Frequency of contamination of coagulation factor concentrates with novel human parvovirus PARV4

Reconstruction of the historic time course of blood-borne virus contamination of clotting factor concentrates, 1974-1992

Factor VIII and IX clotting factor concentrates manufactured from pooled plasma have been identified as potent sources of virus infection in persons with hemophilia (PWHs) in the 1970s and 1980s. To investigate the range and diversity of viruses over this period, we analysed 24 clotting factor concentrates for several blood-borne viruses. Nucleic acid was extracted from 14 commercially produced clotting factors and 10 from nonremunerated donors, preserved in lyophilized form (expiry dates: 1974-1992). Clotting factors were tested by commercial and in-house quantitative PCRs for blood-borne viruses hepatitis A, B, C and E viruses (HAV, HBV, HCV, HEV), HIV- types 1/2, parvoviruses B19V and PARV4, and human pegiviruses types 1 and 2 (HPgV-1,-2). HCV and HPgV-1 were the most frequently detected viruses (both 14/24 tested) primarily in commercial clotting factors, with frequently extremely high viral loads in the late 1970s-1985 and a diverse range of HCV genotypes. Detection frequencies sharply declined following introduction of virus inactivation. HIV-1, HBV, and HAV were less frequently detected (3/24, 1/24, and 1/24 respectively); none were positive for HEV. Contrastingly, B19V and PARV4 were detected throughout the study period, even after introduction of dry heat treatment, consistent with ongoing documented transmission to PWHs into the early 1990s. While hemophilia treatment is now largely based on recombinant factor VIII/IX in the UK and elsewhere, the comprehensive screen of historical plasma-derived clotting factors reveals extensive exposure of PWHs to blood-borne viruses throughout 1970s-early 1990s, and the epidemiological and manufacturing parameters that influenced clotting factor contamination.

Study on genotyping and coinfection rate of human parvovirus 4 among the HTLV-I/II infected blood donors in Khorasan Razavi, Iran

Human Parvovirus 4 (PARV4) is an emerging virus infecting individuals with other blood-borne diseases. This study aimed to determine the prevalence of PARV4 in confirmed HTLVI/II positive samples from blood donors, assessing PARV4 viral load (DNA) and genotyping.

METHODS

A novel qReal-Time PCR, based on a plasmid construct, was developed to simultaneously detect all three PARV4 genotypes using in-house primers and probes. Positive qPCR samples were subjected to nested PCR amplification and subsequent sequencing. Phylogenetic trees were constructed using the Neighbor-joining (N.J.) method.

RESULTS

The coinfection rate of PARV4-DNA in HTLVI/II confirmed infected donors, who were previously deferred, was 14.4 % (13 out of 90), with no observed association with donation status (p = 1.0). Phylogenetic analysis indicated that PARV4-positive samples closely resembled genotype 2 in Iran.qPCR quantification demonstrated significant PARV4 viral loads in positive samples, ranging between 104 and 106 DNA copies/mL of serum.

CONCLUSION

This study presents the first evaluation of HTLVI/II and PARV4coinfection rates among blood donors. Notably, elevated PARV4-DNA titers were detected in HTLVI/II-positive donors. Given PARV's resistance to standard plasma refinery inactivation methods and the absence of its targeted inactivation, its potential impact remains a concern.

