Matthew B. Murphy, Kathryn Moncivais, Arnold Caplan
Recent studies have shown that mesenchymal stem cells originate as pericytes, an entity capable of responding to stimuli.
Identification and Biology of MSCs
Origin and Early Research
Conheim first identified regenerative cells in the late 19th century. Mesenchymal cells were named in the laten 1980s due to their link to the development of mesenchymal tissues during embryonic development.
Tissue Sources of MSC
MSCs can be found in a lot of different adult and fetal tissue “including adipose (fat), dermis (skin), synovial fluid, periosteum, umbilical cord blood, placenta and amniotic fluid.”
Capacity of MSC
Trophic Properties of MSC
MSCs contain growth factors and chemokines that encourage cell reproduction and angiogenesis. The secretion of certain proteins allow MSCs to increase the number of fibroblasts, and the rate of epithelial and endothelial cell division. Trophic effects from MSCs can also contribute to the reduction of scar tissue due to the secretion of “paracrine factors keratinocyte growth factor, stromal cell-derived factor-1 (SDF-1) and macrophage inflammatory protein-1 alpha and beta.”
Anti-inflammatory and Immunomodulatory Properties of MSC
MSCs can assist with inflammatory conditions via paracrine mechanisms and the modulation of anti-inflammatory and immune mechanisms. MSCs reduce the proliferation of inflammatory immune cells, such as “T cells, natural killer cells, B cells, monocytes, macrophages and dendritic cells.”
MSCs secrete moderate levels of the human leukocyte antigen class 1 and class 2 making them undetectable to the immune system’s defense mechanisms making them a useful option for allogenic therapies. However, it should be mentioned that there have been several cases of MSC allogenic rejection.
Anti-apoptotic Properties of MSCs
MSCs have been to seen to reverse the process of apoptosis through the secretion of specific proteins.
Antimicrobial Properties of MSC
MSCs secrete a “particular peptide of the cathelicidin family in humans is hCAP-18/LL-37. LL-37” that is able to fight off gram positive and gram negative bacterial infections making it a viable option for systemic and acute infections.
Phenotypic Characterization of MSCs
MSCs can be categorized by the expression of positive or negative CD markers; CD73 (SH-3/4) and CD105 (endoglin or SH-2), followed thereafter by CD90 (Thy-1) and CD44. CD90+/CD105+/CD73+/CD44+ are seen most commonly in fibroblasts and stromal cells. “In 2006, the International Society of Stem Cell Research established a minimum set of criteria for defining MSCs as: (1) plastic-adherent cells; (2) capable of tri-lineage (bone, cartilage and fat) differentiation; (3) phenotypically positive for CD105, CD73 and CD90; and (4) negative for CD45, CD34, CD11b, CD14, CD79a and HLA-DR.59 However, these criteria are based on the characterization of in vitro cultured cells and do not apply to the native in vivo phenotype.”
MSC in Orthopedics and Spine Therapies
Transplanted osteoprogenitor cells from bone marrow are capable of forming ectopic bone through a “minimally invasive treatment for non-union fractures.” Increasing bone marrow concentration and/or ex vivo culture expansion can increase the number of progenitor cells within the host.
Osteonecrosis is a painful bone disease that usually reduces a patients mobility. It is often treated through core decompression, osteotomy and total joint replacement. Combining the use of autologous BM concentrate and a traditional treatment (i.e core decompression) showed a significant reduction in the expression of symptoms.
There needs to be more research conducted on whether autologous and allogenic BM concentrate can increase the rate of tissue regeneration and bone growth in patients getting spinal fusion surgeries.