Expansion of hematopoietic stem cells for transplantation: current perspectives

Hematopoietic stem cells (HSCs) are rare stem cells that have the ability to differentiate into specialized blood cells, including lymphocytes, red blood cells, and platelets [1]. While studies to successfully expand these cells have spanned over the last three decades, a routine method for ex vivo expansion of human HSCs is still not available. However, stem cell biology has progressed in recent years and thus ex vivo expansion of human HSCs should become possible in the near future.Stem cell transplants are a type of stem cell therapy used to treat cancers such as lymphoma and leukemia and other blood-related diseases [2]. Currently, there have been various difficulties associated with ex vivo expansion methods to generate stem cells for clinical therapies. The principle goal of all ex vivo attempts to expand HSCs is to produce a qualitative and quantitative acceptable cell population for bone marrow transplantation. Earliest attempts at ex vivo expansion centered on the use of cytokines known to support lineage committed cells [3]. Many researchers believe that these factors also played a key role in HSC proliferation. Thus, researchers hypothesized that the addition or removal of specific cytokines was able to regulate the survival and expansion of the stem cell population [2,3]. In more recent studies, researchers have focused on factors critical for embryologic development and the importance of signaling pathways that influence HSC self-renewal and expansion [2]. In the near future, it may be demonstrated that the most comprehensive approach may be a combination of various optimized conditions. Ex vivo expansion of HSCs is crucial for their use in the treatment of malignant and non-malignant diseases. Today, HSC gene therapy continues to be a highly attractive treatment option for many disorders including hematologic conditions, immunodeficiencies, and genetic disorders [2].In most bone marrow transplant centers, peripheral blood stem cells (PBSCs) remain the