Transduction of human CD34+ CD38- bone marrow and cord blood-derived SCID-repopulating cells with third-generation lentiviral vectors

The major limitations of Moloney murine leukemia virus (MoMLV)-based vectors for human stem cell applications, particularly those requiring bone marrow (BM) stem cells, include their requirement for mitosis and retroviral receptor expression. New vectors based upon lentiviruses such as HIV-1 exhibit properties that may circumvent these problems. We report that novel third-generation, self-inactivating lentiviral vectors, expressing enhanced green fluorescent protein (EGFP) and pseudotyped with vesicular stomatitis virus G glycoprotein (VSV-G), can efficiently transduce primitive human repopulating cells derived from human BM and cord blood (CB) tested by the SCID-repopulating cell (SRC) assay. Highly purified CD34+ CD38- CB or BM cells were efficiently transduced (4-69%) and stably expressed in EGFP for 40 days in culture following infection for only 24 h without fibronectin, polybrene, or cytokines. Nonobese diabetic/severe combined immune-deficient (NOD/SCID) mice transplanted with transduced cells from either CB or BM donors were well engrafted, demonstrating maintenance of SRC during the infection procedure. Serially obtained femoral BM samples indicated that the proportion of EGFP+ cells within both myeloid and lymphoid lineages was maintained or even increased over time, averaging 42.3 +/- 6.6% for BM donors and 23.3 +/- 7.2% for CB at 12 weeks. Thus, the third-generation lentivectors readily transduce human CB and BM stem cells, under minimal conditions of ex vivo culture, where MoMLV-based vectors are ineffective. Since CB is inappropriate for most therapeutic applications, the efficient maintenance and transduction of BM-derived SRC during the short infection procedure are notable advantages of lentivectors.

Physical therapy intervention (PTI) increases plasma brain-derived neurotrophic factor (BDNF) levels in non-frail and pre-frail elderly women

Biomarkers are important factors in the identification of the frail elderly (higher risk of developing disease) and in assessing the impact of PTI. On the other hand, BDNF has been related to neuroprotection in a series of central nervous system diseases in older age. The levels of BDNF in groups of elderly women classified according to Fried phenotype (non-frail and pre-frail) were compared. We assessed the impact of a PTI on BDNF levels. A convenience sample of 48 elderly women was randomly selected. The PTI group was composed by 20 elderly women selected from this group. Plasma neurotrophic factors, such as BDNF, glial-derived neutrophic factor (GDNF), and nerve growth factor (NGF) were measured by enzyme-linked immunosorbent assay (ELISA). Timed-up-and-go (TUG) test, hand-grip and work/body weight were evaluated before and after the intervention. Plasma concentrations of BDNF were significantly higher in non-frail in comparison to pre-frail elderly women. After the PTI, higher levels of BDNF were found in elderly women (before 351±68 pg/ml and after 593±79 pg/ml; p<0.001). Both groups had an increase in BDNF levels after the PTI. The low levels of BDNF in pre-frail elderly women suggest that this neurotrophic factor may be a key pathophysiological mediator in the syndrome of frailty. The fact that PTI increased BDNF levels in both groups suggests that it may be possible to modify this phenotype.

Retroviral transduction of TLS-ERG initiates a leukemogenic program in normal human hematopoietic cells

Many chimeric oncogenes have been identified by virtue of the association between chromosomal translocation and specific human leukemias. However, the biological mechanism by which these oncogenes disrupt the developmental program of normal human hematopoietic cells during the initiation of the leukemogenic process is poorly understood due to the absence of an appropriate experimental system to study their function. Here, we report that retroviral transduction of TLS-ERG, a myeloid leukemia-associated fusion gene, to human cord blood cells results in altered myeloid and arrested erythroid differentiation and a dramatic increase in the proliferative and self-renewal capacity of transduced myeloid progenitors. Thus, TLS-ERG expression alone induced a leukemogenic program that exhibited similarities to the human disease associated with this translocation. These results provide an experimental examination of the early stages of the human leukemogenic process induced by a single oncogene and establish a paradigm to functionally assay putative leukemogenic genes in normal human hematopoietic cells.

