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Biomedical subjects

A C Lankester

Publications and source records attributed to A C Lankester.

At least 19 recordsLinked to original sources
PubMed2005

Intravenous busulfan in children prior to stem cell transplantation: study of pharmacokinetics in association with early clinical outcome and toxicity.

We studied the pharmacokinetics of intravenous busulfan (Bu) in children in order to further optimize intravenous Bu dosing in relation to toxicity and survival. A total of 31 children undergoing Bu-based conditioning for allogeneic SCT were enrolled in a study. The starting dose was 1.0 mg/kg (age < 4 years) and 0.8 mg/kg (age > or =4 years), four doses per day during 4 days. Dose adjustment was allowed up to a maximum dose of 1.0 mg/kg per dose if the target area under the serum concentration-time curve (AUC) was not reached. Pharmacokinetic studies were performed after the first dose. Donor engraftment was established in 28 out of 31 patients. The average AUC after the first dose was the same in children < 4 years as in children > or =4 years. Mean clearance was higher in children < 4 years than in children > or =4 years. In 35% of all patients, total AUC was within the target AUC. The other children's AUCs were below the target range. No relationships were found between systemic exposure to Bu and toxicity or clinical outcome. We concluded that, in accordance with previous data, within the observed AUCs no clear relationship was observed between Bu AUC and outcome with respect to toxicity, engraftment and relapse.

Adolescent↗
PubMed2005

Allogeneic bone marrow transplantation for juvenile myelomonocytic leukemia: a single center experience of 23 patients.

Juvenile myelomonocytic leukemia (JMML) is a childhood leukemia for which allogeneic BMT is the only curative therapy. At our pediatric stem cell transplantation unit, we performed 26 BMTs in 23 children (age 0.5-12.7 years). Conditioning was CY/TBI based (1980-1996, n=14) or BU/CY/melphalan based (1996-2001, n=9). Donors were HLA-identical siblings (n=11), unrelated volunteers (n=9) or mismatched family members (n=3). A total of 10 patients survive in CR (median follow-up 6.8 years, range 3.1-22.2 years). Relapse or persistent disease was observed in eight and two patients, respectively. Nine of these patients died, one achieved a second remission following acute nonlymphatic leukemia chemotherapy (duration to date 5.3 years). Transplant-related mortality occurred in four patients. Overall survival at 5 and 10 years was 43.5%. Using T-cell-depleted, one-antigen mismatched unrelated donors was the only significant adverse factor associated with relapse in multivariate analysis (P=0.039, hazard ratio 4.9). Together with a trend towards less relapse in patients with graft-versus-host-disease and in patients transplanted with matched unrelated donors, this suggests a graft-versus-leukemia effect of allogeneic BMT in JMML.

Bone Marrow Transplantation↗
PubMed2005

Graft dysfunction and delayed immune reconstitution following haploidentical peripheral blood hematopoietic stem cell transplantation.

For many children with life-threatening hematological diseases, hematopoietic stem cell transplantation (HSCT) is the only curative option. In children lacking a matched related or unrelated donor and with the certainty that, left untreated, death will ensue alternative donors must be sought. Haplo-identical peripheral blood stem cell transplantation (PBSCT) from a healthy parent is a feasible alternative. To reduce the risk of fatal graft-versus-host disease (GvHD) as a complication of transplant across major histocompatibility antigens, intense T-cell depletion is required. Large numbers of purified, cytokine mobilized peripheral stem cells (the so-called mega-dose concept) are required to compensate for the significantly increased risk of either graft failure or early rejection. In our unit, despite this approach, graft dysfunction has, in a significant group of children, proved problematic and, despite salvage attempts at re-transplantation, usually fatal. In children with hematological malignant disease, our overall relapse-free survival is 41%. However, successful transplant outcome has been associated with considerable delays in immune reconstitution that can be implicated in subsequent viral reactivation. We are investigating new strategies to improve the outcome of haplo-identical PBSCT, which may allow us to offer this form of treatment to more children requiring urgent HSCT.

