Ibrutinib inhibits collagen-mediated but not ADP-mediated platelet aggregation.

The BTK (Bruton's tyrosine kinase) inhibitor ibrutinib is associated with an increased risk of bleeding. A previous study reported defects in collagen- and adenosine diphosphate (ADP)-dependent platelet responses when ibrutinib was added ex vivo to patient samples. Whereas the collagen defect is expected given the central role of BTK in glycoprotein VI signaling, the ADP defect lacks a mechanistic explanation. In order to determine the real-life consequences of BTK platelet blockade, we performed light transmission aggregometry in 23 patients receiving ibrutinib treatment. All patients had reductions in collagen-mediated platelet aggregation, with a significant association between the degree of inhibition and the occurrence of clinical bleeding or bruising (P=0.044). This collagen defect was reversible on drug cessation. In contrast to the previous ex vivo report, we found no in vivo ADP defects in subjects receiving standard doses of ibrutinib. These results establish platelet light transmission aggregometry as a method for gauging, at least qualitatively, the severity of platelet impairment in patients receiving ibrutinib treatment.

Feasibility of early discharge strategies for neutropenic fever: outcomes of a Victorian organisational readiness assessment and pilot.

BACKGROUND: Although Australian consensus guidelines support the use of ambulatory care strategies for management of adult patients with low-risk neutropenic fever (NF), few centres have successfully implemented viable programmes. AIMS: To study the feasibility of an early discharge programme for adult patients with low-risk NF and assess organisational factors likely to influence successful implementation across participating Victorian hospitals. METHODS: Four hospitals participated in an organisational readiness assessment preceding selection of a pilot site for programme implementation. Prospective baseline auditing of current practice (i.e. inpatient care until resolution of NF) across three hospitals preceded programme implementation and evaluation. RESULTS: Barriers and facilitators to successful implementation were identified. One hundred and seventeen NF episodes were evaluated during audit phases. The frequency of low-risk NF presentations eligible for early discharge was low (less than two episodes per week). The programme reduced median (interquartile range) duration of parenteral antibiotics and length of stay for eligible patients (n = 11) from 4 (4, 5) days at baseline to 1 (1, 2) day during pilot (P = 0.02) and 4.5 (4, 5) days (baseline) to 2 (1, 3) days (pilot) (P = 0.02) respectively. The proportion of ineligible patients stepped down to oral antibiotics was improved from 38% (baseline) to 67% (pilot). No patients failed ambulatory care requiring readmission into hospital. CONCLUSION: The ambulatory care strategy for management of NF proposed by Australian consensus guidelines has been successfully piloted at a single Victorian centre. Organisational readiness tools can be used to identify potential barriers to the implementation of evidence based practices in patients with NF.

Patients with chronic myeloid leukemia who maintain a complete molecular response after stopping imatinib treatment have evidence of persistent leukemia by DNA PCR.

Around 40-50% of patients with chronic myeloid leukemia (CML) who achieve a stable complete molecular response (CMR; undetectable breakpoint cluster region-Abelson leukemia gene human homolog 1 (BCR-ABL1) mRNA) on imatinib can stop therapy and remain in CMR, at least for several years. This raises the possibility that imatinib therapy may not need to be continued indefinitely in some CML patients. Two possible explanations for this observation are (1) CML has been eradicated or (2) residual leukemic cells fail to proliferate despite the absence of ongoing kinase inhibition. We used a highly sensitive patient-specific nested quantitative PCR to look for evidence of genomic BCR-ABL1 DNA in patients who sustained CMR after stopping imatinib therapy. Seven of eight patients who sustained CMR off therapy had BCR-ABL1 DNA detected at least once after stopping imatinib, but none has relapsed (follow-up 12-41 months). BCR-ABL1 DNA levels increased in all of the 10 patients who lost CMR soon after imatinib cessation, whereas serial testing of patients in sustained CMR showed a stable level of BCR-ABL1 DNA. This more sensitive assay for BCR-ABL1 provides evidence that even patients who maintain a CMR after stopping imatinib may harbor residual leukemia. A search for intrinsic or extrinsic (for example, immunological) causes for this drug-free leukemic suppression is now indicated.

Protective effects of recombinant human antithrombin III in pig-to-primate renal xenotransplantation.

Delayed rejection of pig kidney xenografts by primates is associated with vascular injury that may be accompanied by a form of consumptive coagulopathy in recipients. Using a life-supporting pig-to-baboon renal xenotransplantation model, we have tested the hypothesis that treatment with recombinant human antithrombin III would prevent or at least delay the onset of rejection and coagulopathy. Non-immunosuppressed baboons were transplanted with transgenic pig kidneys expressing the human complement regulators CD55 and CD59. Recipients were treated with an intravenous infusion of antithrombin III eight hourly (250 units per kg body weight), with or without low molecular weight heparin. Antithrombin-treated recipients had preservation of normal renal function for 4-5 days, which was twice as long as untreated animals, and developed neither thrombocytopenia nor significant coagulopathy during this period. Thus, recombinant antithrombin III may be a useful therapeutic agent to ameliorate both early graft damage and the development of systemic coagulation disorders in pig-to-human xenotransplantation.

