PSGL-1, a New Player in the Immune Checkpoint Landscape

项目总结 该项目的目标是确定靶向选择素配体PSGL-1(P-选择素糖蛋白-1)， 代表了一种新的策略来改善免疫介导的黑色素瘤的破坏，可能通过缓解 免疫抑制的多个方面，这是根除肿瘤必须实现的关键因素。PSGL-1 IS 仅由造血细胞表达，是选择素家族高度保守的配体。 黏附分子P、E和L调节细胞迁移，但也结合其他配体，包括 人类和小鼠体内的趋化因子和细胞外基质成分。我们对慢性病毒的研究 感染表明PSGL-1是一种先前未知的T细胞反应的负调控因子 还可以防止对黑色素瘤的有效抗肿瘤反应。在慢性病毒感染模型中 LCMV变种、Clone 13、PSGL-1缺陷小鼠完全阻止慢性化的建立。这些 小鼠产生了CD8和CD4效应T细胞，这些T细胞具有多功能，但未能形成 衰竭的特征是大量抑制受体的表达，包括PD-1，LAG3，CD160， BTLA和TIM3。PSGL-1缺陷的T细胞提高了存活率，导致显著维持 更多的功能效应器T细胞。PSGL-1在耗尽的CD8 T细胞上的机械连接 抑制TCR信号转导，并与PD-1上调有关。在两个黑色素瘤癌症模型中，T细胞 也被抑制，我们发现PSGL-1在肿瘤中的所有造血细胞上都高表达 微环境(TME)。PSGL-1缺陷小鼠显示出对黑色素瘤生长的显著控制，即 再加上更多的肿瘤浸润性，表达表达的多功能CD8和CD4T细胞(TIL) 抑制性受体水平较低。由于靶向PSGL-1导致多重抑制物下调 受体并促进有效的抗肿瘤反应，阻断这一点可能有显著的好处 受体与抑制性受体的组合相比，特别是当毒性较小或不大于 目前的检查站封锁。此外，阻断PSGL-1可能会限制免疫力 对其他疗法无反应或反应不佳的患者的抑制。对于此项目 我们已经建立了PSGL-1条件性KO(PSGL-1FL/FL)小鼠来询问该受体在 黑色素瘤TME中淋巴样和髓样细胞的细胞和转录组分析。我们将使用 用基因验证的药理学方法确定阻断PSGL-1功能是否可以控制 黑色素瘤通过调节TIL生长。这些研究将为免疫调节提供新的见解。 PSGL-1的反应以及该受体在癌症T细胞功能障碍中的作用机制。 最重要的是，这些研究将确定PSGL1是否为癌症免疫治疗的新靶点。

PROJECT SUMMARY The goal of this project is to determine if targeting the selectin-ligand, PSGL-1 (P-selectin glycoprotein-1), represents a novel strategy to improve immune-mediated destruction of melanoma potentially by relieving multiple aspects of immunosuppression, a key element that must be achieved for tumor eradication. PSGL-1 is expressed exclusively by hematopoietic cells, and is a highly conserved ligand for the selectin family of adhesion molecules, P, E, and L, that regulate cell migration, but also binds other ligands that include chemokines and extracellular matrix components in both humans and mice. Our studies of chronic viral infections indicate that PSGL-1 is a previously unrecognized negative regulator of T cell responses that can also prevent effective anti-tumor responses to melanoma. In a chronic viral infection model with the LCMV-variant, Clone 13, PSGL-1-deficient mice completely prevent the establishment of chronicity. These mice developed CD8+ and CD4+ effector T cells that were multifunctional and failed to develop the hallmarks of exhaustion characterized by expression of multitude of inhibitory receptors including, PD-1, Lag3, CD160, BTLA and Tim3. PSGL-1-deficient T cells had improved survival leading to maintenance of a significantly greater number of functional effector T cells. Mechanistically, ligation of PSGL-1 on exhausted CD8 T cells inhibited TCR signaling and was linked to upregulation of PD-1. In two melanoma cancer models where T cells are also suppressed, we found that PSGL-1 was highly expressed on all hematopoietic cells in the tumor microenvironment (TME). PSGL-1-deficient mice showed dramatic control of melanoma growth that was coupled to greater numbers of tumor infiltrating, multifunctional CD8+ and CD4+ T cells (TILs) that expressed lower levels of inhibitory receptors. Since targeting PSGL-1 leads to downregulation of multiple inhibitory receptors and promotes effective anti-tumor responses, there may be significant advantages to blocking this receptor compared to combinations of inhibitory receptors, particularly if toxicity is less, or not greater than with current checkpoint blockades. Furthermore, blocking PSGL-1 may have the potential to limit immune suppression in patients that are unresponsive or have suboptimal responses to other therapies. For this project we have generated PSGL-1 conditional KO (PSGL-1fl/fl) mice to interrogate the function of this receptor on lymphoid and myeloid cells in the melanoma TME by cellular and transcriptome analyses. We will use pharmacologic approaches with genetic validation to determine if blocking PSGL-1 function can control melanoma growth by modulating TILs. These studies will provide new insights into the regulation of immune responses by PSGL-1 and mechanisms by which this receptor can contribute to T cell dysfunction in cancer. Most importantly, these studies will establish whether PSGL1 is a new target for immunotherapy of cancer.