PD-1 Blockade and Neoantigen-Specific T Cell Immunity

 描述（由申请方提供）：检查点抑制剂通过调节共刺激（抗CTLA-4 Ab）或限制肿瘤微环境中活化T细胞的反应（抗PD- 1 Ab）阻断抑制T细胞免疫的调节途径。程序性细胞死亡-1（PD-1）/PD-L1轴代表了阻碍抗肿瘤免疫的适应性免疫抵抗机制。阻断PD-1/PD-L1通路的治疗在晚期皮肤黑色素瘤患者中显示出约30-40%的缓解率。大量证据表明肿瘤反应性T细胞是PD-1阻断的靶点，实际上，浸润性肿瘤边缘处增加的CD 8 + T细胞密度与临床活性密切相关。 T细胞识别肿瘤来源的错义突变，其被翻译为癌细胞在HLA分子上呈递的抗原决定簇（新抗原）内的单个氨基酸取代。有趣的是，对检查点抑制剂的反应与患者中较高的突变负荷相关。 涉及新抗原的黑素瘤和肺癌作为抗肿瘤免疫的靶。对参与抗肿瘤免疫的新抗原靶点的了解应该有助于更深入地了解PD-1阻断如何克服适应性免疫抵抗。我们先前报道了下一代测序、HLA结合预测算法和实验室测定允许鉴定候选黑色素瘤新抗原。重要的是，在树突状细胞（DC）疫苗中掺入这些候选物（作为突变肽）增加了转移性黑素瘤患者中新抗原特异性CD 8 + T细胞的抗原宽度和克隆多样性。 在拟议的概念验证临床试验中，患有晚期皮肤黑色素瘤的患者将接受个性化DC新抗原疫苗，随后接受抗PD-1治疗。将对血液和肿瘤微环境（TME）中的新抗原特异性T细胞群进行表征，以检验以下假设：抗PD-1治疗通过增强TME内的新抗原特异性CD 8+和CD 4 + T细胞免疫来抑制适应性免疫抵抗，从而导致更有效的肿瘤消退。该假设将在以下特定目的的实验中得到解决：（1）表征由包含HLA I类和HLA-DR限制性肿瘤特异性突变肽的个性化DC疫苗制剂引发的新抗原特异性T细胞免疫，以及（2）表征外周血和TME内抗PD-1抗体对疫苗诱导的新抗原特异性T细胞免疫的影响。这项研究将提供有关通过疫苗接种靶向其他HLA I类等位基因和HLA-DR限制性新抗原的可行性和临床获益的新信息，并提供对PD-1阻断增强TME抗肿瘤免疫的机制的更深入理解。这些发现应该为目前抗PD-1单药治疗失败的约60-70%患者的耐药机制提供信息。

 DESCRIPTION (provided by applicant): Checkpoint inhibitors block regulatory pathways that suppress T cell immunity either by modulating co- stimulation (anti-CTLA-4 Ab) or limiting responses of activated T cells in the tumor microenvironment (anti-PD- 1 Ab). The program cell death-1 (PD-1)/PD-L1 axis represents a mechanism of adaptive immune resistance that impedes anti-tumor immunity. Therapies that block the PD-1/PD-L1 pathway have shown ~30-40% response rates in patients with advanced cutaneous melanoma. Substantial evidence implicates tumor- reactive T cells as the targets of PD-1 blockade and, indeed, increased CD8+ T cell densities at the invasive tumor margin are strong correlates of clinical activity. T cells an recognize tumor-derived missense mutations translated as single amino acid substitutions within antigenic determinants (neoantigens) presented on HLA molecules by the cancer cell. Interestingly, response to checkpoint inhibitors correlates with higher mutational load in patients with melanoma and lung cancer implicating neoantigens as the targets of anti-tumor immunity. Knowledge of the neoantigen targets involved in anti-tumor immunity should foster a deeper understanding of how PD-1 blockade overcomes adaptive immune resistance. We previously reported that next generation sequencing, HLA binding prediction algorithms and laboratory assays allowed the identification of candidate melanoma neoantigens. Importantly incorporation of these candidates, as mutated peptides, in a dendritic cell (DC) vaccine increases the antigenic breadth and clonal diversity of neoantigen-specific CD8+ T cells in patients with metastatic melanoma. In the proposed proof-of-concept clinical trial, patients with advanced cutaneous melanoma will receive a personalized DC neoantigen vaccine sequentially followed by anti-PD-1 therapy. Characterization of neoantigen-specific T cell populations in blood and the tumor microenvironment (TME) will be performed to test the hypothesis that anti-PD-1 therapy inhibits adaptive immune resistance by enhancing neoantigen- specific CD8+ and CD4+ T cell immunity within the TME leading to more effective tumor regression. The hypothesis will be addressed in the experiments of the following Specific Aims: (1) To characterize neoantigen-specific T cell immunity elicited by a personalized DC vaccine formulation comprised of HLA class I and HLA-DR-restricted tumor-specific mutated peptides and (2) To characterize, in the peripheral blood and within the TME, the effect of anti-PD-1 antibody on vaccine-induced neoantigen-specific T cell immunity. This study will deliver new information regarding the feasibility and clinical benefit of targeting additional HLA class I alleles and HLA-DR restricted neoantigens by vaccination and provide a deeper understanding of the mechanisms by which PD-1 blockade enhances anti-tumor immunity in the TME. These findings should inform on the mechanisms of resistance for the ~60-70% of patients that currently fail anti-PD-1 monotherapy.