New insights into the performance characteristics of the Planova-series hollow-fiber parvovirus filters using confocal and electron microscopy

Virus filtration remains a critical step in the downstream process for the production of monoclonal antibodies and other mammalian cell-derived biotherapeutics. Recent studies have shown large differences in virus capture behavior of different virus filters, although the origin of these differences is still unclear. The objective of this study was to use confocal and scanning electron microscopy to directly evaluate the capture of virus-size nanoparticles in Planova 20N and BioEX hollow-fiber virus filters. Confocal images of fluorescent nanoparticles were quantified using ImageJ image processing software based on the measured fluorescence intensity of the labeled nanoparticles. Nanoparticle capture by the Planova BioEX was independent of transmembrane pressure from 10 to 45 psi. In contrast, the Planova 20N showed significant differences in nanoparticle capture profile at low pressure, consistent with literature data showing virus breakthrough under these conditions. Images obtained after a process interruption show significant migration of previously captured nanoparticles in the Planova 20N filters but not in the BioEX. These results provide important insights into the nature of virus capture in different virus filters and its dependence on the underlying structure of the virus filtration membranes.     

An atypical pacemaker pocket hematoma containing chyliform fluid

Subcutaneous hematoma is a complication of cardiac device implantation. In most cases, it is drained or spontaneously reabsorbed. While cases of chylothorax are rare, and cases of pseudochylothorax even rarer, previous cases of accumulation of chyliform material in the subcutaneous pockets of cardiac devices are anecdotal. We present a case of a 60-year-old man with antiphospholipids antibody syndrome and rheumatoid arthritis, who underwent dual-chamber ICD implantation in December 2020; the procedure was complicated by a pocket hematoma, which required surgical drainage. After 7 months, the man returned owing to heart failure, with evidence of the reappearance of a large swelling in the ICD pocket; this was tolerated for months by the patient and was no longer controlled. We drained 100ml of gold-colored, odorless liquid, and found no evidence of blood material in the pocket. The liquid was not pus, as culture testing proved negative for bacterial growth. Chemical-physical examination revealed elevated cholesterol concentration (704 mg/dl) and low levels of triglycerides (80 mg/dl; plasma cholesterol values were 91mg/dl, and triglycerides 48 mg/dl). Microscopic examination revealed isolated leukocytes and rare erythrocytes immersed in mucoid material; cytological analysis showed a carpet of macrophages filled with cholesterol. This evidence supports the diagnosis of pseudochyle fluid, formed by the degradation of a hematoma left intact in a closed cavity for more than 6 months. This is an extremely rare case of chyliform fluid documented in an ICD pocket.     

Molecular mapping deep within a living human organ: analysis of microvessel function on the timescale of seconds and with sub-micrometre spatial resolution

Visualising vascular endothelial cell function in individual blood microvessels allows elucidation of molecular interactions at the vascular wall, the first barrier between blood-borne therapeutic agent and its target. Functional analysis in situ requires sub-micrometer spatial resolution and tagged molecules generating contrast in living blood vessels. Light microscopy fulfills these requirements, particularly if fluorescent tags deliver the contrast. However, vascular arborisations in living organs defy morpho-functional analysis, filling tissues with closely meshed three-dimensional networks which are inaccessible to optical imaging. We protocol here successful morpho-functional analysis of microvascular processing in a living organ, the human placental cotyledon. Fluorescence-tagged tracer was positionally fixed by snap-freezing, frozen sections were cut, freeze-dried and heat-fixed. A brief histochemical procedure then labelled all vascular elements in the sections, providing fluorescence contrast in two colour channels. Mosaic monochromatic images acquired in both channels delivered high-resolution maps of centimeter-wide tissue areas. Quantitative analysis of the images’ greyscale histograms defined objectifiable, reproducible thresholds, used to reduce the images to colour-coded wide-area functional maps tracking placental vascular processing of the tagged molecules. Rapid positional fixing of tracer with reduction of images to maps was combined with ultrastructural tracking to elucidate vascular processing at scales of nanometres and seconds.     

Toward in vitro-to-in vivo translation of monoclonal antibody pharmacokinetics: Application of a neonatal Fc receptor-mediated transcytosis assay to understand the interplaying clearance mechanisms

Monoclonal antibodies (mAbs) are a rapidly growing drug class for which great efforts have been made to optimize certain molecular features to achieve the desired pharmacokinetic (PK) properties. One approach is to engineer the interactions of the mAb with the neonatal Fc receptor (FcRn) by introducing specific amino acid sequence mutations, and to assess their effect on the PK profile with in vivo studies. Indeed, FcRn protects mAbs from intracellular degradation, thereby prolongs antibody circulation time in plasma and modulates its systemic clearance. To allow more efficient and focused mAb optimization, in vitro input that helps to identify and quantitatively predict the contribution of different processes driving non-target mediated mAb clearance in vivo and supporting translational PK modeling activities is essential. With this aim, we evaluated the applicability and in vivo-relevance of an in vitro cellular FcRn-mediated transcytosis assay to explain the PK behavior of 25 mAbs in rat or monkey. The assay was able to capture species-specific differences in IgG-FcRn interactions and overall correctly ranked Fc mutants according to their in vivo clearance. However, it could not explain the PK behavior of all tested IgGs, indicating that mAb disposition in vivo is a complex interplay of additional processes besides the FcRn interaction. Overall, the transcytosis assay was considered suitable to rank mAb candidates for their FcRn-mediated clearance component before extensive in vivo testing, and represents a first step toward a multi-factorial in vivo clearance prediction approach based on in vitro data.     

