Pre-analytical considerations in the development of a prototype SARS-CoV-2 antigen ARCHITECT automated immunoassay.

OBJECTIVES: To evaluate pre-analytical challenges related to high-volume central laboratory SARS-CoV-2 antigen testing with a prototype qualitative SARS-CoV-2 antigen immunoassay run on the automated Abbott ARCHITECT instrument. METHODS: Contrived positive and negative specimens and de-identified nasal and nasopharyngeal specimens in transport media were used to evaluate specimen and reagent on-board stability, assay analytical performance and interference, and clinical performance. RESULTS: TCID50/mL values were similar for specimens in various transport media. Inactivated positive clinical specimens and viral lysate (USA-WA1/2020) were positive on the prototype immunoassay. Within-laboratory imprecision was ≤0.10 SD (<1.00 S/C) with a ≤10% CV (≥1.00 S/C). Assay reagents were stable on board the instrument for 14 days. No high-dose hook effect was observed with a SARS-CoV-2 stock of Ct 13.0 (RLU>1.0 × 106). No interference was observed from mucin, whole blood, 12 drugs, and more than 20 cross-reactants. While specimen stability was limited at room temperature for specimens with or without viral inactivation, a single freeze/thaw cycle or long-term storage (>30 days) at -20 °C did not adversely impact specimen stability or assay performance. Specificity of the prototype SARS-CoV-2 antigen immunoassay was ≥98.5% and sensitivity was ≥89.5% across two ARCHITECT instruments. Assay sensitivity was inversely correlated with Ct and was similar to that reported for the Roche Elecsys® SARS-CoV-2 Ag immunoassay. CONCLUSIONS: The prototype SARS-CoV-2 antigen ARCHITECT immunoassay is sensitive and specific for detection of SARS-CoV-2 in nasal and nasopharyngeal specimens. Endogenous proteases in mucus may degrade the target antigen, which limits specimen storage and transport times and complicates assay workflow.

Proposed update to the taxonomy of the genera Hepacivirus and Pegivirus within the Flaviviridae family.

Proposals are described for the assignment of recently reported viruses, infecting rodents, bats and other mammalian species, to new species within the Hepacivirus and Pegivirus genera (family Flaviviridae). Assignments into 14 Hepacivirus species (Hepacivirus A-N) and 11 Pegivirus species (Pegivirus A-K) are based on phylogenetic relationships and sequence distances between conserved regions extracted from complete coding sequences for members of each proposed taxon. We propose that the species Hepatitis C virus is renamed Hepacivirus C in order to acknowledge its unique historical position and so as to minimize confusion. Despite the newly documented genetic diversity of hepaciviruses and pegiviruses, members of these genera remain phylogenetically distinct, and differ in hepatotropism and the possession of a basic core protein; pegiviruses in general lack these features. However, other characteristics that were originally used to support their division into separate genera are no longer definitive; there is overlap between the two genera in the type of internal ribosomal entry site and the presence of miR-122 sites in the 5' UTR, the predicted number of N-linked glycosylation sites in the envelope E1 and E2 proteins, the presence of poly U tracts in the 3' UTR and the propensity of viruses to establish a persistent infection. While all classified hepaciviruses and pegiviruses have mammalian hosts, the recent description of a hepaci-/pegi-like virus from a shark and the likely existence of further homologues in other non-mammalian species indicate that further species or genera remain to be defined in the future.

Expanded classification of hepatitis C virus into 7 genotypes and 67 subtypes: updated criteria and genotype assignment web resource.

