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J P Leonard

Publications and source records attributed to J P Leonard.

At least 19 recordsLinked to original sources
PubMed2003

Elitek-rasburicase: an effective means to prevent and treat hyperuricemia associated with tumor lysis syndrome, a Meeting Report, Dallas, Texas, January 2002.

Renal precipitation of uric acid associated with tumor lysis syndrome (TLS) is a major complication in the management of leukemia, lymphoma, and other drug-sensitive cancers. Management of hyperuricema has historically consisted of administration of allopurinol, hydration, alkalinization to maintain pH between 7.0 and 7.3, and in some cases diuresis. Allopurinol, a xanthine analogue, blocks xanthine oxidase and formation of uric acid. Urate oxidase converts uric acid to allantoin, which is 5-10 times more soluble than uric acid. Homo sapiens cannot express urate oxidase because of a nonsense mutation. Urate oxidase was initially purified from Aspergillus flavus fungus. Treatment with this nonrecombinant product had been effective in preventing renal precipitation of uric acid in cancer patients, but was associated with a relatively high frequency of allergic reactions. This enzyme was recently cloned from A. flavus and is now manufactured as a recombinant protein. Clinical trials have shown this drug to be more effective than allopurinol for prevention and treatment of hyperuricemia in leukemia and lymphoma patients. This drug has been approved in Europe as well as the US and several clinical trials are in progress to further determine its clinical utility in other patient subsets. The purpose of this meeting was to discuss usefulness of recombinant urate oxidase, also known as rasburicase, Fasturtec, and Elitek, for the management of TLS in certain cancer patients.

Adolescent↗
PubMed2001

The combination of chemotherapy and systemic immunotherapy with soluble B7-immunoglobulin G leads to cure of murine leukemia and lymphoma and demonstration of tumor-specific memory responses.

Major mechanisms underlying poor immune responses to autologous tumor-associated antigens are overwhelming tumor kinetics and the absence of effective T-cell costimulation by antigen-presenting cells. To address these issues, leukemia and lymphoma mice were treated with the combination of chemotherapy and systemic immunotherapy with recombinant soluble murine B7-immunoglobulin G (IgG) molecules. In this report, 3 murine models were used, a radiation-induced SJL acute myeloid leukemia, a transplantable spontaneous SJL lymphoma, and the C57BL/6 EL-4 thymic lymphoma. Various treatment modalities were evaluated: single treatments with either B7-IgG or chemotherapy as well as combination therapies. The results demonstrate the following: (1) in all tumor models, the combination of chemotherapy and soluble B7-IgGs is more potent than either therapy alone, leading to cure of tumor-bearing animals; (2) the therapeutic responses are T-cell-dependent, because combined therapy is not efficacious in severe combined immunodeficient mice; (3) the rejection of tumor cells leads to the development of tumor-specific immunity, because cured mice are immune to the rejected tumor but not to a different syngeneic tumor; and (4) (51)Cr release assays show that rejection of tumor cells leads to the development of very potent tumor-specific cytotoxic T-lymphocyte activity. On the basis of these results, it is proposed that chemotherapy-mediated tumor reduction, together with consequent augmented tumor-antigen presentation to activated T cells, are primary mechanisms leading to curative responses. The safety profile of the B7-IgG fusion proteins and their synergy with chemotherapy strongly suggest that the combination regimen is a promising strategy in cancer treatment.

Acute Disease↗
PubMed2001

Myelin/axonal pathology in interleukin-12 induced serial relapses of experimental allergic encephalomyelitis in the Lewis rat.

Lewis rats, on recovery from monophasic clinical experimental allergic encephalomyelitis (EAE), can be induced to develop repeated paralytic relapses with a graded reduction in clinical severity following intraperitoneal administration of IL-12. By the time of the third relapse, the number and size of inflammatory cuffs in the spinal cord were reduced with the makeup of the cellular infiltrate shifting to a significantly increased number of B cells. Serum levels of myelin basic protein (MBP)-specific IgG1 and IgG2b were found to rise over time while MBP and MBP peptide-positive macrophages and microglia became evident in perivascular cuffs and in spinal cord parenchyma, indicative of myelin phagocytosis. Axonal death was observed in semithin and EM sections of spinal cord in third relapse animals in association with iNOS and tPA immunostaining throughout gray and white matter. These neurotoxic or excitotoxic agents may contribute to axonal damage directly or indirectly by activated microglia and macrophages, leading to limited damage of the axonal-myelin unit.