Parvovirus 4 in Individuals with Severe Hemophilia A and Matched Control Group

Background: Hemophilia is a well-known bleeding disorder with worldwide distribution. Replacement therapy, using plasma-derived or recombinant coagulation factors, comprises a gold standard regimen for the treatment. Regardless of the advancements made in viral inactivation methods in the production of plasma-derived coagulation factors, the possibility of transmission of new viral infections remained as a noticeable concern yet. The aim of the current study was to investigate the status of parvovirus 4 (PARV4) in severe hemophilia A, von Willebrand disease (vWD), and healthy control. Materials and Methods: In the current case-control study, 76 patients with hemophilia and vWD and 60 individuals from their family members entered the study. Nested PCR used to determine the presence of PARV4 in study subjects (76 cases). To characterize the PARV4 genotype, positive samples subjected to sequencing and phylogenetic analysis. Results: PARV4 genome detected in 11 (14.47%) patients with bleeding disorders. Among whom, nine patients (14.75%) were with severe hemophilia A and two (13.33%) patients with vWD. Only five healthy controls (8.33%) were positive for PARV4. All PARV4 sequences were found to be genotype 1. Conclusion: PARV4 infection in patients with hemophilia and vWD was higher than the control group. While detection of PARV4 DNA in patients with bleeding disorders may not necessarily reflect a clinical urgency, future investigations are needed to define the clinical significance of PARV4. It seems the detection of the virus immune signature of PARV4 infection, particularly in the context of acute and persistent infections, needs to focus on cellular and tissue targets.

Simoctocog alfa for the treatment of hemophilia A

INTRODUCTION

Hemophilia A is the most frequent inherited bleeding disorder and most challenging coagulation disorder. To combat this, a number of new improved rFVIII/IX concentrates have recently been approved. Some of them are derived from protein fusion biotechnology or pegylation to extend their half-life (HL). However, prophylaxis has become a standard of care to prevent arthropathy in hemophiliacs though the need of frequent venipunctures is a major obstacle to primary prophylaxis. The new Extended Half-Life (EHL) rFIX concentrates allow increased intervals, while the improved HL of new rFVIII was moderate. rFVIII Simoctocog alfa is produced in Human Embryonic Kidney (HEK) cells and the post-translational modifications performed by HEK cells are very similar to those occurring in the native FVIII. Areas covered: Herein, the author provides a review of simoctocog alfa with its contents including information on simoctocog alfa's manufacturing, clinical trials, safety and tolerability. They also give their expert opinion and future perspectives on this therapy. Expert opinion: An important advantage of simoctocog alfa is the possibility to omit at least 30% of venipunctures with prophylaxis. Consequently, the standard three times weekly bolus administrations may be reduced to twice weekly, meaning approximately 50 fewer venipunctures per year. This may be particularly helpful to children.

Simultaneous detection and differentiation of human parvovirus B19 and human parvovirus 4 by an internally controlled multiplex quantitative real-time PCR

Human parvovirus B19 (B19V) and human parvovirus 4 (PARV4) are two parvoviruses known to infect humans and transmit through blood and plasma derived medicinal products (PDMPs). Inactivation of the two parvoviruses has proven to be difficult and nucleic acid testing (NAT) would be an efficient means to exclude viruses. In this study, an internally controlled multiplex quantitative real-time PCR (qPCR) assay for B19V and PARV4 simultaneous detection and quantification was established and evaluated. The optimized multiplex qPCR assay allowed for simultaneous detection of all of the genotypes (1-3) of B19V and PARV4, with equal limit of quantification (LOQ) of 5 copies/μL, rather than other blood-borne viruses. It had a wide dynamic range of reliable amplification linearity of at least 8 orders of magnitude. Low standard deviations (SD) of quantification cycle (Cq) values and low coefficients of variation (CV) of copy numbers for both B19V and PARV4 suggested a high level of repeatability and reproducibility for the multiplex qPCR assay. This multiplex qPCR assay can be served as a readily applicable approach to screen plasma units intended for further manufacturing into PDMPs to reduce the risk of parvoviruses infection by such products and may also be useful for the detection of B19V/PARV4 co-infection or co-existence.

