From cell biology to cell therapy

Kirill Stasevich, biologist

"Science and Life" No. 6-2015

The article is published on the website "Elements" 

Cell biology is a scientific discipline located at the junction of several areas of modern biology and medicine. Studying "in vitro" molecular biochemical processes, such as, for example, the interaction of signaling proteins or lipid synthesis, it must be borne in mind that they actually occur in the cell. It was for research in the field of cell biology that two prizes were awarded by the Moscow Government for young scientists in 2014 in the nomination "Biology and Medical Sciences".

The point of the work of antibodies is to accurately recognize a foreign molecule (it can be either a bacterial toxin, or a protein that forms the envelope of the virus, or something else). The "bad" molecules associated with antibodies and their owners – pathogens – are neutralized and destroyed by immune cells.

Immunity in its usual form – with special organs, with a huge number of different cells and proteins – is considered a characteristic feature of animals, and even then not all, but mainly vertebrates (although some elements of the immune system can be found in invertebrates). Nevertheless, there are also plant antibodies, they even have a special name in English: "plantibody" – "plant", plant + "antibody", antibody. However, these are not plants' own antibodies – in the work of Doctor of Biological Sciences T. Komarova and her colleagues, we are talking about animal proteins-immunoglobulins, whose genes are injected into the plant organism.

Why was it necessary? It would not be an exaggeration to say that without a variety of methods based on the use of antibodies, modern biotechnology and medicine would be like without hands. Immunoglobulins are used everywhere, starting with the purification of the necessary molecules from the accompanying "garbage" to diagnostics: if you need to detect a parasite in a biological sample, then with the help of highly specific and strongly binding antibodies to the parasite, you can determine even a negligible amount of it. Custom-made immunoglobulins allow performing rather subtle research in fundamental science, they have also found the widest application in medicine: in particular, antibodies against cancer cell proteins can inhibit tumor growth.

But where to get antibodies? The obvious answer is from immunized animals: researchers inject a rat, or goat, or rabbit with some kind of antigen (for example, bacterial protein), and then extract the necessary immunoglobulins from the animal's blood. However, immunity in response to the antigen produces many varieties of antibodies, and the desired variety with the required characteristics has to be separated from others. There is also the technology of monoclonal antibodies, when a clone of immune cells is obtained, synthesizing only one variant of immunoglobulins. Such a method is also not easy in itself, suffice it to say that it is based on the fusion of two cells into one: a B-lymphocyte, carrying information about the desired antibody, combines with a cancerous myeloma cell. As a result, the hybrid receives from myeloma the ability to infinitely divide and simultaneously produce antibodies. But if it is necessary to obtain a lot of antibodies – for example, for clinical treatment – then their production using hybridomic technology will take quite a long time.

At some point, the idea arose that the production of antibodies could be simplified and accelerated if plants were used. To do this, the gene of the desired immunoglobulin is taken from an immunized animal and injected into a plant cell. Practice has shown that it is much easier, cheaper and safer to make antibodies in plants: a large number of immunoglobulins can be obtained without resorting to repeated immunizations, without using pathogens and vaccines – plant cells themselves synthesize the necessary protein. And it is much easier to get transgenic plants than transgenic animals.

Last year, an experimental preparation of such plant antibodies called ZMapp saved the lives of several Ebola patients. Artificial immunoglobulins can also be used against malignant tumors. In 2011, T. Komarova and her colleagues from the A. N. Belozersky Institute of Physico-Chemical Biology, the N. I. Vavilov Institute of Genetics and the N. N. Blokhin Cancer Center published an article in the journal PLoS ONE describing the production of plant antibodies used in the treatment of breast cancer. By itself, such a drug called trastuzumab, or "Herceptin", has been around for a long time – by binding to an onco-protein of one of the varieties of tumors, immunoglobulins suppress its growth. The authors obtained tobacco plants that synthesized these antibodies. Tests have confirmed that herbal trastuzumab also stops the division of tumor cells and stops the development of the disease. The researchers went further and "taught" plants the synthesis of three more types of antibodies: the first one blocks the development of blood vessels in the tumor, thereby inhibiting its growth, the other two are directed against breast cancer cells themselves. Animal experiments have shown that the new immunoglobulins have higher anti-cancer activity than commercial Herceptin. After clinical trials, they can be recommended for the diagnosis and treatment of a malignant tumor (of course, if the test results are positive).