Comparison of three methods of CD34+ cell enumeration in peripheral blood: dual-platform ISHAGE protocol versus single-platform, versus microvolume fluorimetry.

BACKGROUND: Quantitation of peripheral blood (PB) CD34(+) cells is now an established method for timing PBPC harvesting. Recent refinements to the dual-platform ISHAGE gating strategy for CD34(+) cells has seen the introduction of microbeads to enable absolute counting of cells on a single instrument platform. This eliminates the need for total WBCC performed on an automated hematology analyzer and potentially increases the analytical precision of the methodology. At the same time, alternative methods for CD34(+) cell enumeration have started to emerge, notably microvolume fluorimetry, which forms the basis of the fully-automated STELLer CD34 method using the Imagn 2000. METHODS: We performed a three-way evaluation of these methods. Sixty-eight samples of PB from 42 patients undergoing PBPC mobilization were analyzed by all three methods and correlations between all three calculated. The two-platform ISHAGE method was used as the reference method. RESULTS: Precision and linearity of the single-platform and STELLer CD34 assays were excellent. Correlation with the dual-platform reference method was also excellent (single-platform method slope = 1.03, intercept = -0.03 and R(2) = 0.9325, STELLer CD34 assay slope = 0.827, intercept = 4.27, R(2) =0.8215). Bias, determined by Bland-Altman analysis, was 1.16 and -1.62 for single platform and STELLer CD34 assay respectively. CONCLUSION: The three methods of CD34(+) cell enumeration gave equivalent results. The single-platform methodology negated the need for a separate white cell analyzer, while the STELLer CD34 methodology was technically the simplest.

Ex Vivo Stromal Cell Electroporation of Factor IX cDNA for Treatment of Hemophilia B.

Hemophilia B is an X-linked genetic disorder that typically results from chronic circulating deficiency of blood coagulation factor IX (FIX) (1). While the occurrence of hemophilia B is significantly less frequent than hemophilia A (factor VIII, deficiency) it has received special attention as a model for gene therapy. This is because hemophilia B is one of the least complicated genetic diseases from the point of view of demonstrating the proof of principle of a gene therapy protocol. Specifically, hemophilia B is a single gene recessive disorder and a wide range of tissues can be targeted for FIX gene delivery and strict regulation of FIX expression is not required. In addition, the 2.8 kb FIX cDNA is much smaller than the 9 kb FVIII cDNA, and FIX expression in transfected mammalian cells has been less problematic than FVIII expression (2). Since clinical severity of bleeding episodes closely corresponds to a patient's FIX activity, achieving even partial restoration of normal FIX levels in the bloodstream can alleviate internal bleeding. Individuals with FIX levels less than 1% of normal experience severe symptomatic episodes but providing roughly 5% of normal levels (i.e., 250 ng/mL plasma) can significantly reduce the frequency and severity of bleeding episodes and reduce long term complications (3). Treatment of hemophilia B primarily relies on intravenous injections of FIX protein purified from pooled human plasma, or very recently, on newly developed recombinant FIX. Treatment is applied typically only when bleeding episodes have occurred or are expected, for example, in case of a trauma or surgery. Although the risk of viral transmission of HIV and hepatitis viruses has been largely eliminated the absolute safety of any product derived from blood cannot be guaranteed. Furthermore, supplies of factor concentrates are limited and costs (especially if prophylactic treatment is being considered) are high. Thus, the application of gene therapy to hemophilia, whereby long-term correction of factor IX deficiency might be achieved, would be extremely useful.

VLA-4 is involved in the engraftment of the human pre-B acute lymphoblastic leukaemia cell line NALM-6 in SCID mice.

Attachment of human pre-B leukaemic cells to human or murine bone marrow stromal cells in vitro is largely mediated by the beta1 integrin VLA-4 binding to VCAM-1. Cells subsequently migrate within the stroma, a process also involving VLA-4. A variant of the pre-B acute lymphoblastic leukaemia cell line NALM-6, designated 4A1, lacking expression of VLA-4, was generated by radiation-induced mutagenesis followed by several rounds of negative selection with immunomagnetic beads, fluorescence activated cell sorting and clonal expansion. In vitro assays using 4A1 cells showed reduced binding to, and migration under, the murine stromal line M2-10B4. Sublethally irradiated mice (n=19) with severe combined immunodeficiency were injected intravenously with NALM-6 cells. Animals developed signs of leukaemia with hind-limb paralysis at a median of 30 d (95% confidence interval 28-30). Although there were no gross abnormal findings at autopsy, histological analysis revealed extensive marrow replacement and focal liver infiltration with leukaemic blasts, which were confirmed to be of human origin by flow cytometry. 12 mice were injected with a similar number of cells from the VLA-4-negative variant cell line 4A1. Six mice developed signs of leukaemia after 43-74d, with the remaining six being free of signs of disease after > 100d (P<0.001). Mice in this group with leukaemia had a lower incidence of hind-limb paralysis and less leukaemic infiltration in the marrow, but in some cases had large tumour nodules elsewhere. After a single 500 microg intraperitoneal injection of anti-murine VCAM-1 monoclonal antibody (MK2.7), five additional mice were injected with an identical number of wild-type (VLA-4+) NALM-6. All animals developed signs of leukaemia after a similar period to those injected with wild-type NALM-6 only. These results demonstrate that the beta1 integrin VLA-4 is involved in the engraftment of the pre-B-cell leukaemic cell line NALM-6 in SCID mice, although the interaction with VCAM-1 is unlikely to be the sole explanation.

