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。在另一项研究中，重组酿酒酵母（酵母-CEA）被证明是小鼠树突状细胞（DC）的有效激活剂。重组酿酒酵母（酵母）代表了在癌症或传染病的疫苗免疫治疗方案中递送抗原的独特和有吸引力的载体，因为它已被证明是非常安全的，并且可以多次给予宿主。在这里报道的研究中，我们描述了重组酵母对小鼠未成熟DC的治疗效果。研究了表达人CEA作为模型抗原的酵母。小鼠皮下注射酵母癌胚抗原导致引流淋巴结中主要组织相容性复合体（MHC）II类+细胞和总抗原呈递细胞迅速增加。用酵母CEA处理后，DC迅速升高MHC I类和II类、许多共刺激分子和其他DC成熟标志物，并分泌一系列I型炎性细胞因子。基因表达阵列还揭示了许多细胞因子和趋化因子mRNA的快速上调，以及参与信号转导和抗原摄取的基因。功能研究表明，增强的同种异体特异性反应性的树突状细胞与酵母癌胚抗原或控制酵母治疗。此外，用酵母CEA处理DC导致CEA特异性CD 8 + T细胞在体外以MHC限制性方式特异性活化。最后，用酵母-CEA接种CEA-Tg小鼠在体内引起抗原特异性CD 4（+）和CD 8+免疫应答。因此，这些发现共同构成了在癌症或传染病的疫苗接种方案中使用重组酵母的科学原理。

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. In another study, recombinant Saccharomyces cerevisiae (yeast-CEA) was shown to be a potent activator of murine dendritic cells (DCs). Recombinant Saccharomyces cerevisiae (yeast) represents a unique and attractive vehicle to deliver antigens in vaccine immunotherapy protocols for cancer or infectious disease, in that it has been shown to be extremely safe and can be administered multiple times to hosts. In the studies reported here, we describe the effects of treatment with recombinant yeast on murine immature DCs. Yeast expressing human CEA as a model antigen was studied. Injection of mice subcutaneously with yeast-CEA resulted in rapid increases in major histocompatibility complex (MHC) class II+ cells and total antigen-presenting cells in draining lymph nodes. Post-treatment with yeast-CEA, DCs rapidly elevated both MHC class I and class II, numerous costimulatory molecules and other DC maturation markers, and secreted a range of Type I inflammatory cytokines. Gene expression arrays also revealed the rapid up-regulation of numerous cytokine and chemokine mRNAs, as well as genes involved in signal transduction and antigen uptake. Functional studies demonstrated enhanced allospecific reactivity of DCs following treatment with yeast-CEA or control yeast. Additionally, treatment of DCs with yeast-CEA resulted in specific activation of CEA-specific CD8+ T cells in an MHC-restricted manner in vitro. Lastly, vaccination of CEA-Tg mice with yeast-CEA elicited antigen-specific CD4(+) and CD8+ immune responses in vivo. Thus, these findings taken together form a scientific rationale for the use of recombinant yeast in vaccination protocols for cancer or infectious diseases.