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David T Scadden

Publications and source records attributed to David T Scadden.

At least 55 records · Page 3Linked to original sources
PubMed2004

In vivo self-renewing divisions of haematopoietic stem cells are increased in the absence of the early G1-phase inhibitor, p18INK4C.

Self-renewal of stem cells is critical for tissue repair and maintenance of organ integrity in most mammalian systems. The relative asymmetry between self-renewal and differentiation in balance with apoptosis determines the size and durability of a stem-cell pool. Regulation of the cell cycle is one of the fundamental mechanisms underlying determination of cell fate. Absence of p21(Cip1/Waf1), a late G1-phase cyclin-dependent kinase inhibitor (CKI), has previously been shown to enable cell-cycle entry of haematopoietic stem cells, but leads to premature exhaustion of the stem cells under conditions of stress. We show here that deletion of an early G1-phase CKI, p18(INK4C), results in strikingly improved long-term engraftment, largely by increasing self-renewing divisions of the primitive cells in murine transplant models. Therefore, different CKIs have highly distinct effects on the kinetics of stem cells, possibly because of their active position in the cell cycle, and p18(INK4C) appears to be a strong inhibitor limiting the potential of stem-cell self-renewal in vivo.

Animals↗
PubMed2004

Defective immune function of primary effusion lymphoma cells is associated with distinct KSHV gene expression profiles.

Primary effusion lymphomas (PEL) are uniformly infected with Kaposi's sarcoma-associated herpesvirus (KSHV), and thus likely present both tumor and viral antigens to the immune system. In order to grow unrestricted and cause disease, multiple immune evasion strategies may be utilized by PEL to evade immune surveillance. Using six well-established PEL cell lines and comparing these to Epstein-Barr virus-transformed B cell lines and peripheral blood B cells, significant differences were found in the surface expression of molecules involved in antigen presentation, T cell activation and cell-cell adhesion. Significantly reduced stimulation of cytotoxic T lymphocytes, lowered sensitivity to natural killer cell-mediated lysis and impaired function as antigen presenting cells in mixed leukocyte reactions were found for three PEL cell lines with particularly low CD54, CD58 and CD81 expression. Comparative microarray analysis demonstrated specific patterns of KSHV-encoded gene expression that were associated with the different immune functions of these cell lines. Thus, the present data suggest that distinct patterns of KSHV gene expression may be associated with particular phenotypic and functional characteristics of PEL cells, which may influence PEL pathogenesis.

Adult↗
PubMed2003

Ephrin receptor, EphB4, regulates ES cell differentiation of primitive mammalian hemangioblasts, blood, cardiomyocytes, and blood vessels.

Differentiation of pluripotent embryonic stem (ES) cells is associated with expression of fate-specifying gene products. Coordinated development, however, must involve modifying factors that enable differentiation and growth to adjust in response to local microenvironmental determinants. We report here that the ephrin receptor, EphB4, known to be spatially restricted in expression and critical for organized vessel formation, modifies the rate and magnitude of ES cells acquiring genotypic and phenotypic characteristics of mesodermal tissues. Hemangioblast, blood cell, cardiomyocyte, and vascular differentiation was impaired in EphB4-/- ES cells in conjunction with decreased expression of mesoderm-associated, but not neuroectoderm-associated, genes. Therefore, EphB4 modulates the response to mesoderm induction signals. These data add differentiation kinetics to the known effects of ephrin receptors on mammalian cell migration and adhesion. We propose that modifying sensitivity to differentiation cues is a further means for ephrin receptors to contribute to tissue patterning and organization.

Animals↗
PubMed2003

P2Y-like receptor, GPR105 (P2Y14), identifies and mediates chemotaxis of bone-marrow hematopoietic stem cells.

Hematopoiesis in mammals undergoes a developmental shift in location from fetal liver to bone marrow accompanied by a gradual transition from highly proliferative to deeply quiescent stem cell populations. P2Y receptors are G-protein-coupled nucleotide receptors participating in vascular and immune responses to injury. We identified a P2Y-like receptor for UDP-conjugated sugars, GPR105 (P2Y14), with restricted expression on primitive cells in the hematopoietic lineage. Anti-GPR105 antibody selectively isolated a subset of hematopoietic cells within the fetal bone marrow, but not in the fetal liver, that was enriched for G0 cell cycle status and for in vitro stem-cell-like multipotential long-term culture capability. Conditioned media from bone marrow stroma induced receptor activation and chemotaxis that was sensitive to G alpha i and anti-receptor antibody inhibition. GPR105 is a G-protein-coupled receptor identifying a quiescent, primitive population of hematopoietic cells restricted to bone marrow. It mediates primitive cell responses to specific hematopoietic microenvironments and extends the known immune system functions of P2Y receptors to the stem cell level. These data suggest a new class of receptors participating in the regulation of the stem cell compartment.

