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Biomedical subjects

D Levitt

Publications and source records attributed to D Levitt.

At least 19 recordsLinked to original sources
PubMed2004

The sociodemographic profile, risk categories and prevalence of HIV infection among people attending a London same-day testing clinic, 2000-2001.

The objectives were to determine the sociodemographic profile, risk category, and prevalence of HIV infection amongst people attending a confidential clinic providing counselling, medical advice and results of HIV antibody testing on the same day of consultation. Data were collected on all 1749 individuals attending the same-day HIV testing clinic at the Royal Free Hospital, London and proceeding to HIV testing between June 2000 and May 2001. One thousand, one hundred and forty-eight men and 601 women (mean age 33.3 years) were tested for HIV antibodies. The primary risk for HIV infection was heterosexual contact (69.9%; 1224/1749) and homosexual contact (27.7%; 485/1749). Fifty individuals tested HIV-positive (42 men and eight women). HIV seroprevalence was 2.8% (50/1749) and was highest among men who reported risk through homosexual contact (6.2%; 30/485). The rates for heterosexual men and women were 1.8% (12/648) and 1.4% (8/576), respectively, though they were highest among Black Caribbean (12%; 3/25) and Black African attendees from sub-Saharan African countries (11.2%; 18/160). Of the total number attending the clinic, more than half (56%; 981/1749) had previously been tested and received a negative test result. Of the fifty HIV antibody-positive individuals, 26%, (13) had previously received a negative result and had all reported risk through homosexual contact. Thirty of the HIV antibody-positive individuals were asymptomatic, 14 were symptomatic and three were diagnosed with an AIDS-defining condition. Half of all HIV-positive attendees (51.2%; 22/43) presented at the time of testing with CD4 cell counts below the normal range (>400x10(6)/l). The high HIV seroprevalence among homosexual men, some of whom had previously tested negative, suggests that HIV prevention strategies used within this group may need to be reassessed. The continuing high HIV seroprevalence among individuals from African countries suggests that this population require specific targeting for HIV risk reduction and information on the advantages of early diagnosis and treatment.

Adolescent↗
PubMed2003

Treatment of relapsed or refractory acute myeloid leukemia with humanized anti-CD33 monoclonal antibody HuM195.

HuM195 is a humanized, unconjugated, anti-CD33 monoclonal antibody. Fifty adult patients with relapsed or refractory AML were randomized to receive HuM195 at a dose of 12 or 36 mg/m(2) by intravenous infusion over 4 h on days 1-4 and 15-18. Patients with stable or responding disease received two additional cycles on days 29-32 and 43-46. HuM195 was given as first salvage therapy in 24 patients and as second or subsequent salvage therapy in 26 patients. Pretreatment blast percentage in the marrow was between 5 and 30% in 20 patients with the others having blast counts greater than 30%. The median age of patients was 62 years (range 26-86) and CD33 was detected in 95% of patients for whom immunophenotyping was available. Of 49 evaluable patients, two complete and one partial remission were observed. All three responses were in patients treated at the 12 mg/m(2) dose level and all had baseline blast percentages less than 30%. Decreases in blast counts ranging from 30 to 74% were seen in nine additional patients. Infusion-related events of fever and chills occurred in the majority of patients and were generally mild and primarily related to the first dose of antibody. No hepatic, renal or cardiac toxicities were observed and other adverse events such as nausea, vomiting, mucositis and diarrhea were uncommon or felt to be unrelated to HuM195. In addition, anti-HuM195 responses were not detected. HuM195 as a single agent has minimal, but observable, anti-leukemic activity in patients with relapsed or refractory AML and activity is confined to patients with low burden disease. No significant differences in clinical efficacy or toxicity were seen between the two dose levels of antibody. HuM195 was well tolerated with infusion-related fevers and chills the predominant toxicities seen. Meaningful clinical efficacy of this unconjugated monoclonal antibody may be realized only in patients with minimal residual disease, or in combination with chemotherapy.

Adult↗
PubMed2001

Randomized, placebo-controlled, double-blind study of a cytomegalovirus-specific monoclonal antibody (MSL-109) for prevention of cytomegalovirus infection after allogeneic hematopoietic stem cell transplantation.