Safety of Cultivated Limbal Epithelial Stem Cell Transplantation for Human Corneal Regeneration

Ex vivo cultivated limbal stem cell transplantation is a promising technique for the treatment of limbal stem cell deficiency. While the results of the clinical trials have been extensively reported since the introduction of the technique in 1997, little has been reported regarding the potential health risks associated with production processes and transplantation techniques. Culture procedures require the use of animal and/or human-derived products, which carry the potential of introducing toxic or infectious agents through contamination with known or unknown additives. Protocols vary widely, and the risks depend on the local institutional methods. Good manufacturing practice and xeno-free culture protocols could reduce potential health risks but are not yet a common practice worldwide. In this review, we focus on the safety of both autologous- and allogeneic-cultivated limbal stem cell transplantation, with respect to culture processes, surgical approaches, and postoperative strategies.

Human parvovirus 4 'PARV4' remains elusive despite a decade of study

Human parvovirus 4 ('PARV4') is a small DNA tetraparvovirus, first reported in 2005. In some populations, PARV4 infection is uncommon, and evidence of exposure is found only in individuals with risk factors for parenteral infection who are infected with other blood-borne viruses. In other settings, seroprevalence studies suggest an endemic, age-associated transmission pattern, independent of any specific risk factors. The clinical impact of PARV4 infection remains uncertain, but reported disease associations include an influenza-like syndrome, encephalitis, acceleration of HIV disease, and foetal hydrops. In this review, we set out to report progress updates from the recent literature, focusing on the investigation of cohorts in different geographical settings, now including insights from Asia, the Middle East, and South America, and discussing whether attributes of viral or host populations underpin the striking differences in epidemiology. We review progress in understanding viral phylogeny and biology, approaches to diagnostics, and insights that might be gained from studies of closely related animal pathogens. Crucial questions about pathogenicity remain unanswered, but we highlight new evidence supporting a possible link between PARV4 and an encephalitis syndrome. The unequivocal evidence that PARV4 is endemic in certain populations should drive ongoing research efforts to understand risk factors and routes of transmission and to gain new insights into the impact of this virus on human health.

Human Parvoviruses

Parvovirus B19 (B19V) and human bocavirus 1 (HBoV1), members of the large Parvoviridae family, are human pathogens responsible for a variety of diseases. For B19V in particular, host features determine disease manifestations. These viruses are prevalent worldwide and are culturable in vitro, and serological and molecular assays are available but require careful interpretation of results. Additional human parvoviruses, including HBoV2 to -4, human parvovirus 4 (PARV4), and human bufavirus (BuV) are also reviewed. The full spectrum of parvovirus disease in humans has yet to be established. Candidate recombinant B19V vaccines have been developed but may not be commercially feasible. We review relevant features of the molecular and cellular biology of these viruses, and the human immune response that they elicit, which have allowed a deep understanding of pathophysiology.

First report of human parvovirus 4 detection in Iran

Parvovirus 4 (PARV4) is an emerging and intriguing virus that currently received many attentions. High prevalence of PARV4 infection in high-risk groups such as HIV infected patients highlights the potential clinical outcomes that this virus might have. Molecular techniques were used to determine both the presence and the genotype of circulating PARV4 on previously collected serum samples from 133 HIV infected patients and 120 healthy blood donors. Nested PCR was applied to assess the presence of PARV4 DNA genome in both groups. PARV4 DNA was detected in 35.3% of HIV infected patients compared to 16.6% healthy donors. To genetically characterize the PARV4 genotype in these groups, positive samples were randomly selected and subjected for sequencing and phylogenetic analysis. All PARV4 sequences were found to be genotype 1 and clustered with the reference sequences of PARV4 genotype 1. J. Med. Virol. 88:1314-1318, 2016. © 2016 Wiley Periodicals, Inc.