Muscle strength, muscle balance, physical function and plasma interleukin-6 (IL-6) levels in elderly women with knee osteoarthritis (OA)

An increased circulating level of inflammatory cytokines has been associated with sarcopenia, functional disability, chronic diseases, and mortality in the elderly. Osteoarthritis (OA) is a disease common to this population, the seriousness of articular degeneration has been associated to the increase in some cytokines, IL-6 among them. The aim of the present study was to correlate IL-6 plasma levels with muscle strength, endurance, muscle balance hamstring/quadriceps (H/Q) and physical function in 80 elderly women (71.2 ± 5.3) with knee OA. IL-6 was measured using enzyme-linked immunosorbent assay (ELISA). Quadriceps and hamstring muscle strength, endurance and hamstring-quadriceps muscle balance were assessed using a Biodex system 3 pro(®) isokinetic dynamometer. Physical function was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Spearman's correlation coefficient was used to explore the relationship between the outcomes at the significance level of α=0.05. IL-6 was inversely correlated to the endurance of the hamstring muscles (r=-0.232; p=0.03) and muscle balance (H/Q) on the lower right side at 180°/s (r=-0.254; p=0.023). No significant correlation between IL-6, muscle strength and physical function was found. Our results show that elevated levels of IL-6 may possibly contribute to the reduction of the endurance of hamstring muscles and H/Q muscle balance in the elderly studied.

Tibiotalar contact area and pressure distribution: the effect of mortise widening and syndesmosis fixation

An unconstrained cadaver ankle model was designed to reevaluate the effect of ankle mortise widening and syndesmotic fixation on the load-bearing characteristics of the tibiotalar joint. Tibiotalar contact area, centroid shift, and mean contact pressure were quantified using a pressure-sensitive film technique. Six fresh-frozen below-knee amputation specimens were axially loaded with 500 N in three positions: neutral, 10 degrees of dorsiflexion, and 20 degrees of plantarflexion. The tibiotalar contact area and centroid position for each specimen in its intact state were first determined and then compared with values obtained after syndesmotic fixation, mortise widening of 2 and 4 mm, and deep deltoid ligament transection. Syndesmotic fixation significantly decreased joint contact area but did not consistently affect centroid position. However, unlike earlier studies, which used more constrained ankle fracture models, mortise widening with or without deltoid rupture was not found to significantly affect contact area, centroid position, or joint contact pressure. When statically loaded, the talus moved to its position of maximal congruence in the mortise, rather than displacing laterally along with the lateral malleolus.

Posterior cruciate ligament-sparing versus posterior cruciate ligament-sacrificing arthroplasty. Functional results using the same prosthesis

The functional outcomes of 143 total knee arthroplasties performed by 1 surgeon between 1988 and 1992 were reviewed. Ninety-three procedures were carried out with sacrifice of the posterior cruciate ligament (PCL); in 50, the PCL was preserved. All cases were performed using the Kinemax prosthesis (Howmedica, Rutherford, NJ). Demographically, there were no differences between the 2 patient groups. Patients were evaluated over a mean follow-up period of 3 years (range, 2-6 years) using the 100-point Hospital for Special Surgery knee scoring system. The data revealed no difference in clinical or early radiographic outcome between PCL-sacrificing and PCL-retaining arthroplasties and support the argument that PCL sacrifice should be considered in cases in which extensive releases and complex ligamentous balancing are required.

Development of a novel osteochondral graft for cartilage repair

This study reports the development of a novel osteochondral graft for cartilage repair. A technique of proteoglycan extraction via timed enzymatic digestion with hyaluronidase and trypsin and subsequent processing with a chloroform-methanol solution to remove cellular debris from a fresh-frozen bovine osteochondral sample is a method described to prepare a stable biological carrier of low immunogenicity. Lyophilization of the carrier followed by rehydration in a suspension of lapine chondrocytes produced a chimeric xenograft that succeeded in vivo in enhancing cartilage repair. In a pilot study, full-thickness articular cartilage defects treated with these xenografts demonstrated improved healing compared to untreated defects or defects treated with unseeded grafts at 2, 6, and 12 weeks postimplantation. The xenograft provoked a mild inflammatory response; however this did not impede the repair process. Further investigation of this novel chimeric xenograft eventually may yield a method of cartilage repair superior to current methods of treatment.