Acute Disease↗
PubMed2001

Identification of mouse NMDA receptor subunit NR2A C-terminal tyrosine sites phosphorylated by coexpression with v-Src.

The protein tyrosine kinase Src is known to regulate NMDA receptors in native neurons. While NR2A, NR2B and NR2D are known to be phosphorylated on tyrosine residues, the exact sites have remained unidentified. Immunoprecipitation of NMDA receptor subunits followed by western blotting was used to analyze the state of tyrosine phosphorylation of recombinant NMDA receptor subunits expressed in HEK293 cells. Using antiphosphotyrosine antibody PY20, we find that on expression in HEK cells, v-Src and Fyn cause detectable tyrosine phosphorylation only of NR2A. Because a stronger signal was produced by the constitutively active v-Src, the general region of v-Src phosphorylation was delimited by expression of a series of truncation mutants of NR2A. Site-directed mutagenesis on candidate sites within the likely region allowed identification of three sites, Y1292, Y1325, and Y1387 that account for a significant fraction of the total PY20 signal. Two of these sites, Y1292 and Y1387, were suggested to control current modulation by Src in previous studies of HEK cells expressing NR1/NR2A. One of these sites, Y1325, has not yet been evaluated for effects on receptor current. A unique tyrosine site, Y1267, was shown not to be a site of detectable phosphorylation, in accordance with its Src-independent regulation of receptor currents.

Animals↗
PubMed2001

Biology and management of mantle cell lymphoma.

Mantle cell lymphoma is a distinct subtype and accounts for approximately 5 to 10% of non-Hodgkin lymphomas. The malignant cells express pan B-cell markers, including CD19, CD20 and CD22, and the T-cell marker CD5, whereas CD10 and CD23 expression are usually absent. By cytogenetic analysis, the t(11;14)(q13;q32) translocation is commonly observed, resulting in overexpression of cyclin D1. This entity often combines some unfavorable clinical features of the indolent and aggressive lymphoma subtypes, as it is generally incurable and relatively aggressive. It is most commonly observed in men 50 to 70 years of age and is characterized by disseminated disease, usually involving lymph nodes, bone marrow, and spleen. Frequently, there is extranodal involvement including the gastrointestinal tract. These tumors are incurable with the currently available therapeutic options, with usual time to progression after chemotherapy of approximately 1 year. Newer chemotherapy regimens (including stem cell transplantation) and monoclonal antibody-based therapies have shown limited evidence of additional benefit. Overall, the prognosis for patients with mantle cell lymphoma remains poor, and novel strategies are needed.

Age of Onset↗
PubMed2001

Evidence for direct protein kinase-C mediated modulation of N-methyl-D-aspartate receptor current.

Protein kinase-C (PKC) activation differentially affects currents from N-methyl-D-aspartate (NMDA) type glutamate receptors depending upon their subunit composition. Experiments using chimeras initially indicated that the cytoplasmic C-terminal tails of NR2B (responsive to PKC) and NR2C (unresponsive to PKC) subunits contain the amino acid residues responsible for the observed disparity of PKC effects. However, truncation and point mutation experiments have suggested that PKC action on NMDA receptors may be entirely indirect, working via the phosphorylation of associated proteins. Here we suggest that PKC does, in fact, affect NR2B/NR1-011 NMDA currents by direct phosphorylation of the NR2B tail at residues S1303 and S1323. Replacement of either of these residues with Ala severely reduces PKC potentiation. To verify that S1303 and S1323 are sites of direct phosphorylation by PKC, synthetic peptides from the regions surrounding these sites were used as substrates for in vitro assays with purified rat brain PKC. These results indicate that PKC can directly phosphorylate S1303 and S1323 in the NR2B C terminus, leading to enhanced currents through NMDA receptor channels. The direct action of PKC on certain NMDA receptor subtypes may be important in any physiological or pathological process where PKC and NR2B/NR1 receptors interact.

