Costimulatory protein B7-1 enhances the cytotoxic T cell response and antibody response to hepatitis B surface antigen.

There is a need for more effective therapy for chronic virus infections. A principle natural mechanism for elimination of virus-infected host cells is activation of viral antigen-specific cytotoxic T lymphocytes (CTL). In an effort to develop methods of inducing virus-specific CTL responses that might be utilized in therapy of virus infections, we have investigated the effect of B7, a costimulatory factor for T-cell activation. In this study we show that delivery of genes encoding human B7-1 and a viral antigen in the same recombinant viral vector to cells of mice induces a greater viral antigen-specific CTL response than does similar delivery of the viral antigen gene alone. Two recombinant adenovirus vectors were constructed with the foreign genes inserted in the early region 3. One of them (Ad1312) directed expression of the surface antigen gene of hepatitis B virus (HBS); the other (Ad1310) directed coexpression of HBS and human B7-1 (CD80) by means of an internal ribosomal entry site placed between the two coding sequences. When inoculated into BALB/c mice, both vectors induced a viral surface antigen-specific CTL response. The response induced by Ad1310 was stronger than that by Adl312 as measured by a chromium release assay for CTL activity and limiting dilution analysis for CTL precursor frequency, indicating that the B7-1 gene co-delivered with the HBS gene had an enhancing effect on the CTL response against surface antigen. Ad1310 also induced a higher titer of antibody against surface antigen than did Ad1312. This result suggests that expression of a costimulatory protein and a viral antigen in the same cells in vivo induces stronger immune responses than expression of the antigen alone. This could be a novel strategy for development of both preventive and therapeutic vaccines against infectious agents.

慢性病毒感染领域亟需更为高效的治疗手段。机体清除病毒感染宿主细胞的核心天然免疫机制，是激活病毒抗原特异性细胞毒性T淋巴细胞（cytotoxic T lymphocytes, CTL）。为研发可应用于病毒感染治疗的病毒特异性CTL应答诱导方法，本研究针对T细胞活化共刺激因子B7的作用效果展开了探究。本研究证实：将编码人B7-1与病毒抗原的基因通过同一重组病毒载体递送至小鼠细胞后，其所诱导的病毒抗原特异性CTL应答强度，显著高于仅递送病毒抗原基因的实验组。本研究构建了两种重组腺病毒载体，外源基因均插入于载体的早期区域3（E3区）。其中一株载体（Ad1312）用于表达乙型肝炎病毒表面抗原基因（HBS）；另一株载体（Ad1310）则通过置于两个编码序列之间的内部核糖体进入位点（internal ribosomal entry site），实现HBS与人B7-1（CD80）的共表达。将两种载体接种至BALB/c小鼠体内后，二者均可诱导病毒表面抗原特异性CTL应答。通过CTL活性铬释放实验及CTL前体频率极限稀释分析法检测结果显示，Ad1310诱导的应答强度显著高于Adl312，这表明与HBS基因共递送的B7-1基因，可增强针对病毒表面抗原的CTL应答。相较于Ad1312，Ad1310还可诱导更高滴度的病毒表面抗原特异性抗体。该研究结果表明：在体内同一细胞中共表达共刺激蛋白与病毒抗原，所引发的免疫应答强度高于仅单独表达病毒抗原的情况。这一发现可为抗感染性病原体的预防性及治疗性疫苗研发提供全新策略。