Interferon-gamma limits the effectiveness of peptide vaccines for cancer

描述(申请人提供)：开发有效的基于T细胞的癌症免疫疗法，无论是治疗性疫苗的形式还是过继T细胞疗法，仍然是肿瘤免疫学领域的主要研究领域之一。我们实验室最近设计了一种新的免疫策略(TriVax)，由CD8T细胞表位的合成肽、Poly-IC佐剂(一种Toll样受体激动剂)和免疫共刺激抗体组成。在小鼠恶性黑色素瘤模型中，我们观察到TriVax能够诱导大量抗原特异性的肿瘤反应性CD8T细胞反应，可达到总CD8T细胞的50%以上。在评估TriVax对已建立的B16黑色素瘤的治疗效果时，我们观察到，在没有干扰素-γ的情况下，抗肿瘤效果(肿瘤排斥反应和增加生存期)显著更好。这些观察结果是矛盾的，因为干扰素γ长期以来一直被认为是一种提供强大抗肿瘤作用的效应细胞因子。进一步的体外实验表明，疫苗产生的CD8T细胞在干扰素γ处理B16黑色素瘤细胞时识别B16黑色素瘤细胞的效率较低，支持我们的体内抗肿瘤观察。这些结果令人费解，因为用干扰素γ处理B16黑色素瘤细胞后，MHC-I分子的表达显著增加，这应该是增强而不是降低肿瘤的T细胞抗原性。我们推测，经干扰素γ处理后，T细胞识别的特异性多肽/MHC-I复合体(同源MHC-I)没有增加到与无关肽/MHC-I(非同源)复合体相同的程度，从而降低了肿瘤细胞的整体特异性表位密度，导致肿瘤细胞的抗原性降低。此外，我们假设肿瘤细胞上过多的非同源MHC-I通过降低CD8分子将LCK淋巴细胞特异性酪氨酸激酶招募到免疫突触中的能力来阻止T细胞的充分激活。此外，肿瘤暴露于干扰素γ后，CD8T细胞抑制受体的配体(PD1和LAG3)的表达增加，这也不利于对TriVax免疫治疗的治疗反应。这项应用的两个主要目的是阐明干扰素γ对CD8T细胞免疫治疗效果产生负面影响的机制，并探索克服这些障碍的方法，以便为已有的恶性肿瘤开发更有效的治疗策略。为了验证我们的假设并实现这些目标，我们建议研究以下特定目标：1)探讨干扰素γ降低黑色素瘤对CD8T淋巴细胞的抗原性的机制；2)评估干扰素γ诱导的肿瘤细胞上PD1和LAG3配体的表达在TriVax抗黑色素瘤疗效中的重要性。3)探索通过克服干扰素γ的负效应来提高TriVax治疗效果的策略；4)用TriVAX评价干扰素γ在小鼠乳腺癌模型中的负效应。这些研究的结果将有助于阐明干扰素γ在基于T细胞的肿瘤免疫治疗中似乎扮演的双重角色，并将使我们能够为已建立的癌症设计更有效的治疗策略。

DESCRIPTION (provided by applicant): The development of effective T cell based immunotherapy for cancer, either in the form of a therapeutic vaccine or as adoptive T cell therapy continues to be one of the major areas of research in the field of tumor immunology. Our laboratory has recently designed a novel immunization strategy (TriVax), consisting of synthetic peptides corresponding to CD8 T cell epitopes, Poly-IC adjuvant (a Toll-like receptor agonist) and immune costimulatory antibodies. Using a mouse model of malignant melanoma we observed that TriVax was capable of inducing large antigen-specific, tumor reactive CD8 T cell responses that can amount to more than 50% of the total CD8 T cells. When evaluating the therapeutic effects of TriVax against established B16 melanomas, we observed that the anti-tumor effects (tumor rejection and increased survival) were significantly better in the absence of interferon-gamma (IFNγ). These observations are paradoxical since IFNγ has long been considered to be an effector cytokine that provides strong anti-tumor effects. Further in vitro experiments have revealed that vaccine generated CD8 T cells were able to recognize B16 melanoma cells less effectively when the tumor cells were treated with IFNγ supporting our in vivo anti-tumor observations. These results are puzzling since treatment of B16 melanoma cells with IFNγ increases significantly the expression of MHC-I molecules, which should augment, not decrease the tumor's T cell antigenicity. We hypothesize that the specific peptide/MHC-I complexes (cognate MHC-I) recognized by the T cells are not increased to the same extent as the irrelevant peptide/MHC-I (non-cognate) complexes after treatment with IFNγ, reducing the overall specific epitope density and leading to a decrease in the antigenicity of tumor cells. In addition, we hypothesize that excess of non-cognate MHC-I on tumor cells prevents the full activation of the T cells by reducing the ability of the CD8 molecules to recruit the Lck lymphocyte-specific tyrosine kinase into the immunological synapse. Furthermore, exposure of tumors to IFNγ enhances the expression of ligands for CD8 T cell inhibitory receptors (PD1 and LAG3), which are also detrimental for the therapeutic response to TriVax immunotherapy. The two main objectives of this application will be to clarify the mechanisms by which IFNγ exerts a negative effect in the therapeutic efficacy of CD8 T cell immunotherapy and to investigate means to overcome these obstacles in order to develop more effective therapeutic strategies for established malignancies. To test our hypotheses and fulfill these objectives we propose to study the following specific aims: 1) To investigate the mechanisms by which IFNγ reduces the antigenicity of melanoma for CD8 T lymphocytes; 2) To assess the importance of the IFNγ induced expression of PD1 and LAG3 ligands on tumor cells for the therapeutic efficacy of TriVax against melanoma. 3) To explore several strategies to enhance the therapeutic efficacy of TriVax by overcoming the negative effects of IFNγ; and 4) To evaluate the negative effects of IFNγ using TriVax in a mouse model of breast cancer. The results of these studies will help clarify the dual role that IFNγ appears to play in T cell based tumor immunotherapy and will allow us to design more effective therapeutic strategies for established cancers.