Pathogen inactivation and removal methods for plasma-derived clotting factor concentrates

Pathogen safety is crucial for plasma-derived clotting factor concentrates used in the treatment of bleeding disorders. Plasma, the starting material for these products, is collected by plasmapheresis (source plasma) or derived from whole blood donations (recovered plasma). The primary measures regarding pathogen safety are selection of healthy donors donating in centers with appropriate epidemiologic data for the main blood-transmissible viruses, screening donations for the absence of relevant infectious blood-borne viruses, and release of plasma pools for further processing only if they are nonreactive for serologic markers and nucleic acids for these viruses. Despite this testing, pathogen inactivation and/or removal during the manufacturing process of plasma-derived clotting factor concentrates is required to ensure prevention of transmission of infectious agents. Historically, hepatitis viruses and human immunodeficiency virus have posed the greatest threat to patients receiving plasma-derived therapy for treatment of hemophilia or von Willebrand disease. Over the past 30 years, dedicated virus inactivation and removal steps have been integrated into factor concentrate production processes, essentially eliminating transmission of these viruses. Manufacturing steps used in the purification of factor concentrates have also proved to be successful in reducing potential prion infectivity. In this review, current techniques for inactivation and removal of pathogens from factor concentrates are discussed. Ideally, production processes should involve a combination of complementary steps for pathogen inactivation and/or removal to ensure product safety. Finally, potential batch-to-batch contamination is avoided by stringent cleaning and sanitization methods as part of the manufacturing process.

Studies on the inactivation of human parvovirus 4

BACKGROUND

Human parvovirus 4 (PARV4) is a novel parvovirus, which like parvovirus B19 (B19V) can be a contaminant of plasma pools used to prepare plasma-derived medicinal products. Inactivation studies of B19V have shown that it is more sensitive to virus inactivation strategies than animal parvoviruses. However, inactivation of PARV4 has not yet been specifically addressed.

STUDY DESIGN AND METHODS

Treatment of parvoviruses by heat or low-pH conditions causes externalization of the virus genome. Using nuclease treatment combined with real-time polymerase chain reaction, the extent of virus DNA externalization was used as an indirect measure of the inactivation of PARV4, B19V, and minute virus of mice (MVM) by pasteurization of albumin and by low-pH treatment. Infectivity studies were performed in parallel for B19V and MVM.

RESULTS

PARV4 showed greater resistance to pasteurization and low-pH treatment than B19V, although PARV4 was not as resistant as MVM. There was a 2- to 3-log reduction of encapsidated PARV4 DNA after pasteurization and low-pH treatment. In contrast, B19V was effectively inactivated while MVM was stable under these conditions. Divalent cations were found to have a stabilizing effect on PARV4 capsids. In the absence of divalent cations, even at neutral pH, there was a reduction of PARV4 titer, an effect not observed for B19V or MVM.

CONCLUSION

In the case of heat treatment and incubation at low pH, PARV4 shows intermediate resistance when compared to B19V and MVM. Divalent cations seem important for stabilizing PARV4 virus particles.

Production of human parvovirus 4 VP2 virus-like particles in yeast and their evaluation as an antigen for detection of virus-specific antibodies in human serum

BACKGROUND

Human parvovirus 4 (PARV4) is a recently discovered member of the Parvoviridae family, which is not closely related to any previously discovered human parvoviruses. PARV4 has been isolated from the plasma of individuals with symptoms of acute viral infection; however, until recently PARV4 had not been associated with any disease, and its prevalence in the human population is yet to be established.

METHODS

The major capsid protein VP2 of PARV4 was generated in the yeast Saccharomyces cerevisiae and used for serological detection of virus-specific IgG and IgM in the sera of low-risk individuals.

RESULTS

One hundred and seventy serum specimens obtained from patients with acute respiratory diseases were tested for PARV4-specific IgG and IgM antibodies. Sixteen individuals (9.4%) were diagnosed as seropositive, including 6 IgM and IgG positive, 6 IgM positive/IgG negative and 4 IgG positive/IgM negative. Seven of the 16 seropositive individuals were between the ages of 3 and 11 with no evidence of parenteral exposure to PARV4 infection.

CONCLUSION

Our data demonstrate that recombinant yeast-derived VP2 protein, self-assembled to virus-like particles, can represent a useful tool when studying the seroprevalence of PARV4 infection. The presence of PARV4-specific antibodies in a low-risk group may indicate the possibility of alternative routes of virus transmission.