ADP-ribosyl Cyclase↗
PubMed2003

Myeloid expression of cytochrome P450 4F3 is determined by a lineage-specific alternative promoter.

The cytochrome P450 4F3 (CYP4F3) gene encodes two functionally distinct enzymes that differ only by the selection of exon 4 (CYP4F3A) or exon 3 (CYP4F3B). CYP4F3A inactivates leukotriene B4, a reaction that has significance for controlling inflammation. CYP4F3B converts arachidonic acid to 20-hydroxyeicosatetraenoic acid, a potent activator of protein kinase C. We have previously shown that mRNAs coding for CYP4F3A and CYP4F3B are generated from distinct transcription start sites in neutrophils and liver. We therefore investigated mechanisms that regulate the cell-specific expression of these two isoforms. Initially, we analyzed the distribution of CYP4F3 in human leukocytes and determined a lineage-specific pattern of isoform expression. CYP4F3A is expressed in myeloid cells and is coordinate with myeloid differentiation markers such as CD11b and myeloperoxidase during development in the bone marrow. In contrast, CYP4F3B expression is restricted to a small population of CD3+ T lymphocytes. We identified distinct transcriptional features in myeloid, lymphoid, and hepatic cells that indicate the presence of multiple promoters in the CYP4F3 gene. The hepatic promoter depends on a cluster of hepatocyte nuclear factor sites 123-155 bp upstream of the initiator ATG codon. The myeloid promoter spans 400 bp in a region 468-872 bp upstream of the ATG codon; it is associated with clusters of CACCT sites and can be activated by ZEB-2, a factor primarily characterized as a transcriptional repressor in cells that include lymphocytes. ZEB-2 interacts with C-terminal binding protein and Smads, and this would provide opportunities for integrating environmental signals in myelopoiesis and inflammation.

Base Sequence↗
PubMed2003

Ex vivo targeting of p21Cip1/Waf1 permits relative expansion of human hematopoietic stem cells.

Relative quiescence is a defining characteristic of hematopoietic stem cells. Reasoning that inhibitory tone dominates control of stem cell cycling, we previously showed that mice engineered to be deficient in the cyclin-dependent kinase inhibitor, p21Cip1/Waf1 (p21), have an increased stem cell pool under homeostatic conditions. Since p21 was necessary to maintain stem cell quiescence and its absence sufficient to permit increased murine stem cell cycling, we tested whether reduction of p21 alone in human adult-derived stem cells could affect stem cell proliferation. We demonstrate here that interrupting p21 expression ex vivo resulted in expanded stem cell number and in vivo stem cell function compared with control, manipulated cells. Further, we demonstrate full multilineage reconstitution capability in cells where p21 expression was knocked down. Therefore, lifting the brake on cell proliferation by altering cell cycle checkpoints provides an alternative paradigm for increasing hematopoietic stem cell numbers. This approach may be useful for relative ex vivo human stem cell expansion.

ADP-ribosyl Cyclase↗
PubMed2003

Multiple measures of HIV burden in blood and tissue are correlated with each other but not with clinical parameters in aviremic subjects.

OBJECTIVES: To determine the levels of residual HIV DNA and RNA in blood and gut reservoirs in aviremic patients, assess correlations among compartmental measurements of HIV burden, and evaluate association with clinical parameters. DESIGN: Cross-sectional analysis of baseline data only, on 40 patients enrolled in phase II study evaluating efficacy of autologous gene-modified CD4+ and CD8+ T cells. All patients were on stable antiretroviral regimen with undetectable plasma HIV RNA (< 50 copies/ml). METHODS: Measurements repeatedly performed over 8-12 weeks pre-intervention: blood HIV DNA, analysis of rectal mucosa-associated lymphoid tissue for both HIV RNA and HIV DNA, and quantitative co-culture of HIV from CD8-depleted peripheral blood mononuclear cells (PBMC). RESULTS: Quantifiable levels of HIV detected in compartments despite undetectable levels of plasma HIV RNA: HIV co-culture of PBMC (88%), blood HIV DNA (95%), rectal biopsy HIV DNA (95%), rectal biopsy HIV RNA (65%). A significant correlation existed among various measures of HIV burden (HIV co-culture, blood HIV DNA, rectal biopsy HIV RNA and DNA) but not between assays and clinical parameters [duration of highly active antiretroviral therapy (HAART), type of HAART]. All assays had comparable or less variability than in plasma viral load assays; HIV co-culture had the highest coefficient of variability whereas the blood HIV DNA assay had the lowest and was considered the most reliable assay. CONCLUSIONS: The data support safety, feasibility and high compliance of quantifying reservoirs of residual HIV in treated subjects with undetectable plasma HIV RNA. Lack of correlation between levels of HIV in residual reservoirs and duration of HAART suggests treatment-mediated viral suppression alone does not lead to reproducible decay in HIV reservoirs.

