Filgotinib, a JAK1 Inhibitor, Modulates Disease-Related Biomarkers in Rheumatoid Arthritis: Results from Two Randomized, Controlled Phase 2b Trials

INTRODUCTION

The Janus kinase (JAK) inhibitor therapeutic class has shown significant clinical benefit in the treatment of rheumatoid arthritis (RA). We sought to gain insight into the mode of action and immunological effects of filgotinib, a JAK1 selective inhibitor, in active RA by analyzing secreted and cell-based biomarkers key to RA pathophysiology in two phase 2b trials of filgotinib in active RA.

METHODS

Immune cell subsets and 34 serum biomarkers were analyzed longitudinally over 12 weeks using blood samples collected from patients with active RA receiving filgotinib (100 or 200 mg once daily) or placebo (PBO) in the two phase 2b trials (DARWIN 1, on a background of methotrexate, and DARWIN 2, as monotherapy).

RESULTS

Consistently across both studies, filgotinib treatment decreased multiple immune response biomarkers that have key roles in RA for immune response, and decreased markers that promote matrix degradation, angiogenesis, leukocyte adhesion, and recruitment. Filgotinib did not significantly modulate T and natural killer (NK) lymphoid subsets, but slightly increased B cell numbers after 12 weeks. Multiple correlations were observed for changes in biomarkers with disease activity score 28-CRP. MIP1β showed modest predictivity at baseline for ACR50 response at 12 weeks in the 100 mg filgotinib dose across both studies (AUROC, 0.65 and 0.67, p < 0.05).

CONCLUSIONS

Filgotinib regulates biomarkers from multiple pathways, indicative of direct and indirect network effects on the immune system and the stromal response. These effects were not associated with reductions of major circulating lymphoid populations.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01888874, NCT01894516.

Acetyl-CoA Carboxylase Inhibitor GS-0976 for 12 Weeks Reduces Hepatic De Novo Lipogenesis and Steatosis in Patients With Nonalcoholic Steatohepatitis

BACKGROUND & AIMS

Increased de novo lipogenesis (DNL) contributes to the pathogenesis of nonalcoholic steatohepatitis (NASH). Acetyl-CoA carboxylase catalyzes the rate-limiting step in DNL. We evaluated the safety and efficacy of GS-0976, a small molecule inhibitor of acetyl-CoA carboxylase, in patients with NASH.

METHODS

In an open-label prospective study, patients with NASH (n = 10) received GS-0976 20 mg orally once daily for 12 weeks. NASH was diagnosed based on a proton density fat fraction estimated by magnetic resonance imaging (MRI-PDFF) ≥10% and liver stiffness by magnetic resonance elastography (MRE) ≥2.88 kPa. The contribution from hepatic DNL to plasma palmitate was measured by 14 days of heavy water labeling before and at the end of treatment. We performed the same labelling protocol in an analysis of healthy volunteers who were not given DNL (controls, n = 10). MRI-PDFF and MRE at baseline, and at weeks 4 and 12 of GS-0976 administration, were measured. We analyzed markers of liver injury and serum markers of fibrosis.

RESULTS

The contribution of hepatic DNL to plasma palmitate was significantly greater in patients with NASH compared with controls (43% vs 18%) (P = .003). After 12 weeks administration of GS-0976, the median hepatic DNL was reduced 22% from baseline in patients with NASH (P = .004). Compared with baseline, reductions in MRI-PDFF at week 12 (15.7% vs 9.1% at baseline; P = .006), liver stiffness by MRE (3.4 kPa vs 3.1 kPa at baseline; P = .049), TIMP metallopeptidase inhibitor 1 (275 ng/mL vs 244 ng/mL at baseline; P = .049), and serum level of alanine aminotransferase (101 U/L vs 57 U/L at baseline; P = .23) were consistent with decreased hepatic lipid content and liver injury. At week 12, 7 patients (70%) had a ≥30% decrease in MRI-PDFF.

CONCLUSION

In an open-label study, patients with NASH given GS-0976 for 12 weeks had reduced hepatic DNL, steatosis, and markers of liver injury. ClinicalTrials.gov no: NCT02856555.

