Natural ocean iron fertilization and climate variability over geological periods.

Marine primary producers are largely dependent on and shape the Earth's climate, although their relationship with climate varies over space and time. The growth of phytoplankton and associated marine primary productivity in most of the modern global ocean is limited by the supply of nutrients, including the micronutrient iron. The addition of iron via episodic and frequent events drives the biological carbon pump and promotes the sequestration of atmospheric carbon dioxide (CO2 ) into the ocean. However, the dependence between iron and marine primary producers adaptively changes over different geological periods due to the variation in global climate and environment. In this review, we examined the role and importance of iron in modulating marine primary production during some specific geological periods, that is, the Great Oxidation Event (GOE) during the Huronian glaciation, the Snowball Earth Event during the Cryogenian, the glacial-interglacial cycles during the Pleistocene, and the period from the last glacial maximum to the late Holocene. Only the change trend of iron bioavailability and climate in the glacial-interglacial cycles is consistent with the Iron Hypothesis. During the GOE and the Snowball Earth periods, although the bioavailability of iron in the ocean and the climate changed dramatically, the changing trend of many factors contradicted the Iron Hypothesis. By detangling the relationship among marine primary productivity, iron availability and oceanic environments in different geological periods, this review can offer some new insights for evaluating the impact of ocean iron fertilization on removing CO2 from the atmosphere and regulating the climate.

Split-Thickness Skin Grafting: A Primer for Orthopaedic Surgeons.

Soft-tissue defects pose a unique challenge to the treating orthopaedic surgeon. Such defects are commonly encountered after orthopaedic injuries or infection, and the management of these wounds varies significantly. Skin grafting has gained popularity in the management of such soft-tissue defects due to its ability to provide coverage, re-epithelialize, and have a relatively high success rate. One of the most frequently used types of skin graft in orthopaedics is the split-thickness skin graft (STSG). Understanding the proper indications, technique, and management of the STSG foreshadows its success or failure. This review focuses on the indications, technique, alternatives, and complications surrounding the utilization of the STSG in the management of orthopaedic injuries.

Experimental Techniques to Assess Coral Physiology in situ Under Global and Local Stressors: Current Approaches and Novel Insights.

Coral reefs are declining worldwide due to global changes in the marine environment. The increasing frequency of massive bleaching events in the tropics is highlighting the need to better understand the stages of coral physiological responses to extreme conditions. Moreover, like many other coastal regions, coral reef ecosystems are facing additional localized anthropogenic stressors such as nutrient loading, increased turbidity, and coastal development. Different strategies have been developed to measure the health status of a damaged reef, ranging from the resolution of individual polyps to the entire coral community, but techniques for measuring coral physiology in situ are not yet widely implemented. For instance, while there are many studies of the coral holobiont response in single or limited-number multiple stressor experiments, they provide only partial insights into metabolic performance under more complex and temporally and spatially variable natural conditions. Here, we discuss the current status of coral reefs and their global and local stressors in the context of experimental techniques that measure core processes in coral metabolism (respiration, photosynthesis, and biocalcification) in situ, and their role in indicating the health status of colonies and communities. We highlight the need to improve the capability of in situ studies in order to better understand the resilience and stress response of corals under multiple global and local scale stressors.

Impact of Having a Planned Additional Operation at Time of Liver Transplant on Graft and Patient Outcomes.

Advances in liver transplantation (LT) have allowed for expanded indications and increased surgical complexity. In select cases, additional surgery may be performed at time of LT rather than prior to LT due to the significant risks associated with advanced liver disease. We retrospectively studied the characteristics and outcomes of patients who underwent an additional planned abdominal or cardiac operation at time of LT between 2011-2019. An additional operation (LT+) was defined as a planned operation performed under the same anesthetic as the LT but not directly related to the LT. In total, 547 patients were included in the study, of which 20 underwent LT+ (4%). Additional operations included 10 gastrointestinal, 5 splenic, 3 cardiac, and 2 other abdominal operations. Baseline characteristics between LT and LT+ groups were similar. The median total operating time was significantly longer in LT+ compared to LT only (451 vs. 355 min, p = 0.002). Graft and patient survival, intraoperative blood loss, transfusion of blood products, length of hospital stay, and post-operative complications were not significantly different between groups. In carefully selected patients undergoing LT, certain additional operations performed at the same time appear to be safe with equivalent short-term outcomes and liver graft survival as those undergoing LT alone.

