AE37 peptide vaccination in prostate cancer: a 4-year immunological assessment updates on a phase I trial |
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Authors: | Sonia A Perez Eleftheria A Anastasopoulou Panagiotis Tzonis Cécile Gouttefangeas Hubert Kalbacher Michail Papamichail Constantin N Baxevanis |
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Institution: | 1. Cancer Immunology and Immunotherapy Center, Saint Savas Cancer Hospital, Building No. 2, 3rd Floor, 171 Alexandras Avenue, 11522, Athens, Greece 2. Department of Immunology, Institute for Cell Biology, Eberhard-Karls University, Tübingen, Germany 3. Interfaculty Institute of Biochemistry, Eberhard-Karls University, Tübingen, Germany
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Abstract: | In our recent phase I trial, we demonstrated that the AE37 vaccine is safe and induces HER-2/neu-specific immunity in a heterogeneous population of HER-2/neu + prostate cancer patients. Herein, we tested whether one AE37 boost can induce long-lasting immunological memory in these patients. Twenty-three patients from the phase I study received one AE37 boost 6-month post-primary vaccinations. Local/systemic toxicities were evaluated following the booster injection. Immunological responses were monitored 1-month (long-term booster; LTB) and 3-year (long-term immunity; LTI) post-booster by delayed-type hypersensitivity, IFN-γ ELISPOT and proliferation assays. Regulatory T cell (Treg) frequencies, plasma transforming growth factor-β (TGF-β) and indoleamine 2,3-deoxygenase (IDO) activity levels were also determined at the same time points. The AE37 booster was safe and well tolerated. Immunological monitoring revealed vaccine-specific long-term immunity in most of the evaluated patients during both LTB and LTI, although individual levels of immunity during LTI were decreased compared with those measured 3 years earlier during LTB. This was paralleled with increased Tregs, TGF-β levels and IDO activity. One AE37 booster generated long-term immunological memory in HER-2/neu + prostate cancer patients, which was detectable 3 years later, albeit with a tendency to decline. Boosted patients had favorable clinical outcome in terms of overall and/or metastasis-free survival compared with historical groups with similar clinical characteristics at diagnosis. We suggest that more boosters and/or concomitant disarming of suppressor circuits may be necessary to sustain immunological memory, and therefore, further studies to optimize the AE37 booster schedule are warranted. |
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