GS-0976 Reduces Hepatic Steatosis and Fibrosis Markers in Patients With Nonalcoholic Fatty Liver Disease

BACKGROUND & AIMS

De novo lipogenesis is increased in livers of patients with nonalcoholic steatohepatitis (NASH). Acetyl-coenzyme carboxylase catalyzes the rate-limiting step in this process. We evaluated the safety and efficacy of GS-0976, an inhibitor of acetyl-coenzyme A carboxylase in liver, in a phase 2 randomized placebo-controlled trial of patients with NASH.

METHODS

We analyzed data from 126 patients with hepatic steatosis of at least 8%, based on the magnetic resonance imaging-estimated proton density fat fraction (MRI-PDFF), and liver stiffness of at least 2.5 kPa, based on magnetic resonance elastography measurement or historical biopsy result consistent with NASH and F1-F3 fibrosis. Patients were randomly assigned (2:2:1) to groups given GS-0976 20 mg, GS-0976 5 mg, or placebo daily for 12 weeks, from August 8, 2016 through July 18, 2017. Measures of hepatic steatosis, stiffness, serum markers of fibrosis, and plasma metabolomics were evaluated. The primary aims were to confirm previous findings and evaluate the relation between dose and efficacy.

RESULTS

A relative decrease of at least 30% from baseline in MRI-PDFF (PDFF response) occurred in 48% of patients given GS-0976 20 mg (P = .004 vs placebo), 23% given GS-0976 5 mg (P = .43 vs placebo), and 15% given placebo. Median relative decreases in MRI-PDFF were greater in patients given GS-0976 20 mg (decrease of 29%) than those given placebo (decrease of 8%; P = .002). Changes in magnetic resonance elastography-measured stiffness did not differ among groups, but a dose-dependent decrease in the fibrosis marker tissue inhibitor of metalloproteinase 1 was observed in patients given GS-0976 20 mg. Plasma levels of acylcarnitine species also decreased in patients with a PDFF response given GS-0976 20 mg. GS-0976 was safe, but median relative increases of 11% and 13% in serum levels of triglycerides were observed in patients given GS-0976.

CONCLUSIONS

In a randomized placebo-controlled trial of patients with NASH, we found 12-week administration of GS-0976 20 mg decreased hepatic steatosis, selected markers of fibrosis, and liver biochemistry. ClinicalTrials.gov ID NCT02856555.

Interrogation of transcriptomic changes associated with drug-induced hepatic sinusoidal dilatation in colorectal cancer

Drug-related sinusoidal dilatation (SD) is a common form of hepatotoxicity associated with oxaliplatin-based chemotherapy used prior to resection of colorectal liver metastases (CRLM). Recently, hepatic SD has also been associated with anti-delta like 4 (DLL4) cancer therapies targeting the NOTCH pathway. To investigate the hypothesis that NOTCH signaling plays an important role in drug-induced SD, gene expression changes were examined in livers from anti-DLL4 and oxaliplatin-induced SD in non-human primate (NHP) and patients, respectively. Putative mechanistic biomarkers of bevacizumab (bev)-mediated protection against oxaliplatin-induced SD were also investigated. RNA was extracted from whole liver sections or centrilobular regions by laser-capture microdissection (LCM) obtained from NHP administered anti-DLL4 fragment antigen-binding (F(ab’)₂ or patients with CRLM receiving oxaliplatin-based chemotherapy with or without bev. mRNA expression was quantified using high-throughput real-time quantitative PCR. Significance analysis was used to identify genes with differential expression patterns (false discovery rate (FDR) < 0.05). Eleven (CCL2, CCND1, EFNB2, ERG, ICAM1, IL16, LFNG, NOTCH1, NOTCH4, PRDX1, and TGFB1) and six (CDH5, EFNB2, HES1, IL16, MIK67, HES1 and VWF) candidate genes were differentially expressed in the liver of anti-DLL4- and oxaliplatin-induced SD, respectively. Addition of bev to oxaliplatin-based chemotherapy resulted in differential changes in hepatic CDH5, HEY1, IL16, JAG1, MMP9, NOTCH4 and TIMP1 expression. This work implicates NOTCH and IL16 pathways in the pathogenesis of drug-induced SD and further explains the hepato-protective effect of bev in oxaliplatin-induced SD observed in CRLM patients.

