摘要：Mesenchymal stem/progenitor cells (MSC/MPC) from a variety of tissue sources (bone marrow, adipose tissue, fat pads, synovial membranes, synovial fluid, skin, muscle and periosteal tissue) have been widely applied for tissue engineering applications to generate replacements for injured or degenerated tissues. Alternatively, they have also been injected as free cells in an attempt to facilitate in vivo repair. Nearly all studies reported have used mixed cell populations of MSC/MPC, usually defined by cell surface phenotypes and/or functional ability to differentiate towards multiple cell lineages. Using more detailed cell surface phenotyping and limiting dilution approaches to isolate individual MSC/MPC clones have indicated that such mixed cell populations are very heterogeneous. In addition subsets of cells from different sources may have epigenetic modifications. While it is clear that MSC/MPC cells exhibit heterogeneity, the question of why this is the case has not been well addressed. This review will address some of these issues, as well as provide some insights into the implications when using such diverse cells for tissue engineering applications.

摘要：The knee is a multi-component organ system comprised of several tissues which function coordinately to provide mobility. Injury to any one component compromises the integrity of the system and leads to adaptation of the other components. Over time, such events often lead to dysfunction and degeneration of the knee. Therefore, there has been considerable research emphasis to repair injured components in the knee including cartilage, menisci, and ligaments. Approaches to improving healing and repair/regeneration of knee tissues have included surgery, anti-sense gene therapy, injection of growth factors and inflammatory cytokine antagonists, transplantation of in vitro expanded chondrocytes, enhancement of endogenous cells via microfracture, injection of mesenchymal stem cells, and implantation of in vitro tissue engineered constructs. Some of these approaches have lead to temporary improvement in knee functioning, while others offer the potential to restore function and tissue integrity for longer periods of time. This article will review the status of many of these approaches, and provide a perspective on their limitations and potential to contribute to restoration of knee function across the lifespan.