MSL-109 is a monoclonal antibody specific to the cytomegalovirus (CMV) glycoprotein H with high neutralizing capacity. In a prospective, randomized, double-blind study, allogeneic hematopoietic stem cell transplantation (HSCT) recipients with positive donor and/or recipient serology for CMV before transplantation received either 60 mg/kg MSL-109 (n = 59), 15 mg/kg MSL-109 (n = 60), or placebo (n = 60) intravenously every 2 weeks from day -1 until day 84 after transplantation. CMV pp65 antigenemia, CMV-DNA load in plasma, and viremia by culture were tested weekly. Primary end points were development of pp65 antigenemia at any level and/or viremia for which ganciclovir was given. There was no statistically significant difference in CMV pp65 antigenemia or viremia among patients in the 60-mg group (pp65 antigenemia, 47%; viremia, 15%), the 15-mg group (52%; 23%), and the placebo group (45%; 17%). There was also no difference in maximum levels of pp65 antigenemia, time to clearance of pp65 antigenemia after start of ganciclovir, CMV disease, invasive bacterial and fungal infections, time to neutrophil and platelet engraftment, acute graft-versus-host disease, days of hospitalization, and overall survival rate among the 3 groups. However, a subgroup analysis of CMV-seronegative recipients with a seropositive donor (D+/R-) showed a transiently improved survival rate by day 100 in MSL-109 recipients (mortality: 60-mg group, 1/13; 15-mg group, 1/12; placebo group, 6/10 [P = .02 for 60-mg versus placebo groups; P = .08 for 15-mg versus placebo groups]); by the end of follow-up, the difference was no longer statistically significant. The improved survival rate in D+/R- patients could not be attributed to a reduction in CMV disease; however, MSL-109 was associated with improved platelet engraftment and less grade III to IV acute graft-versus-host disease in this subgroup. In a subgroup analysis of CMV-seropositive recipients of MSL-109 (D+/R+ and D-/R+), overall mortality was increased compared to that of the placebo group (P = .12 for the 60-mg versus placebo groups, P = .05 for the 15-mg versus placebo groups, and P = .04 for the dose levels combined versus placebo). MSL-109 was well tolerated and no immune response to the drug was observed. Thus, MSL-109 was safe but did not reduce CMV infection in allogeneic HSCT recipients. The transient survival advantage seen early after transplantation in CMV D+/R- patients and the negative effect on survival in seropositive patients remain unexplained. Thus, there is no evidence that MSL-109 is beneficial in CMV-seropositive HSCT recipients.

Adult↗
PubMed2000

A mechanism of membrane neutral lipid acquisition by the microsomal triglyceride transfer protein.

The microsomal triglyceride transfer protein (MTP) and apolipoprotein B (apoB) belong to the vitellogenin (VTG) family of lipid transfer proteins. MTP is essential for the intracellular assembly and secretion of apoB-containing lipoproteins, the key intravascular lipid transport proteins in vertebrates. We report the predicted three-dimensional structure of the C-terminal lipid binding cavity of MTP, modeled on the crystal structure of the lamprey VTG gene product, lipovitellin. The cavity in MTP resembles those found in the intracellular lipid-binding proteins and bactericidal/permeability-increasing protein. Two conserved helices, designated A and B, at the entrance to the MTP cavity mediate lipid acquisition and binding. Helix A (amino acids 725-736) interacts with membranes in a manner similar to viral fusion peptides. Mutation of helix A blocks the interaction of MTP with phospholipid vesicles containing triglyceride and impairs triglyceride binding. Mutations of helix B (amino acids 781-786) and of N780Y, which causes abetalipoproteinemia, have no impact on the interaction of MTP with phospholipid vesicles but impair triglyceride binding. We propose that insertion of helix A into lipid membranes is necessary for the acquisition of neutral lipids and that helix B is required for their transfer to the lipid binding cavity of MTP.

Amino Acid Sequence↗
PubMed2000

Identification of the enzymatic active site of CD38 by site-directed mutagenesis.