Proof of Concept for an Automated Image Analysis Method to Quantify Rat Bone Marrow Hematopoietic Lineages on H&E Sections

The bone marrow is an important site for assessment of the hematopoietic toxicity of new drug candidates. Here, we extended our previous work, where we developed a computer algorithm to automatically quantitate overall bone marrow cell density by analyzing digitized images of standard hematoxylin and eosin (H&E) slides of rat bone marrow and further evaluated the capability to quantify myeloid: erythroid + lymphoid (M:EL) ratio and megakaryocyte cell density. We tested the algorithm in a toxicity study, where rats were dosed with two molecules known to affect bone marrow composition, monomethyl auristatin E, and a Bcl-xL inhibitor. The image analysis method detected significant changes in M:EL and megakaryocyte number that were either not found or semiquantitatively described by manual microscopic observation of the same slides. The image analysis results were consistent with other more established but time-consuming methods that measure changes in bone marrow cell composition: smear cytology, flow cytometry, and microscopic assessment. Our work demonstrates the feasibility of a rapid and more quantitative assessment of changes in bone marrow cell lineage composition using a computer algorithm compared to microscopic examination of H&E-stained bone marrow sections.

MEK and ERK Kinase Inhibitors Increase Circulating Ceruloplasmin and Cause Green Serum in Rats

Inhibition of the mitogen-activated protein kinase/extracellular signal-regulated (MAPK/ERK) pathway is an attractive therapeutic approach for human cancer therapy. In the course of evaluating structurally distinct small molecule inhibitors that target mitogen-activated protein kinase kinase (MEK) and ERK kinases in this pathway, we observed an unusual, dose-related increase in the incidence of green serum in preclinical safety studies in rats. Having ruled out changes in bilirubin metabolism, we demonstrated a 2- to 3-fold increase in serum ceruloplasmin levels, likely accounting for the observed green color. This was not associated with an increase in α-2-macroglobulin, the major acute phase protein in rats, indicating that ceruloplasmin levels increased independently of an inflammatory response. Elevated serum ceruloplasmin was also not correlated with changes in total hepatic copper, adverse clinical signs, or pathology findings indicative of copper toxicity, therefore discounting copper overload as the etiology. Both ERK and MEK inhibitors led to increased ceruloplasmin secretion in rat primary hepatocyte cultures in vitro, and this increase was associated with activation of the Forkhead box, class O1 (FOXO1) transcription factor. In conclusion, increased serum ceruloplasmin induced by MEK and ERK inhibition is due to increased synthesis by hepatocytes from FOXO1 activation and results in the nonadverse development of green serum in rats.

Abstract 2096: Mechanistic insights into the pathogenesis of anti-DLL4-related hepatic sinusoidal dilatation

Background: The Delta-like 4 (DLL4)-mediated NOTCH signaling pathway is an attractive therapeutic target in cancer. However, chronic blockade of DLL4 signalling has been observed to result in vascular toxicities, such as hepatic sinusoidal dilatation. As the underlying pathogenesis is unclear, the current study was undertaken to interrogate gene expression changes and potential safety biomarkers associated with anti-DLL4 related hepatic sinusoidal dilatation.

Methods: Formalin-fixed paraffin-embedded (FFPE) liver sections were derived from male and female cynomolgus monkeys administered FDLL8566 (recombinant humanized anti-DLL4 F(ab’)2 antibody) by intravenous injection once weekly for 8 weeks at dose levels of 0, 5, 15 and 50 mg/kg/week (n = 3/sex/group). RNA was extracted from whole liver sections and laser capture-microdissected (LCM) hepatic regions with or without sinusoidal dilatation. mRNA expression was quantified using a high-throughput RT-qPCR approach, with 96 pre-validated, species-specific TaqMan gene expression assays. A non-parametric statistical test was used to assess differential gene expression between sinusoidal dilatation-affected and non-affected liver tissues. The Benjamini-Hochberg multiple testing comparison error-based False-Discovery-Rate (FDR) method was applied to calculate the adjusted p-values for each probe set.

Results: Fourteen candidate genes were differentially expressed between sinusoidal dilatation-affected and non-affected cynomolgus monkey livers with an FDR adjusted p value &lt;0.05. The presence of sinusoidal dilatation could be discriminated based on hierarchical clustering and principal component analysis (PCA). Modulation of expression in genes associated with the VEGF/NOTCH pathway, vascular remodeling, and inflammation were related to anti-DLL4-induced sinusoidal dilatation.

