Tumor microenvironment (TME) formation is a major cause of immunosuppression. The TME consists of a considerable number of macrophages and stromal cells that have been identified in multiple tumor types. CCL2 is the strongest chemoattractant involved in macrophage recruitment and a powerful initiator of inflammation. Evidence indicates that CCL2 can attract other host cells in the TME and direct their differentiation in cooperation with other cytokines. Overall, CCL2 has an unfavorable effect on prognosis in tumor patients because of the accumulation of immunosuppressive cell subtypes. However, there is also evidence demonstrating that CCL2 enhances the anti-tumor capability of specific cell types such as inflammatory monocytes and neutrophils. The inflammation state of the tumor seems to have a bi-lateral role in tumor progression. Here, we review works focusing on the interactions between cancer cells and host cells, and on the biological role of CCL2 in these processes.

Pyroptosis has been reported to improve the immunosuppressive tumor microenvironment and may be a strategy to enhance osteosarcoma treatment. The extent to which modulation of mitochondria could induce tumor pyroptosis to enhance immunotherapy has not been characterized. We synthesized a mitochondria-targeting polymer micelle (OPDEA-PDCA), in which poly[2-(N-oxide-N,N-diethylamino)ethyl methacrylate] (OPDEA) was used to target mitochondria and the conjugated dichloroacetate (DCA) was used to inhibit pyruvate dehydrogenase kinase 1 (PDHK1). This conjugate induced pyroptosis through initiation of mitochondrial oxidative stress. We found that OPDEA-PDCA targeted mitochondria and induced mitochondrial oxidative stress through the inhibition of PDHK1, resulting in immunogenic pyroptosis in osteosarcoma cell lines. Moreover, we showed that OPDEA-PDCA could induce secretion of soluble programmed cell death-ligand 1 (PD-L1) molecule. Therefore, combined therapy with OPDEA-PDCA and an anti-PD-L1 monoclonal antibody significantly suppressed proliferation of osteosarcoma with prolonged T cell activation. This study provided a strategy to initiate pyroptosis through targeted modulation of mitochondria, which may promote enhanced antitumor efficacy in combination with immunotherapy.

The poor progress of immunotherapy on osteosarcoma patients requires deeper delineation of immune tolerance mechanisms in the osteosarcoma microenvironment and a new therapeutic strategy. Clearance of apoptotic cells by phagocytes, a process termed “efferocytosis,” is ubiquitous in tumors and mediates the suppression of innate immune inflammatory response. Considering the massive infiltrated macrophages in osteosarcoma, efferocytosis probably serves as a potential target, but is rarely studied in osteosarcoma. Here, we verified M2 polarization and PD-L1 expression of macrophages following efferocytosis. Pharmacological inhibition and genetic knockdown were used to explore the underlying pathway. Moreover, tumor progression and immune landscape were evaluated following inhibition of efferocytosis in osteosarcoma model. Our study indicated that efferocytosis promoted PD-L1 expression and M2 polarization of macrophages. Ëfferocytosis was mediated by MerTK receptor in osteosarcoma and regulated the phenotypes of macrophages through the p38/STAT3 pathway. By establishing the murine osteosarcoma model, we emphasized that inhibition of MerTK suppressed tumor growth and enhanced the T cell cytotoxic function by increasing the infiltration of CD8 + T cells and decreasing their exhaustion. Our findings demonstrate that MerTK-mediated efferocytosis promotes osteosarcoma progression by enhancing M2 polarization of macrophages and PD-L1-induced immune tolerance, which were regulated through the p38/STAT3 pathway.

