Breaking tolerance to mEGP self-antigen

描述（由申请人提供）：大多数肿瘤抗原（Ag）也在正常组织中表达，因此在荷瘤宿主中诱导免疫耐受。然而，这些自身蛋白是可用于主动特异性免疫治疗的主要靶点。这些疗法需要在动物模型中开发，以模仿癌症患者的情况。人胃肠道癌相关Ag GA733 （EpCAM）已成为肿瘤患者被动和主动免疫治疗的合适靶点。在正常和肿瘤组织中表达人Ag的同源物——小鼠上皮糖蛋白（mEGP）的小鼠提供了针对GA733 Ag主动特异性免疫治疗的相关动物模型。我们的主要目标是确定在这种肿瘤模型系统中显著且可重复地抑制已建立小鼠结肠癌细胞生长的疫苗。我们的主要假设是mEGP的模拟物，由于与mEGP相似，但不完全相同，将有效地免疫小鼠并诱导已建立的mEGP阳性结肠癌的消退。具体来说，我们将：1)验证mEGP模拟物诱导对已建立的皮下肿瘤和内脏转移的保护性免疫的假设。这包括：a) mEGP模拟物的产生和选择（抗独特型抗体[Ab2]， Ab2片段，从Ab2的VH和VL区衍生的肽或短基因，从合成文库衍生的肽并模仿抗mEGP单克隆抗体识别的表位，mEGP CTL表位的肽和短基因）；b)评估疫苗在小鼠治疗环境中抑制CT26-mEGP结肠癌细胞皮下和内脏转移性生长的能力。2)确定mEGP模拟物抑制肿瘤生长的机制。这包括：a)评估mEGP模拟物免疫后肿瘤消退小鼠的体液免疫反应（细胞毒性抗体）和细胞免疫反应（增殖、细胞毒性和延迟型超敏淋巴细胞）；b)确定抗体、CD8+或CD4+ T淋巴细胞、记忆淋巴细胞和表位扩散在肿瘤生长抑制中的直接作用。本研究为结直肠癌患者接种GA733抗原疫苗提供了依据。

DESCRIPTION (provided by applicant): Most tumor antigens (Ag) are also expressed by normal tissues and therefore induce immunological tolerance in the tumor-bearing host. Yet, these self proteins are major targets available for active specific immunotherapies. These therapies need to be developed in animal models that mimic the conditions in cancer patients. The human gastrointestinal carcinoma-associated Ag GA733 (EpCAM) has been a suitable target for passive and active immunotherapy of these tumors in cancer patients. Mice expressing the homologue of the human Ag, murine epithelial glycoprotein (mEGP), on normal and tumor tissues provide a relevant animal model of active specific immunotherapy against the GA733 Ag. Our major goal is to define vaccines that significantly and reproducibly inhibit growth of established mouse colon carcinoma cells in this tumor model system. Our major hypothesis is that mimics of mEGP, by virtue of being similar, but not identical to mEGP will effectively immunize mice and induce regression of established, mEGP-positive colon carcinomas. Specifically we will: 1) Test the hypothesis that mEGP mimics induce protective immunity against established, subcutaneous tumors and visceral metastasis. This involves: a) Generation and selection of mEGP mimics (anti-idiotypic antibodies [Ab2], Ab2 fragments, peptides or minigenes derived from the VH and VL regions of Ab2, peptides derived from synthetic libraries and mimicking the epitope recognized by anti-mEGP monoclonal antibody, and peptides and minigenes of mEGP CTL epitopes); and b) Evaluation of vaccines for their capacity to inhibit subcutaneous and visceral, metastatic growth of CT26-mEGP colon carcinoma cells in the therapeutic setting in mice. 2) Determine the mechanism of tumor growth inhibition by mEGP mimics. This involves: a) Evaluation of humoral immune responses (cytotoxic antibodies) and cellular immune responses (proliferative, cytotoxic and delayed-type hypersensitive lymphocytes in mice with regressing tumors after immunization with mEGP mimics; b) Determination of the direct role in tumor growth inhibition of antibodies, CD8+ or CD4+ T lymphocytes, memory lymphocytes, and epitope spreading. The proposed studies provide the basis for vaccinations of colorectal cancer patients against the GA733 Ag.