UNLABELLED: The 2005 consensus proposal for the classification of hepatitis C virus (HCV) presented an agreed and uniform nomenclature for HCV variants and the criteria for their assignment into genotypes and subtypes. Since its publication, the available dataset of HCV sequences has vastly expanded through advancement in nucleotide sequencing technologies and an increasing focus on the role of HCV genetic variation in disease and treatment outcomes. The current study represents a major update to the previous consensus HCV classification, incorporating additional sequence information derived from over 1,300 (near-)complete genome sequences of HCV available on public databases in May 2013. Analysis resolved several nomenclature conflicts between genotype designations and using consensus criteria created a classification of HCV into seven confirmed genotypes and 67 subtypes. There are 21 additional complete coding region sequences of unassigned subtype. The study additionally describes the development of a Web resource hosted by the International Committee for Taxonomy of Viruses (ICTV) that maintains and regularly updates tables of reference isolates, accession numbers, and annotated alignments (http://talk.ictvonline.org/links/hcv/hcv-classification.htm). The Flaviviridae Study Group urges those who need to check or propose new genotypes or subtypes of HCV to contact the Study Group in advance of publication to avoid nomenclature conflicts appearing in the literature. While the criteria for assigning genotypes and subtypes remain unchanged from previous consensus proposals, changes are proposed in the assignment of provisional subtypes, subtype numbering beyond "w," and the nomenclature of intergenotypic recombinant. CONCLUSION: This study represents an important reference point for the consensus classification of HCV variants that will be of value to researchers working in clinical and basic science fields.

Antibody engineering to generate anti-tumor-associated glycoprotein 72 mouse recombinant CC49 IgG with improved solubility, purity, and thermal stability.

Tumor-associated glycoprotein 72 (TAG-72) is a mucin that is overexpressed heterogeneously on the surface of cancer cells, and is a potential target for immunotherapies for various cancer types. As a tumor marker, TAG-72 is measured with the cancer antigen (CA) 72-4 immunoassay. The murine monoclonal antibody (mAb) CC49 is a second-generation IgG that targets an antigen on TAG-72; however, CC49 has an unfavorable propensity to aggregate, which results in antibody impurity, instability, and low solubility and thus low potency and efficacy for therapeutic and diagnostic applications. Sequence analysis of CC49 revealed aggregation-prone motifs in the variable domain of the light chain. Using antibody engineering approaches, we developed three aggregation-resistant CC49 mIgG2a mutants (CC49M1, CC49M2, and CC49M3). The engineered CC49 mIgG2a mutants retained compatible binding performance with a significantly higher thermal stability. The CC49 mIgG2a mutants also demonstrated an almost 15-fold improvement in solubility, with 97% purity vs 70% purity of the parent molecule at 0.3 mg/mL. The enhanced stability and improved solubility of engineered CC49 could have significant advantages for diagnostic and therapeutic applications.

Development of a new automated IL-6 immunoassay.

OBJECTIVES: Quantitative detection of interleukin-6 (IL-6) in serum and plasma can help monitor immune responses and the development of acute inflammation to guide patient management. We developed an IL-6 immunoassay for use with the automated ARCHITECT system for detecting an increase in the inflammatory response. METHODS: Immunized mouse sera were tested and selected B-cells were harvested for fusion with myeloma cells. A panel of monoclonal antibodies were produced, from which capture and detection monoclonal antibodies for the prototype IL-6 immunoassay were selected and screened on the ARCHITECT instrument. The antibody pair that most effectively captured and detected IL-6 was selected to develop a prototype IL-6 immunoassay. Calibrator and panel preparations using an internal recombinant IL-6 standard were compared to serum panels prepared with the IL-6 International Standard 89/548. Assay specificity and spike recovery were determined, and assay sensitivity was compared with the Roche EUA Elecsys IL-6 assay run on the cobas analyzer. RESULTS: Twenty-one antibodies in 441 antibody pairs were screened. The prototype IL-6 assay showed high sensitivity with an estimated limit of detection of 0.317 pg/mL and limit of quantitation of <1.27. Spike recovery was 90%-110% in serum and plasma. The internal recombinant human IL-6 calibrator showed excellent stability for 63 days at 2-8 °C. The prototype IL-6 immunoassay was specific for IL-6, exhibited no cross reactivity to related cytokines and interleukins, and was 10-fold more sensitive than the Elecsys IL-6 assay. CONCLUSIONS: The prototype ARCHITECT IL-6 automated immunoassay is a reliable and robust method for the quantitative determination of IL-6 in human serum and plasma.

