Newswise — Tsukuba, Japan—Hematopoietic stem cells (HSCs) are infrequent cells located in the marrow that generate red blood cells, white blood cells, and platelets. Their proper operation is vital for the development and well-being of an organism. Consequently, abnormalities in the genetic material of hematopoietic stem cells (mutations) can result in compromised blood generation and grave illnesses.

Gene therapy aims to address such genetic disorders. A revolutionary technique that has revolutionized the entire domain in recent times is CRISPR/Cas9, an advanced method for gene editing through clustered regularly interspaced palindromic repeats/Cas9. By employing this approach, it becomes feasible to alter detrimental mutations and replace HSCs with restored functionality, potentially achieving a complete cure for the disease.

Nevertheless, the CRISPR/Cas9 system possesses imperfections. It solely rectifies mutations in a minute proportion of cells and may introduce fresh mutations that could be perilous into other cells. Consequently, the careful selection of corrected cells prior to transplantation becomes pivotal.

In 2019, the research team disclosed a technique for expanding HSCs extensively by employing a culture system based on polymers and cytokines. Addressing this issue, the authors have now devised an innovative culture system using a novel high-molecular-weight polymer. This system enables the proliferation of individual HSCs into transplantable cell colonies that exhibit a remarkable capacity for blood production after a prolonged period of ex vivo cultivation. Following the editing of a mutation in a mouse model with immune deficiency, the authors individually cultivate several hundred HSCs and meticulously examine them for clones exclusively carrying the desired genetic modification, ensuring successful engraftment. Through this method, the proportion of corrected HSCs suitable for transplantation can be elevated from 20%-30% to 100%, effectively eliminating potentially hazardous mutations from the graft. We strongly believe that this culture system holds the potential to enhance the efficiency and safety of genome editing in HSCs.

This work was supported by the German Research Foundation (BE 6847/1-1 to H.J.B.), the Japan Society for the Promotion of Science (JSPS; #20K16234 to M.S.J.L., #23K15315 to H.J.B., #21F21108 and #20K21612 to S.Y.), the Kay Kendall Leukaemia Fund (A.C.W.), the Japan Science and Technology Agency (JST; #18071245 to C.C.), and the Japanese Agency for Medical Research and Development (AMED; #21bm0404077h0001 and #21bm0704055h0002 to S.Y.). The D.G.K. laboratory is supported by a Blood Cancer UK Bennett Fellowship (15008), an ERC Starting Grant (ERC-2016-STG-715371), a CR-UK Programme Foundation award (DCRPGF\100008), the MRC Mouse Genetics Network Haematopoiesis Cluster (MC_PC_21043), and an MRC-AMED joint award (MR/V005502/1).

Journal Link: Cell Stem Cell