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打破免疫耐受并引起治疗性抗肿瘤反应。酿酒酵母是一种非致病酵母，以前曾被用作诱导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。本研究旨在确定用表达人癌胚抗原(CEA)的重组酿酒酵母构建物(CEA-CEA)免疫CEA转基因(CEA-TG)小鼠是否产生CEA特异性T细胞反应和抗肿瘤活性。用酵母CEA免疫CEA-TG小鼠，在一次和多次给药或每次多点接种后检测CD4+和CD8+T细胞应答。抗肿瘤活性取决于肺转移瘤和皮下转移瘤的生长和总存活率(S.C.)胰腺肿瘤模型。这些研究表明，重组酵母可打破耐受性，且(A)酵母-CEA构建体可诱导CEA特异的CD4+和CD8+T细胞反应；(B)每次接种后，反复给予酵母-CEA可导致更多的抗原特异性T细胞应答；(C)在多个部位接种酵母-CEA可比在单个部位给予相同剂量的疫苗诱导更大的T细胞应答；(D)在肺部转移和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CEA转基因(CEA-TG)小鼠，可诱导CEA特异性免疫反应，降低肿瘤负担，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整合到癌症免疫治疗方案中的理论基础。对两个或两个以上疫苗平台进行比较的研究历来根据每个平台诱导免疫反应的能力对其进行评估，并可能得出结论，即一种疫苗比另一种更有效(S)，从而建议开发更有效的疫苗用于临床研究。或者，这些研究已经证明了由于抗原特异性T细胞群体的放大，多样化的初始和增强方案的优势。在这里，我们假设两个针对同一抗原的疫苗平台可能会诱导共享的和不同的抗原特异性T细胞群体，并检查了两种不同的疫苗可以同时使用的可能性。我们使用重组痘病毒疫苗和酵母疫苗，从血清细胞因子应答、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细胞亲和力和T细胞抗原特异性肿瘤细胞杀伤等方面比较了两种平台诱导的T细胞群。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(YYEE-CEA)免疫可诱导出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，同时接种两种针对同一抗原的疫苗可以诱导更多样化的T细胞群，从而增强抗肿瘤效果。这些研究为未来的临床研究提供了理论基础，这些研究调查同时给予针对单一抗原的疫苗平台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.