CD38 is a ubiquitous protein originally identified as a lymphocyte antigen and recently also found to be a multifunctional enzyme participating in the synthesis and metabolism of two Ca(2+) messengers, cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate. It is homologous to Aplysia ADP-ribosyl cyclase, where the crystal structure has been determined. Residues of CD38 corresponding to those at the active site of the Aplysia cyclase were mutagenized. Changing Glu-226, which corresponded to the catalytic residue of the cyclase, to Asp, Asn, Gln, Leu, or Gly eliminated essentially all enzymatic activities of CD38, indicating it is most likely the catalytic residue. Photoaffinity labeling showed that E226G, nevertheless, retained substantial NAD binding activity. The secondary structures of these inactive mutants as measured by circular dichroism were essentially unperturbed as compared with the wild type. Other nearby residues were also investigated. The mutants D147V and E146L showed 7- and 19-fold reduction in NADase activity, respectively. The cADPR hydrolase activity of the two mutants was similarly reduced. Asp-155, on the other hand, was crucial for the GDP-ribosyl cyclase activity since its substitution with either Glu, Asn, or Gln stimulated the activity 3-15-fold, whereas other activities remained essentially unchanged. In addition to these acidic residues, two tryptophans were also important, since all enzyme activities of W125F, W125Y, W189G and W189Y were substantially reduced. This is consistent with the two tryptophans serving a substrate positioning function. A good correlation was observed when the NADase activity of all the mutants was plotted against the cADPR hydrolase activity. Homology modeling revealed all these critical residues are clustered in a pocket near the center of the CD38 molecule. The results indicate a strong structural homology between the active sites of CD38 and the Aplysia cyclase.

ADP-ribosyl Cyclase↗
PubMed1999

A humanized anti-CD3 antibody, HuM291, with low mitogenic activity, mediates complete and reversible T-cell depletion in chimpanzees.

BACKGROUND: An anti-CD3 antibody that reduces cytokine release syndrome (CRS) while maintaining immunosuppression would be a major advance in the treatment of acute allograft rejection. A humanized (Hu) anti-CD3 IgG2 Ab, HuM291 gamma2 M3 (HuM291; Protein Design Labs, Inc., Mountain View, CA), was engineered with mutations in the upper CH2 region of the Fc domain. The mutations were intended to reduce affinity for Fcgamma receptors, thought to be relevant to CRS. METHODS: In vitro studies using chimpanzee peripheral blood mononuclear cells (PBMCs) were conducted to characterize HuM291 and to establish an animal model. A multidose study was conducted in chimpanzees to evaluate the safety, pharmacokinetics, immunomodulatory activity, and immunogenicity of HuM291, when administered at doses ranging from 0.1 to 10 mg. RESULTS: HuM291 bound to and effectively downmodulated CD3 from chimpanzee PBMCs and stimulated substantially less cytokine secretion and proliferation of chimpanzee PBMCs compared with OKT3 (Orthoclone OKT3; Ortho Pharmaceutical Corp., Raritan, NJ). Multiple doses of HuM291 (0.1, 1.0, or 10 mg/dose) were not associated with adverse events, signs of toxicity, or CRS, despite cytokine release. HuM291 exhibited a long elimination t1/2 (81.5 hr) and, after three 10-mg doses, sustained serum concentrations > 1000 ng/ml were maintained for 1 week. Multiple 10-mg doses induced complete depletion of circulating CD2+CD3+ T cells for up to 10 days after the last dose; T cells recovered by Day 28. Anti-HuM291 Abs were observed in only 4 of 12 animals and were transient in 2 of those animals. CONCLUSIONS: In vitro, HuM291 is substantially less mitogenic than OKT3. In chimpanzees, HuM291 effectively depleted peripheral T cells without eliciting clinical signs of CRS, and recovered T cells were functionally normal.

Animals↗
PubMed1998

The homo-dimeric form of ADP-ribosyl cyclase in solution.