Animals↗
PubMed2001

Immunotherapy of Non-Hodgkin's lymphomas.

Recent years have witnessed the development of a variety of promising immunotherapies for treating patients with non-Hodgkin's lymphomas. Foremost among these advances is the exciting success of monoclonal antibodies directed against lymphocyte surface antigens. Rituximab is a chimeric (human-mouse) anti-CD20 antibody that induces responses in approximately half of the patients with relapsed indolent lymphomas and a third of patients with relapsed aggressive lymphomas when used as a single agent. Response rates appear even higher (up to 70%) for newly diagnosed patients treated with Rituximab monotherapy. Other promising antibodies for treatment of B cell malignancies include epratuzumab (anti-CD22), CAMPATH-1H (anti-CD52w), and Hu1D10 (anti-class II HLA). Even more exciting than antibody monotherapy is the prospect of combination antibody therapy (e.g. rituximab + epratuzumab) or combination chemotherapy and antibody therapy. In this regard, a recent phase III randomized trial from the GELA group in France demonstrated statistically significantly superior complete and overall response rates and superior event-free and overall survivals for elderly patients with newly diagnosed diffuse aggressive B cell lymphomas treated with CHOP + rituximab compared with CHOP alone. Confirmatory cooperative group trials combining chemotherapy with antibody therapies are currently underway. Another approach to augment the efficacy of antibodies is to deploy them in radiolabeled form. Iodine-131, Yttrium-90, and Copper-67 labeled monoclonal antibodies targeting CD-20, CD-22, HLA class II, and other cell surface antigens have been tested and demonstrate higher overall response rates (50-80%) and complete response rates (20-40%) than unlabeled antibodies. Pilot studies combining radiolabeled antibodies with either standard dose chemotherapy or myeloablative chemoradiotherapy with stem cell transplantation also appear very promising. Lymphoma vaccines have also produced very encouraging results in single institution studies at Stanford and the National Cancer Institute, with responding patients demonstrating superior event-free and overall survival than historical controls. Phase III randomized trials of idiotype vaccines are currently underway and novel new vaccine approaches are also being tested.

Antibodies, Monoclonal↗
PubMed2001

Interleukin-12 gene therapy vaccines: directing the immune system against minimal residual leukemia.

Current overall survival rates for patients with AML remain poor and there is need for novel therapeutic approaches. One such approach is to use the patient's own immune system to eliminate minimal residual disease. Recent advances in genetic manipulation of tumor cells, together with a better understanding of the immune mechanisms controlling the host-tumor relationship have led to a flurry of preclinical and clinical studies on tumor cell vaccines. Here we present a brief overview of genetic manipulation of tumor cells, and highlight important principles of cancer immunity and cancer vaccines. Special emphasis is given on recent work on the role of interleukin-12 (IL-12) based vaccines in murine AML. These studies have shown that vaccines with AML cells, genetically modified to secrete IL-12, are potent stimulators of the immune system and lead to the development of both prophylactic and therapeutic anti-leukemia immunity.

Animals↗
PubMed2000

Treatment of nonlaparotomized (clinical) stage I and II Hodgkin's disease patients by extended field and splenic irradiation.

PURPOSE: At the New York Presbyterian Hospital-Cornell Medical Center, patients with unequivocal clinical stage I and IIA Hodgkin's disease (HD) have been treated with mantle, splenic, and extended field radiation therapy (EFRT) (without surgical staging). A 24-year retrospective review was conducted to determine the effectiveness of our patient selection on the outcome of patients treated with this modality. METHODS AND MATERIALS: During the period 1971 to 1994, 94 patients with clinically staged HD, with favorable prognostic factors, were retrospectively reviewed. Patients with pathological or equivocal staging, "B" symptoms, bulk disease, history of previous chemotherapy, and/or Stage III or IV disease were excluded from our analysis. There were 27 Stage IA and 67 Stage IIA patients. All patients were treated to 3600 cGy with a 400 cGy boost to the involved field. The median follow-up was 52 months, mean of 62.1 months. RESULTS: Ten of 94 patients (10.5%) relapsed. Seven of the relapses were in the pelvis, one submandibularily, one in the tonsil, and one in the axilla. Nine of the relapses had nodular sclerosis histology, one had lymphocyte predominance, and none had mixed cellularity. The median time to relapse was 38 months; mean time 42. 3 months. All patients are alive, well and free of disease, including nine who received subsequent chemotherapy and one who underwent autotransplantation. CONCLUSIONS: Careful clinical staging of early, asymptomatic HD patients treated with mantle, splenic, and EFRT may obviate the need for exploratory laparotomy.