Tumorigenicity of adenovirus-transformed rodent cells is influenced by at least two regions of adenovirus type 12 early region 1A

Chimeric adenovirus type 5 (Ad5)/Ad12 early region 1A (E1A) genes were used to transform primary baby rat kidney cells in cooperation with Ad12 E1B, and the resulting cell lines were assayed for tumorigenicity in syngeneic rats. It was found that lines were nontumorigenic when transformed by hybrid E1A genes consisting of the amino-terminal 80 amino acids from Ad12 including conserved region 1 (CR1), with the remaining portion from Ad5. In contrast, cell lines transformed by hybrids containing Ad12 E1A sequences from the amino terminus to the leftmost border of CR3 or beyond were tumorigenic. To extend these results, sequences spanning CR2 and CR3 of Ad5 E1A were replaced with the homologous regions of Ad12 E1A and additional transformed cell lines were established. These lines were weakly-to-moderately tumorigenic, suggesting that Ad12 E1A sequences between CR2 and CR3 may be involved in tumorigenicity but are not the sole factors influencing it. Interestingly, examination of an E1A sequence alignment indicated that the region between CR2 and CR3 of Ad12 E1A is also conserved in the corresponding sequence of simian adenovirus type 7, which, like Ad12, is highly oncogenic. This region is characterized by the presence of a stretch of several alanine residues and is similar to a motif present in a number of proteins with transcriptional repression activity. The possibility that this region may influence tumorigenicity by means of a transcriptional regulatory mechanism is discussed.

Identification of adenovirus E1A regions which affect MHC class I expression and susceptibility to cytotoxic T lymphocytes

To map and characterize functional differences between the E1A oncoproteins of Ad5 and Ad12, we previously constructed a series of hybrid Ad5/12 E1A genes and used them in combination with Ad12 E1B to transform Hooded Lister rat cells. At least two regions within the first exon of Ad12 E1A which influenced tumorigenicity were identified. In this report, again using the hybrid Ad5/12 E1A (plus Ad12 E1B) transformants, we further examined the role of these regions in tumorigenicity by analyzing their effect on cell surface major histocompatibility complex class I expression and sensitivity to class I-restricted CD8+ cytotoxic T lymphocytes (CTLs). Results of these studies suggest that expression of either of the Ad12 E1A regions implicated in tumorigenicity could down-regulate cell surface class I levels. However, neither class I down-regulation nor sensitivity to allogeneic CTLs was shown to strictly correlate with the tumorigenic capacities of the transformed rat cells. Another factor influencing the tumorigenicity of Ad5 E1 and Ad12 E1 transformants may be the ability of their E1A products to encode CTL epitopes. To this end, we provide evidence suggesting that CTL epitopes may be encoded by Ad5 E1A but not by Ad12 E1A, since expression of certain portions of the Ad5 E1A protein conferred susceptibility to syngeneic Ad5 E1-specific CTLs in vitro, while Ad12 E1A expression did not confer susceptibility to syngeneic Ad12 E1-specific CTLs.

A rapid screening procedure for the identification of high-titer retrovirus packaging clones

We have developed a viral RNA (vRNA) dot blot assay for rapid identification of high-titer retrovirus vector production by packaging cell clones. The procedure employs Trizol LS reagent to purify vRNA from packaging cell supernatants, a sensitive dot blot assay, and Phosphorlmager technology to quantify packaged viral genomes in 2 days. Experiments performed on viral supernatants of known biological titer demonstrated that the vRNA dot blot assay was extremely sensitive and that dot intensity correlated directly with viral titer. It is often necessary to analyze approximately 100 virus producing cell clones, making this method useful as a rapid screen to identify the highest virus producing clones. The vRNA dot blot assay consistently identified a subset of candidate high-titer producer cell clones. In three independent screens the supernatant with the highest biological titer was produced by one of the previously defined candidate high-titer producer clones. Our procedure greatly facilitates virus titration by: (1) rapidly eliminating the vast majority of low-titer producer cell clones; (2) accurately identifying the subset of candidate high-titer producer clones for further biological titration and assessment of the proviral genomic structure; and (3) reducing laborious tissue culture manipulations to a minimum. Furthermore, the reliance of this method on molecular detection makes it ideally suited for the isolation of high-titer clones lacking a drug selection marker.

Characterization and retroviral transduction of an early human lymphomyeloid precursor assayed in nonswitched long-term culture on murine stroma