Evolution of CD8+ T cell responses after acute PARV4 infection

PARV4 is a small DNA human virus that is strongly associated with hepatitis C virus (HCV) and HIV infections. The immunologic control of acute PARV4 infection has not been previously described. We define the acute onset of PARV4 infection and the characteristics of the acute-phase and memory immune responses to PARV4 in a group of HCV- and HIV-negative, active intravenous drug users. Ninety-eight individuals at risk of blood-borne infections were tested for PARV4 IgG. Gamma interferon enzyme-linked immunosorbent spot assays, intracellular cytokine staining, and a tetrameric HLA-A2-peptide complex were used to define the T cell populations responding to PARV4 peptides in those individuals who acquired infection during the study. Thirty-five individuals were found to be PARV4 seropositive at the end of the study, eight of whose baseline samples were found to be seronegative. Persistent and functional T cell responses were detected in the acute infection phase. These responses had an active, mature, and cytotoxic phenotype and were maintained several years after infection. Thus, PARV4 infection is common in individuals exposed to blood-borne infections, independent of their HCV or HIV status. Since PARV4 elicits strong, broad, and persistent T cell responses, understanding of the processes responsible may prove useful for future vaccine design.

Parvovirus transmission by blood products - a cause for concern?

The introduction of dual viral inactivation of clotting factor concentrates has practically eliminated infections by viruses associated with significant pathogenicity over the last 20 years. Despite this, theoretical concerns about transmission of infection have remained, as it is known that currently available viral inactivation methods are unable to eliminate parvovirus B19 or prions from these products. Recently, concern has been raised following the identification of the new parvoviruses, human parvovirus 4 (PARV4) and new genotypes of parvovirus B19, in blood products. Parvoviruses do not cause chronic pathogenicity similar to human immunodeficiency virus or hepatitis C virus, but nevertheless may cause clinical manifestations, especially in immunosuppressed patients. Manufacturers should institute measures, such as minipool polymerase chain reaction testing, to ensure that their products contain no known viruses. So far, human bocavirus, another new genus of parvovirus, has not been detected in fractionated blood products, and unless their presence can be demonstrated, routine testing during manufacture is not essential. Continued surveillance of the patients and of the safety of blood products remains an important ongoing issue.

No evidence of presence of parvovirus 4 in a Swedish cohort of severely immunocompromised children and adults

The recently discovered human parvovirus 4 (PARV4) has been associated with seropositivity for human immunodeficiency virus, hepatitis B virus and hepatitis C virus. High prevalence is seen especially in intravenous drug users. The virus has been detected in blood products and persons who have been repeatedly transfused have shown to be a risk-group. Furthermore, reports from different parts of the world suggesting a prevalence ranging from zero to one third of the healthy population and the virus is thought to cause a latent or persistent infection. We investigated the presence of PARV4 DNA and parvovirus B19 (B19) DNA in serum from 231 severely immunocompromised cancer patients that have been exposed for blood products. Compared to B19, which was found in 3.9% of the patients, we found no evidence of PARV4. Our results may indicate a very low prevalence of the virus in Sweden, and it would be useful to measure the real PARV4 exposure of the healthy population as well as individuals with known risk factors by serology.

