Introduction: The definition of stem cells is predicated on two fundamental criteria: first, the capacity for self-renewal, which refers to the ability to undergo cell division for the purpose of preserving and perpetuating their own population; and second, developmental potency—the ability to differentiate and specialize into various functional cell types.
In mammals, these cells are primarily classified into two main types: embryonic stem cells (ESCs), which are isolated from the inner cell mass (ICM) of a blastocyst, and adult stem cells (somatic stem cells), which reside within the fully differentiated tissues of an adult organism and function as the body's internal repair system.
In terms of developmental potential, cells possessing the ability to generate all cell types of an adult organism are described as pluripotent. Furthermore, based on their source and clinical application, these cells are utilized in three forms: autologous (derived from the same individual), allogeneic (derived from a genetically non-identical donor of the same species), and xenogeneic (derived from a different species).
Methods: This article was prepared and compiled using a narrative review method, based on a systematic examination and analysis of authoritative scientific sources available in specialized databases.
Results: Stem cells contribute to the repair and regeneration of damaged tissues through numerous and complex mechanisms. These mechanisms are not limited to direct differentiation and cellular replacement but also include the secretion of a wide array of paracrine factors, chemokines, and extracellular vesicles. These secretions simultaneously create a potent anti-inflammatory effect, inhibit programmed cell death (apoptosis), stimulate angiogenesis (neovascularization), prevent fibrosis and scar tissue formation, and activate resident progenitor cells within the host tissue to perform repair.
A key immunological feature that makes these cells suitable for transplantation is their very low expression of Major Histocompatibility Complex (MHC) molecules. This results in low immunogenicity and a significantly reduced risk of graft rejection.
In terms of clinical applications, these cells cover a broad spectrum of diseases: Hematology and Oncology, Cardiovascular diseases, Neurological disorders, Musculoskeletal diseases, and other regenerative applications.
The findings indicate that stem cells possess high potential for treating a variety of diseases. In the context of cancer, these cells can directly target cancer cells and inhibit tumor growth and metastasis. Furthermore, by repairing tissues damaged by treatment modalities such as radiotherapy and chemotherapy, they significantly contribute to improving patients' quality of life.
Regarding Alzheimer's disease, stem cells are capable of regenerating and repairing damaged neural cells. By replacing lost neurons and producing substances that prevent further neurodegeneration, they can slow disease progression and even lead to improvements in cognitive function in patients.
In the treatment of cardiovascular diseases, stem cells have the ability to repair damaged heart tissue. They can differentiate into cardiomyocytes to repair scarred cardiac tissue. Additionally, by promoting the formation of new blood vessels (angiogenesis), they improve blood supply to the heart muscle and enhance cardiac function.
Although these therapeutic approaches have shown promising results, several challenges remain that require further investigation. These include identifying the optimal cell source, determining the appropriate dosage, and refining cell delivery methods.
Nevertheless, the future of stem cell therapy appears very bright. With ongoing scientific and technological advancements, it is hopeful that these therapies will soon become standard and accessible treatment options for patients.
Conclusion: Stem cells, with their unique characteristics of self-renewal and multilineage differentiation potential, constitute the cornerstone of regenerative medicine and one of the most promising research fields in 21st-century medicine. While hematopoietic stem cell transplantation stands as a well-established and life-saving treatment, providing a robust proof-of-concept for the therapeutic power of these cells, their use for treating other chronic and degenerative diseases remains largely in the research and clinical trial phases. The full realization of their immense therapeutic potential necessitates the continuation and intensification of basic research to achieve a deeper understanding of their biology, coupled with robust translational research to overcome safety, technical, and ethical challenges, and to develop standardized, reproducible, and safe protocols. Undoubtedly, sustained investment and effort in this direction will pave the way for a future with curative treatments for many of today's incurable diseases.