The GB viruses: a review and proposed classification of GBV-A, GBV-C (HGV), and GBV-D in genus Pegivirus within the family Flaviviridae.

In 1967, it was reported that experimental inoculation of serum from a surgeon (G.B.) with acute hepatitis into tamarins resulted in hepatitis. In 1995, two new members of the family Flaviviridae, named GBV-A and GBV-B, were identified in tamarins that developed hepatitis following inoculation with the 11th GB passage. Neither virus infects humans, and a number of GBV-A variants were identified in wild New World monkeys that were captured. Subsequently, a related human virus was identified [named GBV-C or hepatitis G virus (HGV)], and recently a more distantly related virus (named GBV-D) was discovered in bats. Only GBV-B, a second species within the genus Hepacivirus (type species hepatitis C virus), has been shown to cause hepatitis; it causes acute hepatitis in experimentally infected tamarins. The other GB viruses have however not been assigned to a genus within the family Flaviviridae. Based on phylogenetic relationships, genome organization and pathogenic features of the GB viruses, we propose to classify GBV-A-like viruses, GBV-C and GBV-D as members of a fourth genus in the family Flaviviridae, named Pegivirus (pe, persistent; g, GB or G). We also propose renaming 'GB' viruses within the tentative genus Pegivirus to reflect their host origin.

Engineering of the hepatitis C virus helicase for enhanced seroreactivity.

Hepatitis C Virus c33, a recombinant protein comprising residues 1192-1457 of NS3 helicase, has been a mainstay of HCV serology for decades. With seven unpaired cysteines, seroreactivity of E. coli expressed c33 is dependant on reductants. While engineering a c33 replacement for new anti-HCV serological tests, we sought to reduce oxidation sensitivity, a liability for immunodiagnostic reagent stability. A series of cysteine-to-serine substituted variants of a c33-like antigen was constructed and evaluated for reactivity against a panel of HCV-positive sera. Several variants were essentially nonreactive while others exhibited reactivity similar to or better than the wild-type construct. One demonstrated equivalent potency to wild-type but also diminished DTT dependence. To explore enhanced anti-NS3 reactivity, we constructed and examined an expanded series of antigens comprising individual helicase domains, the full-length helicase, additional cysteine-to-serine variants, and variants at positions critical to catalytic activity. Immunoassays using these latter NS3 helicase recombinants demonstrated that domain 1 possessed significantly more seroreactivity than previously believed, that the use of soluble full-length helicase protein enhanced sensitivity by several-fold over c33, and that anti-NS3 helicase seroreactivity was further enhanced by the introduction of point mutations which altered the catalytic activity or oxidation sensitivity of the antigen.

Newly discovered hepatitis C virus minicores circulate in human blood.

Hepatitis C virus (HCV) is one of the most prevalent causes of chronic blood-borne infections worldwide. Despite developments of highly effective treatments, most infected individuals are unaware of their infection. Approximately 75% of infections are in low- and middle-income countries; therefore, continuing research in HCV molecular virology and the development of vaccines and affordable diagnostics is required to reduce the global burden. Various intracellular forms of the HCV nucleocapsid (core) protein are produced in cell culture; these comprise the conventional p21 core and the newly discovered shorter isoforms (minicores). Minicores lack the N-terminus of p21 core. This study was conducted to determine if minicores are secreted in cell culture and more importantly if they circulate in the blood of individuals infected with HCV. We also developed a new monoclonal antibody that detects minicores targeting a C-terminal region common to p21 core and minicores. Direct evidence of minicores requires western blot analysis to distinguish the detection of p21 core from minicores. However, the sensitivity for western blot detection of HCV proteins from blood is nil without their prior purification/enrichment from blood. Therefore, we developed a purification method based on a heparin/Mn+2 precipitation of apolipoprotein B-containing lipoproteins because HCV is thought to circulate as a hybrid lipoviral particle. Minicores are secreted in culture when cells are grown in the presence of human serum. The heparin/Mn+2 precipitate from HCV-infected cell culture supernatants and from the blood of 4 patients with high-titer genotype-1 HCV contained minicores. Conclusion: Minicores are major newly discovered HCV proteins that are secreted and circulate in blood during natural infections. Minicore proteins have translational potential as targets in diagnostic assays and in vaccine development. (Hepatology Communications 2018;2:21-28).