In the hierarchy of human hematopoietic progenitors, long-term culture-initiating cells (LTC-IC) and extended LTC-IC belong to the earliest cell populations that can be assayed in vitro. We report the identification of a multipotential lymphomyeloid progenitor detected in a nonswitch culture system. We observed the emergence of CD33+ myeloid and CD19+ B-lymphoid cells following plating of lineage-depleted (Lin-) CD34 -enriched or purified CD34+ CD38- cord blood cells on MS-5 stroma in the absence of exogenous cytokines. Both CD19+ CD20- pro-B and CD19+ CD20+ pre-B lymphocytes coexist with myeloid cells in long-term culture. A limiting dilution approach was used to show that a single CD34+ CD38- cell can generate lymphomyeloid progeny in conventional (5-week) and extended (10-week) cultures. Most of the clones in long-term culture or extended long-term culture contained not only lymphoid and myeloid cells, but also myeloid clonogenic progenitors. A high proportion of CD34+ CD38- cells gave rise to lymphomyeloid clones after 5 and 10 weeks of culturing (up to 48% and 16%, respectively), which distinguishes the assay reported here from those using switch culture conditions. We performed retroviral gene transfer experiments involving 1-3 days of exposure of Lin CD34+ -enriched cells to virus encoding enhanced green fluorescent protein. Monitoring of gene transfer efficiency into LTC-IC by enhanced green fluorescent protein fluorescence showed that it is possible to achieve marking of lymphomyeloid LTC-IC, albeit to a lesser extent than myeloid-restricted LTC-IC.

Genetic polymorphisms of inflammasome genes associated with pediatric acute lymphoblastic leukemia and clinical prognosis in the Brazilian Amazon

The immune system plays an important role in the control of cancer development. To investigate the possible association of inflammasome genes to childhood leukemia we performed a case-control study with 158 patients with acute lymphoblastic leukemia and 192 healthy individuals. The IL1B and IL18 genetic polymorphisms were genotyped by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) and NLRP1, NLRP3 and P2RX7 were genotyped using Real Time quantitative PCR (qPCR). The IL1B C/T rs19644 genotype was associated with the risk of developing ALL (C/C vs. C/T + T/T OR: 2.48 [95% CI: 1.26-4.88, p = 0.006]; C/C vs C/T OR: 2.74 [95% CI: 1.37-5.51, p = 0.003]) and the NLRP1 A/T rs12150220 (OR: 0.37 [95% CI: 0.16-0.87, p = 0.023]) was associated with protection against infectious comorbidities. It was not found association between NLRP3 and P2RX7 polymorphisms and acute lymphoblastic leukemia in our study. Our results suggest that the inflammasome single-variant polymorphisms (SNVs) may play a role in the development and prognostic of childhood leukemia. However, this finds requires further study within a larger population in order to prove it.

Influence of socio-demographic, clinical and functional factors on the severity of dementia

Dementia is one of the most relevant illnesses due to its functional impact on the elderly. The aim of the present study was to determine the influence of socio-demographic, clinical, cognitive and functional factors on the severity of dementia in elderly individuals. One hundred six elderly individuals with a diagnosis of dementia as determined by the DSM-IV/APA participated in the study. Cognition was assessed by the mini-mental state examination (MMSE); functional performance of basic and instrumental activities of daily living (BADLs and IADLs) was assessed by the Katz index (KI), Lawton-Brody index (LBI) and Pfeffer index (PI). The severity of dementia was established through the clinical dementia rating (CDR). In order to determine the influence of factors on the degree of dementia, ordinal regression analysis was performed. Age, MMSE, KI, LBI and PI scores had statistically significant associations to the severity of dementia. However, only the age (odds ratio (OR) = 0.197; confidence interval (CI) = 0.060-0.643) and performance in IADLs (LBI: OR = 1.237, CI = 1.077-1.422; PI: OR = 0.641, CI = 0.548-0.750) were maintained in the final ordinal regression model, R(2) = 0.818. The results show that elderly individuals over 80 years of age and those with a more compromised performance in IADLs have a greater chance of exhibiting more severe degrees of dementia. These findings suggest that the ability to perform IADLs may be an important variable in differentiating degrees of the severity of dementia.

The first exon of Ad12 E1A excluding the transactivation domain mediates differential binding of COUP-TF and NF-kappa B to the MHC class I enhancer in transformed cells

The major histocompatibility complex class I enhancer is the target for adenovirus-12 E1A-mediated down-regulation of class I transcription. In Ad12 transformed rodent cells, the class I enhancer is down-regulated through increased binding of the repressor COUP-TF to the R2 element and decreased binding of the activator NF-kappa B (p50/p65) to the R1 element. The reduced surface levels of class I antigens contribute to the tumorigenic potential of Ad12 transformed cells by favoring their immunoescape from cytotoxic T-lymphocytes. Previous studies using transformed cells containing hybrid Ad5/Ad12 E1A (plus Ad12 E1B) genes have indicated that sequences within the first exon of the 266R Ad12 E1A gene are required for class I down-regulation and tumorigenesis. In this study we demonstrate that these same sequences, which exclude the Ad12 CR3 transactivation domain, are also required for increased COUP-TF binding to the R2 element and decreased NF-kappa B binding to the R1 element of the class I enhancer. We further show that diminished NF-kappa B binding is not due to a lack of NF-kappa B1-p50 in the nuclei of Ad12 transformed rat cells.