Adolescent↗
PubMed2000

Cutting edge: identification of GL50, a novel B7-like protein that functionally binds to ICOS receptor.

By the genetic selection of mouse cDNAs encoding secreted proteins, a B7-like cDNA clone termed mouse GL50 (mGL50) was isolated encoding a 322-aa polypeptide identical with B7h. Isolation of the human ortholog of this cDNA (hGL50) revealed a coding sequence of 309 aa residues with 42% sequence identity with mGL50. Northern analysis indicated GL50 to be present in many tissues including lymphoid, embryonic yolk sac, and fetal liver samples. Of the CD28, CTLA4, and ICOS fusion constructs tested, flow cytometric analysis demonstrated only mouse ICOS-IgG binding to mGL50 cell transfectants. Subsequent phenotyping demonstrated high levels of ICOS ligand staining on splenic CD19+ B cells and low levels on CD3+ T cells. These results indicate that GL50 is a specific ligand for the ICOS receptor and suggest that the GL50-ICOS interaction functions in lymphocyte costimulation.

Amino Acid Sequence↗
PubMed2000

The postsynaptic density protein PSD-95 differentially regulates insulin- and Src-mediated current modulation of mouse NMDA receptors expressed in Xenopus oocytes.

The NMDA subtype of glutamate receptor is physically associated with the postsynaptic density protein PSD-95 at glutamatergic synapses. The channel activity of NMDA receptors is regulated by different signaling molecules, including protein tyrosine kinases. Because previous results have suggested a role for protein kinase C (PKC) in insulin potentiation of NMDA currents in oocytes, the effects of coexpression of PSD-95 on insulin and PKC potentiation of NMDA currents from these receptors were compared. Another primary objective was to determine if PSD-95 could enable Src to potentiate currents from NR2A/NR1 and NR2B/NR1 receptors expressed in Xenopus oocytes. The results show opposite effects of PSD-95 coexpression on Src and insulin modulation of NR2A/NR1 receptor currents. Src potentiation of mouse NR2A/NR1 currents required PSD-95 coexpression. In contrast, PSD-95 coexpression eliminated insulin-mediated potentiation of NR2A/NR1 receptor currents. PSD-95 coexpression also eliminated PKC potentiation of NR2A/NR1 receptor currents. PSD-95 may therefore play a key role in controlling kinase modulation of NR2A/NR1 receptor currents at glutamatergic synapses.

Animals↗
PubMed1999

Vaccines with interleukin-12-transduced acute myeloid leukemia cells elicit very potent therapeutic and long-lasting protective immunity.

Interleukin-12 (IL-12) is a heterodimeric cytokine mediating a dynamic interplay between T cells and antigen-presenting cells (APCs). Preclinical studies have demonstrated that recombinant murine IL-12 (rmIL-12) promotes specific antitumor immunity mediated by T cells in several types of tumors. However, the in vivo antitumor properties of IL-12 in acute myeloid leukemia (AML) have not been previously reported. We show here in a murine AML model that systemic administration of rmIL-12 significantly delays tumor growth but is incapable of rescuing mice from lethal leukemia. In contrast, AML cells genetically modified to express IL-12 (IL12-AML) using murine stem cell virus (MSCV) p40 + p35 elicit very potent antileukemic activity. Vaccines with lethally irradiated IL12-AML cells protect naive mice against challenge with wild-type AML cells and, more importantly, can cure mice bearing a considerable leukemic burden. Immunized mice show no signs of systemic IL-12 toxicity and their spleen histology is comparable with naive mice spleen. In vivo depletion of IL-12, interferon-gamma (IFN-gamma), or CD8(+) T cells after injections with live IL12-AML cells abrogates completely the antileukemia immune responses. Studies on the in vitro effects of IFN-gamma on AML cells demonstrate enhanced expression of major histocompatibility complex (MHC) and accessory molecules and induction of the costimulatory molecules B7.1 and B7.2, but no significant direct antiproliferative effect. (51)Cr release assays show that rejection of live IL12-AML cells supports the development of long-lasting leukemia-specific cytotoxic T lymphocyte (CTL) activity. In conclusion, our results demonstrate that IL12-AML vaccination is a safe and potent immunotherapeutic approach that has a great potential to eliminate minimal residual disease in patients with AML.