Myeloma-Derived Light Chain Paired with a Diagnostic Monoclonal Antibody Hinders Immunoassay Performance.

Monoclonal antibodies are widely used as the capture and detection reagents in diagnostic immunoassays. In the past, myeloma fusion partners expressing endogenous heavy and/or light chains were often used to generate hybridoma cell lines. As a result, mixed populations of antibodies were produced that can cause inaccurate test results, poor antibody stability, and significant lot-to-lot variability. We describe one such scenario where the P3U1 (P3X63Ag8U.1) myeloma fusion partner was used in the generation of a hybridoma producing protein induced vitamin K absence/antagonist-II (PIVKA II) antibody. The hybridoma produces three subpopulations of immunoglobulin as determined by ion exchange (IEx) chromatography that exhibit varying degrees of immunoreactivity (0%, 50%, or 100%) to the target antigen as determined by Surface Plasmon Resonance. To produce an antibody with the highest possible sensitivity and specificity, the antigen-specific heavy and light chain variable domains (VH and VL) were cloned from the hybridoma and tethered to murine IgG1 and kappa scaffolds. The resulting recombinant antibody was expressed in Chinese hamster ovary cells and is compatible for use in a diagnostic immunoassay.

A non-isotopic method for the determination of activity of the thermostable NAD-dependent DNA ligase from Thermus thermophilus HB8.

A simple and accurate method for determination of enzymatic activity of the NAD-dependent DNA ligase of Thermus thermophilus HB8 has been developed that requires no radiolabeled substrates. lambda-DNA digested with BstEII provides two substrate DNA molecules (fragments 1 and 4) containing 12 base pair cohesive ends that are stably annealed at the assay temperature of 45 degrees C. One cohesive end unit is defined as the amount of enzyme required to achieve 50% ligation of fragment 1 in 15 min at 45 degrees C. Percent ligation is determined by analysis of reaction products, produced in reactions containing serial dilutions of enzyme, separated by agarose gel electrophoresis and photographed using a digital imaging device. Imaging software quantifies the amounts of fragment 1 and non-substrate fragment 7 present in the each lane (reaction). The latter is used to normalize the amount of fragment 1. This normalization process corrects for variations in sample loading, electrophoretic artifacts, and optical distortion of the gel image. A negative control containing no enzyme allows calculation of percent substrate ligated into product. Unit activity is then calculated from a dose-response curve in which percent of fragment 1 ligated is plotted against the log(10) of the enzyme dilution factor.

Generation of human neutrophil gelatinase-associated lipocalin monoclonal antibodies for use in ARCHITECT® assay.

Development of a robust immunoassay requires the selection of monoclonal antibodies with desired properties. These properties generally include kinetics parameters such as on-rate and off-rate (i.e., binding affinity), and, often times, the ability to form a sandwich with the analyte of interest. We sought to obtain antibodies suitable for development of an immunoassay capable of detecting human neutrophil gelatinase-associated lipocalin (NGAL), a glycosylated lipocalin of 25 kDa expressed in kidney tubules in response to injury that has been shown to be a urinary biomarker capable of diagnosing acute kidney injury. We immunized CAF1/J and RBF/DnJ mouse strains with recombinant NGAL, and a robust immune response, as measured by serum antibody titer, was observed among all CAF1/J mice. Antibodies secreted from mouse B cell-myeloma hybridomas were screened by enzyme immunoassay (EIA) and by surface plasmon resonance using a method we termed hybrid supernatant kinetic screening. Approximately 300 hybrid clones were evaluated by this technique to identify antibodies with the kinetic binding parameters meeting criteria required for further assay development (i.e., rapid association and slow dissociation). This data, along with epitope grouping, cell growth, cell viability, and antibody secretion, were used to identify antibodies for testing in the ARCHITECT assay.

