Image Source: GettyImage
This newly established system uses an optimal chemically defined cell culture medium, thereby providing a suitable alternative to systems using typical cytokine-containing media in vitro. The new research could help advance multiple hematopoietic stem cell-related therapies in clinical development and potentially save lives.
Hematopoietic stem cells (HSCs) are important immature blood cells in the bone marrow that can be triggered to differentiate into any blood cell type. Hematopoietic stem cell transplantation can be used to treat diseases in which the bone marrow is damaged and can no longer produce healthy blood cells, but the widespread and safe use of hematopoietic stem cells has been limited by obstacles to cell growth and expansion in the laboratory (i.e., outside the body). Now, in a new study, researchers from research institutions including the University of Tsukuba, the University of Tokyo, and Keio University in Japan have established a novel culture system that supports the long-term expansion of hematopoietic stem cells in vitro. The relevant research results were published in the journal Nature on March 2, 2023, with the title of the paper “Chemically defined cytokine-free expansion of human hematopoietic stem cells”.
Human hematopoietic stem cells are often readily obtained from umbilical cord blood, but this produces insufficient numbers of hematopoietic stem cells to allow for proper transplantation. Although ex vivo hematopoietic stem cell expansion is clearly necessary, this goal has been elusive. In previous studies, cell signaling molecules called cytokines and a protein called albumin were often used to stimulate the expansion of blood stem cells, but only resulted in short-term expansion.
Professor Satoshi Yamazaki, co-corresponding author of the paper, explained, “Other groups have used new methods to expand hematopoietic stem cells in vitro, including adding small molecules, certain hydrogels, various growth factors or small molecule inhibitors to the cell culture medium, showed promising results.”
Although cytokines were once thought to be indispensable for the growth of hematopoietic stem cells in vitro, in this new study, the authors speculate that there are other suitable alternatives. Starting with mouse hematopoietic stem cells, they had previously shown that albumin could be replaced by a synthetic polymer. This not only overcomes the problem of variability associated with albumin between batches used in different experiments but also prevents the negative impact of impurities that often occur.
When the authors applied this approach to human hematopoietic stem cells, they noticed that they did not proliferate as well as mouse hematopoietic stem cells. After molecular analysis, they observed decreased activity of important signaling molecules called PI3K and AKT. To address this, they found that adding chemicals that activate PI3K and AKT significantly improved the growth of human hematopoietic stem cells.
“We also found that adding a receptor agonist called butyzamide stimulated the proliferation of hematopoietic stem cells, providing a good alternative to the usual cytokines used in the past,” said Prof. Yamazaki.
Adding a compound called UM171, along with a specific polymer, improved the outcome by supporting the expansion of long-term blood stem cells. Using a technique called RNA sequencing, the authors confirmed the success of this in vitro expansion system on gene expression in single cells. Furthermore, by transplanting ex vivo-expanded hematopoietic stem cells into mice, they found that the hematopoietic stem cells expanded by this new culture system successfully colonized and grew in mice.
Given the importance of ex vivo expansion of human hematopoietic stem cells, this newly established system uses an optimal chemically defined cell culture medium, thereby providing a suitable alternative to systems using typical cytokine-containing media. The new research could help advance multiple hematopoietic stem cell-related therapies in clinical development and potentially save lives.
Masatoshi Sakurai et al. Chemically defined cytokine-free expansion of human haematopoietic stem cells . Nature, 2023, doi:10.1038/s41586-023-05739-9.