Increasing porcine PARV4 prevalence with pig age in the U.S. pig population

A novel parvovirus in pigs currently known as porcine PARV4 was recently discovered in pigs in Asia and Europe. The objective of this study was to investigate if porcine PARV4 is present in the U.S. pig population using a newly developed quantitative real-time PCR assay. Lung tissues obtained from 483 pigs across five different age groups with varying disease manifestations (reproductive failure/abortion, enteritis, respiratory disease, systemic/central nervous disease) were tested. While porcine PARV4 DNA was not detected in fetuses (0/28) or suckling pigs (0/15), it was detected in pigs from 10 of 16 states with increasing prevalence rates in the older pigs. Specifically, porcine PARV4 DNA was detected in 5.6% (10/178) of the nursery pigs, 18.7% (44/235) of the grow-finish pigs and 22.2% (6/27) of the mature pigs tested. Genome sequence comparison and phylogenetic analysis of U.S. porcine PARV4s confirmed that they have similar genomic characteristics and 97.6-99.1% sequence identities to available porcine PARV4 sequences from China, Romania, and the U.K. Porcine PARV4 was identified in 14.4% of respiratory cases and in 11.6% of cases with a history of systemic/central nervous system disease. As strict non-diseased controls were not included in this study, a possible role of porcine PARV4 in these disease manifestations remains inconclusive. To the authors' knowledge, this is the first description of porcine PARV4 in the U.S. pig population.

High prevalence of human parvovirus 4 infection in HBV and HCV infected individuals in shanghai

Human parvovirus 4 (PARV4) has been detected in blood and diverse tissues samples from HIV/AIDS patients who are injecting drug users. Although B19 virus, the best characterized human parvovirus, has been shown to co-infect patients with hepatitis B or hepatitis C virus (HBV, HCV) infection, the association of PARV4 with HBV or HCV infections is still unknown.

The aim of this study was to characterise the association of viruses belonging to PARV4 genotype 1 and 2 with chronic HBV and HCV infection in Shanghai.

Serum samples of healthy controls, HCV infected subjects and HBV infected subjects were retrieved from Shanghai Center for Disease Control and Prevention (SCDC) Sample Bank. Parvovirus-specific nested-PCR was performed and results confirmed by sequencing. Sequences were compared with reference sequences obtained from Genbank to derive phylogeny trees.

The frequency of parvovirus molecular detection was 16–22%, 33% and 41% in healthy controls, HCV infected and HBV infected subjects respectively, with PARV4 being the only parvovirus detected. HCV infected and HBV infected subjects had a significantly higher PARV4 prevalence than the healthy population. No statistical difference was found in PARV4 prevalence between HBV or HCV infected subjects. PARV4 sequence divergence within study groups was similar in healthy subjects, HBV or HCV infected subjects.

Our data clearly demonstrate that PARV4 infection is strongly associated with HCV and HBV infection in Shanghai but may not cause increased disease severity.

Molecular characterization of the newly identified human parvovirus 4 in the family Parvoviridae

Human parvovirus 4 (PARV4) is an emerging human virus, and little is known about the molecular aspects of PARV4 apart from its incomplete genome sequence, which lacks information of the termini. We analyzed the gene expression profile of PARV4 using a nearly full-length HPV4 genome in a replication competent system in 293 cells. We found that PARV4 utilizes two promoters to transcribe non-structural protein- and structural protein-encoding mRNAs, respectively, which were polyadenylated at the right end of the genome. Three major proteins, including the large non-structural protein NS1a, whose mRNA is spliced, and capsid proteins VP1 and VP2, were detected. Additional functional analysis of the NS1a revealed its capability to induce cell cycle arrest at G2/M phase in ex vivo-generated human hematopoietic stem cells. Taken together, our characterization of the molecular features of PARV4 suggests that PARV4 represents a new genus in the family Parvoviridae.

Discovery and genomic characterization of a novel ovine partetravirus and a new genotype of bovine partetravirus

Partetravirus is a recently described group of animal parvoviruses which include the human partetravirus, bovine partetravirus and porcine partetravirus (previously known as human parvovirus 4, bovine hokovirus and porcine hokovirus respectively). In this report, we describe the discovery and genomic characterization of partetraviruses in bovine and ovine samples from China. These partetraviruses were detected by PCR in 1.8% of bovine liver samples, 66.7% of ovine liver samples and 71.4% of ovine spleen samples. One of the bovine partetraviruses detected in the present samples is phylogenetically distinct from previously reported bovine partetraviruses and likely represents a novel genotype. The ovine partetravirus is a novel partetravirus and phylogenetically most related to the bovine partetraviruses. The genome organization is conserved amongst these viruses, including the presence of a putative transmembrane protein encoded by an overlapping reading frame in ORF2. Results from the present study provide further support to the classification of partetraviruses as a separate genus in Parvovirinae.