Epidemiology and outcomes of primary sclerosing cholangitis with and without inflammatory bowel disease in an Australian cohort.

BACKGROUND & AIMS: Epidemiological data on primary sclerosing cholangitis (PSC) outside the Northern hemisphere are limited. Similarly, the impact of inflammatory bowel disease (IBD) on PSC outcomes remains unclear. We aimed to study the epidemiology and outcomes of PSC patients with and without IBD in an Australian cohort. METHODS: We retrospectively studied PSC patients attending two tertiary referral hospitals over 20 years. Diagnosis of PSC was made according to international guidelines by positive cholangiography and/or liver biopsy (for small duct PSC) with supporting clinical and laboratory evidence. RESULTS: Of 208 PSC patients (61% male) were studied (2271patient-years follow-up). The median age of PSC diagnosis was similar for PSC-IBD and PSC-only patients (40 years vs 42 years, P = .35). All 33 deaths occurred in PSC-IBD patients while there were no deaths in PSC-only patients (21% vs 0%, P < .01). However, there were no significant differences in liver transplantation (PSC-only 25% vs PSC-IBD 31%, P = .45) and transplant-free survival between PSC-only and PSC-IBD patients (P = .43). On multivariate Cox regression, only elevated international normalized ratio (INR) was associated with a greater risk of death or liver transplant (HR 2.0, 95% CI 1.1-3.6, P = .02). Development of gastrointestinal malignancy was higher in the PSC-IBD group compared to PSC-only group (22% vs 2%, P < .01). CONCLUSION: Australian PSC patients have similar characteristics compared to European and North American cohorts. IBD is a significant predictor of gastrointestinal malignancies. Deaths were more common in PSC-IBD but overall transplant-free survival remained similar in PSC-IBD and PSC-only groups. An elevated INR was an independent predictor of death or liver transplantation.

The Involvement of Acetaldehyde in Ethanol-Induced Cell Cycle Impairment.

BACKGROUND: Hepatocytes metabolize the vast majority of ingested ethanol. This metabolic activity results in hepatic toxicity and impairs the ability of hepatocytes to replicate. Previous work by our group has shown that ethanol metabolism results in a G2/M cell cycle arrest. The intent of these studies was to discern the roles of acetaldehyde and reactive oxygen, two of the major by-products of ethanol metabolism, in the G2/M cell cycle arrest. METHODS: To investigate the role of ethanol metabolites in the cell cycle arrest, VA-13 and VL-17A cells were used. These are recombinant Hep G2 cells that express alcohol dehydrogenase or alcohol dehydrogenase and cytochrome P450 2E1, respectively. Cells were cultured with or without ethanol, lacking or containing the antioxidants N-acetylcysteine (NAC) or trolox, for three days. Cellular accumulation was monitored by the DNA content of the cultures. The accumulation of the cyclin-dependent kinase, Cdc2 in the inactive phosphorylated form (p-Cdc2) and the cyclin-dependent kinase inhibitor p21 were determined by immunoblot analysis. RESULTS: Cultures maintained in the presence of ethanol demonstrated a G2/M cell cycle arrest that was associated with a reduction in DNA content and increased levels of p-Cdc2 and p21, compared with cells cultured in its absence. Inclusion of antioxidants in the ethanol containing media was unable to rescue the cells from the cell cycle arrest or these ethanol metabolism-mediated effects. Additionally, culturing the cells in the presence of acetaldehyde alone resulted in increased levels of p-Cdc2 and p21. CONCLUSIONS: Acetaldehyde produced during ethanol oxidation has a major role in the ethanol metabolism-mediated G2/M cell cycle arrest, and the concurrent accumulation of p21 and p-Cdc2. Although reactive oxygen species are thought to have a significant role in ethanol-induced hepatocellular damage, they may have a less important role in the inability of hepatocytes to replace dead or damaged cells.

Harmful algal blooms and climate change: Learning from the past and present to forecast the future.