ADP-ribosyl cyclase is a multi-functional enzyme that catalyzes the formation of two Ca2+ signaling molecules, cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP). X-ray crystallography of three different crystal forms shows that it is a non-covalent dimer. Chemical cross-linking and dynamic light scattering were used in this study to determine if the cyclase is also a non-covalent dimer in solution. Treatment of the cyclase in dilute solution (0.05 mg/ml) with dimethylsuberimidate resulted in complete conversion to a species with molecular weight about twice that of the monomeric cyclase. Prolonged cross-linking of the cyclase at four times higher concentration produced also only the covalently linked dimers and no multimer formation was observed. The cross-linked dimer retained full enzymatic activity and readily catalyzed the formation of cADPR from NAD, NAADP from NADP, cyclic ADP-ribose phosphate from NADP, and cyclic GDP-ribose from nicotinamide guanine dinucleotide. Analysis of the autocorrelation functions obtained from dynamic light scattering measurements indicated the cyclase solution (2 mg/ml) was composed of a single molecular species and its diffusion coefficient was measured to be 7. 4x10-7 cm2/s. Computer modeling using the crystallographic dimensions of the non-covalent cyclase dimer, a donut shaped molecule with a central cavity and overall dimensions of 7x6x3 nm, gave a value for the diffusion coefficient essentially the same as that measured. These results indicate the cyclase is a non-covalent dimer in solution.

ADP-ribosyl Cyclase↗
PubMed1997

Telomerase activity and survival of patients with node-positive breast cancer.

BACKGROUND: Shortening of telomeres (specialized structures at the ends of chromosomes) beyond a certain length may signal a cell to stop dividing and to enter senescence. A ribonucleoprotein enzyme, telomerase, is a key component in maintaining telomere length. Because the majority of cancers express telomerase but most normal somatic tissues do not, we measured the level of telomerase expression in primary breast cancer specimens for correlation with traditional prognostic indicators and disease outcome. METHODS: Telomerase activity was measured in frozen human breast cancer specimens by use of the Telomeric Repeat Amplification Protocol (TRAP) assay. The level of telomerase activity was expressed as total product generated (TPG) and was corrected for specimen cellularity by expressing it as a ratio of TPG to the sample's 28S ribosomal RNA content. RESULTS: A preliminary study of 150 breast cancer specimens demonstrated that telomerase activity correlated with the fraction of cells in S phase of the cell cycle (r(sp) = .23). In a larger prognostic study of 398 tumors from patients with lymph node-positive breast cancer, telomerase expression correlated with S-phase fraction, progesterone receptor level, DNA ploidy, and lymph node status. After correcting for sample cellularity, increasing TPG levels were associated with decreased disease-free survival (P = .041) and overall survival (P = .009) of the patients. The telomerase activity level remained strongly predictive of death (P = .027) and marginally predictive of disease recurrence (P = .08) after adjustment for other prognostic factors. All P values are two-sided. CONCLUSIONS: Telomerase activity in human breast cancers is associated with a more aggressive tumor phenotype in patients.

Adult↗
PubMed1997

Concurrent phase I trials of intravenous interleukin 6 in solid tumor patients: reversible dose-limiting neurological toxicity.

Interleukin 6 (IL-6) has antitumor activity comparable to IL-2 in murine models with less toxicity. Because the biological effects of intermittent and continuous infusions may differ, we conducted two concurrent Phase I trials of daily x5, 1-h, and continuous 120-h i.v. infusions to determine the toxicity, biological effects, and maximum tolerated dose of i.v. IL-6. Cohorts of six patients with advanced cancer received escalating doses (1, 3, 10, 30, 100, and 150 microgram/kg/day) of recombinant human IL-6 on days 1-5 and 8-12 of each 28-day course (1-h trial) or on days 1-5 of each 21-day course (120-h trial). Treatment was administered in regular inpatient wards and in outpatient clinics and was withheld in the event of grade 3 toxicity. Sixty-nine patients (1-h trial, n = 40; 120-h trial, n = 29) were enrolled, including 27 with renal cancer and 16 with melanoma. All were ambulatory, and 40 were asymptomatic. Fever (97%), anemia (78%), fatigue (56%), nausea or vomiting (49%), and elevated serum transaminase levels (42%) were the most frequent toxicities. Transient hypotension developed in 23 patients (33%). There were three deaths during the study due to progressive disease and/or infection. There were no objective responses. Dose-related increases in platelet counts and C-reactive protein levels were detected in most patients. Principal dose-limiting toxicities included atrial fibrillation (1 episode in the 1-h trial and 4 episodes in the 120-h trial) and neurological toxicities (3 episodes in the 1-h trial and 4 episodes in the 120-h trial). The neurological toxicities included confusion, slurred speech, blurred vision, proximal leg weakness, paraparesis, and ataxia. These effects were transient and reversed when IL-6 was discontinued. IL-6 can be given by i.v. infusion at biologically active doses with acceptable toxicity. Dose-limiting toxicities consisted mainly of a spectrum of severe but transient neurological toxicities and occasional episodes of atrial fibrillation. The maximum tolerated doses recommended for use with these i.v. schedules in Phase II trials are 100 microgram/kg/day by daily x5 1-h infusion and 30 microgram/kg/day by 120-h infusion. Phase II trials will be performed to determine the antitumor activity of IL-6 and better define its toxicity. Patients in these and other IL-6 studies should be monitored closely for neurological and cardiac effects.