Adolescent↗
PubMed2005

Adenovirus infection in children after allogeneic stem cell transplantation: diagnosis, treatment and immunity.

Human adenoviruses (HAdV) are a frequent cause of potentially fatal infections in patients after allogeneic stem cell transplantation, especially in children. Monitoring of serum/plasma by real-time quantitative PCR is a sensitive tool for the recognition of patients at risk of a potentially fatal infection and for the evaluation of the efficacy of treatment. Data from a retrospective study and from a prospective study demonstrate that recovery of immunity after transplantation is essential for the elimination of HAdV infection. The feasibility of several approaches for the manipulation of immunity in the immunocompromised host to prevent a fatal course of the infection is discussed.

Adenovirus Infections, Human↗
PubMed2005

Allogeneic stem cell transplantation in X-linked lymphoproliferative disease: two cases in one family and review of the literature.

X-linked lymphoproliferative disease (XLP) is a rare immunodeficiency caused by mutations in the signaling lymphocyte activating molecule-associated protein/SH2D1A gene and characterized by a dysregulated immune response to Epstein-Barr virus and other pathogens. The clinical presentation is heterogeneous and includes fulminant infectious mononucleosis, lymphoma, hypogammaglobulinemia and aplastic anemia. XLP is associated with a high morbidity and overall outcome is poor. At present, allogeneic stem cell transplantation (alloSCT) is the only curative treatment. XLP patients may be recognized in various stages of disease and even when symptoms are not yet evident. We here present two related XLP patients in different stages of disease that were both treated successfully with alloSCT using a matched unrelated donor. In addition, we have reviewed all reported cases of alloSCTs in XLP patients. Based on these results and in order to improve the final outcome, we conclude that alloSCT should be recommended in both symptomatic and asymptomatic XLP patients.

Child↗
PubMed2004

Effect of ribavirin on the plasma viral DNA load in patients with disseminating adenovirus infection.

Adenovirus (AdV) infections are an increasingly frequent and potentially fatal complication in allogeneic stem cell transplant recipients. To determine the antiviral potential of ribavirin in an unbiased way, 4 patients without immune recovery were prospectively analyzed by quantitative measurement of plasma AdV DNA load. Administration of ribavirin at the first signs of AdV dissemination was not accompanied by a decrease in the plasma AdV DNA load in any of these patients, and an increase in the AdV load was even documented in 3. These observations question the potential of ribavirin to improve the outcome for patients with disseminating AdV infection and support a critical evaluation of antiviral treatments for AdV infection that involves the kinetics of virus DNA load as an objective parameter of viral replication.

Adenovirus Infections, Human↗
PubMed2003

[From gene to disease; CD40 ligand deficiency as the cause of X-linked hyper-IgM-syndrome].

X-linked hyper-IgM syndrome (XHIM) is a rare congenital immunodeficiency disorder, characterised by a defect in both humoral and cellular immune responses. In XHIM, the membrane glycoprotein CD40 ligand (expressed on activated T-cells) is deficient, which compromises T-cell interactions with antigen-presenting cells. Patients with XHIM present with severe, recurrent infections, predominantly of the respiratory and gastrointestinal tract. The gene encoding the CD40 ligand is located on the long arm of the X chromosome.

CD4-Positive T-Lymphocytes↗
PubMed2003

Paediatric allogeneic bone marrow transplantation for homozygous beta-thalassaemia, the Dutch experience.

