As a cutting-edge medical technology, stem cell technology has broad application prospects in the clinical treatment of a variety of diseases, and is a forward-looking emerging industry vigorously supported by the state and government. However, in some studies, we can see significant individual differences in the effectiveness of stem cell therapy, such as:
(1) In a study of patients with osteoarthritis, 70% of patients had significant improvement in symptoms after receiving stem cell therapy, but 30% of patients still failed to achieve the expected results within a certain period of time. This suggests that stem cell therapy is effective for most people, but there are individual differences.
(2) Another study in patients with myocardial infarction showed that about 60% of patients had improved cardiac function after receiving stem cell infusion, but 40% of patients still had no obvious effect. This is further evidence of the versatility of stem cell therapy effects.
These data underscore the fact that the effects of stem cell therapy are diverse, ranging from fast and slow, deep to shallow, with some lasting and mild, to rapid and short-lived. Why do stem cells vary so much? Today we're going to look at it from a clinical perspective.
1. Individual differences affect effect differences
Each person's body is like a unique fingerprint, which is different. The effectiveness of stem cell therapy is influenced by several factors that vary from person to person, including genetics, health status, and age.
(1) Genetic differences: Genes determine the way the human body reacts to foreign substances, including stem cells. Some people's genes may make them respond quickly to stem cell therapy, while others may take longer to see results. Just like someone is naturally sensitive to certain medications, while someone needs a higher dose to see an effect.
(2) Health status: The health status of the body will also affect the efficacy of stem cells. A healthy person's internal environment is more conducive to stem cell growth and function, while people with chronic diseases or weakened immune systems may need more time and intervention to achieve results. It's like growing crops on fertile land is easier to harvest than growing on barren land.
(3) Age factor: With the increase of age, the body's self-repair ability gradually weakens. The body of the young is like the land of spring, full of life and vitality, while the body of the elderly is more like a winter wasteland, with a relatively low ability to repair. As a result, stem cells may show results more quickly in younger people, while more time and support may be needed in older people.
Second, the type and quality of stem cells affect the effect differences
There are many types of stem cells, including embryonic stem cells and adult stem cells, and these different types of stem cells differ in their differentiation ability and immunogenicity. In addition, the quality of stem cells is also a core factor affecting the effectiveness of interventions. High-quality stem cells not only have a better differentiation potential, but they also have a lower immunogenicity, which allows them to adapt more effectively to the in vivo environment and demonstrate their therapeutic effects.
Roughly define "cell mass" to refer to the biological potency of a unit cell or a single cell; The higher the potency, the better the cell quality. In September 2023, the State Administration for Market Regulation and the Standardization Administration of the People's Republic of China jointly issued the first national standard for human stem cells in mainland China, "Technical Specifications for the Management of Pluripotent Stem Cells in Biobanks", which mentions that the main factors affecting the quality of stem cells include cell source, cell growth activity, cell viability, cell survival rate, etc.
1. Cell source
In order to obtain high-quality stem cells, the source of the cells is particularly important. As humans age, the viability of cells will gradually decrease, and whether you choose allogeneic transplantation or "self-sufficiency", the age and physical condition of the cell donor themselves will have an impact on the quality of the cells. In 2019, a research team from the University of Leeds in the United Kingdom collected bone marrow mesenchymal stem cells from 67 healthy donors (aged 19-89) and confirmed through in vitro culture that the number and proliferation ability of stem cells in young people are significantly higher than those in the elderly.
△ Stem cells in the young group (19-40), middle age group (41-60) and old group (61-89 years) after 14 days of culture in the culture medium
△ The cell body of the young stem cell is full and has an obvious spindle-shaped; Senescent stem cell bodies are large and flattened
From the perspective of age, embryonic tissue sources or embryo-like cells such as umbilical cord/placental mesenchymal stem cells should be the optimal solution. First of all, the donor must be screened to prove that there is no infection with specific viruses (including HIV, HBV, HCV, HTLV, EBV, CMV, etc.), and there is no treponemal infection. Secondly, in addition to viral infection, many diseases can also affect the function and effect of mesenchymal stem cells, such as genetic diseases, autoimmune diseases and some chronic diseases.
FOR EXAMPLE, A STUDY PUBLISHED IN STEM CELLS TRANSLATIONAL MEDICINE IN SEPTEMBER 2021 CONFIRMED THAT LONG-TERM DIABETES TYPE II DIABETES REDUCES STEM CELL PROLIFERATION, IMMUNOSUPPRESSIVE POTENTIAL, AND SURVIVAL.
△Characterization comparison of autologous bone marrow-derived mesenchymal stem cells (BM-MSCs) in healthy group (group 1) and patients with type 2 diabetes mellitus (duration of diabetes: group 2: < 5 years, group 3: 5-10 years, group 4: > 10 years)
Despite the potential therapeutic efficacy of stem cell therapy for type II diabetes, some patients have received contradictory results with the use of autologous stem cells, due to the disease affecting the molecular and cellular characteristics of the patient's autologous stem cells, particularly alterations in metabolic activity and mitochondrial DNA.
2. Cell growth activity and generation
The growth activity of cells reflects the proliferation and differentiation ability of cells, and is an important indicator to evaluate the quality of stem cells. There are many criteria for growth activity, such as cell doubling time, cell cycle, colony formation rate, telomerase activity, etc., and these indicators are affected by cell generations.