Acute Disease↗
PubMed1999

Autocrine regulation of IL-12 receptor expression is independent of secondary IFN-gamma secretion and not restricted to T and NK cells.

The biological response to IL-12 is mediated through specific binding to a high affinity receptor complex composed of at least two subunits (designated IL-12Rbeta1 and IL-12Rbeta2) that are expressed on NK cells and activated T cells. The selective loss of IL-12Rbeta2 expression during Th2 T cell differentiation suggests that regulation of this receptor component may govern IL-12 responsiveness. In murine assays, down-regulation of IL-12Rbeta2 expression can be prevented by treatment with IFN-gamma, indicating that receptor expression and hence IL-12 responsiveness may be regulated, at least in part, by the local cytokine milieu. In this study, we report that cellular expression of both IL-12Rbeta1 and beta2 mRNA is increased in the lymph nodes of naive mice following systemic administration of murine rIL-12 (rmIL-12). Changes in IL-12R mRNA were associated with increased IFN-gamma secretion following ex vivo activation of lymph node cells with rmIL-12, indicating the presence of a functional receptor complex. Expression of IL-12R mRNA was not restricted to lymph node T cells, and its autocrine regulation was independent of secondary IFN-gamma secretion. Data from fractionated lymph node cells as well as rmIL-12-treated B cell-deficient mice suggest that IL-12-responsive B cells may represent an alternative cellular source for IFN-gamma production. However, the strength of the biological response to rmIL-12 is not governed solely by receptor expression, as rmIL-12-induced IFN-gamma secretion from cultured lymph node cells is accessory cell dependent and can be partially blocked by inhibition of B7 costimulation.

Animals↗
PubMed1999

Protein kinase C potentiation of currents from mouse zeta1/epsilon2 NMDA receptors expressed in Xenopus oocytes depends on f-actin/g-actin cycling.

NMDA currents from Xenopus oocytes expressing recombinant zeta1/epsilon2 NMDA receptors can be potentiated by activation of protein kinase-C (PKC) and also demonstrate time-dependent rundown. In order to determine whether cytoskeletal proteins are involved in either of these phenomena, experiments were performed using the f-actin stabilizer phalloidin, the f-actin de-stabilizer cytochalasin-D, and the microtubule stabilizer taxol. Phalloidin treatment both prevented rundown and inhibited PKC-potentiation of whole-cell currents but did not affect baseline current amplitudes. Treatment with cytochalasin-D also prevented rundown and inhibited PKC-potentiation of whole-cell currents, but baseline currents from cytochalasin treated cells were only 50% as large as those from control cells. Taxol had no effect on either rundown or PKC potentiation of NMDA currents. The results indicate that both spontaneous rundown and PKC potentiation of currents from heterologously expressed zeta1/epsilon2 NMDA receptors depend on dynamic actin polymerization/depolymerization but do not involve changes in microtubules.

Actins↗
PubMed1999

Protein kinase C modulation of recombinant NMDA receptor currents: roles for the C-terminal C1 exon and calcium ions.

Protein kinase C (PKC) positively modulates NMDA receptor (NMDAR) currents. In contrast to previous reports, this study determines the importance of individual exons in the mechanism underlying the potentiation process by examining the complete set of eight naturally occurring splice variants expressed in Xenopus oocytes both as homomers and as heteromeric NR1/NR2A or NR1/NR2B complexes. After PKC stimulation, homomeric currents demonstrated a high level of potentiation ( approximately 500% of untreated baseline currents) that reduced to a lower level ( approximately 300% of baseline) in variants containing the first C-terminal exon (C1). An ANOVA showed that only C1 and no other exon or interaction of exons determined the degree of NMDAR current modulation by PKC. When recordings were performed in solutions in which barium replaces calcium, only the lower form of potentiation was observed, regardless of the splice variant exon composition. This suggested an important role for calcium in the PKC modulation of homomeric NMDA splice variant currents in which the C1 exon also participates. The effectiveness of the C1 exon to reduce the higher form of potentiation is modulated by heteromeric assemblies with NR2A heteromers yielding smaller levels of potentiation and a larger C1 exon effect compared with NR2B heteromers. The heteromers demonstrated the higher form of potentiation even in the absence of calcium. Furthermore, calcium had different effects in the potentiation of the heteromers depending on the NR2 subunit. This study refines the region of the NR1 subunit involved in a modulation crucial to the function of NMDA receptors and provides evidence that the NR2A and NR2B subunits realize this modulation differentially.

