Tumors are one of the main causes of death in humans. The development of safe and effective methods for early diagnosis and treatment of tumors is a difficult problem that needs to be solved urgently. It is well established that the occurrence of tumors involves complex biological mechanisms, and the tumor microenvironment (TME) plays an important role in regulating the biological behavior of tumors. Cancer-associated fibroblasts (CAFs) are a group of activated fibroblasts with significant heterogeneity and plasticity in the tumor microenvironment. They secrete a variety of active factors to regulate tumor occurrence, development, metastasis, and therapeutic resistance. Although most studies suggest that CAFs have significant tumor-promoting functions, some evidence indicates that they may have certain tumor-suppressive functions in the early stage of tumors. Current research on CAFs continues to face many challenges, and the heterogeneity of their origin, phenotype, and function is a major difficulty and hot spot. To provide new perspectives for the research on CAFs and tumor diagnosis and treatment, this review summarizes the definition, origin, biomarkers, generation mechanism, functions, heterogeneity, plasticity, subpopulations, pre-metastasis niches (PMN), immune microenvironment, and targeted therapy of CAFs, describes the research progress and challenges, and proposes possible future research directions based on existing reports.
Somatic gene therapies require targeted transfer of the therapeutic gene(s) into stem cells that proliferate and then differentiate and express the gene in a tissue-restricted manner. We have developed an approach for gene therapy using marrow cells that takes advantage of the osteoblast specificity of the osteocalcin promoter to confine expression of chimeric genes to bone. Adherent marrow cells, carrying a reporter gene [chloramphenicol acetyltransferase (CAT)] under the control of a 1.7-kilobase rat osteocalcin gene promoter, were expanded ex vivo. After transplantation by intravenous infusion, engrafted donor cells in recipient mice were detected by the presence of the transgene in a broad spectrum of tissues. However, expression of the transgene was restricted to osteoblasts and osteocytes, as established by biochemical analysis of CAT activity and immunohistochemical analysis of CAT expression at the single cell level. Our data indicate that donor cells achieved long-term engraftment in various tissues of the recipients and that the CAT gene under control of the osteocalcin promoter is expressed specifically in bone. Thus, transplantation of multipotential marrow cells containing the osteocalcin promoter-controlled transgene provides an efficacious approach to deliver therapeutic gene expression to osteoblasts for treatment of bone disorders or tumor metastasis to the skeleton.
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