Conclusions: This work highlights the involvement of the NOTCH pathway in the maintenance of hepatic sinusoidal homeostasis in the nonhuman primate (NHP). As preclinical toxicities in NHPs have translated to patients for other anti-DLL4 inhibitors, the changes in candidate genes and potential mechanism of toxicity identified in this study are likely to be relevant to humans. The phenotypic characteristics of hepatic sinusoidal dilatation associated with anti-DLL4 resemble the microscopic and molecular features observed in the liver following oxaliplatin treatment of patients (including involvement of angiogenesis), suggesting that similar molecular mechanisms of hepatic toxicity may exist between anti-DLL4 and oxaliplatin.

This work was supported by an EU funded Industry Academia Pathways and Partnerships Marie Curie Award (AngioTox) Grant Number 251528.

Citation Format: Monika A. Jarzabek, Rupal Desai, Yuda Zhu, Christina Z. de Zafra, Joe Beyer, Gary Cain, Rajiv Raja, Annette T. Byrne, Priti Hegde, Jacqueline M. Tarrant. Mechanistic insights into the pathogenesis of anti-DLL4-related hepatic sinusoidal dilatation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2096.

Exploiting selective BCL-2 family inhibitors to dissect cell survival dependencies and define improved strategies for cancer therapy

The BCL-2/BCL-XL/BCL-W inhibitor ABT-263 (navitoclax) has shown promising clinical activity in lymphoid malignancies such as chronic lymphocytic leukemia. However, its efficacy in these settings is limited by thrombocytopenia caused by BCL-XL inhibition. This prompted the generation of the BCL-2-selective inhibitor venetoclax (ABT-199/GDC-0199), which demonstrates robust activity in these cancers but spares platelets. Navitoclax has also been shown to enhance the efficacy of docetaxel in preclinical models of solid tumors, but clinical use of this combination has been limited by neutropenia. We used venetoclax and the BCL-XL-selective inhibitors A-1155463 and A-1331852 to assess the relative contributions of inhibiting BCL-2 or BCL-XL to the efficacy and toxicity of the navitoclax-docetaxel combination. Selective BCL-2 inhibition suppressed granulopoiesis in vitro and in vivo, potentially accounting for the exacerbated neutropenia observed when navitoclax was combined with docetaxel clinically. By contrast, selectively inhibiting BCL-XL did not suppress granulopoiesis but was highly efficacious in combination with docetaxel when tested against a range of solid tumors. Therefore, BCL-XL-selective inhibitors have the potential to enhance the efficacy of docetaxel in solid tumors and avoid the exacerbation of neutropenia observed with navitoclax. These studies demonstrate the translational utility of this toolkit of selective BCL-2 family inhibitors and highlight their potential as improved cancer therapeutics.

Preclinical models of nicotinamide phosphoribosyltransferase inhibitor-mediated hematotoxicity and mitigation by co-treatment with nicotinic acid

Nicotinamide adenine dinucleotide (NAD) is an essential co-factor in glycolysis and is a key molecule involved in maintaining cellular energy metabolism. Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step of an important salvage pathway in which nicotinamide is recycled into NAD. NAMPT is up-regulated in many types of cancer and NAMPT inhibitors (NAMPTi) have potential therapeutic benefit in cancer by impairing tumor metabolism. Clinical trials with NAMPTi APO-866 and GMX-1778, however, failed to reach projected efficacious exposures due to dose-limiting thrombocytopenia. We evaluated preclinical models for thrombocytopenia that could be used in candidate drug selection and risk mitigation strategies for NAMPTi-related toxicity. Rats treated with a suite of structurally diverse and potent NAMPTi at maximum tolerated doses had decreased reticulocyte and lymphocyte counts, but no thrombocytopenia. We therefore evaluated and qualified a human colony forming unit-megakaryocyte (CFU-MK) as in vitro predictive model of NAMPTi-induced MK toxicity and thrombocytopenia. We further demonstrate that the MK toxicity is on-target based on the evidence that nicotinic acid (NA), which is converted to NAD via a NAMPT-independent pathway, can mitigate NAMPTi toxicity to human CFU-MK in vitro and was also protective for the hematotoxicity in rats in vivo. Finally, assessment of CFU-MK and human platelet bioenergetics and function show that NAMPTi was toxic to MK and not platelets, which is consistent with the clinically observed time-course of thrombocytopenia.