Prevalence of nucleic acid sequences specific for human parvoviruses, hepatitis A and hepatitis E viruses in coagulation factor concentrates

BACKGROUND AND OBJECTIVES

Due to their high resistance to inactivation procedures, nonenveloped viruses such as parvovirus B19, human bocavirus (HBoV), human parvovirus 4 (PARV4), hepatitis A (HAV) and hepatitis E virus (HEV) pose a particular threat to blood products. Virus transmission to patients treated with blood products presents an additional burden to disease. We determined the frequency and the amount of nucleic acid specific for nonenveloped viruses in recently manufactured preparations of commercial coagulation factor concentrates.

MATERIALS AND METHODS

At least three different batches of each of 13 different plasma-derived and recombinant coagulation factor products were tested for the presence and the amount of nucleic acid for parvovirus B19, HBoV, human parvovirus 4, hepatitis A virus and HEV by using quantitative polymerase chain reaction.

RESULTS

Whereas none of the recombinant products tested positive for any of these viruses, parvovirus B19 DNA with amounts ranging between 2×10(1) and 1.3×10(3) genome equivalents/ml was detected in five plasma-derived products. In addition to parvovirus B19 genotype 1, genotypes 2 and 3 were observed in two batches of a factor VIII/von-Willebrand factor product. In two products (one factor VIII concentrate and one activated prothrombin complex concentrate), a combination of both genotypes 1 and 2 of parvovirus B19 was detected.

CONCLUSION

The data show that nucleic acids from several relevant nonenveloped viruses are not found at detectable levels in coagulation factor concentrates. In some cases, parvovirus B19 DNA was detectable at low levels. Testing of the plasma pools for the full range of parvovirus genotypes is advocated for ensuring product safety.

Human bocavirus capsid structure: insights into the structural repertoire of the parvoviridae

Human bocavirus (HBoV) was recently discovered and classified in the Bocavirus genus (family Parvoviridae, subfamily Parvovirinae) on the basis of genomic similarity to bovine parvovirus and canine minute virus. HBoV has been implicated in respiratory tract infections and gastroenteric disease in children worldwide, yet despite numerous epidemiological reports, there has been limited biochemical and molecular characterization of the virus. Reported here is the three-dimensional structure of recombinant HBoV capsids, assembled from viral protein 2 (VP2), at 7.9-A resolution as determined by cryo-electron microscopy and image reconstruction. A pseudo-atomic model of HBoV VP2 was derived from sequence alignment analysis and knowledge of the crystal structure of human parvovirus B19 (genus Erythrovirus). Comparison of the HBoV capsid structure to that of parvoviruses from five separate genera demonstrates strong conservation of a beta-barrel core domain and an alpha-helix, from which emanate several loops of various lengths and conformations, yielding a unique surface topology that differs from the three already described for this family. The highly conserved core is consistent with observations for other single-stranded DNA viruses, and variable surface loops have been shown to confer the host-specific tropism and the diverse antigenic properties of this family.

The detection of parvoviruses

Parvovirus B19 is a single-stranded DNA virus which causes severe disease in immunocompromised patients and foetal loss in pregnant women. It is classified as an Erythrovirus and this genus also comprises two related viral genotypes (so-called LaLi/A6 (genotype 2) and V9 (genotype 3)) which appear to be immunologically indistinguishable from Parvovirus B19. Serological and nucleic acid test (NAT) systems to detect Parvovirus B19-mediated infection are commercially available; however, some NAT systems are genotype-specific. International standard preparations of Parvovirus B19 IgG and DNA have been produced for assay standardisation purposes, and to ensure consistency of assay manufacture and performance. Immunological assays, such as B-cell ELISpot, T-cell stimulation, and cytokine detection can also be used to confirm exposure to Parvovirus B19. Immunohistochemical techniques, employing commercially available monoclonal antibodies, are used to localise the virus in infected tissue and Parvovirus B19 viral antigen can also be detected in serum and plasma using antigen-specific ELISA. NAT systems have also been described to detect newly identified parvoviruses such as human bocavirus (HBoV), PARV4, and PARV5, although absolute confirmation of clinical diseases associated with these agents is required. This chapter describes the current status of detection systems for all the aforementioned parvoviruses, with particular emphasis on Erythrovirus detection by serological, NAT, and immunological approaches.

