下一代癌症免疫疗法可能会利用免疫增强剂来选择性地激活宿主免疫系统对抗肿瘤细胞。抑制免疫抑制的检查点抑制剂（CPI），如抗PD1/PDL-1，已经显示出前所未有的成功，但只对具有已经“热”的（免疫原性）肿瘤的20-30%的患者有效。在这方面，肿瘤内注射免疫增强剂是一种有前途的方法，因为它们可以与CPI协同作用，通过诱导肿瘤内的免疫刺激来克服对免疫疗法的抵抗。其中一种免疫增强剂是粒细胞巨噬细胞集落刺激因子（GM-CSF），它的功能是在肿瘤中招募和激活抗原呈递细胞（树突状细胞），从而引发抗肿瘤免疫反应。然而，GM-CSF的关键问题是缺乏功效和由GM-CSF从肿瘤组织渗漏引起的系统毒性风险。我们设计了肿瘤保留型GM-CSF，这些GM-CSF既安全又强效，可用于局部治疗实体肿瘤。工程GM-CSF（eGM-CSF）通过基因重组将肿瘤-ECM（细胞外基质）结合肽与GM-CSF融合而成。eGM-CSF在体外和体内均表现出增强的肿瘤结合和强效的免疫活性。在肿瘤内注射后，肿瘤保留型的eGM-CSF持续存在于肿瘤中，从而减轻了系统毒性，并引发局部免疫激活，有效地将不响应免疫的“冷”肿瘤变成“热”肿瘤。

Next-generation cancer immunotherapies may utilize immunostimulants to selectively activate the host immune system against tumor cells. Checkpoint inhibitors (CPIs) like anti-PD1/PDL-1 that inhibit immunosuppression have shown unprecedented success but are only effective in the 20-30% of patients that possess an already "hot" (immunogenic) tumor. In this regard, intratumoral (IT) injection of immunostimulants is a promising approach since they can work synergistically with CPIs to overcome the resistance to immunotherapies by inducing immune stimulation in the tumor. One such immunostimulant is granulocyte macrophage-colony-stimulating factor (GMCSF) that functions by recruiting and activating antigen-presenting cells (dendritic cells) in the tumor, thereby initiating anti-tumor immune responses. However, key problems with GMCSF are lack of efficacy and the risk of systemic toxicity caused by the leakage of GMCSF from the tumor tissue. We have designed tumor-retentive versions of GMCSF that are safe yet potent immunostimulants for the local treatment of solid tumors. The engineered GMCSFs (eGMCSF) were synthesized by recombinantly fusing tumor-ECM (extracellular matrix) binding peptides to GMCSF. The eGMCSFs exhibited enhanced tumor binding and potent immunological activity in vitro and in vivo. Upon IT administration, the tumor-retentive eGMCSFs persisted in the tumor, thereby alleviating systemic toxicity, and elicited localized immune activation to effectively turn an unresponsive immunologically "cold" tumor "hot".