Mesenchymal stem cells (MSCs) have been used to repair connective tissue defects in several animal models. Compared to "natural healing" controls (no added cells), MSC-collagen gel constructs in rabbit tendon defects significantly improve repair biomechanics. However, ectopic bone forms in 28% of MSC-treated rabbit tendons. To understand the source of bone formation, three studies were performed. In the first study, the hypothesis was tested that MSCs delivered during surgery contribute to bone formation in the in vivo repair site. Adjacent histological sections in the MSC-treated repair tissue were examined for pre-labeled MSCs and for cells showing positive alkaline phosphatase (ALP) activity. Both cells were observed in serial sections in regions of ectopic bone. Contralateral "natural healing" tendons lacked both markers. In the other two studies, the effects of osteogenic supplements and construct geometry (monolayer vs. 3-D) on ALP activity were studied to test three hypotheses: that rabbit MSCs increase ALP activity over time in monolayer culture conditions; that adding osteogenic inducing supplements to the culture medium increases cellular protein in monolayer culture; and that rabbit MSCs increase ALP activity both in monolayer and in 3-D constructs, with and without media supplements. Culture in monolayer under similar conditions to in vivo (as in the first study) did not increase ALP at 2 or 4 weeks. Medium designed to increase osteogenic activity significantly increased cell numbers (cellular protein increased by 260%) but did not affect ALP activity either in monolayer or 3 -0 constructs (p > 0.12). However, MSCs in 3-D constructs exhibited higher ALP activity than cells in monolayer, both in the presence (p < 0.005) and absence of supplement (p < 0.045). These results suggest that in vitro conditions may critically influence cell differentiation and protein expression.Mechanisms responsible for these effects are currently under investigation.

Mesenchymal stem cells (MSCs) were isolated from bone marrow, culture-expanded, and then seeded at 1, 4, and 8 million cells/mL onto collagen gel constructs designed to augment tendon repair in vivo. To investigate the effects of seeding density on the contraction kinetics and cellular morphology, the contraction of the cell/collagen constructs was monitored over time up to 72 h in culture conditions. Constructs seeded at 4 and 8 million cells/mL showed no significant differences in their gross appearance and dimensions throughout the contraction process. By contrast, constructs seeded at 1 million cells/mL initially contracted more slowly and their diameters at 72 h were 62 to 73% larger than those seeded at higher densities. During contraction, MSCs reoriented and elongated significantly with time. Implants prepared at higher seeding densities showed more well aligned and elongated cell nuclei after 72 h of contraction. Changes in nuclear morphology of the MSCs in response to physical constraints provided by the contracted collagen fibrils may trigger differentiation pathways toward the fibroblastic lineage and influence the cell synthetic activity. Controlling the contraction and organization of the cells and matrix will be critical for successfully creating tissue engineered grafts.

Successful bone tissue engineering depends on the scaffold's ability to allow nutrient diffusion to and waste removal from the regeneration site, as well as provide an appropriate mechanical environment. Since bone is highly vascularized, scaffolds that provide greater mass transport may support increased bone regeneration. Permeability encompasses the salient features of three-dimensional porous scaffold architecture effects on scaffold mass transport. We hypothesized that higher permeability scaffolds will enhance bone regeneration for a given cell seeding density. We manufactured poly-e-caprolactone scaffolds, designed to have the same internal pore design and either a low permeability (0.688 · 10 /N-s), respectively. Scaffolds were seeded with bone morphogenic protein-7-transduced human gingival fibroblasts and implanted subcutaneously in immune-compromised mice for 4 and 8 weeks. Micro-CT evaluation showed better bone penetration into high permeability scaffolds, with blood vessel infiltration visible at 4 weeks. Compression testing showed that scaffold design had more influence on elastic modulus than time point did and that bone tissue infiltration increased the mechanical properties of the high permeability scaffolds at 8 weeks. These results suggest that for polycaprolactone, a more permeable scaffold with regular architecture is best for in vivo bone regeneration. This finding is an important step toward the end goal of optimizing a scaffold for bone tissue engineering.

Invasive mold infections (IMIs) are a major source of morbidity and mortality among lung transplant recipients (LTR) yet information regarding the epidemiology of IMI in this population are limited. From 2001–2006, multicenter prospective surveillance for IMIs among LTR was conducted by the Transplant-Associated Infection Surveillance Network. The epidemiology of IMI among all LTR in the cohort is reported. Twelve percent (143/1173) of LTRs under surveillance at 15 U.S. centers developed IMI infections. The 12-month cumulative incidence of IMIs was 5.5%; 3-month all-cause mortality was 21.7%. s caused the majority (70%)of IMIs; non-infections (39; 27%) included: (5), mucormycosis (3), and “unspecified” or “other” mold infections (31). Late-onset IMI was common: 52% occurred within one year post-transplant (median 11 months, range 0–162 months). IMIs are common late-onset complications with substantial mortality in LTRs. LTRs should be monitored for late-onset IMIs and prophylactic agents should be optimized based on likely pathogen.

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