As the essential sexual hormone, estrogen and its receptor has been proved to participate in the regulation of autoimmunity diseases and anti-tumor immunity. The adjustment of tumor immunity is related to the interaction between cancer cells, immune cells and tumor microenvironment, all of which is considered as the potential target in estrogen-induced immune system regulation. However, the specific mechanism of estrogen-induced immunity is poorly understood. Typically, estrogen causes the nuclear localization of estrogen/estrogen receptor complex and alternates the transcription pattern of target genes, leading to the reprogramming of tumor cells and differentiation of immune cells. However, the estrogen-induced non-canonical signal pathway activation is also crucial to the rapid function of estrogen, such as NF-κB, MAPK-ERK, and β-catenin pathway activation, which has not been totally illuminated. So, the investigation of estrogen modulatory mechanisms in these two manners is vital for the tumor immunity and can provide the potential for endocrine hormone targeted cancer immunotherapy. Here, this review summarized the estrogen-induced canonical and non-canonical signal transduction pathway and aimed to focus on the relationship among estrogen and cancer immunity as well as immune-related tumor microenvironment regulation. Results from these preclinical researches elucidated that the estrogen-target therapy has the application prospect of cancer immunotherapy, which requires the further translational research of these treatment strategies.

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This study aims to investigate the differentiation trajectory of osteosarcoma cells and to construct molecular subtypes with their respective characteristics and generate a multi-gene signature for predicting prognosis. Integrated single-cell RNA-sequencing (scRNA-seq) data, bulk RNA-seq data and microarray data from osteosarcoma samples were used for analysis. Via scRNA-seq data, time-related as well as differentiation-related genes were recognized as osteosarcoma tumor stem cell-related genes (OSCGs). In Gene Expression Omnibus (GEO) cohort, osteosarcoma patients were classified into two subtypes based on prognostic OSCGs and it was found that molecular typing successfully predicted overall survival, tumor microenvironment and immune infiltration status. Further, available drugs for influencing osteosarcoma via prognostic OSCGs were revealed. A 3-OSCG-based prognostic risk score signature was generated and by combining other clinic-pathological independent prognostic factor, stage at diagnosis, a nomogram was established to predict individual survival probability. In external independent TARGET cohort, the molecular types, the 3-gene signature as well as nomogram were validated. In conclusion, osteosarcoma cell differentiation occupies a crucial position in many facets, such as tumor prognosis and microenvironment, suggesting promising therapeutic targets for this disease.

Effective and accurate delivery of drugs to tissue with spinal cord injury (SCI) is the key to rehabilitating neurological deficits. Sustained-release microspheres (MS) have excellent degradability and can aid in the long-term release of drugs. However, the burst release phenomenon can cause unexpected side effects. Herein, we developed and optimized an injectable poly(lactic-co-glycolic acid) (PLGA) MS loaded with melatonin(Mel), which were mixed further with Laponite hydrogels (Lap/MS@Mel, a micro-gel compound) in order to reduce the burst release of MS. Thus, these MS were able to achieve stable and prolonged Mel release, as well as synergistic Lap hydrogel in order to repair neural function in SCI by in situ injection. In clinical practice, patients with SCI have complicated conditions and significant inter-individual differences, which means that a single route of administration does not meet actual clinical needs. Thus, the nanospheres are synthesized and subsequently coated with platelet membrane (PM) in order to form PM/MS@Mel (nano-PM compound) for sustained and precision-targeted delivery of Mel intravenously in the SCI. Notably, optimized microsphere delivery systems have improved Mel regulation polarization of spinal microglial/macrophages, which can reduce loss of biomaterials due to macrophage-induced immune response during implantation of spinal cord tissue. These two new delivery systems that are based on MS provide references for the clinical treatment of SCI, according to different requirements.

Gold nanorods (GNRs) are intensively explored for the application in cancer therapy, which has motivated the development of photothermal therapy (PTT) multifunctional nanoplatforms based on GNRs to cure osteosarcoma (OS). However, the major limitations include the toxicity of surface protectants of GNRs, unsatisfactory targeting therapy, and the resistant effects of photothermal-induced autophagy, so the risk of relapse and metastasis of OS increase. In the present study, the GNR multifunctional nanoplatforms were designed and synthesized to deliver transcription factor EB (TFEB)-siRNA–targeting autophagy; then, the resistance of autophagy to PTT and the pH-sensitive cell-penetrating membrane peptide (CPP) was weakened, which could improve the tumor-targeting ability of the GNR nanoplatforms and realize an efficient synergistic effect for tumor treatment. Meanwhile, it is worth noting that the GNR nanoplatform groups have anti-lung metastasis of OS. This study provides a new reference to improve the efficacy of OS clinically.