Adult↗
PubMed1996

Acting on a living will: a physician's dilemma.

The implementation of a living will can give rise to ethical dilemmas for the patient's family and the health care professionals involved. The case reported here raises questions about the right of patients to self-determination, the importance of quality-of-life considerations in treatment decisions and physicians' obligations with respect to the implementation of living wills. Physicians should ensure in advance that the instructions set out in a living will are unambiguous and should bring to the patient's attention any ethical difficulties that they foresee in carrying out those instructions.

Aged↗
PubMed1996

Comparison of four cytokine regimens for mobilization of peripheral blood stem cells: IL-3 alone and combined with GM-CSF or G-CSF.

Improved methods for mobilization may reduce the number of aphereses required to collect adequate numbers of peripheral blood stem cells (PBSC) and hasten engraftment following high-dose therapy. Mobilization with cytokines alone enables engraftment after myeloablative therapy. The optimal cytokine regimen for mobilization has not been established. The study evaluated the effects of four interleukin-3-containing cytokine regimens administered during steady state hematopoiesis on PBSC mobilization in 30 patients with breast cancer or lymphoid malignancies. These regimens included IL-3 alone (Arm 1), sequential IL-3 --> G-GSF (Arm 2), sequential IL-3 --> GM-CSF (Arm 3) and combined IL-3 + G-CSF (Arm 4). Consecutive days of apheresis were performed until a target of 4-6 x 10(8) mononuclear cells/kg were collected. All patients received intravenous GM-CSF after PBSC infusion. Median days to an ANC > or = 500/ microliters in Arm 3(22 days) was significantly slower than for patients in Arm 2 (13 days) but not significantly different from patients in Arm 1 or Arm 4. There was no significant difference in platelet engraftment or days of hospitalization between the study arms. Addition of GM-CSF to IL-3-containing mobilization regimens results in collection of PBSC that lead to delayed engraftment. Further development of Arms 1, 2, and 4 appear warranted.

Adult↗
PubMed1996

Creating a living will. Experience at a multilevel geriatric facility.

PROBLEM: How to ensure that residents of a multilevel long-term care facility are able to indicate treatment preferences for the future (when they will be unable to participate in decision making). OBJECTIVE OF PROGRAM: To review the methods used to create a "living will" document suitable for a long-term care population that can be used as a guide and template for other long-term care populations. MAIN COMPONENTS OF THE PROGRAM: The process includes gathering information, developing possible models, designing the document, the review process, and implementing the document. CONCLUSIONS: Developing a living will document is not a simple process. The design should suit the population for whom the document is developed. Primary care physicians, other health care providers, and clergy should provide input.

Aged↗
PubMed1995

Phase I trial of recombinant interleukin 3 before and after carboplatin/etoposide chemotherapy in patients with solid tumors: a southwest oncology group study.