Isolation and characterization of the MSP1 genes from Plasmodium malariae and Plasmodium ovale.

The merozoite surface protein 1 (MSP1) is the principal surface antigen of the blood stage form of the Plasmodium parasite. Antibodies recognizing MSP1 are frequently detected following Plasmodium infection, making this protein a significant component of malaria vaccines and diagnostic tests. Although the MSP1 gene sequence has been reported for Plasmodium falciparum and Plasmodium vivax, this gene has not been identified for the other two major human-infectious species, Plasmodium malariae and Plasmodium ovale. MSP1 genes from these two species were isolated from Cameroon blood donor samples. The genes are similar in size to known MSP1 genes and encode proteins with interspecies conserved domains homologous to those identified in other Plasmodium species. Sequence and phylogenetic analysis of all available Plasmodium MSP1 amino acid sequences clearly shows that the Po and Pm MSP1 sequences are truly unique within the Plasmodium genus and not simply Pf or Pv variants.

Detection of Plasmodium falciparum, P. vivax, P. ovale, and P. malariae merozoite surface protein 1-p19 antibodies in human malaria patients and experimentally infected nonhuman primates.

Approximately 3.2 billion people live in areas where malaria is endemic, and WHO estimates that 350 to 500 million malaria cases occur each year worldwide. This high prevalence, and the high frequency of international travel, creates significant risk for the exportation of malaria to countries where malaria is not endemic and for the introduction of malaria organisms into the blood supply. Since all four human infectious Plasmodium species have been transmitted by blood transfusion, we sought to develop an enzyme-linked immunosorbent assay (ELISA) capable of detecting antibodies elicited by infection with any of these species. The merozoite surface protein 1 (MSP1), a P. falciparum and P. vivax vaccine candidate with a well-characterized immune response, was selected for use in the assay. The MSP1 genes from P. ovale and P. malariae were cloned and sequenced (L. Birkenmeyer, A. S. Muerhoff, G. Dawson, and S. M. Desai, Am. J. Trop. Med. Hyg. 82:996-1003, 2010), and the carboxyl-terminal p19 regions of all four species were expressed in Escherichia coli. Performance results from individual p19 ELISAs were compared to those of a commercial test (Lab 21 Healthcare Malaria enzyme immunoassay [EIA]). The commercial ELISA detected all malaria patients with P. falciparum or P. vivax infections, as did the corresponding species-specific p19 ELISAs. However, the commercial ELISA detected antibodies in 0/2 and 5/8 individuals with P. malariae and P. ovale infections, respectively, while the p19 assays detected 100% of individuals with confirmed P. malariae or P. ovale infections. In experimentally infected nonhuman primates, the use of MSP1-p19 antigens from all four species resulted in the detection of antibodies within 2 to 10 weeks postinfection. Use of MSP1-p19 antigens from all four Plasmodium species in a single immunoassay would provide significantly improved efficacy compared to existing tests.

Microheterogeneous monoclonal antibody subspecies with differential hepatitis C virus core antigen binding properties identified by SEC-HPLC.