Association between the IL1B-511 C>T polymorphism and the risk of hematologic malignancies: data from a meta-analysis

The relationship between the IL1B-511C>T (rs16944) polymorphism and the risk of developing hematologic malignancies remains controversial. Thus, we performed a meta-analysis to evaluate the association between IL1B-511C>T polymorphism and the risk of developing hematologic malignancies. A comprehensive search was conducted to identify all eligible studies on IL1B-511C>T polymorphism and hematologic malignancies. Twelve case-control studies, with 2,896 cases and 3,716 controls, were selected for the analysis. The overall data failed to indicate a significant association between IL1B-511C>T polymorphism and the risk of hematologic malignancies (OR:1.06, 95% Confidence Interval [CI]: 0.93-1.22). Moreover, non-significant associations were observed in a stratified analysis according to neoplasm type (multiple myeloma, Hodgkin's lymphoma, and non-Hodgkin's lymphoma), ethnicity (European and Asian), and Hardy-Weinberg equilibrium. In summary, our results suggest that there is no association between the IL1B-511C>T polymorphism and the risk of hematologic malignancies. As such, further large-scale studies are needed to confirm our findings.

A dual-role for IL-10: From leukemogenesis to the tumor progression in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer in the world, and accounts for 25% of all childhood cancers among children under 15 years of age. Longitudinal studies have shown that children with ALL are born with a deregulated immune response that, together with postnatal environmental exposures, favor the onset of the disease. In this context, IL-10, a key cytokine in the regulation of the immune response, presents itself as a paradoxical mediator, initially influencing the development of ALL through the regulation of inflammatory processes and later on the progression of malignancy, with the increase of this molecule in the leukemia microenvironment. According to the literature, this cytokine plays a critical role in the natural history of the disease and plays an important role in two different though complex scenarios. Thus, in this review, we explore the dual role of IL-10 in ALL, and describe its biological characteristics, immunological mechanisms and genetics, as well as its impact on the leukemia microenvironment and its clinical implications.

Enhanced megakaryocyte and erythroid development from normal human CD34(+) cells: consequence of enforced expression of SCL

The product of the SCL gene is a basic helix-loop-helix (bHLH) transcription factor that is essential for the development of hematopoietic stem cells in both the embryo and the adult. However, once the stem cell compartment is established, the function of SCL in subsequent differentiation and commitment events within normal hematopoietic cells remains undefined. The aim of the current study was to investigate this role using purified normal human hematopoietic CD34(+) cells. An SCL retrovirus was used to transduce CD34(+) cells isolated from human bone marrow, peripheral blood, and umbilical cord blood. Enforced expression of SCL increased by a median of twofold the number of erythroid colonies, with an increase in both colony size and the rate of hemoglobinization. Unexpectedly, enforced expression in CD34(+) cells also significantly increased the number of megakaryocyte colonies, but with no impact on the size of colonies. There was no consistent effect on the number nor size of granulocyte-macrophage (GM) colonies. The proliferative effect of enforced SCL expression on erythroid cells was attributed to a shortened cell cycle time; the self-renewal capacity of erythroid or GM progenitors was unchanged, as was survival of cells within colonies. These results demonstrate a role for SCL in determining erythroid and megakaryocyte differentiation from normal human hematopoietic CD34(+) cells.

Active site mutants of Escherichia coli citrate synthase. Effects of mutations on catalytic and allosteric properties

We report properties of five active site mutants of Escherichia coli citrate synthase, in which histidine 264, aspartate 362, and phenylalanine 383 were replaced by alanines, and arginines 387 and 407 by leucines. All mutants have much lower turnover numbers than wild type enzyme; the strongest effect was with the arginine 387 mutant, perhaps because the substrate, oxaloacetate, binds in a different orientation. The arginine 407 mutant has lost most of its ability to distinguish alpha-ketoglutarate, a competitive inhibitor, from oxaloacetate. The mutations of histidine 264 and aspartate 362 affect steady-state kinetics as would be anticipated from current models for citrate synthase catalysis, and resemble mutations of these residues, in pig heart and E. coli enzyme, reported by others. Mutations of residues 264, 362, and 383 also affect allosteric properties. With the phenylalanine 383 mutant, acetyl-CoA saturation is strongly sigmoid, even in the presence of the activator, KCl, implying a marked shift of the allosteric equilibrium toward the T state. The histidine 264 mutant appears to be shifted toward R state and shows weaker binding of the allosteric inhibitor, NADH; thus this mutation also affects the allosteric site, 25-30 A away.