Recombinant human interleukin 3 (rhIL-3, expressed in Escherichia coli) is a hematopoietic growth factor with protean biological effects on bone marrow in animal models, including enhanced granulocyte and platelet production and the capacity to ameliorate chemotherapy-induced bone marrow toxicity. We, therefore, undertook a Phase I trial in patients with advanced solid tumors and normal bone marrow function. Cohorts of four to six patients each received daily s.c. doses of rhIL-3 (SDZ-ILE-964; Sandoz) at dose levels of 1. 0, 2.5, 5.0, and 10.0 microgram/kg according to the following schedule: cycle 1, rhIL-3 days 1-14; cycle 2, carboplatin (350 mg/m2) on day 1 and etoposide (100 mg/m2) on days 1-3; and cycle 3, carboplatin (350 mg/m2) on day 1, etoposide (100 mg/m2) on days 1-3, and rhIL-3 on days 4-17. Each cycle was a total of 28 days. An analysis of 20 patients entered into all four escalating dose levels revealed that, during cycle 1, absolute neutrophil count (ANC) increased from a median baseline of 6,643/mm3 to a median of 12,692/mm3, and platelets increased from a median baseline of 314,000/mm3 to a median of 465,000/mm3. When cycle 2 was compared with cycle 3, the median ANC nadir increased from 192/mm3 to 988/mm3, and the mean ANC nadir increased from 458/mm3 to 1,297/mm3. Median platelet count nadirs increased from 29,000/mm3 to 84,000/mm3, and the mean nadir platelet counts increased from 72,000/mm3 to 129,000/mm3. Total days on which platelets were <50,000/mm3 was 52 for cycle 2 and 19 for cycle 3. The maximum tolerated dose of rhIL-3 was 5.0 microgram/kg/day; dose-limiting toxicities included fatigue, chills, fever, and headache. These data suggest a clear but variable biological activity observed with IL-3, as measured by the reduction in the depth and duration of thrombocytopenia and/or neutropenia when cycle 2 was compared with cycle 3. rhIL-3 is a promising cytokine that may help to ameliorate the bone marrow toxicity observed with the use of chemotherapeutic agents.

Adult↗
PubMed1994

A phase I trial of intravenous interleukin-6 in patients with advanced cancer.

Eighteen patients were treated with escalating doses of recombinant, Escherichia coli-derived human interleukin-6 (IL-6) intravenously every 8 h. Therapy was given for two cycles of 7 days each separated by a week off therapy. Fevers and chills were observed in most patients. Mild renal and liver function abnormalities were noted at higher doses of IL-6. Dose-limiting toxicity was reached at 30 micrograms/kg i.v. every 8 h due to reversible neurotoxicity, but significant rapidly reversible anemia and hyperglycemia were seen at lower doses. Platelet counts, white blood cell counts, and acute phase reactant levels were substantially elevated. No antitumor responses were seen. A maximum tolerated dose of 10 micrograms/kg i.v. every 8 h for two 7-day cycles is recommended for future phase II trials.

Acute-Phase Proteins↗
PubMed1994

Effect of recombinant human interleukin-3 on haematological recovery from chemotherapy-induced myelosuppression.

Patients with non-small-cell lung cancer (NSCLC) were treated with ICE chemotherapy (ifosfamide 2000 mg/m2, days 1-3; carboplatin 300 mg/m2, day 1; etoposide 75 mg/m2, days 1-3) intravenously (i.v.) during the first 3 d of a maximum of four 28 d treatment cycles. Interleukin-3 (IL-3) was administered in cycles 2 and 4 as a daily subcutaneous (s.c.) injection on days 5-18. Cohorts of three patients were treated at dosage levels of 0.5, 1.25, 2.5, 5.0, 10.0 and 15.0 micrograms/kg/d. At 15.0 micrograms/kg/d a 'flu-like' syndrome of myalgias, arthralgias and fatigue was considered dose-limiting. Other toxicities were headache, fever, urticaria, arrhythmia, chills and flushing. Subsequently, nine patients were added to the group receiving 10 micrograms/kg/d. 27 patients received IL-3 after their second course of ICE. At 10 and 15 micrograms/kg/d, IL-3 in cycle 2 was associated with enhanced haematological recovery. Depth of neutrophil nadir and days of neutropenia (ANC < 0.5 x 10(9)/l) were reduced in 9/13 patients and in 8/11 patients, respectively. No effect was seen on platelet nadir or days of thrombocytopenia. IL-3 was well tolerated up to 10 micrograms/kg/d when given as a daily s.c. injection. Results suggest IL-3 as a potential adjunct to chemotherapy, and further studies to explore administration of IL-3 in combination with other cytokines in this setting are warranted.

Adolescent↗