Adult↗
PubMed2003

Stem cells and immune reconstitution in AIDS.

The hematopoietic system generally has reserve sufficient to tolerate significant insult and regenerative capacity to overcome most damage due to infectious agents. However, HIV infection results in a progressive decline in hematopoietic function and even in the context of potent, anti-retroviral therapy is able to only incompletely reconstitute immune function. The ability of the immune system to respond to HIV itself remains compromised, a defect that leaves infected individuals with a lifelong dependence on medications. The capability of stem cells and the thymus to restore function and their limitations in the context of HIV infection are discussed in this review.

Acquired Immunodeficiency Syndrome↗
PubMed2003

Immune reconstitution in HIV infection and its relationship to cancer.

HIV infection results in formidable immune dysfunction, widely affecting the immune system, but typified by T lymphopenia. This dysfunction includes a perturbed immune response to several persistent viruses that have a propensity to cause tumors. Effective control of HIV replication by highly active antiretroviral therapy (HAART) results in regeneration of the damaged immune system, and recent advances have allowed this immune reconstitution to be better defined. This article describes the immunodeficiency caused by HIV and the response of the immune system to HAART, with specific reference to the immune response to cancers associated with HIV infection.

HIV Infections↗
PubMed2002

The protease inhibitor ritonavir inhibits the functional activity of the multidrug resistance related-protein 1 (MRP-1).

BACKGROUND: Efflux pumps situated on the plasma membrane, such as P-glycoprotein (Pgp) and the multidrug resistance related-protein 1 (MRP-1), have been shown to extrude HIV protease inhibitors from the cell. MRP-1 is present on many barrier sites throughout the body, such as the blood-brain and blood-testis interfaces and could reduce the concentration of protease inhibitors in these sanctuary sites for HIV-1 replication. Factors that modulate efflux pump function in vivo are poorly defined. OBJECTIVE: To analyze the inhibitory potential of the anti-retroviral drugs indinavir, amprenavir, ritonavir, lamivudine or zidovudine to modulate MRP-1 function. METHODS: Effect of anti-HIV drugs on the efflux pump activity of MRP-1 was evaluated in the presence of increasing concentrations of human plasma, using UMCC-1/VP cells which stably over-express MRP-1. MRP-1 activity was abrogated by probenecid. The potential of blocking MRP-1 function for an extended (3 day) time period, was also examined in MRP-1 over-expressing cells cultured with either probenecid or the anti-retroviral drugs and a cytotoxic compound (etoposide) that is transported by MRP-1. RESULTS: Ritonavir inhibited the functional activity of MRP-1 similarly to probenecid, as demonstrated by re-sensitization of MRP-1 over-expressing cells to cytotoxic effects of etoposide. Inhibition by ritonavir was inversely related to the concentration of human plasma added to the cells (r2 = 0.89). Other anti-HIV drugs didn't affect the MRP-1 mediated efflux of etoposide. CONCLUSIONS: These data may be exploitable to further improve sanctuary site concentrations of anti-HIV or anti-cancer drugs by using ritonavir as a lead compound to develop more potent MRP-1 inhibitors.

Anti-HIV Agents↗
PubMed2002

Heterologous cells cooperate to augment stem cell migration, homing, and engraftment.