Climate change pressures will influence marine planktonic systems globally, and it is conceivable that harmful algal blooms may increase in frequency and severity. These pressures will be manifest as alterations in temperature, stratification, light, ocean acidification, precipitation-induced nutrient inputs, and grazing, but absence of fundamental knowledge of the mechanisms driving harmful algal blooms frustrates most hope of forecasting their future prevalence. Summarized here is the consensus of a recent workshop held to address what currently is known and not known about the environmental conditions that favor initiation and maintenance of harmful algal blooms. There is expectation that harmful algal bloom (HAB) geographical domains should expand in some cases, as will seasonal windows of opportunity for harmful algal blooms at higher latitudes. Nonetheless there is only basic information to speculate upon which regions or habitats HAB species may be the most resilient or susceptible. Moreover, current research strategies are not well suited to inform these fundamental linkages. There is a critical absence of tenable hypotheses for how climate pressures mechanistically affect HAB species, and the lack of uniform experimental protocols limits the quantitative cross-investigation comparisons essential to advancement. A HAB "best practices" manual would help foster more uniform research strategies and protocols, and selection of a small target list of model HAB species or isolates for study would greatly promote the accumulation of knowledge. Despite the need to focus on keystone species, more studies need to address strain variability within species, their responses under multifactorial conditions, and the retrospective analyses of long-term plankton and cyst core data; research topics that are departures from the norm. Examples of some fundamental unknowns include how larger and more frequent extreme weather events may break down natural biogeographic barriers, how stratification may enhance or diminish HAB events, how trace nutrients (metals, vitamins) influence cell toxicity, and how grazing pressures may leverage, or mitigate HAB development. There is an absence of high quality time-series data in most regions currently experiencing HAB outbreaks, and little if any data from regions expected to develop HAB events in the future. A subset of observer sites is recommended to help develop stronger linkages among global, national, and regional climate change and HAB observation programs, providing fundamental datasets for investigating global changes in the prevalence of harmful algal blooms. Forecasting changes in HAB patterns over the next few decades will depend critically upon considering harmful algal blooms within the competitive context of plankton communities, and linking these insights to ecosystem, oceanographic and climate models. From a broader perspective, the nexus of HAB science and the social sciences of harmful algal blooms is inadequate and prevents quantitative assessment of impacts of future HAB changes on human well-being. These and other fundamental changes in HAB research will be necessary if HAB science is to obtain compelling evidence that climate change has caused alterations in HAB distributions, prevalence or character, and to develop the theoretical, experimental, and empirical evidence explaining the mechanisms underpinning these ecological shifts.

Characterization of putative iron responsive genes as species-specific indicators of iron stress in thalassiosiroid diatoms.

Iron (Fe) availability restricts diatom growth and primary production in large areas of the oceans. It is a challenge to assess the bulk Fe nutritional health of natural diatom populations, since species can differ in their physiological and molecular responses to Fe limitation. We assayed expression of selected genes in diatoms from the Thalassiosira genus to assess their potential utility as species-specific molecular markers to indicate Fe status in natural diatom assemblages. In this study, we compared the expression of the photosynthetic genes encoding ferredoxin (a Fe-requiring protein) and flavodoxin (a Fe-free protein) in culture experiments with Fe replete and Fe stressed Thalassiosira pseudonana (CCMP 1335) isolated from coastal waters and Thalassiosira weissflogii (CCMP 1010) isolated from the open ocean. In T. pseudonana, expression of flavodoxin and ferredoxin genes were not sensitive to Fe status but were found to display diel periodicities. In T. weissflogii, expression of flavodoxin was highly responsive to iron levels and was only detectable when cultures were Fe limited. Flavodoxin genes have been duplicated in most diatoms with available genome data and we show that T. pseudonana has lost its copy related to the Fe-responsive copy in T. weissflogii. We also examined the expression of genes for a putative high affinity, copper (Cu)-dependent Fe uptake system in T. pseudonana. Our results indicate that genes encoding putative Cu transporters, a multi-Cu oxidase, and a Fe reductase are not linked to Fe status. The expression of a second putative Fe reductase increased in Fe limited cultures, but this gene was also highly expressed in Fe replete cultures, indicating it may not be a useful marker in the field. Our findings highlight that Fe metabolism may differ among diatoms even within a genus and show a need to validate responses in different species as part of the development pipeline for genetic markers of Fe status in field populations.

Iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas.