Development of a safety biomarker signature to detect hepatic sinusoidal dilation associated with an anti-DLL4 biotherapeutic

CONTEXT

Biomarkers of lesion-specific drug induced liver toxicity are currently lacking.

OBJECTIVE

To develop a biomarker signature using routine clinical pathology parameters that predict hepatic sinusoidal dilation related to anti-DLL4 biotherapeutics.

METHODS

Random forest and factor analysis was used to construct a signature of routine laboratory tests to detect microscopically confirmed sinusoidal dilation of the liver.

RESULTS

A biomarker signature was developed comprising two scores (S1 and S2) with area under the curve (AUC) for sinusoidal dilation prediction of 0.81, 0.85 and 0.96 in three rat studies and 0.48 and 0.81 in two monkey studies.

CONCLUSION

A unique, two-dimensional signature of liver parameters and red blood cell parameters could detect sinusoidal dilation in multiple preclinical species.

Unexpected hematologic effects of biotherapeutics in nonclinical species and in humans

Biotherapeutics are expanding the arsenal of therapeutics available for treating and preventing disease. Although initially thought to have limited side effects due to the specificity of their binding, these drugs have now been shown to have potential for adverse drug reactions including effects on peripheral blood cell counts or function. Hematotoxicity caused by a biotherapeutic can be directly related to the activity of the biotherapeutic or can be indirect and due to autoimmunity, biological cascades, antidrug antibodies, or other immune system responses. Biotherapeutics can cause hematotoxicity primarily as a result of cellular activation, cytotoxicity, drug-dependent and independent immune responses, and sequelae from initiating cytokine and complement cascades.  The underlying pathogenesis of biotherapeutic-induced hematotoxicity often is poorly understood. Nonclinical studies have generally predicted clinical hematotoxicity for recombinant cytokines and growth factors.  However, most hematologic liabilities of biotherapeutics are not based on drug class but are species specific, immune-mediated, and of low incidence. Despite the potential for unexpected hematologic toxicity, the risk-benefit profile of most biotherapeutics is favorable; hematologic effects are readily monitorable and managed by dose modification, drug withdrawal, and/or therapeutic intervention.  This article reviews examples of biotherapeutics that have unexpected hematotoxicity in nonclinical or clinical studies. 

Current practices in preclinical drug development: gaps in hemostasis testing to assess risk of thromboembolic injury

The Health and Environmental Sciences Institute Cardiac Biomarkers Working Group surveyed the pharmaceutical development community to investigate practices in assessing hemostasis, including detection of hypocoagulable and hypercoagulable states. Scientists involved in discovery, preclinical, and clinical research were queried on laboratory evaluation of endothelium, platelets, coagulation, and fibrinolysis during safety assessment studies. Results indicated that laboratory assessment of hemostasis is inconsistent among institutions and not harmonized between preclinical and clinical studies. Hemostasis testing in preclinical drug safety studies primarily focuses on the risk of bleeding, whereas the clinical complication of thrombosis is seldom assessed. Our results reveal the need for broader utilization of biomarkers to detect altered hemostasis (e.g., endothelial and platelet activation) to improve preclinical safety assessments early in the drug development process. Survey respondents indicated a critical lack of validated markers of hypercoagulability and subclinical thrombosis in animal testing. Additional obstacles included limited blood volume, lack of cross-reacting antibodies for hemostasis testing in laboratory species, restricted availability of specialized hemostasis analyzers, and few centers of expertise in animal hemostasis testing. Establishment of translatable biomarkers of prothrombotic states in multiple species and strategic implementation of testing on an industry-wide basis are needed to better avert untoward drug complications in patient populations.