T-lymphocyte depletion of bone marrow grafts compromises engraftment, suggesting a facilitating mechanism provided by the T cells that has been shown to associate with CD8(+) but not CD4(+) T cells. Explanations for this phenomenon have focused on immune targeting of residual host cells or cytokine production. We provide evidence for an alternative mechanism based on cooperative effects on cell motility. We observed that engraftment of CD34(+) cells in a beta(2)-microglobulin-deficient nonobese diabetic/severe combined immunodeficiency (beta(2)m(-/-) NOD/SCID) mouse model paralleled clinical observations in humans, with an enhancing effect noted from the addition of CD8(+) cells but not CD4(+) cells. This correlated with CD8(+) augmentation of CD34(+) cell homing to the bone marrow in vivo and CD8(+) cell-associated increases of CD34(+) cell transmigration through a bone marrow endothelial cell line in vitro. The cooperative interaction was not sensitive to brefeldin A inhibition of protein secretion. However, cytochalasin D-induced inhibition of CD8(+) cytoskeletal rearrangements abrogated CD34(+) transendothelial migration and impaired CD34(+) cell homing in vivo. CD8(+) cells did not migrate in tandem with CD34(+) cells or alter endothelial barrier integrity; rather, they affected phosphotyrosine-mediated signaling in CD34(+) cells in response to the chemokine stromal derived factor-1alpha (SDF-1alpha). These data demonstrate cell-cell cooperativity between different cell types in mediating chemotactic events and provide one potential explanation for the clinically observed effect of CD8(+) cells on bone marrow transplantation. This modification of cell migration by neighboring cells provides broad possibilities for combinatorial effects between cells of different types to influence cell localization.

Animals↗
PubMed2002

Absence of biologically important Kaposi sarcoma-associated herpesvirus gene products and virus-specific cellular immune responses in multiple myeloma.

Kaposi sarcoma-associated herpesvirus (KSHV) has been associated with several diseases, but the association between KSHV and multiple myeloma (MM) remains controversial. To address this issue, we studied patients with MM for the presence of viral RNA transcripts as well as KSHV-specific cellular immune responses. Highly sensitive reverse transcription-polymerase chain reaction assays for detection of viral transcripts of KSHV open reading frame (ORF) 26, ORF72, and ORF74 did not detect viral gene transcripts in long-term cultures of bone marrow stromal cells from 23 patients with MM. Moreover, sensitive assays for KSHV ORF65-specific and ORF73-specific cytotoxic T-lymphocyte (CTL) activity that readily and routinely detect CTLs specific for ORF65 and ORF73 in patients positive for human immunodeficiency virus and KSHV did not show any specific responses in 16 patients with MM, despite the presence of positive Epstein-Barr virus-specific CTLs in all cases. These data therefore do not show a biologically important association between ongoing KSHV infection and MM.

Antigens, Viral↗
PubMed2002

Multicenter trial of low-dose paclitaxel in patients with advanced AIDS-related Kaposi sarcoma.

BACKGROUND: Treatment options are limited for patients with advanced acquired immunodeficiency syndrome (AIDS)-related Kaposi sarcoma (AIDS-KS) whose disease has progressed after receiving therapy with liposomal anthracyclines or combination chemotherapy with doxorubicin (Adriamycin), bleomycin, and vincristine (ABV). This study was performed to assess the safety and efficacy of a novel dose and schedule of paclitaxel in patients with AIDS-KS who failed to respond to previous systemic chemotherapy. METHODS: This was an open-label, multicenter Phase II study. Eligible patients had advanced AIDS-KS consisting of at least 25 mucocutaneous lesions, visceral disease, or lymphedema, and had failed to respond to at least one previous systemic chemotherapy regimen. Patients were treated with paclitaxel at a dose of 100 mg/m(2) given intravenously over 3 hours, every 2 weeks. Primary efficacy end points were tumor response, time to progression, time to treatment failure, and survival. Quality of life and adverse events were evaluated using the Symptom Distress Scale (SDS) and the World Health Organization Toxicity Criteria, respectively. RESULTS: One hundred and seven male patients with advanced AIDS-KS were enrolled from nine participating sites. The median entry CD4+ lymphocyte count was 41/mm(3) (range 0-1139). Previous treatment regimens included ABV in 52, liposomal daunorubicin in 49, and liposomal doxorubicin in 40 patients. Forty-one patients (38%) received two or more previous chemotherapy regimens. Protease inhibitor use during the study was reported by 82 (77%) patients overall; 47 patients (44%) were receiving a protease inhibitor before study entry. Complete or partial response was documented in 60 patients (56%). The median duration of response was 8.9 months. Major response rate was similar when comparing patients not on a protease inhibitor at the time of response (59%) with patients on a protease inhibitor at time of response (54%). However, protease inhibitor use had a significant impact on survival (P = 0.04). Grade 4 neutropenia was reported in 35% of patients; other life-threatening side effects were uncommon. Significant improvements were seen in the total quality of life scores measured by the SDS, including significant improvement in KS-related symptoms such as facial disease, tumor-associated edema, and pulmonary involvement. CONCLUSION: Paclitaxel given every 2 weeks induces major tumor regression in the majority of patients with advanced KS who failed to respond to previous systemic chemotherapy. Paclitaxel is associated with significant improvement in quality of life with acceptable toxicity and should be considered as an effective treatment option for patients with advanced KS.