Oceanic high-nitrate, low-chlorophyll environments have been highlighted for potential large-scale iron fertilizations to help mitigate global climate change. Controversy surrounds these initiatives, both in the degree of carbon removal and magnitude of ecosystem impacts. Previous open ocean enrichment experiments have shown that iron additions stimulate growth of the toxigenic diatom genus Pseudonitzschia. Most Pseudonitzschia species in coastal waters produce the neurotoxin domoic acid (DA), with their blooms causing detrimental marine ecosystem impacts, but oceanic Pseudonitzschia species are considered nontoxic. Here we demonstrate that the sparse oceanic Pseudonitzschia community at the high-nitrate, low-chlorophyll Ocean Station PAPA (50 degrees N, 145 degrees W) produces approximately 200 pg DA L(-1) in response to iron addition, that DA alters phytoplankton community structure to benefit Pseudonitzschia, and that oceanic cell isolates are toxic. Given the negative effects of DA in coastal food webs, these findings raise serious concern over the net benefit and sustainability of large-scale iron fertilizations.

14-3-3 activation of DNA binding of p53 by enhancing its association into tetramers.

Activation of the tumour suppressor p53 on DNA damage involves post-translational modification by phosphorylation and acetylation. Phosphorylation of certain residues is critical for p53 stabilization and plays an important role in DNA-binding activity. The 14-3-3 family of proteins activates the DNA-binding affinity of p53 upon stress by binding to a site in its intrinsically disordered C-terminal domain containing a phosphorylated serine at 378. We have screened various p53 C-terminal phosphorylated peptides for binding to two different isoforms of 14-3-3, epsilon and gamma. We found that phosphorylation at either S366 or T387 caused even tighter binding to 14-3-3. We made by semi-synthesis a tetrameric construct comprised of the tetramerization plus C-terminal domains of p53 that was phosphorylated on S366, S378 and T387. It bound 10 times tighter than did the monomeric counterpart to dimeric 14-3-3. We showed indirectly from binding curves and directly from fluorescence-detection analytical ultracentrifugation that 14-3-3 enhanced the binding of sequence-specific DNA to p53 by causing p53 dimers to form tetramers at lower concentrations. If the in vitro data extrapolate to in vivo, then it is an attractive hypothesis that p53 activity may be subject to control by accessory proteins lowering its tetramer-dimer dissociation constant from its normal value of 120-150 nM.

Determining subnanomolar iron concentrations in oceanic seawater using a siderophore-modified film analyzed by infrared spectroscopy.

Iron is a bioactive trace element in seawater that regulates photosynthetic carbon dioxide drawdown and export from surface waters by phytoplankton in upward of 40% of the world's oceans. While autonomous sensor arrays are beginning to provide high-resolution data on temporal and spatial scales for some key oceanographic parameters, current analytical methods for iron are not amenable to autonomous platforms because of the need for user involvement and wet chemistry-based approaches. As a result, very large gaps remain in our understanding of iron distribution and chemistry in seawater. Here we present a straightforward nanostructure-based method to measure dissolved iron in natural seawater. The device comprises an iron-specific chelating biomolecule, desferrioxamine B (DFB), covalently immobilized on a mesoporous silica film. Changes in infrared spectral signatures of the immobilized DFB upon Fe(III) complexation provide an accurate and precise measure of iron on the surface of a chip exposed to seawater. The current system has a detection limit of approximately 50 pM for a 1-L sample at pH 1.7 and was used to measure dissolved iron in subarctic Pacific waters without interference from other elements in seawater. This technology provides a major step toward obtaining accurate iron measurements on autonomous research platforms.

Structure of tumor suppressor p53 and its intrinsically disordered N-terminal transactivation domain.

Proteins with intrinsically disordered domains are implicated in a vast range of biological processes, especially in cell signaling and regulation. Having solved the quaternary structure of the folded domains in the tumor suppressor p53 by a multidisciplinary approach, we have now determined the average ensemble structure of the intrinsically disordered N-terminal transactivation domain (TAD) by using residual dipolar couplings (RDCs) from NMR spectroscopy and small-angle x-ray scattering (SAXS). Remarkably, not only were we able to measure RDCs of the isolated TAD, but we were also able to do so for the TAD in both the full-length tetrameric p53 protein and in its complex with a specific DNA response element. We determined the orientation of the TAD ensemble relative to the core domain, found that the TAD was stiffer in the proline-rich region (residues 64-92), which has a tendency to adopt a polyproline II (PPII) structure, and projected the TAD away from the core. We located the TAD in SAXS experiments on a complex between tetrameric p53 and four Taz2 domains that bind tightly to the TAD (residues 1-57) and acted as "reporters." The p53-Taz2 complex was an extended cross-shaped structure. The quality of the SAXS data enabled us to model the disordered termini and the folded domains in the complex with DNA. The core domains enveloped the response element in the center of the molecule, with the Taz2-bound TADs projecting outward from the core.