Phosphorous dysregulation induced by MEK small molecule inhibitors in the rat involves blockade of FGF-23 signaling in the kidney

MEK, a kinase downstream of Ras and Raf oncogenes, constitutes a high priority target in oncology research. MEK small molecule inhibitors cause soft tissue mineralization in rats secondary to serum inorganic phosphorus (iP) elevation, but the molecular mechanism for this toxicity remains undetermined. We performed investigative studies with structurally distinct MEK inhibitors GEN-A and PD325901 (PD-901) in Sprague-Dawley rats. Our data support a mechanism that involves FGF-23 signal blockade in the rat kidney, causing transcriptional upregulation of 25-hydroxyvitamin D(3) 1-alpha-hydroxylase (Cyp27b1), the rate-limiting enzyme in vitamin D activation, and downregulation of 1,25-dihydroxyvitamin D(3) 24-hydroxylase (Cyp24a1), the enzyme that initiates the degradation of the active form of vitamin D. These transcriptional changes increase serum vitamin D levels, which in turn drive the increase in serum iP, leading to soft tissue mineralization in the rat.

Blood cytokines as biomarkers of in vivo toxicity in preclinical safety assessment: considerations for their use

In the drive to develop drugs with well-characterized and clinically monitorable safety profiles, there is incentive to expand the repertoire of safety biomarkers for toxicities without routine markers or premonitory detection. Biomarkers in blood are pursued because of specimen accessibility, opportunity for serial monitoring, quantitative measurement, and the availability of assay platforms. Cytokines, chemokines, and growth factors (here referred to collectively as cytokines) show robust modulation in proximal events of inflammation, immune response, and repair. These are key general processes in many toxicities; therefore, cytokines are commonly identified during biomarker discovery studies. In addition, multiplexed cytokine immunoassays are easily applied to biomarker discovery and routine toxicity studies to measure blood cytokines. However, cytokines pose several challenges as safety biomarkers because of a short serum half-life; low to undetectable baseline levels; lack of tissue-specific or toxicity-specific expression; complexities related to cytokine expression with multiorgan involvement; and species, strain, and interindividual differences. Additional challenges to their application are caused by analytical, methodological, and study design-related variables. A final consideration is the strength of the relationship between changes in cytokine levels and the development of phenotypic or functional manifestations of toxicity. These factors should inform the integrated judgment-based qualification of novel biomarkers in preclinical, and potentially clinical, risk assessment. The dearth of robust, predictive cytokine biomarkers for specific toxicities is an indication of the significant complexity of these challenges. This review will consider the current state of the science and recommendations for appropriate application of cytokines in preclinical safety assessment.

The role of flow cytometry in companion animal diagnostic medicine

Flow cytometry is a powerful tool for characterising the composition of complex cell populations. The accuracy and precision of this technology for describing and enumerating cells exceeds traditional methods. The number of diagnostic veterinary laboratories with access to a dedicated machine is increasing, and there is the potential to offer a clinical flow cytometry service. The improved availability of monoclonal antibodies (mAb) to cell markers expressed by the leukocytes of companion animals, permits the implementation of comprehensive mAb panels suitable for diagnosis of lympho- and myeloproliferative disease. Reticulated erythrocyte and platelet quantification, antiglobulin assays for immune-mediated cytopenias, lymphocyte subset analysis, and immunophenotyping of lymphoma and leukemia, have been validated for companion animal samples on the flow cytometer. It is now timely to consider the role of flow cytometry in diagnostic practice, and the requirement for quality assurance and standardization of testing procedures.

Tetraspanins: molecular organisers of the leukocyte surface

Tetraspanins are a large superfamily of cell surface membrane proteins characterised by their four transmembrane domains. They are expressed in a wide variety of cell types and have functional roles in processes, such as cellular adhesion, motility, activation and tumour invasion. Leukocytes express Collapse

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MESH Headings

• Animals
• Antigen Presentation
• B-Lymphocytes/immunology
• Cell Membrane/immunology
• Humans
• Integrins/immunology
• Leukocytes/immunology
• Lymphocyte Activation
• Membrane Proteins/chemistry
• Membrane Proteins/genetics
• Membrane Proteins/immunology
• Mice
• Mice, Knockout
• Signal Transduction
• T-Lymphocytes/immunology

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Affiliation(s)

Jacqueline M Tarrant The Walter and Eliza Hall Institute, 1G Royal Parade, 3050, Parkville, Victoria, Australia
Lorraine Robb
Annemiek B van Spriel
Mark D Wright

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The absence of Tssc6, a member of the tetraspanin superfamily, does not affect lymphoid development but enhances in vitro T-cell proliferative responses

