Sanda M G, Restifo N P, Walsh J C, Kawakami Y, Nelson W G, Pardoll D M, Simons J W
Brady Urological Institute and Oncology Center, Johns Hopkins School of Medicine, Baltimore, MD, USA.
J Natl Cancer Inst. 1995 Feb 15;87(4):280-5. doi: 10.1093/jnci/87.4.280.
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.
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.
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.
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.
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.
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.
基因修饰的肿瘤细胞疫苗在包括前列腺癌在内的恶性肿瘤动物模型中已显示出疗效。I类主要组织相容性复合体（MHC）在这类治疗的细胞靶点中的组装和功能对于确定特定细胞因子分泌型肿瘤疫苗的疗效至关重要。
为了帮助指导人类前列腺癌基因工程疫苗治疗的开发，通过分析前列腺癌细胞中I类MHC组装情况来评估潜在的免疫抵抗途径。
通过表型、分子和功能检测对转移来源的人前列腺癌细胞系（LNCaP、PPC-1、DU-145、PC-3和TSU）以及正常前列腺来源的细胞系（TP-2）中的I类MHC组装进行表征。通过流式细胞术检测组装的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基因产物TAP-2）的mRNA水平；并使用痘苗载体的嵌合重组系统测量抗原加工情况。尝试通过γ干扰素刺激和用小鼠I类MHC重链cDNA转染来恢复抗原加工。
与正常前列腺来源的对照相比，在五个前列腺癌细胞系中的两个（LNCaP和PPC-1）中，组装的I类MHC表达不足。尽管有丰富的I类MHC和β2-微球蛋白信息，但PPC-1细胞中TAP-2 mRNA表达不足。γ干扰素诱导TAP-2表明PPC-1中存在TAP-2信息的编码序列。对细胞毒性T淋巴细胞（CTL）裂解的抗性表明PPC-1细胞在抗原转运方面存在功能缺陷；γ干扰素逆转分子缺陷导致功能性抗原加工的恢复。相比之下，LNCaP细胞具有有效的抗原转运，但尽管有丰富的I类MHC RNA，I类MHC重链功能却存在缺陷；尽管对γ干扰素刺激无反应，但这种缺陷对I类MHC重链cDNA转染有反应。
转移性前列腺癌细胞可通过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先前关于肺癌中TAP基因低表达的研究（同时I类MHC重链低表达）形成对比，并为控制人类癌症中TAP-2基因表达的调节途径提供了证据，该途径可能不影响I类MHC重链表达。
在前列腺癌基因治疗的临床应用中，这些发现为专注于能够规避单纯依赖I类MHC介导的CTL对肿瘤细胞识别的策略提供了理论依据。