Necrotizing fasciitis: Diagnosis and management of an occult infective focus.

Necrotizing fasciitis is a life-threatening, fulminant disease that is a diagnostic and therapeutic challenge. Presenting with a triad of findings including progressive erythema, severe dermatological edema and severe pain disproportionate to the physical findings, this disease is a surgical emergency. Delayed diagnosis and surgical debridement lead to higher mortality. Early extensive surgical debridement, aggressive antibiotic therapy, invasive monitoring and intensive care management determine the outcome in most cases. In patients who fail to demonstrate clinical improvement, profound sepsis and its sequela -systemic inflammatory response - have frequently been implicated. It is these patients that need to be carefully re-evaluated for 'hidden' foci of infection that may be the real cause of the patient's decline. Once detected, these occult foci can be surgically debrided, resulting in dramatic improvement. Two illustrative cases, one with occult endo- and panophthalmitis and the other with an unusual involvement of deeper muscle planes and the nodal basin, demonstrate this point. This consumptive process gathers momentum at an alarming speed, hence, the treatment must be aggressive and prompt.

La fasciite nécrosante est une maladie fulminante mettant la vie en danger, sans compter que c'est un défi diagnostique et thérapeutique. Se manifestant par une triade d'observations, y compris un érythème évolutif, un œdème dermatologique grave et une douleur marquée disproportionnée par rapport aux observations physiques, cette maladie est une urgence opératoire. Un retard du diagnostic et du débridement chirurgical entraîne un taux de mortalité plus élevé. Dans la plupart des cas, un débridement chirurgical précoce extensif, une antibiothérapie énergique, une surveillance envahissante et une prise en charge en soins intensifs déterminent l'issue. Chez les patients qui n'affichent pas d'amélioration clinique, une septicémie profonde et ses séquelles (une réponse inflammatoire systémique), se produisent souvent. Ce sont ces patients qui ont besoin d'une réévaluation attentive afin de dépister des foyers « cachés ¼ d'infection qui pourraient être la véritable cause du déclin du patient. Une fois dépisté, ces foyers occultes peuvent faire l'objet d'un débridement chirurgical, ce qui entraîne une amélioration remarquable. Deux cas, l'un accompagné d'endophtalmie et de panophtalmie occultes et l'autre, de l'atteinte inhabituelle des plans musculaires plus profonds et du bassin nodal, démontrent ce point. Ce processus consomptif gagne de la vitesse à un rythme alarmant. C'est pourquoi le traitement doit être rapide et dynamique.

Tendon function after replantation: prognostic factors and strategies to enhance total active motion.

The purpose of this study was to determine the important prognostic factors for recovery of tendon function as measured by total active movement (TAM) in patients undergoing digital replantation. More important, the authors wanted to establish which factors may be manipulated to maximize motion. A retrospective review of 48 patients (103 digital rays) who underwent replantation was performed. Average TAM for all digits was 129 deg. Zone 1 and zone 5 injuries had better TAM than injuries in zones 2, 3, and 4, which had TAM values not significantly different from one another. Avulsion injuries fared significantly worse than other mechanisms of injury. TAM values were not affected by age, type of bone fixation, number of arteries repaired, or number of digits injured. Digits with both the profundus and the superficialis tendons repaired had significantly better TAM values relative to one-tendon fingers. Similarly, fingers treated with an "early" mobilization regime also exhibited better movement. Small numbers of injured digits in some groups may have limited our ability to detect significant differences.

Extramammary Paget's disease of the perineum: Avoiding pitfalls in diagnosis and management.

Extramammary Paget's disease (EMPD) is a rare entity, especially in the perinoscrotal region, and typically presents in elderly white patients as a pruritic white or red patch in the area of distribution of apocrine glands. Typically, it affects a single site. Since its manifestations are insidious and easily misdiagnosed, the appropriate management is delayed. Management of this problem is complex and effective treatment can not only lower recurrence rates but also provide an optimal reconstructive result. The present report describes three patients with scrotal EMPD. Based on literature search, the etiopathology, diagnosis and management of these lesions is discussed. Reconstructive options, with special emphasis on scrotal lesions, are also discussed.