MUC18, a member of the immunoglobulin superfamily, is expressed on bone marrow fibroblasts and a subset of hematological malignancies.

Despite the importance of bone marrow stromal cells in hemopoiesis, the profile of surface molecule expression is relatively poorly understood. Mice were immunized with cultured human bone marrow stromal cells in order to raise monoclonal antibodies to novel cell surface molecules, which might be involved in interactions with hemopoietic cells. Three antibodies, WM85, CC9 and EB4 were produced, and were found to identify a 100-110 kDa antigen on bone marrow fibroblasts. Molecular cloning revealed the molecule to be MUC18 (CD146), a member of the immunoglobulin superfamily, previously described as a marker of metastatic melanoma. In addition to the expected expression on melanoma cell lines and endothelial cells, a number of human leukemic cell lines were found to express MUC18, including all six T leukemia lines tested, one of five B lineage lines and one of four myeloid lines. Analysis of bone marrow samples from patients revealed positivity in 20% of B lineage ALL (n = 20), one of three T-ALL, 15% of AML (n = 13) and 43% of various B lymphoproliferative disorders (n = 7). No apparent reactivity was observed with mononuclear cells from normal peripheral blood or bone marrow, including candidate hemopoietic stem cells characterized by their expression of the CD34 antigen. However, positive selection of bone marrow mononuclear cells labeled with MUC18 antibody revealed a rare subpopulation (<1%) containing more than 90% of the stromal precursors identified in fibroblast colony-forming assays. The structure and tissue distribution of MUC18 suggest a functional role in regulation of hemopoiesis.

Long-term survival and proliferation of precursor-B acute lymphoblastic leukemia cells on human bone marrow stroma.

Leukemic cells frequently persist in the bone marrow of patients treated for acute lymphoblastic leukemia (ALL), and may regrow to produce relapse. We have used a long-term co-culture system to analyze the interaction of ALL blasts with components of the marrow microenvironment. Blast cells from 10 cases of precursor-B ALL were cultured on allogeneic human bone marrow stromal layers at 37 degrees C in microtiter wells, and replated when stroma showed evidence of deterioration. Leukemic cells from seven of 10 cases showed evidence of survival and proliferation beyond 30 days in culture, while in three cases there was a progressive decline in the number of viable leukemic cells by 7-21 days. Two cases continued to proliferate for 149 to 332+ days, while five underwent senescence after 34-52 days. In the two cases with long-term proliferation, the leukemic identity of the cells was confirmed by immunophenotyping, cytogenetics, and demonstration of clonal immunoglobulin gene rearrangements. Evidence of selection of leukemic subclones was seen in two cases, with immumophenotypic evidence of loss of CD10 and CD34 antigens, and acquisition of CD20 and surface mu chain. The leukemic cells in these cases grew either in clumps attached to the surface of the stroma, or as'cobblestone areas' beneath the stromal cells. Survival and growth of two evaluable cases was dependent on the continuing presence of stromal cells in the culture system. In one case, direct contact with stroma was shown to be necessary to main- tain viability, while blast cells from the other case survived equally well when separated from the stroma by a 0.4-micron pore size microporous membrane. These results indicate that leu- kemic cells from the majority of cases of precursor-B ALL are able to persist and undergo proliferation in vitro in the presence of normal marrow stroma. This process appears dependent on either direct cell-cell contact, or on diffusible factors derived from the stroma. The availability of ALL cells capable of indefinite proliferation under these conditions will allow further analysis of the mechanisms mediating leukemic cell proliferation.

Methaemoglobinaemia produced by phenazopyridine (Pyridium) in a man with chronic obstructive airways disease.

Life threatening methaemoglobinaemia developed after prolonged therapeutic use of phenazopyridine (Pyridium) in a patient with chronic obstructive airways disease. The combination of chronic obstructive airways disease and oxidant drugs (methaemoglobinaemia) may be lethal. The use of phenazopyridine should be abandoned. Certainly there is no indication to use it for more than a few days in any patient.