We reviewed the results of the Dutch paediatric bone marrow transplant (BMT) program for children receiving HLA-identical BMT for beta-thalassaemia major over an 18-year period. In all, 19 patients underwent a total of 21 transplants in our treatment centre between July 1984 and February 2002. Eight females (age 0.3-12 years; median 5 years) and 11 males (age 0.8-18 years; median 6 years) were included. Information, prospectively collected, included molecular defects, donor genotype, beta/alpha-globin expression rates, serum ferritin levels, hepato-splenomegaly, chelation history, virology screening, liver pathology together with post-transplant outcome inclusive of leucocyte chimerism. In total, 11 patients received standard busulphan/cyclophosphamide (Bu/Cy) conditioning, with or without ATG. Stable engraftment was seen in 5/11 with late rejection occurring in six patients. Of these, two children underwent a second successful SCT. For this group, overall event-free survival (EFS) and disease-free survival (DFS) were 90 (10/11) and 64% (7/11), respectively. The probability of rejection was 55%. Subsequent addition of melphalan to the conditioning regimen resulted in long-term stable engraftment in all patients with an EFS/DFS for this group of 90% (9/10). Treatment-related mortality, irrespective of conditioning, was low at 5% (1/19 patients). Veno-occlusive disease (VOD) occurred in 19% (4/21 transplants) and acute GvHD in 19% (4/21 transplants). Post-BMT beta/alpha synthetic ratio measurement monitored donor erythroid engraftment and predicted rejection with a return to transfusion dependency. Maintained full donor chimerism is indicative of stable engraftment both for leucocyte and erythroid lineages, whereas mixed donor chimerism is not. Our results emphasise the importance of the conditioning regimen and post-transplant chimerism surveillance predictive of rejection or long-term stable engraftment.

Adolescent↗
PubMed2002

[Two brothers with familial hemophagocytic lymphohistiocytosis, treated by transplantation of stem cells from a single unrelated donor].

In two Turkish brothers familial haemophagocytic lymphohistiocytosis (FHLH) was diagnosed at 3 years and 2.5 months, respectively. FHLH is a rare autosomal recessive condition with a typical clinical presentation including prolonged fever, failure to thrive, irritability and hepatosplenomegaly. Laboratory evaluations show cytopenia (at least two out of the three cell lines), hypertriglyceridaemia and hypofibrinogenaemia. A pathognomonic sign is haemophagocytosis in bone marrow or tissue biopsy. Both patients were treated with stem-cell transplants using bone marrow and peripheral blood stem cells, respectively, from one unrelated donor. They showed a good haematological recovery, with minor complications, and at follow-up after one year were free of disease. Immune suppression can induce prolonged remission in FHLH, but cure is only achieved after a successful allogeneic stem-cell transplantation. Without transplantation, the prognosis is very poor.

Bone Marrow Transplantation↗
PubMed2002

[A flow diagram for the diagnosis of acute, non-traumatic joint complaints during childhood, retrospectively applied to 115 children].

Acute, non-traumatic joint complaints during childhood can be caused by conditions which require a quick and adequate recognition and treatment as well as by conditions in which an expectant policy can be pursued. On the basis of certain data from the anamnesis, supplemented with findings from the physical examination it is often possible to arrive at a (probable) diagnosis. An algorithm was designed, the differential steps of which were: fever, C-reactive protein titre, involvement of the hip joint, the presence of extra-articular manifestations and the results of a full blood count, erythrocyte sedimentation rate and imaging techniques. When this algorithm was retrospectively applied to the disease data of 115 children with acute, non-traumatic joint complaints, for whom the diagnosis in the status was taken as the gold standard, the correct diagnosis was established for every single child: for 98 (85.2%) by the shortest route and for 17 (14.8%) indirectly. In the case of 4 children, use of this algorithm would have led to unnecessary laboratory investigations and/or treatment. None of the diseases requiring immediate treatment were missed.

Acute Disease↗
PubMed2002

Quantification of adenovirus DNA in plasma for management of infection in stem cell graft recipients.

We used a real-time polymerase chain reaction method for quantification of adenovirus to monitor the dynamics of viral DNA load in plasma in pediatric stem-cell graft recipients. Two cases are described to demonstrate that detection and quantification of the adenovirus DNA load at regular intervals may be important to document the stage of adenovirus infection, to make decisions on clinical intervention, and to accurately monitor the response to antiviral therapy.

Adenoviridae↗
PubMed1997

Defective TCR-mediated signaling in synovial T cells in rheumatoid arthritis.

