Provide protection for human life and health (open book to learn new)

The picture shows human embryonic stem cells under a microscope. Profile picture Draft: Zhao Kairu

At present, facing the world's scientific and technological frontier, facing the main economic battlefield, facing the major needs of the country, and facing the people's life and health, the majority of scientists and scientific and technological workers are constantly marching towards the breadth and depth of science and technology. Among them, in the field of stem cells, mainland scientific researchers have achieved major original scientific research results in recent years. Hematopoietic stem cell transplantation (bone marrow transplantation) for the treatment of leukemia has been continuously improved, and the world's first stem cell cure for children's dilated cardiomyopathy has been realized, and the use of chemical small molecules to transform human adult cells into stem cells...

With the continuous development of life science research, human understanding of stem cells has gradually deepened, and stem cell-related scientific research achievements have played an increasingly important role in disease treatment and regenerative medicine. The application of stem cell technology can not only treat diseases that were difficult to treat in the past, such as leukemia and immune system diseases, but also extend the exhibition of organoid technology to accelerate the development of new drugs, help precision medicine, and even promote the leap forward in regenerative medicine, such as the treatment of Alzheimer's disease, the repair of aging organs, etc. It can be said that stem cell research and application continue to provide protection for the life and health of the people.

"Everything in life", a variety of types, to maintain life and vitality

To understand stem cells, we must first understand cells. As we all know, cells are the basic building blocks of the human body. There are about 40 trillion to 60 trillion cells in an adult body. The cells that make up the body are not only numerous but also well-defined, with nerve cells dominating thought, muscle cells producing movement, fat cells storing energy, immune cells mediating immune protection, and so on. Different types of cells are further combined to form tissues, organs and systems that enable the human body to complete a variety of life activities. Amazingly, so many different kinds of cells come from one cell at the beginning of life, and that is the fertilized egg. Fertilized eggs proliferate to produce embryonic stem cells, which further proliferate and differentiate into more than 200 kinds of cells in the human body, eventually growing into a complete individual.

Just as a trunk can grow branches, branches, and leaves that can blossom and bear fruit, stem cells are progenitor cells that can self-renew and differentiate into various types of cells. In the process of ontology, stem cells proliferate and differentiate into various types of cells to build tissues and organs. After development is complete, when tissues and organs are damaged, inflammation occurs, or homeostasis changes in the body, stem cells act as "seed cells" that can differentiate and replenish the cells needed at this time to complete the repair. At the end of life activity, when the vitality of stem cells declines, it is difficult to meet the replacement needs of new cells to replace senescent degenerate cells, and individuals appear senescent phenotypes.

According to the stage of development, stem cells can be divided into embryonic stem cells and adult stem cells. Embryonic stem cells are cells cultured from inner cell clumps in early embryos, which are colloquially, the cells of "everything in life", that is, they can theoretically induce differentiation into all kinds of cells in the body. Such cells can be massively expanded, frozen and revived in vitro without losing their original properties. Adult stem cells are undifferentiated cells that exist in adult tissue, also known as tissue stem cells. Such cells are able to renew themselves and can be specialized into functional cells that make up the tissue, like "cell factories." At present, the adult stem cells found include hematopoietic stem cells, bone marrow mesenchymal stem cells, neural stem cells, muscle stem cells, cutaneous epidermal stem cells, retinal stem cells and so on.

According to the differentiation potential, stem cells can be divided into totipotent stem cells, pluripotent stem cells and unipotent stem cells. As the name suggests, topotent stem cells have the ability to differentiate into any type of cell in the body, and have the potential to differentiate into complete individuals, such as embryonic stem cells. Pluripotent stem cells have the ability to produce multiple types of cells, but cannot develop into complete individuals. For example, hematopoietic stem cells can differentiate into a variety of blood cells, and bone marrow mesenchymal stem cells can differentiate into cells of mesoderm tissues such as bone, cartilage, muscle, and fat. Unipotent stem cells can only differentiate in a single direction in adult tissues and organs, producing a type of cell.

A powerful tool for a wide range of applications, disease treatment and regenerative medicine

Health is everyone's aspiration, and stem cells have great potential in disease treatment and regenerative medicine. Some developed countries have taken the lead in using stem cell transplantation technology to treat diseases, and the mainland is also carrying out clinical research on stem cell therapy for diseases. According to statistics, more than 6,000 stem cell clinical trials around the world involve hundreds of diseases.