High frequencies of exposure to the novel human parvovirus PARV4 in hemophiliacs and injection drug users, as detected by a serological assay for PARV4 antibodies

BACKGROUND

PARV4 is a human parvovirus that was first detected in and cloned from an individual with a human immunodeficiency virus (HIV) seroconversion-like illness and that subsequently persisted in the lymphoid tissue and bone marrow. In contrast to human parvovirus B19 infections, PARV4 infections are most frequently detected in injection drug users (IDUs), particularly those who are coinfected with HIV type 1 (HIV-1). To investigate the routes of transmission of PARV4 and to ascertain whether infections are acquired through plasma-derived blood products, we developed a novel anti-PARV4 enzyme-linked immunosorbent assay (ELISA) to determine its seroprevalence in subjects with parenteral exposure.

METHODS

PARV4 viral protein 2 (VP2) was expressed and used as antigen in an indirect ELISA, to detect anti-PARV4 immunoglobulin G.

RESULTS

All 50 adult control subjects who were nonparenterally exposed to PARV4 were anti-PARV4 negative, in contrast to HIV-infected and HIV-uninfected IDUs, who had antibody frequencies of 67% and 33%, respectively. Predominantly parenteral transmission was confirmed by the finding of similar frequencies of infection among HIV-coinfected and HIV-uninfected hemophiliacs (11 of 20 individuals and 4 of 15 individuals, respectively) who were treated with nonvirally inactivated factor VIII/factor IX, whereas all but 1 of the 35 nonhemophiliac siblings of these siblings were found to be seronegative (despite having close household contact).

CONCLUSIONS

The present study provides convincing evidence that PARV4 is primarily transmitted parenterally. Evidence for widespread infection of hemophiliacs treated with nonvirally inactivated clotting factor creates fresh safety concerns for plasma-derived blood products, particularly because parvoviruses are relatively resistant to virus inactivation.

Emerging trends in plasma-free manufacturing of recombinant protein therapeutics expressed in mammalian cells

Mammalian cells are the expression system of choice for therapeutic proteins, especially those requiring complex post‐translational modifications. Traditionally, these cells are grown in medium supplemented with serum and other animal‐ or human‐derived components to support viability and productivity. Such proteins are also typically added as excipients and stabilizers in the final drug formulation. However, the transmission of hepatitis B in the 1970s and of hepatitis C and HIV in the 1980s through plasma‐derived factor VIII concentrates had catastrophic consequences for hemophilia patients. Thus, due to regulatory concerns about the inherent potential for transmission of infectious agents as well as the heterogeneity and lack of reliability of the serum supply, a trend has emerged to eliminate the use of plasma‐derived additives in the production and formulation of recombinant protein therapeutics. This practice began with products used in the treatment of hemophilia and is progressively expanding throughout the entire industry. The plasma‐free method of producing recombinant therapeutics is accomplished by the use of both cell culture media and final product formulations that do not contain animal‐ or human‐derived additives. A number of recombinant therapeutic proteins for the treatment of several different diseases have been produced by plasma‐free processes, with the objective of improving safety by eliminating blood‐borne pathogens or by reducing immunogenicity. This review describes the factors that drove the development of plasma‐free protein therapeutics and provides examples of advances in manufacturing that have made possible the removal of human and animal‐derived products from all steps of recombinant protein production.