The fact is that the immunoglobulin gene is delivered to the plant by the bacterium Agrobacterium tumefaciens. By itself, it is a pathogen that causes the appearance of crown galls – tumor formations on the plant. But it has a remarkable feature from the point of view of genetic engineering: a bacterium can transfer part of its genome to a plant cell, and bacterial DNA is embedded in a plant chromosome. That is, bioengineers who have received an immunoglobulin gene have two tasks: to introduce it into such a section of bacterial DNA from which a bacterium can embed it into the DNA of a plant, and to ensure the penetration of a bacterium into a plant cell. In other words, we need to find a way to overcome plant protection against pathogens. And here Tatiana Komarova and her colleagues have already managed to achieve some important results: it turned out that the gaseous methanol that plants emit when damaged is necessary to protect against bacteria. Moreover, methanol serves as a signal by which the damaged plant warns neighbors about the danger. That is, if you want to introduce a bacterium with an immunoglobulin gene into plant tissues, you need to take into account the methanol protection and warning system.

As you know, stem cells differ from others in that they have no specialization and can only divide all the time. They are needed in order to replenish the stock of ordinary, specialized cells – epithelial, muscle, blood and others, which gradually fail and die. In the descendants of stem cells, differentiation programs can be included, so that the cell as a result "learns" a specific "craft".

Stem cells have been used for a long time – and not unsuccessfully – for medical purposes. It's not just about simply replacing the burned areas of the skin with new ones grown in a test tube in case of severe burns. With the help of stem technologies, it is possible to create elements of the retina of the eye and transplant it to the blind, or to grow insulin-producing cells of the pancreas and transplant them to diabetics. Finally, new neurons can be grown and transplanted to those who have had a massive stroke.

However, having discovered impressive practical prospects for the use of stem cells, researchers quickly encountered several specific problems associated with cellular "raw materials". If we take "omnipotent" embryonic stem cells, which can give rise to absolutely any cell type, then ethical difficulties arise – is it possible to disassemble a human embryo for spare parts? The embryonic material was replaced by learning how to convert ordinary cells of the body into an undifferentiated, stem state. But such artificial analogues, called induced pluripotent stem cells, can behave unpredictably and trigger malignant processes.

Fortunately, there are many semi–specialized, or progenitor, stem cells in the body - they live with a person all his life, serving some specific tissue or organ and giving rise to a small spectrum of cellular varieties. Such cells do not even need to be taken out of the body and somehow grown in the laboratory, it is enough to stimulate their work right on the spot, in the tissue or in the organ that needs them.

Scientific project http://www.vechnayamolodost.ru/pages/stvolovyekletki/premzareg23.html Candidate of Medical Sciences Anastasia Efimenko from Lomonosov Moscow State University under the title "The influence of risk factors on stem and progenitor cells and the processes of repair and regeneration in the body" is just devoted to how aging and diseases affect the properties of stem cells. The researchers were able to show that cardiovascular and metabolic diseases, such as coronary heart disease and diabetes mellitus, coupled with age weaken the ability of stem cells to divide and synthesize bioactive molecules necessary for regenerative processes. This is understandable – after all, diseases hit all the cells of the organ, including those that should restore this very organ. That is, if we are talking about cell-stem methods for an elderly patient, then we must imagine exactly what his stem cells can and cannot do. And we need to know what a person was sick with, what lifestyle he led and what risk factors his stem and progenitor cells were exposed to. In other words, a personalized approach is needed, which is being talked about more and more often in modern medicine.

The experiments of A. Efimenko and her colleagues showed that age and disease strongly affect the VEGF protein, or vascular endothelial growth factor: stem cells stop synthesizing it and therefore their stem properties deteriorate considerably. If the cells are injected with an additional VEGF gene, they will rejuvenate; this is manifested, among other things, in the fact that modified stem cells and progenitor cells more actively stimulate vascular growth and restore blood flow in ischemic tissues. Researchers are also developing other genetic tools for cell repair, and those that already exist have successfully passed most of the stages of preclinical trials. However, unfortunately, it does not go further – clinical research stumbles upon the lack of proper laws that would regulate cellular experiments in the clinic, no matter how promising in the sense of public benefit they may be.

The Award of the Moscow Government to Young Scientists in 2014 marked really relevant projects that are at the forefront of modern biology. I would like to hope that this will draw attention to the purely organizational and administrative-legal problems that science has to face and the solution of which depends not only and not so much on the researchers themselves.

Portal "Eternal youth" http://vechnayamolodost.ru

19.11.2015