In rheumatoid arthritis (RA), the functional status of T cells is incompletely understood. Synovial T cells display phenotypic evidence of former activation, but there is poor production of T cell-derived cytokines in the synovium. In addition, synovial T cell proliferation upon mitogenic and antigenic stimulation was decreased compared with that in peripheral blood T cells. Moreover, previous reports revealed that early Ca2+ rises induced by TCR/CD3 stimulation were decreased in RA T cells compared with those in healthy controls. To investigate the molecular mechanisms of RA synovial T cell hyporesponsiveness, we analyzed the TCR/CD3-mediated protein tyrosine phosphorylation in RA peripheral blood and synovial fluid (SF) T cells. SF T cells exhibited a decreased overall tyrosine phosphorylation pattern upon stimulation. Most notably, the induction of phosphorylation of p38 was virtually absent. Moreover, we found that tyrosine phosphorylation of the TCR zeta-chain, one of the most proximal events in TCR signaling, is clearly diminished in RA SF T cells. The decrease in tyrosine phosphorylation was accompanied by a decrease in detectable levels of zeta-protein within synovial T cells. These results suggest that a defective TCR signaling underlies the hyporesponsiveness of synovial T cells in RA.

Arthritis, Rheumatoid↗
PubMed1996

Alteration of B-cell antigen receptor signaling by CD19 co-ligation. A study with bispecific antibodies.

The activation of B-cell antigen receptor-associated protein tyrosine kinases is an early and crucial event in B-cell signaling. Apart from the B-cell antigen receptor (BCR), the B-cell-specific transmembrane glycoprotein CD19 has also been shown to directly activate intracellular signaling cascades. In addition, because CD19 and the BCR are associated on the surface of activated B-cells, it has been proposed that close approximation between these two entities is crucial for optimal B-cell triggering. To test this hypothesis, bispecific antibodies were generated that bind membrane IgM and CD19 simultaneously. Although CD19 bispecific antibodies strongly induced tyrosine phosphorylation, they were, in contrast to muF(ab)2 fragments, unable to induce a proliferative response. Detailed analysis of the early signaling events showed that compared with muF(ab)2 fragments CD19 bispecific antibodies potently raised the intracellular [Ca2+], which was correlated with an efficient tyrosine phosphorylation of syk. Strikingly, the assembly of Grb2 complexes that may couple the BCR to p21(ras) was clearly altered by the CD19 bispecific antibody. In addition to the reported Shc and 145-kDa phosphoproteins, a prominent 90-95-kDa phosphoprotein resembling CD19 was detected in the Grb2 complexes. Thus, studies with CD19 bispecific antibodies show that CD19 co-ligation both quantitatively and qualitatively alters BCR signaling.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Compartmentalization of B-cell antigen receptor functions.

Receptor tyrosine kinases (RTK), like the PDGF-receptor, translate information from the extracellular environment into cytoplasmic signals that regulate a spectrum of cellular functions. RTK molecules consist of ligand binding extracellular domains, cytoplasmic kinase domains and tyrosine phosphorylation sites [Ullrich and Schlessinger, 1990 (Cell 61, 203-212); Heldin, 1992 (EMBO J. 11, 4251-4259)]. Upon ligand-induced RTK oligomerization, the kinase domains will become activated and induce auto(trans)phosphorylation of a number of cytoplasmic tyrosine residues. These phosphorylated tyrosine residues are incorporated in distinct sequence motifs and act as specific docking sites for SH2 domain-containing proteins [Songyang et al., 1993 (Cell 72, 767-778)]. In contrast to single- or oligo-chain RTK, immunological receptors such as antigen receptors, FcR and cytokine receptors are multi-chain complexes in which distinct receptor functions appear to be compartmentalized in distinct polypeptides. Here, we summarize current knowledge on the structural and functional characteristics of the B-cell antigen receptor complex (BCR) and address the specific ability of accessory molecules to recruit intracellular signaling intermediates towards the activated receptor complex.

