Antigen Specific T-Helper to Enhance Antitumor Immunity

越来越多的证据表明，CD4+辅助T细胞(Th)对于诱导有效的抗肿瘤反应至关重要。然而，细胞内的肿瘤抗原通常很难被处理并呈递给MHC-II类，限制了关键的CD4+Th细胞的激活。在我们最近的研究中，一个模型细胞内肿瘤抗原MAGE-3在基因上与一个前导序列和一个DC靶向域相连，以受体介导的内化DC激活和抗原递呈。表达sMAGE3-Fc融合蛋白(逆转录)的转导树突状细胞可诱导良好的抗原特异性CTL反应和抗肿瘤活性。在这项提案中，我们将扩大这项初步研究的长期目标，通过激活抗原特异性Th和CTL反应来开发更有效的肿瘤疫苗。我们推测，用来自同一抗原或逆转录原的Th表位免疫来激活CD4+Th，将为CTL提供同源帮助，因此，可能是提高现有肿瘤疫苗效力的有效手段。具体地说，我们将比较Retrogen和其他MHC II类靶向方法，并测试CD4+Th是否在Retgen增强小鼠抗肿瘤免疫反应中发挥关键作用。我们将利用逆转录病毒对II类抗原提呈的能力和人类白细胞抗原II类转基因小鼠的可用性，在MAGE-3和相关肿瘤抗原中鉴定新的II类限制性表位。此外，我们将产生人类白细胞抗原A2和DR3/4双转基因小鼠，以测试抗原特异性Th细胞的激活是否可以增强肿瘤疫苗的效力。我们还将在人源化小鼠中测试来自同一抗原的Th表位是否比非特异性Th刺激更有效，以及逆转录基因转导的DC是否可以比同时冲击Th和CTL表位的DC诱导更强大的抗肿瘤CTL和Th反应。这项拟议的研究将确定通过Th多肽或逆转录基因免疫激活抗原特异性Th是否可以增强CTL和抗肿瘤反应，以及逆转录基因转导的DC是否比Th和CTL表位或重组蛋白冲击的DC更有效地诱导抗肿瘤免疫反应。

Increasing evidence suggests that CD4+ helper T-cells (Th) are critical for the induction of an effective antitumor response. However, intracellular tumor antigens are usually difficult to be processed and presented to MHC class-II, limiting the activation of critical CD4+ Th cells. In our recent study, a model intracellular tumor antigen, MAGE-3, was genetically linked to a leader sequence and to a DC targeting domain for receptor- mediated internalization for DC activation and antigen presentation. Superior antigen-specific CTL responses and antitumor activity were induced by transduced DCs expressing the sMAGE3-Fc fusion protein (retrogen). In this proposal, we will extend this preliminary study with a long-term goal of developing more potent tumor vaccines by activating both antigen-specific Th and CTL responses. We hypothesize that activation of CD4+ Th by immunization with Th epitopes derived from the same antigen or retrogens will provide cognate help to CTLs and, thus, may be an effective means to enhance the potency of current tumor vaccines. Specifically, we will compare retrogen with other MHC class II targeting approaches and test if CD4+ Th plays a critical role in the enhancement of anti-tumor immune responses by retrogen in mice. We will identify novel class-II-restricted epitopes in MAGE-3 and related tumor antigens by utilizing the ability of retrogens to class II antigen presentation and the availability of HLA class-II transgenic mice. Furthermore, we will generate HLA-A2 and DR3/4 double transgenic mice to test if activation of antigen-specific Th cells can enhance the potency of tumor vaccines. We will also test if Th epitopes from the same antigen are more potent than nonspecific Th stimuli and if retrogen- transduced DC can induce more potent antitumor CTL and Th responses than DC pulsed with both Th and CTL epitopes in humanized mice. This proposed study will determine if activation of antigen-specific Th via immunization with either Th peptides or retrogen can enhance CTL and antitumor responses and if retrogen-transduced DCs are more potent than DCs pulsed with both Th and CTL epitopes or recombinant proteins to induce antitumor immune responses.