The use of growth factors to increase the rate of regenerate consolidation

Two types of growth factors were used in an attempt to improve the quality of the regenerate bone in canine tibias after Ilizarov lengthening. Mechanical testing, biochemical analysis and histology did not demonstrate appreciable differences between the treated and the control limbs.

Pulmonary actinomycosis masquerading as lung cancer: A case report

Pulmonary actinomycosis is a rare yet important and challenging diagnosis to make. It is commonly confused with other lung diseases, such as tuberculosis and bronchogenic carcinoma, leading to delay diagnosis or misdiagnosis. A 49-year-old man presented with a chronic cough, hemoptysis, and pleuritic chest pain. His initial imaging studies including computed tomography (CT) was suggestive of bronchogenic carcinoma. A subsequent CTguided biopsy was consistent with pulmonary actinomycosis and excluded the possibility of bronchogenic carcinoma. He was treated with antibiotic therapy and achieved remission with complete radiological resolution upon follow-up.

Insights Regarding the Role of Inflammasomes in Leukemia: What Do We Know?

Inflammation is a physiological mechanism of the immune response and has an important role in maintaining the hematopoietic cell niche in the bone marrow. During this process, the participation of molecules produced by innate immunity cells in response to a variety of pathogen-associated molecular patterns and damage-associated molecular patterns is observed. However, chronic inflammation is intrinsically associated with leukemogenesis, as it induces DNA damage in hematopoietic stem cells and contributes to the creation of the preleukemic clone. Several factors influence the malignant transformation within the hematopoietic microenvironment, with inflammasomes having a crucial role in this process, in addition to acting in the regulation of hematopoiesis and its homeostasis. Inflammasomes are intracellular multimeric complexes responsible for the maturation and secretion of the proinflammatory cytokines interleukin-1β and interleukin-18 and the cell death process via pyroptosis. Therefore, dysregulation of the activation of these complexes may be a factor in triggering several diseases, including leukemias, and this has been the subject of several studies in the area. In this review, we summarized the current knowledge on the relationship between inflammation and leukemogenesis, in particular, the role of inflammasomes in different types of leukemias, and we describe the potential therapeutic targets directed at inflammasomes in the leukemic context.

Expansion of human cord blood CD34(+)CD38(-) cells in ex vivo culture during retroviral transduction without a corresponding increase in SCID repopulating cell (SRC) frequency: dissociation of SRC phenotype and function

Current procedures for the genetic manipulation of hematopoietic stem cells are relatively inefficient due, in part, to a poor understanding of the conditions for ex vivo maintenance or expansion of stem cells. We report improvements in the retroviral transduction of human stem cells based on the SCID-repopulating cell (SRC) assay and analysis of Lin(-) CD34(+)CD38(-) cells as a surrogate measure of stem cell function. Based on our earlier study of the conditions required for ex vivo expansion of Lin(-)CD34(+) CD38(-) cells and SRC, CD34(+)-enriched lineage-depleted umbilical cord blood cells were cultured for 2 to 6 days on fibronectin fragment in MGIN (MSCV-EGFP-Neo) retroviral supernatant (containing 1.5% fetal bovine serum) and IL-6, SCF, Flt-3 ligand, and G-CSF. Both CD34(+)CD38(-) cells (20.8%) and CFC (26.3%) were efficiently marked. When the bone marrow of engrafted NOD/SCID mice was examined, 75% (12/16) contained multilineage (myeloid and B lymphoid) EGFP(+) human cells composing as much as 59% of the graft. Half of these mice received a limiting dose of SRC, suggesting that the marked cells were derived from a single transduced SRC. Surprisingly, these culture conditions produced a large expansion (166-fold) of cells with the CD34(+)CD38(-) phenotype (n = 20). However, there was no increase in SRC numbers, indicating dissociation between the CD34(+)CD38(-) phenotype and SRC function. The underlying mechanism involved apparent downregulation of CD38 expression within a population of cultured CD34(+)CD38(+) cells that no longer contained any SRC function. These results suggest that the relationship between stem cell function and cell surface phenotype may not be reliable for cultured cells. (Blood. 2000;95:102-110)