Faculty Bibliography

Hypomorphic RAG mutants with severely reduced V(D)J recombination activity cause Omenn Syndrome (OS), an immunodeficiency with features of immune dysregulation and a restricted TCR repertoire. Precisely how RAG mutants produce autoimmune and allergic symptoms has been unclear. Current models posit that the severe recombination defect restricts the number of lymphocyte clones, a few of which are selected upon Ag exposure. We show that murine RAG1 R972Q, corresponding to an OS mutation, renders the recombinase hypersensitive to selected coding sequences at the hairpin formation step. Other RAG1 OS mutants tested do not manifest this sequence sensitivity. These new data support a novel mechanism for OS: by selectively impairing recombination at certain coding flanks, a RAG mutant can cause primary repertoire restriction, as opposed to a more random, limited repertoire that develops secondary to severely diminished recombination activity

BACKGROUND: Although it is clear that radiation therapy can cause tissue injury, the degree of injury that is observed clinically can be highly variable. It is possible that variability in the methods by which ionizing radiation is delivered can contribute to some of the observed variability. Thus, the purpose of this study was to assess the effects of various fractionation schedules on the growth and differentiation potential of isolated mesenchymal stem cells in vitro. METHODS: Isolated mesenchymal stem cells (triplicate studies) were exposed to a dose of 12 Gy of ionizing radiation as a single dose, in two doses of 6 Gy, or in six doses of 2 Gy. Cellular proliferation and the potential for differentiation along the bone and fat lineage were assessed. Potential mechanisms for injury and protection were evaluated by analyzing the expression of p21 and manganese superoxide dismutase. RESULTS: Delivery of radiation in multiple doses confers significant radioprotection to mesenchymal stem cell proliferation and potential for differentiation. In contrast, delivery of 12 Gy of radiation as a single dose or as two equal doses of 6 Gy results in marked deficiencies in cellular proliferation and potential for multilineage cellular differentiation. CONCLUSIONS: The authors have demonstrated that even minor alterations in fractionation of radiation dose can result in significant effects on the potential of mesenchymal stem cells to differentiate. These findings imply that at least some of the variability in tissue damage after radiation therapy observed clinically may be attributable to differences in the delivery of ionizing radiation.

BACKGROUND: The viability of fat grafts obtained by even a well-established technique remains poorly studied and unknown. This study was designed to determine the viability of fat grafts harvested and refined by the Coleman technique. METHODS: Sixteen adult white women were enrolled in this study. In group 1 (n = 8), fat grafts were harvested and processed with the Coleman technique by a single surgeon from the abdomen of each patient according to his standardized method. In group 2 (n = 8), fat grafts were harvested with the conventional liposuction by another surgeon. After centrifugation, the resulting middle layer of tissue was collected. All fat graft samples were analyzed for the following studies: trypan blue vital staining for viable adipocyte counts, glycerol-3-phophatase dehydrogenase assay, and routine histologic examination. RESULTS: The higher viable adipocyte counts were found in group 1 compared with group 2 (4.11 +/- 1.11 versus 2.57 +/- 0.56 x 10 cells/ml; p < 0.004). The level of glycerol-3-phophatase dehydrogenase activity was significantly higher in group 1 compared with group 2 (0.66 +/- 0.09 versus 0.34 +/- 0.13 U/ml; p < 0.0001). Histologic examination showed normal structure of fragmented fatty tissues in both groups. CONCLUSIONS: Although fat grafts obtained by both methods maintain normal histologic structure, the Coleman technique yields a greater number of viable adipocytes and sustains a more optimal level of cellular function within fat grafts and should be considered superior to conventional liposuction as a preferred method of choice for fat graft harvesting

The bony biochemical environment is a complex system that permits and promotes cellular functions that lead to matrix production and ossification. In Part I of this review, we discussed the important actions of signaling molecules, including hormones, cytokines, and growth factors. Here, we review other constituents of the extracellular matrix, including minerals, fibrinous and nonfibrinous proteins, and enzymes such as the matrix metalloproteinases. We conclude with a discussion of the role of biochemical modulation in endogenous and exogenous tissue engineering