错配修复分子MLH1缺失对大肠癌细胞免疫原性的影响及免疫治疗

Mismatch repair（MMR） deficiency plays an important role in the colorectal cancer development. Recent study had proved colorectal cancer with MMR deficiency was tolerance to the 5-Fu based chemotherapy. However, in our randomized phase II clinical trial of dendritic cell (DC) therapeutic vaccine in the treatment of metastatic colorectal cancer(CRC), patients with high microsatellite instability (MSI-H),which is close related to MMR, achieved better response to the DC vaccination. The immunological mechanism was unclear. In this study, we establish the MLH1(one of the most important MMR molecules) deficiency or normal expression CRC model, to look for the different expression molecules by protenomics and DNA chip technology between them，identify the key molecules which would be a novel tumor antigen to induce stronger specific cellular immunity against cancer and prove the CRC with MMR deficiency would be sensitive to DC vaccination. Finally, explore a novel strategy to the treatment of patients with MMR deficiency CRC to enhance the clinical response beyond the 5-Fu based chemotherapy.

错配修复(MMR)功能的缺失是导致大肠癌的发生发展的一个重要原因，目前证实MMR缺失的大肠癌患者对以5-氟尿嘧啶（5-Fu）为基础的化疗方案耐受。我们在树突状细胞(DC)疫苗治疗转移性大肠癌的II期临床研究中发现，与MMR缺失密切相关的高微卫星不稳定(MSI-H)患者显示出对DC免疫治疗更好的疗效，其可能的免疫学机制尚不明了。本课题拟通过建立重要的MMR分子MLH1缺失/MLH1表达模型，通过蛋白组学技术和基因芯片技术筛选并验证MLH1缺失后细胞内基因的突变造成的异常表达分子，探讨这些差异表达的分子是否可以作为新的抗原或靶点参与机体抗肿瘤免疫应答，研究MLH1缺失及导致的差异表达分子其对化疗和DC免疫治疗疗效的影响，探讨MMR缺失患者是否更适合DC免疫治疗及其机制，为提高MMR缺失患者的临床治疗疗效，优化DC免疫治疗临床方案提供理论基础。

本研究是对错配修复分子MLH1缺失对大肠癌细胞免疫原性的影响及免疫治疗的探究。研究表明，MLH1的缺失会引起肿瘤细胞差异分子的产生，其中DDK4是MLH1下游重要的调控分子。细胞模型中证明，MLH1缺失后会导致其下游DKK4的表达上调，并可能通过抑制Wnt/β-catenin信号通路对5-Fu化疗产生抵抗。临床回顾性研究证明，MLH1和DKK4的表达与TNM分型密切相关，在多数临床患者的肿瘤内MLH1缺失会伴随DKK4的表达。MLH1缺失伴随DKK4表达阳性与以5-Fu为基础化疗治疗CRC患者更低的OS密切相关，MLH1缺失或DKK4表达阳性患者预后较差。MLH1缺失的患者中，DKK4表达阳性患者对化疗的疗效较差。本研究结果为5-Fu化疗的耐药机制提供了新的理论基础和证据，也为临床治疗方案的优化和肿瘤的免疫治疗提供了新的思路和方法。