The clearance of human fibrinogen fragments D1, D2, D3 and fibrin fragment D1 dimer in mice

The clearance of human fibrinogen fragments D₁, D₂, D₃ and fibrin fragment D₁ dimer were studied in the mouse model. Clearance of these fragments is a complex process involving clearance from blood into three other compartments. The overall clearance of fragment D₁ and its dimer were essentially identical. Fragments D₂ and D₃ cleared at a progressively slower rate. Competition studies were performed between ¹²⁵I-labeled fragment D₁ and large molar excesses of unlabelled human fragments D₁, D₂, D₃, D₁ dimer, fragment E, fibrinogen, macroalbumin, mannan and asialooroscomucoid. Of these ligands only the fragment D variants competed for the clearance of ¹²⁵I-labeled fragment D₁. Cross-competition was observed when ¹²⁵I-labeled fragment D₁ dimer was cleared in the presence of large molar excesses of fragment D₁. Autopsies demonstrated that injected fragments D₁, D₂, D₃ and D₁ dimer cleared primarily in liver and kidneys. In some clearance studies, livers were perfused with tissue culture fluid, subjected to light microscopic autoradiography, and silver grain counts performed to localize cleared fragment D₁. These experiments indicated that 80% of the liver uptake was in hepatocytes. However, when silver grain counts were normalized for the number of parenchymal and nonparenchymal cells, the distribution of silver grains was essentially identical (1.8 and 1.6 grains per cell, respectively). It is concluded that fragments D₁, D₂, D₃ and D₁ dimer are recognized by a similar clearance pathway. Since neither fibrinogen nor fragment E competed for the clearance of fragment D₁, it is suggested that determinants present in the fragment D domain become exposed after plasmin attack on fibrinogen and are responsible for clearance.     

Nondestructive Measurement of Retinal Glucose Transport and Consumption In Vivo Using NMR Spectroscopy

Abstract: The cellular events underlying various retinopathies are poorly understood but likely involve perturbation of retinal glucose metabolism. Current methods for assessing this metabolism are destructive, thus limiting longitudinal studies. We hypothesize that following an intravitreous injection, the clearance rate of a glucose analogue will be a nondestructive index of retinal glucose transport and metabolism in vivo. First, radiolabeled glucose analogues were injected into the vitreous. After 40 min, the dominant clearance path was posterior via the retina and was consistent with a facilitated transport mechanism. Next, either [6,6-²H₂]glucose or 3-deoxy-3-fluoro- d -glucose was injected into the vitreous of rabbit eyes, and the clearance rate of each analogue was determined over 40 min using, respectively, ²H or ¹⁹F NMR. These rates were interpreted as a function of the retinal glucose transport and consumption. From the NMR data, the rate of retinal glucose consumption was ∼16 times slower than the transport of glucose. These data demonstrate that NMR measurements of glucose analogue clearance rate from the vitreous can provide a nondestructive index of retinal glucose transport and consumption in vivo.     

Ciliary Ultrastructure In Nasal Brushings

Normal ciliary ultrastructure is thought to be necessary for effective function. There has been little or no attempt to quantify ultrastructural abnormalities in nasal disease and assess their significance. In this study we measured nasal ciliary function and examined ciliary ultrastructure in nasal brushings from 35 patients with perennial nasal symptoms refractory to treatment. Ultrastructural defects included microtubular abnormalities, compound cilia and ciliary ‘blebs’. the incidence of abnormal cilia was 16.7%, compared with 9% in controls, but there was only a poor correlation between ultrastructural defects and ciliary beat frequency. One patient had primary ciliary dyskinesia (PCD) with a typical clinical history and immotile cilia. However, only secondary ultrastructural abnormalities were seen. We have been unable to show that ciliary ultrastructural defects form the basis of impaired function. In patients with suspected PCD, nasal brushings should be taken for functional and ultrastructural studies; ideally, a further sample should be obtained for examination of possible primary ultrastructural abnormalities.     

Clearance of porcine circovirus and porcine parvovirus from porcine-derived pepsin by low pH inactivation and cation exchange chromatography

The contamination of oral rotavirus vaccines by porcine circovirus (PCV) raised questions about potential PCV contamination of other biological products when porcine trypsin or pepsin is used in production process. Several methods can be potentially implemented as a safety barrier when animal derived trypsin or pepsin is used. Removal of PCV is difficult by the commonly used viral filters with the pore size cutoff of approximately 20 nm because of the smaller size of PCV particles that are around 17 nm. It was speculated that operating the chromatography step at a pH higher than pepsin's low pI, but lower than pIs, of most viruses would allow the pepsin to flow through the resin and be recovered from the flow through pool whilst the viruses would be retained on the resin. In this study, we investigated low pH inactivation of viruses including PCV Type 1 (PCV1) and PCV1 removal by cation exchange chromatography (CEX) in the presence of pepsin. Both parvovirus and PCV1 could be effectively inactivated by low pH and PCV1 could be removed by POROS 50HS CEX. The POROS 50HS method presented in this article is helpful for designing other CEX methods for the same purpose and not much difference would be expected for similar product intermediates and same process parameters. While the effectiveness needs to be confirmed for specific applications, the results demonstrate that both low pH (pH 1.7) and CEX methods were successful in eliminating PCV1 and thus either can be considered as an effective virus barrier.