Cell passage refers to the number of passages of stem cells in in vitro culture. For example, stem cells that have just been extracted from tissues such as embryos or umbilical cords are the original P0 generation, and after one division, the P1 generation stem cells are obtained, and so on. Every time a cell divides, it loses part of its stemness (multi-directional differentiation potential). With the passage of cells for multiple passages and the prolongation of culture time, their stemness gradually decays, their proliferation becomes slower and slower, and cell senescence accelerates. The figure below shows a comparison of human umbilical cord mesenchymal stem cells in P3 and P15 generations in a study: the degree of cell senescence in P15 generation is much higher than that of P3, and the growth activity is much lower than that of P3.
Theoretically, the higher the cell passage, the more active and stem-free the stem cells are. However, in the process of actual in vitro culture, although the first two or three generations of stem cells are very active, the number is too small, and due to the short culture time, it may also contain harmful substances such as bacteria remaining in the extraction process, and there are unstable factors. However, stem cells with too many passages (after P6 and P7) are abundant in number, but their proliferative ability and genetic stability will decline rapidly, accompanied by a large number of apoptosis. After P15 generation, the apoptosis rate was close to 50%. Therefore, it should not be used for clinical treatment.
It is worth noting that, according to the current research data in the world, the degree of influence of different generations of stem cells on their growth activity, stemness and genetic stability may also be different. For example, studies based on human bone marrow mesenchymal stem cells suggest that cells before the P5 generation are good enough to be used for cell therapy; There are also studies based on mesenchymal stem cells derived from human gingival, periodontal and pulp tissues, and it has concluded that the cell quality before the P15 generation is sufficient to support the clinical application of stem cells; Studies based on human umbilical cord mesenchymal stem cells have shown that there has been a significant gap in some aspects of the data between P6 and P4 stem cells (see figure below), so P4 is more recommended.
In summary, the data of stem cells from P3 to P5 generations are usually still in the high activity range, so they can be considered to be the best choice for quantity, safety and activity, and are the most suitable high-quality stem cells for clinical applications.
3. Cell survival rate
When stem cells are replenished into the body, only living stem cells can really play a role in repair or treatment, and inactivated cells not only hinder their effectiveness, but may also cause toxic reactions in the body. Therefore, cell viability is not only related to cell quality, but also related to the safety of the human body itself. Because of this, domestic regulations have high requirements for the survival rate of stem cell products, usually ≥ 90%.
△ The cell counter shows the survival rate of stem cells
In addition to the activity of stem cells themselves, storage and transportation conditions also affect cell viability. If the storage or transportation conditions are not up to standard, it may lead to cell death, cell membrane rupture and content release, etc., which will not only not have a therapeutic effect, but will lead to the occurrence of adverse events. In addition, the infusion method of cells also has a certain effect on cell viability, if the infusion transplantation speed is too slow and takes too long, there is a possibility of cell death and increased risk of adverse events.
3. Differences in the effect of stem cell infusion methods and doses
The infusion method and dosage of stem cells are also key to the treatment effect. At present, there are two main ways of stem cell infusion: intravenous injection and local injection, and various methods may affect the distribution and survival of stem cells in the body. At the same time, the dosage during infusion should also be adjusted according to the specific condition of the patient, too small dosage may not be able to achieve therapeutic effect, and too large dosage will increase the risk of patient safety. Therefore, the specific situation of the patient and the requirements of treatment effect should be considered in the infusion method and dose selection.
Fourth, the effect of microenvironmental influence in vivo is different
Regulation of the microenvironment within stem cell survival and differentiation receptors. The in vivo microenvironment encompasses a variety of elements such as the extracellular matrix, cytokines, and the immune system, and changes in these elements may affect the function of stem cells and their differentiation pathways. For example, the inflammatory environment can promote the migration and differentiation of stem cells, and the immunosuppressive environment can inhibit the proliferation and differentiation of stem cells. Therefore, changes in the internal microenvironment of the body can also be a factor in the difference in stem cell reinfusion results.
Summary and prospects: how to improve the clinical intervention effect of stem cell technology
In summary, different individuals may show different clinical treatment effects after receiving stem cell intervention due to the influence of factors such as stem cell type and quality, individual patient differences, infusion method and dose, and in vivo microenvironment. Therefore, we need to deeply study the mechanism of action of these influencing factors and optimize treatment plans and strategies to improve the clinical intervention effect of stem cells.
At the same time, a good laboratory cell production enterprise needs to be customized for different individuals, mainly including: (1) customized selection of cell type, quantity, combination of immune cells and stem cells for diseases and individuals, etc., not everyone is a stem cell or immune cell no matter what the disease. (2) In the induction culture of single types of cells, targeted induction and modification will be carried out in combination with the needs of the disease, so that the cells can have functionality and specialization.
In addition, during the cell transplantation process, the donor is adequately supplemented with nutrients to meet its growth needs. It's like the human body is like a piece of land, and only when the soil is properly improved, can the nutrient enhancers provided multiply the benefits, otherwise it will cause a waste of resources. It is also necessary to strengthen monitoring and evaluation before and after stem cell infusion, and identify and deal with possible problems in a timely manner, which will help ensure the safety and effectiveness before and after the intervention.
With the increasing maturity of stem cell technology, the country is also constantly improving the stem cell quality control system, and the entire industry is developing in the direction of standardization, long-term and clinical transformation. It is believed that in the future, a high-quality stem cell will be performed through clinical treatment, so that more people can experience the powerful repair ability of stem cells.
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