Amino Acid Sequence↗
PubMed1996

Antigen receptor function in chronic lymphocytic leukemia B cells.

Functional studies revealed that two groups of B chronic lymphocytic leukemia (B-CLL) can be distinguished based on their capacity to mount a proliferative response following B-cell antigen receptor (BCR) cross-linking. The molecular basis for the functional distinction between these B-CLL groups most probably resides within or proximal to the BCR since non-responsive B-CLL, in marked contrast to responsive B-CLL, do not respond to BCR ligation with tyrosine phosphorylation of cellular substrates and increases in the free intracellular [Ca++]. Detailed biochemical analysis showed overall structural identity between responsive and non-responsive B-CLL with respect to both transmembrane and intracellular associates of the BCR complex. However expression levels of the protein tyrosine kinase syk, which is a key enzyme for the early signalling through the BCR, were found to be markedly lower in non-proliferating B-CLL. Here we will review current functional and biochemical data on responding and non-responding B-CLL and discuss the relevance of these findings for disease progression and our insight into the immunobiology of B-CLL.

Cell Division↗
PubMed1995

Hematopoietic cell phosphatase is recruited to CD22 following B cell antigen receptor ligation.

Hematopoietic cell phosphatase is a nonreceptor protein tyrosine phosphatase that is preferentially expressed in hematopoietic cell lineages. Motheaten mice, which are devoid of (functional) hematopoietic cell phosphatase, have severe disturbances in the regulation of B cell activation and differentiation. Because signals transduced via the B cell antigen receptor are known to guide these processes, we decided to analyze molecular interactions between the hematopoietic cell phosphatase and the B cell antigen receptor. Ligation of the B cell antigen receptor induces moderate tyrosine phosphorylation of hematopoietic cell phosphatase and the formation of a multi-molecular complex containing additional 68-70- and 135-kDa phosphoproteins. In resting B cells most of the hematopoietic cell phosphatase proteins reside in the cytosolic compartment, whereas after B cell antigen receptor cross-linking, a small fraction translocates toward the membrane where it specifically binds to the 135-kDa phosphoprotein. This 135-kDa glycoprotein was identified as CD22, a transmembrane associate of the B cell antigen receptor complex. Together these findings provide the first direct evidence that this cytoplasmic tyrosine phosphatase is involved in antigen receptor-mediated B cell activation, suggesting that in vivo B cell antigen receptor constituents or associated molecules may serve as substrate for its catalytic activity.

Antibodies, Monoclonal↗
PubMed1995

Antigen receptor nonresponsiveness in chronic lymphocytic leukemia B cells.

B chronic lymphocytic leukemia (B-CLL) are clonal populations of mIgM+ or mIgM+/mIgD+ CD5+ B cells that appear to be arrested in the follicular mantle-zone B-cell stage. Functional analyses have shown two groups of B-CLL that can be distinguished based on their capacity to proliferate in response to B-cell antigen receptor complex (BCR) cross-linking. To investigate the molecular basis for this phenomenon, we have analyzed both architecture and functional properties of BCR complexes on these two groups of B-CLL. Both groups were found to express structurally similar BCR. However, protein tyrosine kinase (PTK) activity associated with and specific for BCR constituents was strongly diminished in nonresponsive B-CLL. Moreover, the PTK-dependent assembly of Shc/Grb2 complexes, which may couple the BCR to p21ras, was absent in these B-CLL. Finally, of all PTKs tested, the expression of PTK syk was found to be considerably lower in nonresponsive B-CLL. Thus, absence of mitogenic responses upon BCR cross-linking in particular B-CLL was found to be strictly correlated with diminished induction of BCR-associated PTK activity and lower levels of PTK syk. Because nonresponsive B-CLL closely resembles tolerant autoreactive B cells both functionally and biochemically, distinction between B-CLL with respect to functional properties in vitro may be determined by differences in antigen encounter in vivo.

Adaptor Proteins, Signal Transducing↗