The development of Saccharomyces (yeast) vaccines for cancer therapy

用表达肿瘤抗原的重组酿酒酵母接种疫苗可打破免疫耐受并引发治疗性抗肿瘤反应。酿酒酵母（Saccharomyces cerevisiae）是一种非致病性酵母，以前曾被用作引发对外来抗原和肿瘤相关抗原的免疫反应的载体，并已被证明可以减轻小鼠的肿瘤负担。研究旨在确定用表达人CEA（酵母-CEA）的重组酿酒葡萄球菌构建体接种人癌胚抗原（CEA）转基因（CEA- tg）小鼠（CEA是一种自身抗原）是否能引起CEA特异性t细胞反应和抗肿瘤活性。将CEA-Tg小鼠接种酵母cea，并在一次和多次接种或每次接种多个部位后评估CD4+和CD8+ t细胞应答。在肺转移和皮下胰腺肿瘤模型中，通过肿瘤生长和总生存来确定抗肿瘤活性。这些研究表明重组酵母可以打破耐受性，并且(a)酵母- cea构建引起cea特异性CD4+和CD8+ t细胞反应；(b)每次接种后，反复给药酵母- cea引起抗原特异性t细胞反应增加；(c)在多个部位接种酵母cea疫苗比在单个部位接种相同剂量的疫苗诱导更大的t细胞应答；(d)在肺转移和s.c.胰腺肿瘤模型中，与模拟处理或对照酵母接种小鼠相比，接种酵母- cea的荷瘤小鼠显示肿瘤负荷减轻，总生存率提高。在CEA转基因（CEA- tg）小鼠中，用表达肿瘤相关抗原CEA的热灭活重组酵母接种疫苗可诱导CEA特异性免疫应答，减轻肿瘤负担，并延长总生存期。因此，这些研究形成了将重组酵母- cea和其他重组酵母构建物纳入癌症免疫治疗方案的基本原理。比较两种或两种以上疫苗平台的研究历来根据其诱导免疫反应的能力对每种平台进行评估，并可能得出结论，认为一种疫苗比其他疫苗更有效，从而建议为临床研究开发更有效的疫苗。另外，这些研究已经证明了由于抗原特异性t细胞群的扩增，多样化的启动和增强方案的优势。我们假设针对相同抗原的两种疫苗平台可能诱导共享且不同的抗原特异性t细胞群，并研究了两种不同疫苗同时使用的可能性。利用重组痘病毒和酵母疫苗，我们比较了这两个平台诱导的t细胞群体在血清细胞因子反应、t细胞基因表达、t细胞受体表型、抗原特异性细胞因子表达、t细胞贪婪度和t细胞抗原特异性肿瘤细胞裂解方面的差异。这些研究首次证明，用重组痘病毒平台（rV/F-CEA/TRICOM）或热灭活酵母疫苗平台（yeast- cea）接种可诱导具有共同和独特表型和功能特征的t细胞群。此外，抗原和载体都在诱导不同的t细胞群中发挥作用。我们证明，同时施用针对同一抗原的两种疫苗可诱导更多样化的t细胞群，从而增强抗肿瘤功效。这些研究为未来的临床研究提供了理论基础，研究针对单一抗原的疫苗平台同时施用以增强抗原特异性免疫反应。

Vaccination with a recombinant Saccharomyces cerevisiae expressing a tumor antigen breaks immune tolerance and elicits therapeutic antitumor responses. Saccharomyces cerevisiae, a nonpathogenic yeast, has been used previously as a vehicle to elicit immune responses to foreign antigens, and tumor-associated antigens, and has been shown to reduce tumor burden in mice. Studies were designed to determine if vaccination of human carcinoembryonic antigen (CEA)-transgenic (CEA-Tg) mice (where CEA is a self antigen) with a recombinant S. cerevisiae construct expressing human CEA (yeast-CEA) elicits CEA-specific T-cell responses and antitumor activity. CEA-Tg mice were vaccinated with yeast-CEA, and CD4+ and CD8+ T-cell responses were assessed after one and multiple administrations or vaccinations at multiple sites per administration. Antitumor activity was determined by tumor growth and overall survival in both pulmonary metastasis and subcutaneous (s.c.) pancreatic tumor models. These studies demonstrate that recombinant yeast can break tolerance and that (a) yeast-CEA constructs elicit both CEA-specific CD4+ and CD8+ T-cell responses; (b) repeated yeast-CEA administration causes increased antigen- specific T-cell responses after each vaccination; (c) vaccination with yeast-CEA at multiple sites induces a greater T-cell response than the same dose given at a single site; and (d) tumor-bearing mice vaccinated with yeast-CEA show a reduction in tumor burden and increased overall survival compared to mock-treated or control yeast-vaccinated mice in both pulmonary metastasis and s.c. pancreatic tumor models. Vaccination with a heat-killed recombinant yeast expressing the tumor-associated antigen CEA induces CEA-specific immune responses, reduces tumor burden, and extends overall survival in CEA-transgenic (CEA-Tg) mice. These studies thus form the rationale for the incorporation of recombinant yeast-CEA and other recombinant yeast constructs in cancer immunotherapy protocols.Studies comparing two or more vaccine platforms have historically evaluated each platform based on their ability to induce an immune response and may conclude that one vaccine is more efficacious than the other(s), leading to a recommendation for development of the more effective vaccine for clinical studies. Alternatively, these studies have documented the advantages of a diversified prime and boost regimen due to amplification of the antigen-specific T-cell population. We hypothesize here that two vaccine platforms targeting the same antigen might induce shared and distinct antigen-specific T-cell populations, and examined the possibility that two distinct vaccines could be used concomitantly. Using recombinant poxvirus and yeast vaccines, we compared the T-cell populations induced by these two platforms in terms of serum cytokine response, T-cell gene expression, T-cell receptor phenotype, antigen-specific cytokine expression, T-cell avidity, and T-cell antigen-specific tumor cell lysis. These studies demonstrated for the first time that vaccination with a recombinant poxvirus platform (rV/F-CEA/TRICOM) or a heat-killed yeast vaccine platform (yeast-CEA) elicits T-cell populations with both shared and unique phenotypic and functional characteristics. Furthermore, both the antigen and the vector play a role in the induction of distinct T-cell populations. We demonstrated that concurrent administration of two vaccines targeting the same antigen induces a more diverse T-cell population that leads to enhanced antitumor efficacy. These studies provide rationale for future clinical studies investigating concurrent administration of vaccine platforms targeting a single antigen to enhance antigen-specific immune response.