Overcoming resistance to cancer immunotherapy by targeting MDSC-derived adenosine

肺癌是一种流行病，每年都会消耗许多生命。使用免疫检查点抑制剂（ICI;例如抗PD-1、抗CTLA-4抗体）的癌症免疫疗法彻底改变了转移性肺癌的治疗，导致许多患者的长期完全缓解。尽管如此，仍然迫切需要新的策略，因为并非所有患者都对ICI有反应;此外，耐药性可能发生在那些有反应的患者中。骨髓源性抑制细胞（MDSC），特别是单核细胞MDSC（MMDSC）是有效的免疫抑制性先天免疫细胞，其主动抑制CD 8 + T细胞肿瘤归巢和活化。由于M-MDSC水平在多种人类癌症中升高，并与患者生存率降低相关，我们假设这些细胞有助于抗PD-1抗性。嘌呤核苷，腺苷，在肿瘤微环境（TME）中大量产生，在那里它用于抑制免疫系统并促进肿瘤生长。有证据表明腺苷的过量产生可以介导对ICI的抗性。免疫抑制性腺苷通过细胞表面酶CD 73（外-5 '-核苷酸酶; AMP →腺苷）酶促转化细胞外AMP而产生。我们的初步研究表明，肿瘤细胞来源的前列腺素E2（PGE 2）维持M-MDSC抑制活性，在很大程度上，通过一种新的PGE 2 →cAMP→CREB/STAT 3途径直接诱导细胞表面CD 73表达，导致TME内免疫抑制腺苷增加。该提议的总体假设是肿瘤细胞来源的PGE 2支配M-MDSC中的CD 73表达，导致抗肿瘤CD 8 + T细胞活化的腺苷依赖性抑制的显著增加，最终导致，该提案的主要目标是测试涉及全身施用腺苷脱氨酶（ADA）的新型癌症免疫疗法的抗肿瘤功效。一种将腺苷不可逆地转化为次黄嘌呤核苷（一种非免疫抑制核苷）的酶。聚乙二醇化的牛ADA（PEG-ADA）已经被FDA批准用于ADA相关的严重联合免疫缺陷（ADA-SCID）儿童的酶替代疗法。我们假设PEG-ADA耗尽腺苷介导的T细胞免疫抑制可使肿瘤对PD-1抑制剂治疗敏感，并改善NSCLC患者的临床结局。为了实现所述目的，提出了以下目标：1）描述PGE 2诱导M-MDSC中CD 73表达的信号通路和分子机制; 2）确定在肺癌小鼠模型中抑制PGE 2 →cAMP→CREB/STAT 3 → CD 73 →腺苷通路是否减弱抗PD-1抗性;（3）接受派姆单抗治疗的肺癌患者中，PGE 2 → CD 73 + M-MDSC →腺苷介导的抗PD-1耐药途径。我们提出的研究将为开发一种安全和新型的免疫疗法以减弱肺癌患者的ICI耐药性提供重要的见解。

Lung cancer is a prevalent disease and consumes many lives every year. Cancer immunotherapy using immune checkpoint inhibitors (ICIs; e.g. anti-PD-1, anti-CTLA-4 antibodies) has revolutionized the treatment of metastatic lung cancer, resulting in long-term complete responses for many patients. Nevertheless, there remains an urgent need for new strategies because not all patients respond to ICIs; moreover, resistance can occur in those that do. Myeloid-derived suppressor cells (MDSCs), in particular, monocytic MDSCs (MMDSCs) are potent immunosuppressive innate immune cells that actively inhibit CD8+ T cell tumor homing and activation. Since M-MDSC levels are elevated in multiple human cancers and correlate with decreased patient survival, we postulate that these cells contribute to anti-PD-1 resistance. The purine nucleoside, adenosine, is produced in copious amounts within the tumor microenvironment (TME), where it serves to suppress the immune system and promote tumor growth. There is evidence to suggest that overproduction of adenosine can mediate resistance to ICIs. Immune suppressive adenosine is produced via the enzymatic conversion of extracellular AMP by the cell surface enzyme, CD73 (ecto-5’-nucleotidase; AMP → adenosine). Our preliminary studies demonstrate that tumor cell-derived prostaglandin E2 (PGE2) maintains M-MDSC suppressive activity, in large part, by directly inducing cell surface CD73 expression via a novel PGE2→cAMP→CREB/STAT3 pathway leading to increased immune suppressive adenosine within the TME. The overall hypothesis of this proposal is that tumor cell-derived PGE2 dictates CD73 expression in M-MDSCs leading to substantial increases in adenosine-dependent inhibition of anti-tumor CD8+ T cell activation resulting, ultimately, in anti-PD-1 immunotherapeutic resistance A major goal of this proposal is to test the antitumor efficacy of a novel cancer immunotherapy involving systemic administration of adenosine deaminase (ADA)—an enzyme that irreversibly converts adenosine into inosine, a non-immunosuppresive nucleoside. A pegylated version of bovine ADA (PEG-ADA) is already FDA-approved for use as an enzyme replacement therapy in children with ADA-associated severe combined immunodeficiency (ADA-SCID). We hypothesize that depletion of adenosine-mediated T cell immune suppression by PEG-ADA sensitizes tumors to PD-1 inhibitor therapy and improves clinical outcomes for NSCLC patients. To fulfill the stated objectives, the following aims are proposed: 1) Delineate the signaling pathway and molecular mechanisms by which PGE2 induces CD73 expression in M-MDSCs; 2) Determine whether inhibition of the PGE2→cAMP→CREB/STAT3→CD73→adenosine pathway attenuates anti-PD-1 resistance in a mouse model of lung cancer; and 3) Validate PGE2 → CD73+ M-MDSC → adenosine mediated anti-PD-1 resistance pathway in lung cancer patients receiving pembrolizumab therapy. Our proposed study will provide important insights towards developing a safe and novel immunotherapy to attenuate ICI resistance in lung cancer patients.