Animals↗
PubMed1999

Insulin modulation of cloned mouse NMDA receptor currents in Xenopus oocytes.

Modulation of recombinant N-methyl-D-aspartate receptor (NMDAR) currents by insulin was studied using the Xenopus oocyte expression system. Insulin (0.8 microM, 10 min) regulated NMDAR currents in a subunit-specific manner. Currents from epsilon1/zeta1, epsilon2/zeta1, and epsilon4/zeta1 receptors were variably potentiated, whereas currents from epsilon3/zeta1 receptors were not. Protein tyrosine kinases (PTKs) and protein kinase C were found to be involved in insulin-mediated modulation in an NMDAR subtype-specific way. Pretreatment with a specific PTK inhibitor, lavendustin A, attenuated and blocked the insulin effect on epsilon2/zeta1 and epsilon4/zeta1, respectively. Preincubation with selective protein kinase C inhibitors, staurosporine or calphostin C, depressed the response of epsilon1/zeta1 and epsilon2/zeta1 receptors to insulin. Basal regulation of NMDAR currents by endogenous PTKs and protein tyrosine phosphatases (PTPs) was also investigated. Of the four receptor subtypes, only epsilon1/zeta1 receptor currents were affected by basal PTK inhibition via lavendustin A, whereas PTP inhibition by phenylarsine oxide or orthovanadate enhanced currents from epsilon1/zeta1 and epsilon2/zeta1 receptors. Surprisingly, a stimulatory PTP modulation was observed for epsilon4/zeta1. As NMDAR subunits are differentially expressed in the brain, the observed subtype-specific modulations of NMDAR currents by insulin, PTKs, and PTPs may provide important insights into certain NMDAR-dependent physiological and pathological processes.

Animals↗
PubMed1998

Retroviral transduction of human CD34+ umbilical cord blood progenitor cells with a mutated dihydrofolate reductase cDNA.

Umbilical cord blood cells (UCB) have become a major target population for experimental and clinical studies using transfer of genes involved in inborn enzymatic diseases. Cord blood contains hematopoietic progenitor cells at a high frequency, and expanding these cells ex vivo generates sufficient numbers of hematopoietic precursors for transplantation into adults, e.g., as supportive treatment. As clinical reports about retroviral transduction into UCB cells have not been as encouraging as the first preclinical data, we have established a retroviral transduction system that allows expansion and selection of hematopoietic progenitor cells from UCB. CD34-enriched UCB cells were transduced with a retroviral vector encoding a mutated dihydrofolate reductase cDNA that confers MTX resistance. We observed increased resistance to MTX in transduced granulocyte macrophage-colony forming units (CFU-GM) after co-culture of CD34+ UCB cells with the virus-producing cell line, or after incubation with virus-containing supernatant. The supernatant-based transduction protocol included a prestimulation with recombinant interleukin-1 (rhIL-1), rhkit-ligand, and rhIL-3 to increase the percentage of cells in S phase to greater than 50%. Using this protocol we measured a 72-fold expansion of CFU-GM and a 2.5-fold selective advantage of transduced versus nontransduced progenitor cells after exposure to low-dose methotrexate in liquid culture. Polymerase chain reaction analysis revealed integration of proviral DNA into the majority of transduced colonies before and after ex vivo expansion. The retroviral vector and transduction protocol reported here provides an experimental system for selection and expansion of retrovirally transduced progenitor/stem cells from UCB that may help improve the efficiency of current clinical gene therapy strategies.

Antigens, CD34↗