Acquired Immunodeficiency Syndrome↗
PubMed2002

Receptor tyrosine kinase, EphB4 (HTK), accelerates differentiation of select human hematopoietic cells.

EphB4 (HTK) and its ligand, ephrinB2, are critical for angiogenesis and result in fatal abnormalities of capillary formation in null mice. EphB4 was originally identified in human bone marrow CD34(+) cells by us and has since been reported to be expressed in erythroid progenitors, whereas the ligand ephrinB2 is expressed in bone marrow stromal cells. Reasoning that the developmental relationship between angiogenesis and hematopoiesis implies common regulatory molecules, we assessed whether EphB4 signaling influences the function and phenotype of primitive human hematopoietic cells. Ectopically expressed EphB4 in cell lines of restricted differentiation potential promoted megakaryocytic differentiation, but not granulocytic or monocytic differentiation. Primary cord blood CD34(+) cells transduced with EphB4 resulted in the elevated expression of megakaryocytic and erythroid specific markers, consistent with EphB4 selectively enhancing some lineage-committed progenitors. In less mature cells, EphB4 depleted primitive cells, as measured by long-term culture-initiating cells or CD34(+)CD38(-) cell numbers, and increased progenitor cells of multiple cell types. Effects of ectopic EphB4 expression could be abrogated by either targeted mutations of select tyrosine residues or by the tyrosine kinase inhibitor, genistein. These data indicate that EphB4 accelerates the differentiation of primitive cells in a nonlineage-restricted manner but alters only select progenitor populations, influencing lineages linked by common ancestry with endothelial cells. EphB4 enforces preferential megakaryocytic and erythroid differentiation and may be a molecular bridge between angiogenesis and hematopoiesis.

Antigens, CD34↗
PubMed2002

Notch1 activation increases hematopoietic stem cell self-renewal in vivo and favors lymphoid over myeloid lineage outcome.

Hematopoietic stem cells sequentially pass through a series of decision points affecting self-renewal or lineage-specific differentiation. Notch1 receptor is a known modulator of lineage-specific events in hematopoiesis that we assessed in the context of in vivo stem cell kinetics. Using RAG-1(-/-) mouse stems cells, we documented increased stem cell numbers due to decreased differentiation and enhanced stem cell self-renewal induced by Notch1. Unexpectedly, preferential lymphoid over myeloid lineage commitment was noted when differentiation occurred. Therefore, Notch1 affects 2 decision points in stem cell regulation, favoring self-renewal over differentiation and lymphoid over myeloid lineage outcome. Notch1 offers an attractive target for stem cell manipulation strategies, particularly in the context of immunodeficiency and acquired immunodeficiency syndrome.

Animals↗
PubMed2002

Antitumor activity of oral 9-cis-retinoic acid in HIV-associated Kaposi's sarcoma.

OBJECTIVE: To assess the efficacy, safety and tolerance of oral 9-cis-retinoic acid in HIV-infected patients with Kaposi's sarcoma. METHODS: Sixty-six patients with AIDS-related Kaposi's sarcoma were enrolled at 14 centers; 60 received the study medication and were analyzed and, of these, 45 (75%) had received prior therapy for Kaposi's sarcoma. Once daily oral 9-cis-retinoic acid (alitretinoin, Panretin) was administered at doses up to 140 mg/m2. Most patients (72%) received a maximum dose of 100 mg/m2. Response was assessed using AIDS Clinical Trials Group (ACTG) criteria. RESULTS: The median age was 38 years and the median absolute CD4 cell count was 194 x 10(6) cells/l (range 6-784 x 10(6)). Despite the use of three- and four-drug antiviral regimens (83%), the median HIV RNA at baseline was 8701 copies/ml [range < 500 (lower limit of detection) to 4.24 x 10(6)]. The tumor response rate was 37% (95% confidence interval 25-49). Tumor response was associated with improved quality-of-life measures. There was a significant increase in interleukin 6 (IL-6) levels from baseline to week 4. Responders had significantly lower baseline soluble IL-6 receptor levels (P = 0.029) than non-responders. The median time to response was 9 weeks (mean, 13 weeks; range, 4-36). HIV RNA levels did not change significantly during therapy nor did they correlate with tumor responses. Study drug was discontinued by 28 patients for adverse events, which included headache (13) and skin toxicity (10). CONCLUSION: Oral 9-cis-retinoic acid is an active antitumor drug for AIDS-related Kaposi's sarcoma. Treatment is associated with skin and constitutional toxicity and further studies are needed to improve its long-term tolerance.

Administration, Oral↗