Improved antibody responses to delayed pneumococcal vaccination in splenectomized rats.

Pneumococcal vaccination following splenectomy is widely used as prophylaxis against overwhelming postsplenectomy infection. There remains controversy however, over the timing of vaccination. We hypothesized that delaying vaccination would increase the antibody response. Pneumococcal vaccinations were given at designated intervals to rats that had undergone either a sham abdominal surgery or splenectomy. Sixty male Sprague-Dawley rats, 250 to 400 g, were divided into three groups for vaccination: I, 1 day postoperatively; II, 7 days postoperatively; and III, 28 days postsplenectomy/sham. Serum antibody levels were then determined by enzyme-linked immunosorbent assay at 5 and 21 days after vaccination. Immunoglobulin (Ig) levels after delayed vaccination at 1 week postoperatively and 1 month postoperatively were significantly higher than levels from rats vaccinated 1 day postoperatively. IgM levels after vaccinations 1 week and 1 month postoperatively were also significantly higher than levels of rats vaccinated 1 day postoperatively (P < 0.05 for both IgG and IgM). On the basis of these results, we conclude that delaying vaccination after splenectomy enhances antibody responses.

Cells isolated from adult human skeletal muscle capable of differentiating into multiple mesodermal phenotypes.

Wound healing is the response of tissue to injury that results in scar formation. Tissue regeneration would be a more ideal response. Previously, we have isolated a population of cells from avian, rodent, and rabbit skeletal muscle capable of differentiating into multiple mesodermal phenotypes. The present experiments were designed to determine whether a similar population of cells exist in human skeletal muscle. Separate cell preparations from skeletal muscle on an amputated leg of a 75-year-old female and the pectoralis muscle of a 27-year-old male were enzymatically dissociated and cultured to confluence in Eagle's minimal essential medium with 10 per cent preselected horse serum, then trypsinized, filtered, and slowly frozen in 7.5 per cent dimethylsulfoxide to -80 degrees C. The cells were thawed and plated with the same media plus dexamethasone (a nonspecific differentiation agent) at 10(-10) - 10(-6) M concentrations for up to 6 weeks. Immunological and histochemical staining assays were performed. Phenotypes observed included stem cells with typical stellate morphology (control), skeletal myotubes (anti-myosin), smooth muscle (anti-a-actin), bone (von Kossa stain), cartilage (Alcec blue), and fat (Sudan black B). These experiments establish the existence of a population of mesenchymal stem cells in human skeletal muscle capable of differentiating into multiple mesodermal phenotypes. The possibility exists of manipulating the mesenchymal stem cells to achieve appropriate regeneration of mesenchymal tissues in the injured patient.

Recombinant human bone morphogenetic proteins-2 and -4 induce several mesenchymal phenotypes in culture.

Bone morphogenetic protein has previously been shown to induce the formation of cartilage and bone in vivo. We have isolated a population of mesenchymal stem cells from rat skeletal muscle capable of forming multiple mesodermal morphologies in vitro. These cells were treated with recombinant human bone morphogenetic proteins-2 and -4 to determine the differentiation-inducing activities of bone morphogenetic protein on these cells. The mesenchymal stem cells were cultured in medium with 10% preselected horse serum containing 0 to 100 ng/ml recombinant human bone morphogenetic proteins-2 or -4 for a maximum of 4 weeks. Control cultures maintained the stellate morphology of mesenchymal stem cells. Cultures treated with recombinant human bone morphogenetic protein-2 exhibited discrete cartilage nodules and mineralized bone nodules. The first increase in chondrogenesis was seen at 0.5 ng/ml. Cultures treated with recombinant human bone morphogenetic protein-4 also exhibited an increase in chondrogenesis at the higher concentration of 2 ng/ml. Skeletal myotubes and adipocytes also appeared in cultures treated with either bone morphogenetic protein. Mesenchymal stem cells do respond to inductive factors, but bone morphogenetic proteins-2 and -4 were not specific for the induction of cartilage and bone.

A population of cells resident within embryonic and newborn rat skeletal muscle is capable of differentiating into multiple mesodermal phenotypes.

We have previously shown a population of putative mesenchymal stem cells in the connective tissue surrounding embryonic avian skeletal muscle. These cells differentiate into at least five recognizable phenotypes in culture: fibroblasts, chondrocytes, myotubes, osteoblasts, and adipocytes. We have now isolated a similar population of cells from fetal and newborn rat skeletal muscle. Cells from rat leg muscle were dissected, minced, and then enzymatically digested with a collagenase-dispase solution. The dissociated cells were plated and allowed to differentiate into two recognizable populations: myotubes and stellate mononucleated cells. The cells were then trypsinized, filtered through a 20 microm filter to remove the myotubes, frozen at -80 degrees C, then thawed and replated. In culture the cells maintained their stellate structure. However, under treatment with dexamethasone, a nonspecific differentiating agent, seven morphologic conditions emerged: cells with refractile vesicles that stained with Sudan black B (adipocytes), multinucleated cells that spontaneously contracted in culture and stained with an antibody to myosin (myotubes), round cells whose extracellular matrix stained with Alcian blue, pH 1.0 (chondrocytes), polygonal cells whose extracellular matrix stained with Von Kossa's stain (osteoblasts), cells with filaments that stained with an antibody to smooth muscle a-actin (smooth muscle cells), cells that incorporated acetylated low density lipoprotein (endothelial cells), and spindle-shaped cells that grew in a swirl pattern (fibroblasts). The initial population is tentatively classified as putative mesenchymal stem cells. The presence of these cells point to the existence of stem cells in the postembryonic mammal that could provide a basis for tissue regeneration as opposed to scar tissue formation during wound healing.

Repair of articular cartilage defects using mesenchymal stem cells.

Degeneration of articular cartilage in osteoarthritis is a serious medical problem. We have isolated a population of cells from the connective tissue of mammals termed mesenchymal stem cells (MSCs) for their apparent unlimited growth potential and their ability to differentiate into several phenotypes of the mesodermal lineage, including cartilage and bone. These qualities make them ideal candidates for cartilage repair. We isolated MSCs from adult rabbit muscle and cultured them in vitro into porous polyglycolic acid polymer matrices. The matrices were implanted into 3-mm-diameter full thickness defects in rabbit knees with empty polymer matrices serving as the contralateral controls. The implants were harvested 6 and 12 weeks postop. At 6 weeks, the controls contained fibrocartilage while the experimentals seemed to contain undifferentiated cells. By 12 weeks postop, the controls contained limited fibrocartilage and extensive connective tissue, but no subchondral bone. In contrast, the implants containing MSCs had a surface layer of cartilage approximately the same thickness as normal articular cartilage and normal-appearing subchondral bone. There was good integration of the implant with the surrounding tissue. Implantation of MSCs into cartilage defects appears to effect repair of both the articular cartilage and subchondral bone. Studies are ongoing to further characterize the use of MSCs for cartilage repair.