The development of Saccharomyces (yeast) vaccines for cancer therapy

用表达肿瘤抗原的重组酿酒酵母疫苗接种打破免疫耐受并增强治疗性抗肿瘤应答。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源抗原和肿瘤相关抗原的免疫反应的载体，并已被证明可降低小鼠的肿瘤负荷。设计研究以确定用重组S.表达人CEA（酵母-CEA）的酿酒酵母构建体增强CEA特异性T细胞应答和抗肿瘤活性。CEA-Tg小鼠用酵母-CEA接种疫苗，并且在一次和多次施用或每次施用在多个部位接种疫苗后评估⑶ 4+和⑶ 8 + T细胞应答。通过肺转移和皮下（s.c.）胰腺肿瘤模型。这些研究表明重组酵母可以破坏耐受性，并且（a）酵母-CEA构建体引发CEA特异性的CD 4+和CD 8 + T细胞应答;（B）在每次接种后重复施用酵母-CEA引起抗原特异性T细胞应答增加;（c）在多个位点接种酵母-CEA比在单个位点给予相同剂量诱导更大的T细胞应答;和（d）与模拟处理或对照酵母疫苗接种的小鼠相比，用酵母-CEA疫苗接种的荷瘤小鼠在肺转移和s.c.胰腺肿瘤模型。用表达肿瘤相关抗原CEA的热灭活重组酵母接种疫苗诱导CEA特异性免疫应答，降低肿瘤负荷，并延长CEA转基因（CEA-Tg）小鼠的总生存期。因此，这些研究形成了在癌症免疫治疗方案中掺入重组酵母-CEA和其他重组酵母构建体的基本原理。比较两种或更多种疫苗平台的研究历来根据其诱导免疫应答的能力对每种平台进行评价，并可能得出一种疫苗比其他疫苗更有效的结论，从而建议开发更有效的疫苗用于临床研究。或者，这些研究已经记录了由于抗原特异性T细胞群的扩增而导致的多样化初免和加强方案的优点。我们假设两种靶向相同抗原的疫苗平台可能诱导共享和不同的抗原特异性T细胞群，并检查了两种不同疫苗可以同时使用的可能性。 使用重组痘病毒和酵母疫苗，我们比较了由这两个平台诱导的T细胞群体的血清细胞因子应答、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细胞亲合力和T细胞抗原特异性肿瘤细胞溶解。 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（酵母-CEA）接种可激发具有共同和独特的表型和功能特征的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。 我们证明了同时施用两种靶向相同抗原的疫苗诱导更多样化的T细胞群，从而增强抗肿瘤功效。这些研究为将来的临床研究提供了理论基础，这些临床研究旨在研究靶向单一抗原的疫苗平台的同时给药，以增强抗原特异性免疫应答。

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.