The public is most familiar with the treatment of blood diseases. Hematopoietic stem cell transplantation is the earliest and more common case of stem cell clinical application, mainly for anemia and leukemia, including aplastic anemia, congenital hemogloblastination, chronic bone marrow cell leukemia, etc. Hematopoietic stem cell transplantation is also used in the treatment of certain specific diseases, such as severe combined immunodeficiency diseases, autoimmune diseases multiple sclerosis, etc. The hematopoietic stem cells used in this treatment are mainly derived from umbilical cord hematopoietic stem cells and bone marrow. In the past, such diseases were difficult to cure, but now the application of stem cell therapy brings hope to patients.

Another example is the treatment of skin-related diseases. Stem cells are found in a variety of skin tissues, such as the epidermis, hair follicles and dermis, to maintain skin homeostasis and damage repair. Stem cell therapy can be used for skin lesions. In 2017, scientists regenerated the human epidermis through stem cells, giving a boy new skin. Today, the technology is being used in patients with severe skin burns. In the process of epidermal wound healing, mesenchymal stem cells can accelerate wound healing and reduce scarring by promoting cell migration, angiogenesis, epithelialization and granulation tissue formation. Stem cell dysfunction is an important cause of psoriasis inflammatory response disorders, and clinical trials have found that patients can alleviate psoriasis symptoms for a long time after receiving stem cell therapy. In addition, stem cell therapy is also used in the treatment of androgenic alopecia and alopecia areata, including hair follicle transplantation and stem cell stimulation therapy.

In addition to the direct use of stem cells for disease treatment, various new technologies based on stem cells also have great application potential. For example, organoids based on adult stem cells are not only important models for studying organ development and disease occurrence, but also play a role in personalized treatment of tumors, drug research and development, and regenerative medicine. Organoids are micro-organs with three-dimensional structures that are cultivated in vitro, have complex structures similar to real organs, and can partially simulate the physiological functions of source tissues and organs. Taking the treatment of tumor diseases as an example, the current drugs are mostly generic, but the specific conditions of each patient are different. Organoids can mimic patient organs to help find the right drug and personalize treatment. In terms of drug development, organoids can help build disease models closer to the human body, reduce the cost of new drug research and development, and shorten the research and development cycle.

In the future, the most important application of stem cells may be regenerative medicine. Alzheimer's disease is a neurodegenerative disease, and the use of stem cell technology to replace damaged neurons is being explored in the hope of treating Alzheimer's disease. Further, stem cell technology is expected to be used to repair aging organs, allowing people to prolong their lives and enjoy a high quality of life.

The research and application of stem cells in mainland China have a good foundation and have made a series of important breakthroughs. In terms of research, mainland researchers have used induced pluripotent stem cells to prove the totipotency of such stem cells for the first time through tetraploid blastocyst injection; created a semi-cloning technology to establish a mouse solitary male haploid embryonic stem cell line (also known as sperm-like stem cells), which can functionally replace sperm breeding healthy mice; use stem cells to allow mice with congenital blindness to gain vision; and so on. In terms of application, mainland researchers have established human fetal pancreatic stem cell lines for the first time in the world, which can provide seed cells for the clinical treatment of human diabetes; use umbilical cord mesenchymal stem cells to improve ovarian blood flow, repair ovarian function, and regain the ability to reproduce prematurely aging ovaries; and so on. The breakthrough of these stem cell technologies has played a role in promoting the research and application of stem cells in the mainland, reflecting the transformation of the mainland in the field of stem cells from "following and running" to "leading".

Life and health are scientific issues, and they are also life propositions that everyone has to face. Having a good body full of vitality is a simple and sincere pursuit of people, and it is also the goal of stem cell researchers. As a frontier and hotspot in the life sciences, stem cells still have many unsolved mysteries that deserve our unremitting exploration. With the continuous emergence of research results, stem cells will continue to provide new treatment strategies for difficult and complex diseases and make new contributions to human health.

(The author is an academician of the Chinese Academy of Sciences and a professor at Tsinghua University)

Provide protection for human life and health (open book to learn new)

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