La maladie de Paget extramammaire (MPEM) est une maladie rare qui se manifeste surtout dans la région périnéoscrotale et qui se présente généralement chez des personnes âgées de race blanche sous forme de tache prurigineuse rougeâtre ou blanchâtre dans la zone de distribution des glandes apocrines. D'ordinaire, elle atteint un seul foyer. Puisque ses manifestations sont insidieuses et faciles à mal diagnostiquer, sa prise en charge convenable est retardée. D'ailleurs, cette prise en charge est complexe. Toutefois, un traitement efficace peut non seulement faire chuter le taux de récidive mais également assurer une reconstruction optimale. Le présent rapport décrit trois patients atteints d'une MPEM scrotale. Compte tenu d'une recherche dans la documentation scientifique, l'étiopathologie, le diagnostic et la prise en charge de ces lésions sont abordés. Les possibilités de reconstruction, surtout axées sur les lésions scrotales, sont également examinées.

Ex vivo culture with human brain endothelial cells increases the SCID-repopulating capacity of adult human bone marrow.

Adult human bone marrow (ABM) is an important source of hematopoietic stem cells for transplantation in the treatment of malignant and nonmalignant diseases. However, in contrast to the recent progress that has been achieved with umbilical cord blood, methods to expand ABM stem cells for therapeutic applications have been disappointing. In this study, we describe a novel culture method that uses human brain endothelial cells (HUBECs) and that supports the quantitative expansion of the most primitive measurable cell within the adult bone marrow compartment, the nonobese diabetic/severe combined immunodeficient (NOD/SCID) repopulating cell (SRC). Coculture of human ABM CD34(+) cells with brain endothelial cells for 7 days supported a 5.4-fold increase in CD34(+) cells, induced more than 95% of the CD34(+)CD38(-) subset to enter cell division, and produced progeny that engrafted NOD/SCID mice at significantly higher rates than fresh ABM CD34(+) cells. Using a limiting dilution analysis, we found the frequency of SRCs within fresh ABM CD34(+) cells to be 1 in 9.9 x 10(5) cells. Following HUBEC culture, the estimated frequency of SRCs increased to 1 in 2.4 x 10(5) cells. All mice that received transplants of HUBEC-cultured cells showed B-lymphoid and myeloid differentiation, indicating that a primitive hematopoietic cell was preserved during culture. Noncontact HUBEC cultures also maintained SRCs at a level comparable to contact HUBEC cultures, suggesting that cell-to-cell contact was not required. These data demonstrate that human brain endothelial cells possess a unique hematopoietic activity that increases the repopulating capacity of adult human bone marrow.

Rescue of hematopoietic stem cells following high-dose radiation injury using ex vivo culture on endothelial monolayers.

Military personnel are at significant risk for potentially lethal myeloablative injury secondary to nuclear accident, nuclear attack, or chemical weapons attack. In an attempt to develop culture conditions in which hematopoietic stem cells might be rescued from the effects of radiation, we irradiated (1,000 cGy split dose) 6-week-old C57BL/6 (Ly 5.1) and syngeneic C57BL/6 (Ly 5.2) mice and tested whether bone marrow mononuclear cells (MNCs) harvested postirradiation could be rescued via coculture in porcine microvascular endothelial cell (PMVEC) monolayers. We found that a subpopulation of bone marrow MNCs exposed to 1,000 cGy could be maintained and expanded over 10 days in a PMVEC culture (3.8-fold expansion), whereas liquid suspension culture did not maintain a significant number of hematopoietic cells postirradiation. Colony-forming assays demonstrated that murine MNCs exposed to 1,000 cGy did not give rise to granulocyte/macrophage colony-forming units (CFU-GM), erythroid burst-forming units (BFU-e), or CFU-Mix in 14-day cultures, whereas irradiated MNCs that were subsequently cultured in PMVEC-generated CFU-GM, BFU-e, and CFU-Mix at cloning efficiencies of 1.3%, 0.2%, and 0.2%, respectively. In survival studies, we found that 78% of mice that were irradiated and then transplanted with irradiated/PMVEC-expanded MNCs were alive at day 50, compared with 18% of irradiated control mice (p < 0.05). We also observed that mice transplanted with irradiated/PMVEC-expanded MNCs showed complete hematologic recovery. At 8 weeks post-transplant, we found evidence of Ly 5.1 donor cells in both the bone marrow and the spleen of the transplanted animals, but the levels of engraftment were low (range, 0-5.1%; mean, 1.9%). These results demonstrate that a subpopulation of bone marrow stem cells are capable of surviving the effects of high-dose radiation if these cells are placed in coculture with endothelial cell monolayers.