lifespan of single memory cells being days to weeks, suggesting that these T -cells are self - renewing and can persist without antigen present.7 The factors that determine if a cell becomes an effector or a memory T -cell remain unclear. Central memory cells home to lymphoid tissue where they proliferate vigorously on re -encountering antigen and produce cytotoxic function slowly. Effector memory cells on the other hand proliferate less well, but produce cytokines rapidly and enter non- lymphoid tissue providing immediate protection with re -activation from memory.6 With a second exposure to antigen, either through booster vaccination or a second infection, th e secondary memory response produces higher numbers of memory T-cells.7 Therefore providing booster vaccines should reactivate an acute HER2 -specific anti -tumor immune response against disease that is present and provide further anti -tumor epitope spreading as well as increase the HER2 specific memory T -cell population against further tumor development. C. Rationale for booster vaccination in patients immunized with HER2 CTL pe ptide. Booster vaccinations have been examined previously in cancer vaccines and a single booster vaccination has the 6304p Protocol 118 04/06/2016 10 potential to mount an immune response as great if not greater than initial vaccination.13 The booster vaccination can also widen the spectrum of CD4+ and CD8+ T-cells against protein specific epitopes. A booster vaccine in HER2+ breast cancer patients has previously been shown to be safe a nd immunogenic using the HER2- specific E75 vaccine along with GMCSF adjuvant. The peptide -based HER2 vaccine E75 with GMCSF adjuvant was given as a single booster in 53 patients who had previously received the E75 vaccine by various schedules in previous clinical trials but had not received vaccination for over 6 months. The investigators found that residual CD8+ T-cell immunity existed in 94.4% of patients at 6 months after vaccination but at greater than 6 months after vaccination only 48 of patients ha d residual immunity (p=0.002). Furthermore, the median residual immunity remaining was very low at 0.70% (range 0 to 3.49%). The booster vaccine was well tolerated with only grade 1 and 2 toxicity primarily local injection site reactions and 85% of the patients without E75 specific immunity had achieved increased immunity after the booster vaccination.3 We propose to evaluate HER2 specific immunity and improved memory T -cell response generated using two boosters vaccinations of the HER2 peptide vaccine. Our group has completed a trial using 2 boosters with a DNA vaccine IGFBP2 in 8 ovarian cancer patients and these boosters were found to be safe and their immun ity is currently being evaluated. We therefore seek to evaluate a similar booster series with the HER2 peptide vaccine. D. Immune and metabolic activity measured by fluorodeoxyglucose positron emission tomography (FDG -PET) imaging . Changes in SUV qua ntitated by FDG -PET are a functional measure that is usually associated with disease progression, particularly when evaluating breast cancer bone metastases. In a study of 28 breast cancer patients with bone dominant disease, higher tumor FDG SUVs predict ed a shorter time to disease progression (p<0.006). 14 However there is an emerging role for PET imaging to evaluate patients for immunologic side effects caused by monoclonal checkpoint inhibitor therapy and for measuring immune flare after vaccination. 15,16 FLT -PET imaging of KLH antigen loaded dendritic cell (DC) vaccines in 3 patients with metastatic melanoma to the lymph node showed that only antigen loaded dendritic cells increased PET avidity in draining lymph nodes and remained positive up to 3 weeks after va ccination (Aarntzen PNAS 2011). In another study, FDG -PET scans done within 7 days after receiving the 6th vaccine of a DC vaccination series showed increased metabolic responses of index lesions (even though new lesions appeared simultaneously) and impro ved survival, indicative of an overall antitumor effect of DC vaccines. 17 The authors concluded that it is possible that infiltration of inflammato ry cells might lead to pseudo -progression in SUV; and thus, PET scans may provide a measure to evaluate the activity of immunotherapies over time. In our experience in a patient with HER2 -specific adoptive T -cells, a temporal increase in tumor FDG uptake at sites of metastases over a 48 hour period that resolved by 1 month follow up was associated with significant disease stabilization of 18 months. This suggests that acute increases in tumor metabolism as measured by FDG -PET may identify inflammation ind uced by activated T -cells and could potentially indicate a defined level of inflammation needed to mediate disease regression in HER2 adoptive T -cell studies (Stanton submitted ). Clinical symptoms of tumor flare, such as pain at metastatic sites, after immune modulation have been associated with beneficial clinical responses. After adoptive T -cell therapy for nasopharyngeal carcinoma or breast cancer pain at sites of disease and increase in tumor size temporally related to T -cell infusion was correlated w ith clinical response in specific lesions. 18,19 Therefore, we will compare baseline FDG -PET imaging prior t o the second booster to FDG -PET imaging at 48 hours after the second booster vaccine to evaluate if there is any evidence of acute increase in tumor metabolism suggestive of activated T -cell infiltration and increased inflammation. 3.