BACKGROUND Gene-modified tumor cell vaccines have shown efficacy in animal models of malignancy, including prostate cancer. Class I major histocompatibility complex (MHC) assembly and function in the cellular targets of such therapies is pivotal in determining the efficacy of specific cytokine-secreting tumor vaccines. PURPOSE To help guide development of genetically engineered vaccine therapy for human prostate cancer, potential immune resistance pathways were evaluated by analysis of class I MHC assembly in prostate cancer cells. METHOD Class I MHC assembly in metastasis-derived human prostate cancer cell lines (LNCaP, PPC-1, DU-145, PC-3, and TSU) and a normal prostate-derived cell line (TP-2) were characterized by phenotypic, molecular, and functional assays. Assembled class I MHC and antigen was measured by flow cytometry; mRNA levels of assembly components (class I MHC heavy chain, beta 2-microglobulin, and the antigen transporter gene product TAP-2) were determined; and antigen processing was measured with a chimeric reconstituted system using vaccinia vectors. Restoration of antigen processing was attempted by interferon gamma stimulation and by transfection with mouse class I MHC heavy-chain cDNA. RESULTS Assembled class I MHC was underexpressed in two (LNCaP and PPC-1) of five prostate cancer cell lines compared with normal prostate-derived controls. PPC-1 cells underexpressed TAP-2 mRNA despite abundant class I MHC and beta 2-microglobulin message. Induction of TAP-2 by interferon gamma indicated that coding sequences for TAP-2 message were present in PPC-1. Resistance to cytotoxic T lymphocytes (CTL) lysis showed a functional defect in antigen transport by PPC-1 cells; reversal of the molecular defect with interferon gamma led to restoration of functional antigen processing. In contrast, LNCaP cells had competent antigen transport but deficient class I MHC heavy-chain function despite abundant class I MHC RNA; though refractory to stimulation by interferon gamma, this defect responded to transfection of class I MHC heavy-chain cDNA. CONCLUSIONS Metastatic prostate cancer cells can escape T-cell recognition via divergent mechanisms of defective class I MHC assembly. The specific underexpression of TAP-2 gene product in PPC-1 cells contrasts with prior studies of TAP gene underexpression in lung cancer (which concurrently underexpressed class I MHC heavy chain) and provides evidence for a regulatory pathway controlling TAP-2 gene expression in human cancers that may not affect class I MHC heavy-chain expression. IMPLICATIONS In clinical application of gene therapy for prostate cancer, these findings provide a rationale for focusing on strategies that can circumvent sole reliance on class I MHC-mediated tumor cell recognition by CTL.

中文翻译：

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人类前列腺癌抗原加工缺陷的分子特征。


背景技术基因修饰的肿瘤细胞疫苗已在包括前列腺癌在内的恶性肿瘤动物模型中显示出功效。 I 类主要组织相容性复合体 (MHC) 在此类疗法的细胞靶标中的组装和功能对于确定特定细胞因子分泌肿瘤疫苗的功效至关重要。目的 为了帮助指导人类前列腺癌基因工程疫苗疗法的开发，通过分析前列腺癌细胞中的 I 类 MHC 组装来评估潜在的免疫抵抗途径。方法 转移源性人前列腺癌细胞系（LNCaP、PPC-1、DU-145、PC-3 和 TSU）和正常前列腺源性细胞系（TP-2）中 I 类 MHC 组装的特征在于表型、分子和功能测定。通过流式细胞术测量组装的I类MHC和抗原；测定组装成分（I类MHC重链、β2-微球蛋白和抗原转运蛋白基因产物TAP-2）的mRNA水平；并使用牛痘载体通过嵌合重构系统测量抗原加工。通过干扰素γ刺激和用小鼠I类MHC重链cDNA转染尝试恢复抗原加工。结果 与正常前列腺来源的对照相比，组装的 I 类 MHC 在五种前列腺癌细胞系中的两种（LNCaP 和 PPC-1）中表达不足。尽管 I 类 MHC 和 β2 微球蛋白信息丰富，但 PPC-1 细胞的 TAP-2 mRNA 表达不足。干扰素γ对TAP-2的诱导表明TAP-2信息的编码序列存在于PPC-1中。 对细胞毒性 T 淋巴细胞 (CTL) 裂解的抵抗表明 PPC-1 细胞的抗原转运功能存在缺陷；用干扰素γ逆转分子缺陷导致功能性抗原处理的恢复。相比之下，LNCaP 细胞具有充足的抗原转运能力，但缺乏 I 类 MHC 重链功能，尽管 I 类 MHC RNA 丰富；虽然这种缺陷对干扰素γ的刺激无效，但对I类MHC重链cDNA的转染有反应。结论 转移性前列腺癌细胞可以通过 I 类 MHC 组装缺陷的不同机制逃避 T 细胞识别。 PPC-1细胞中TAP-2基因产物的特异性低表达与肺癌中TAP基因低表达（同时I类MHC重链低表达）的先前研究形成对比，并为控制人类TAP-2基因表达的调控途径提供了证据可能不影响 I 类 MHC 重链表达的癌症。意义 在前列腺癌基因治疗的临床应用中，这些发现为关注可以避免单独依赖 CTL 的 I 类 MHC 介导的肿瘤细胞识别的策略提供了理论依据。