Overcoming resistance to cancer immunotherapy by targeting MDSC-derived adenosine

肺癌是一种流行疾病，每年夺去许多人的生命。使用免疫检查点抑制剂(ICIS；例如，抗PD-1、抗CTLA-4抗体)的癌症免疫治疗已经使转移性肺癌的治疗发生了革命性的变化，导致许多患者的长期完全应答。然而，仍然迫切需要新的策略，因为并不是所有的患者都对ICIS有反应；此外，那些对ICIS有反应的患者可能会出现耐药性。髓系来源的抑制细胞(MDSCs)，尤其是单核细胞MDSCs(MMDSCs)是一种强大的免疫抑制先天免疫细胞，能主动抑制CD8+T细胞肿瘤的归巢和激活。由于M-MDSC水平在多种人类癌症中升高，并与患者生存率下降相关，我们推测这些细胞与抗PD-1耐药有关。嘌呤核苷，腺苷，在肿瘤微环境(TME)中大量产生，在那里它起到抑制免疫系统和促进肿瘤生长的作用。有证据表明，腺苷的过量生产可以介导对ICIS的抵抗。免疫抑制腺苷是通过细胞表面酶CD73(胞外5‘-核苷酸酶；AMP→腺苷)对胞外AMP进行酶转化而产生的。我们的初步研究表明，肿瘤细胞来源的前列腺素E2(PGE_2)在很大程度上是通过一种新的PGE_2→-cAMP-MDSC CREB/STAT3途径直接诱导细胞表面CD73表达，从而增强TME内的免疫抑制腺苷，从而维持M-MDSC的抑制活性。这项建议的总体假设是，肿瘤细胞来源的PGE2控制M-MDSCs中CD73的表达，导致腺苷依赖性抑制抗肿瘤CD8+T细胞激活的大幅增加，最终导致抗PD-1免疫治疗抵抗。该建议的主要目标是测试一种新型癌症免疫疗法的抗肿瘤疗效，该疗法涉及全身给药腺苷脱氨酶(ADA)-一种将腺苷不可逆地转化为肌苷的酶，肌苷是一种非免疫抑制核苷。一种聚乙二醇化的牛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，聚乙二醇腺苷介导的T细胞免疫抑制的耗竭可使肿瘤对PD-1抑制剂治疗敏感，并改善非小细胞肺癌患者的临床预后。为了实现上述目标，我们提出了以下目标：1)阐明前列腺素E_2诱导M-MDSC表达CD73的信号通路和分子机制；2)确定抑制PGE_2→cAMP→CREB/STAT3→CD73→腺苷通路是否能降低肺癌小鼠模型中抗PD-1的耐药性；以及3)验证接受培溴珠单抗治疗的肺癌患者中PGE_2→CD73+M-MDSC→腺苷介导的抗PD-1耐药通路。我们提出的研究将为开发一种安全的、新型的免疫疗法来减轻肺癌患者的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.