The tetraspanins are a family of integral membrane proteins with four transmembrane domains. These molecules form multimolecular networks on the surfaces of many different cell types. Gene-targeting studies have revealed a role for tetraspanins in B- and T-lymphocyte function. We have isolated and deleted a novel tetraspanin, Tssc6, which is expressed exclusively in hematopoietic and lymphoid organs. Using a gene-trapping strategy, we generated an embryonic stem (ES) cell line with an insertion in the Tssc6 locus. Mice were derived from these ES cells and, using RNase protection and reverse transcription-PCR, we demonstrated that the insertion resulted in a null mutation of the Tssc6 allele. Mice homozygous for the gene trap insertion (Tssc6(gt/gt) mice) were viable and fertile, with normal steady-state hematopoiesis. Furthermore, responses to hemolysis and granulocyte colony-stimulating factor-induced granulopoiesis were equivalent to those of wild-type mice. Lymphoid development was normal in Tssc6(gt/gt) mice. Whereas Tssc6(gt/gt) B cells responded normally to lipopolysaccharide, anti-CD40, and anti-immunoglobulin M stimulation, Tssc6(gt/gt) T cells showed enhanced responses to concanavalin A, anti-CD3, and anti-CD28. This increased proliferation by Tssc6-deleted T lymphocytes was due to increased interleukin 2 production following T-cell receptor stimulation. These results demonstrate that Tssc6 is not required for normal development of the hematopoietic system but may play a role in the negative regulation of peripheral T-lymphocyte proliferation.

Overestimation of canine albumin concentration with the bromcresol green method in heparinized plasma samples

Albumin concentrations are routinely measured in dogs with bromcresol green (BCG)-binding assays on automated chemistry analyzers. Several variables affect this assay, including the length of reaction time, sample type, and lack of specificity of BCG for albumin. We observed that albumin concentrations measured with BCG appeared higher in heparinized plasma samples in sick dogs. The objective of this study was to determine the effect of anticoagulant and assay procedure on BCG albumin concentrations in clinically ill dogs. We hypothesized that albumin concentrations would be overestimated in heparinized plasma compared with serum because of the combination of heparin and fibrinogen. Furthermore, we hypothesized that the overestimation would be influenced by assay parameters. Blood was collected from 32 clinically ill dogs into tubes containing heparin, citrate, or no anticoagulant. Citrate was chosen to assess the effect of fibrinogen in the absence of heparin. Albumin concentration was measured in all 3 sample types from each dog using 2 different BCG procedures on an automated chemistry analyzer. The BCG procedures (standard and modified) differed in the wavelengths used for absorbance readings (standard, 600/700; modified, 570/505) and the time point at which absorbance was measured (standard, 100 seconds; modified, 40 seconds). In addition, the modified method incorporated a sample blank. Globulin fractions, fibrinogen concentration, and indices of lipemia, hemolysis, and icterus were evaluated for their contribution to the overestimation of albumin concentration in heparinized plasma compared with serum samples. Albumin concentrations were significantly higher (P </=.05) in heparinized plasma (mean +/- SE, 3.8 +/- 0.1 g/dL) than in serum (3.6 +/- 0.2 g/dL) or citrated plasma (3.2 +/- 0.1 g/dL). Overestimation was evident only with the standard BCG procedure. Multiple linear regression analysis indicated that fibrinogen was largely responsible for the higher albumin concentration in heparinized plasma with the standard method. Based on these results, heparin is not recommended as an anticoagulant for albumin measurement in dogs when using a BCG method unless the assay uses a sample blank and a reaction time of <1 minute.

Diagnosis of chronic myelogenous leukemia in a dog using morphologic, cytochemical, and flow cytometric techniques

Chronic myelogenous leukemia was diagnosed in a 3.5-year-old neutered male Golden Retriever. The diagnosis was based on persistent leukocytosis (>73.0X10(3)/microliter), composed of a proportionate left shift to progranulocytes with no evidence of underlying inflammation, infection, or neoplasia. Marked dysplasia was evident in neutrophils and platelets in peripheral blood. Bone marrow and splenic aspirates were dominated by mature and immature neutrophils with < 2% myeloblasts. Cytochemical and flow cytometric assays confirmed that cells in the peripheral blood and spleen were of committed neutrophil lineage. The dog responded initially to treatment with hydroxyurea, but developed acute undifferentiated leukemia approximately 83 days after initial presentation.