Rejection protection
Bone marrow transplantation (hematopoietic stem cells) has become the standard of treatment for many conditions, including oncological diseases of the blood and lymphatic system, sickle cell anemia, hereditary metabolic disorders and radiation damage. Unfortunately, bone marrow transplantation often does not help because of the rejection reaction from the patient's immune system or the "graft versus host" reaction, in which the injected bone marrow cells attack the patient's healthy cells. These conditions can be fatal. Mesenchymal stromal cells (MSCs) are known to produce compounds that modulate the immune system and mitigate these problems in animal studies. Nevertheless, the results of clinical studies of the effectiveness of MSCs are unsatisfactory, since they are quickly eliminated from the body and can provoke an attack of the patient's immune system. Attempts to encapsulate MSCs in protective volumetric hydrogels also failed, because MSCs in such a massive shell cannot be administered intravenously.
Researchers from the Wyss Institute, Harvard School of Engineering and Applied Sciences. John A. Paulson and the Harvard Stem Cell Initiative reported that they have created a single cell encapsulation technology that effectively protects transplanted MSCs from excretion and immune attack and increases the efficiency of bone marrow transplantation in mice.
Three-dimensional schematic representation of the nucleus (blue-green) and cytoskeleton (yellow) of one encapsulated mesenchymal stromal cell (MSC) surrounded by a thin layer of alginate hydrogel (purple). Source: Wyss Institute.
Cell therapy is becoming increasingly common for the treatment of a number of diseases, and encapsulated cells can be frozen and thawed with minimal impact on their functions. This is of great importance for practical use in medicine.
The discovery is based on a method that the group developed earlier: a microfluidic device for coating individual living cells with a thin layer of alginate-based hydrogel. Cells are covered with microgel capsules, which are so small that their solution can be administered intravenously, unlike bulk hydrogels created by other methods. The MSCs encapsulated in this way remained in the lungs of mice ten times longer than the "pure" MSCs, and remained viable for up to three days.
Since the clinical appeal of MSCs lies in the secretion of compounds that modulate the body's immune system, the researchers needed to test how encapsulation in a microgel would affect the ability of cells to function and resist an immune attack. They changed the microgel by adding a compound that fuses with alginate and makes the microgel tougher. In addition, they cultured encapsulated MSCs, stimulating their division and the production of more cells. MSCs with a new microgel in the body of mice were five times more stable compared to the previous design and lasted an order of magnitude longer compared to pure MSCs.
To provoke an immune response to MSCs, the group incubated encapsulated cells in an environment containing cow embryonic serum, which is recognized by the body as a foreign agent, and then injected them into mice. The rate of excretion of these MSCs was higher than without immune activation, but five times lower than in pure MSCs. Microgels also outperformed pure MSCs when administered to mice with a previously occurring immune response – this is a model of patients who have been shown repeated administration of stem cells.
MSCs under the influence of inflammatory cytokines increase the expression of immunomodulating genes and the synthesis of corresponding proteins. The researchers decided to test whether encapsulation affects this response. They found that pure and encapsulated MSCs had similar levels of gene expression when exposed to the same cytokines, that is, microgels do not affect the effectiveness of MSCs.
The group injected MSC-containing microgel into mice simultaneously with allogeneic (donor) bone marrow, both compatible and incompatible. After nine days, mice that received encapsulated MSCs had twice as many allogeneic bone marrow cells in their bone marrow and blood compared to mice that did not receive MSCs. Encapsulated MSCs also increased the degree of engraftment of allogeneic cells in the recipient's bone marrow compared to pure MSCs.
A slice of MSC (blue) in a thin layer of combined alginate microgel (purple). Source: Wyss Institute.
One of the strengths of this work is that it does not use a genetic approach to increase cell survival in bone marrow transplantation, it complements the methods of genetic engineering. In fact, the new approach may be more effective and safer than trying to directly modify immune cells.
The authors hope to demonstrate the clinical viability of the technique in the near future.
Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru based on the materials of the Wyss Institute: Helping transplanted stem cells stick around and do their jobs.