Interferon-gamma limits the effectiveness of peptide vaccines for cancer

描述（由申请人提供）：以治疗性疫苗或过继性T细胞疗法的形式开发有效的基于T细胞的癌症免疫疗法仍然是肿瘤免疫学领域的主要研究领域之一。本实验室最近设计了一种新的免疫策略（TriVax），由对应于CD 8 T细胞表位的合成肽、Poly-IC佐剂（Toll样受体激动剂）和免疫共刺激抗体组成。使用恶性黑色素瘤的小鼠模型，我们观察到TriVax能够诱导大的抗原特异性、肿瘤反应性CD 8 T细胞应答，其可以达到总CD 8 T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，我们观察到在不存在干扰素-γ（IFNγ）的情况下，抗肿瘤效果（肿瘤排斥和生存率增加）明显更好。这些观察结果是自相矛盾的，因为IFNγ长期以来被认为是提供强抗肿瘤作用的效应细胞因子。进一步的体外实验表明，当用IFNγ处理肿瘤细胞时，疫苗产生的CD 8 T细胞能够较不有效地识别B16黑素瘤细胞，这支持了我们的体内抗肿瘤观察结果。这些结果令人困惑，因为用IFNγ处理B16黑素瘤细胞显著增加了MHC-I分子的表达，这应该增加而不是降低肿瘤的T细胞抗原性。我们假设，在用IFNγ处理后，由T细胞识别的特异性肽/MHC-I复合物（同源MHC-I）没有增加到与不相关肽/MHC-I（非同源）复合物相同的程度，从而降低总体特异性表位密度并导致肿瘤细胞抗原性的降低。此外，我们假设肿瘤细胞上过量的非同源MHC-I通过降低CD 8分子将Lck淋巴细胞特异性酪氨酸激酶募集到免疫突触中的能力来阻止T细胞的完全活化。此外，肿瘤暴露于IFNγ会增强CD 8 T细胞抑制性受体（PD 1和LAG 3）配体的表达，这也不利于TriVax免疫疗法的治疗反应。本申请的两个主要目的是阐明IFNγ对CD 8 T细胞免疫疗法的治疗效果产生负面影响的机制，并研究克服这些障碍的方法，以便为已确定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，我们建议研究以下具体目标：1）研究IFNγ降低黑素瘤对CD 8 T淋巴细胞的抗原性的机制; 2）评估IFNγ诱导肿瘤细胞上PD 1和LAG 3配体表达对TriVax抗黑素瘤疗效的重要性。3)探讨通过克服IFNγ的负作用来增强TriVax治疗效果的几种策略; 4）评价TriVax在小鼠乳腺癌模型中使用IFNγ的负作用。这些研究的结果将有助于阐明IFNγ在基于T细胞的肿瘤免疫治疗中似乎发挥的双重作用，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.