A monoclonal antibody directed against the core protein of hepatitis C virus was characterized for its utility in a sandwich antigen immunoassay wherein the mAb was used as the conjugate. Analysis of unconjugated and acridinium-conjugated monoclonal IgG using a silica-based HPLC size exclusion column revealed the existence of a single, symmetrical peak. Subsequent analysis of unconjugated IgG using a methacrylate-based HPLC size exclusion column revealed the presence of two species of IgG, but only by using a low ionic strength mobile phase buffer. Independent conjugation and testing of the two species showed significant differential reactivity towards HCV core antigen. Isoelectric focusing gels indicated subtle differences in the subspecies composition. Measurement of target peptide dissociation constants using fluorescence correlation spectroscopy indicated that the two HPLC column fractions exhibited a two-fold difference in Kd in low salt buffer that disappeared in high salt buffer. ESI-MS analysis of the fractionated IgG peaks revealed a reduction sensitive modification of the IgG and F(ab')2 of approximately 674 Da. In addition, both IgG and F(ab')2 contained two major heavy chain subspecies differing by about 1216 Da that was reduction insensitive. These modifications were present in only the one of the two SEC-HPLC peaks. These results suggest that this monoclonal antibody consists of microheterogeneous subspecies that exhibit different antigen binding properties associated with differences in post-translational modification of the heavy chain variable region. The choice of size exclusion column matrix and buffer composition was critical to the identification of these monoclonal IgG subspecies.

Genotype dependence of peptide-based immunoassays for the detection of HCV core antibodies.

Detection of hepatitis C virus (HCV) antibodies is partially influenced by the genotype of the infecting isolate. Immunoassays using genotype-1a-derived recombinants or peptides results in diminished reactivity among individuals infected with heterologous genotypes. We examined the magnitude of this effect on detection of core antibodies by using genotype-1a-derived core peptide immunoassays to test 254 HCV anti-core-positive individuals infected with genotypes 1-4 or 6. Peptides corresponding to amino acids 1-18, 10-24, and 11-28 reacted with 60%, 89%, and 85% of all samples, respectively. Peptide 1-18 detected 78% of individuals infected with genotype-1 or 2 but only 43% of those infected with genotypes 3, 4, or 6. Genotype-dependent reactivity was also observed for peptides 10-24 and 11-28. The use of a 34-mer peptide (encompassing amino acids 10-43) within the immunodominant region detected antibodies in 100% of specimens, thereby eliminating the genotype-dependent antibody detection observed with shorter peptides. Sequence differences between peptides and core of the infecting isolate did not entirely account for the genotype-dependent reactivity since some individuals displayed reactivity to peptides containing up to seven amino acid differences relative to the sequence of the infecting isolate, while others with identical core sequences had little or no reactivity. Thus, HCV core sequence divergence accounts for only a portion of the differential core antibody detectability observed when non-type-specific peptides are used. Differences in immune response between individuals infected with identical isolates also plays a significant role in core antibody detection using short peptides.

A previously unrecognized sixth genotype of GB virus C revealed by analysis of 5'-untranslated region sequences.

GB virus C (GBV-C) is a positive-strand RNA virus that infects a large proportion of the world's human population. It has been classified tentatively as a member of the Flaviviridae family and has been shown to exist as a group of five closely related genotypes. Recently, we reported the first full-length genome sequence of a genotype 5 isolate from South Africa. As part of the analysis of that sequence, a phylogenetic tree was elucidated from the 5'-untranslated region (UTR) that showed excellent congruence to the tree produced by analysis of complete open reading frame sequences. When 5'-UTR analysis was broadened subsequently to include additional isolates from around the globe, a heretofore unrecognized GBV-C genotype was discovered in Indonesia. When first reported in 2000, these isolates were described as constituting a novel fifth genotype. However, comparison to isolates from the then-known fourth and fifth genotypes (from Myanmar/Vietnam and South Africa, respectively) was not performed. A dataset of 121 GBV-C 5'-UTR sequences was complied and included representatives of the fourth and fifth genotypes as well as the "novel" Indonesian sequences and demonstrated, with strong support via bootstrap analysis, the existence of a sixth GBV-C genotype among infected individuals in Indonesia. The discovery of this sixth genotype emphasizes the diverse nature of GBV-C isolates and may have important implications for the interpretation of studies involving GBV-C/HIV co-infected individuals.

African origin of GB virus C determined by phylogenetic analysis of a complete genotype 5 genome from South Africa.

GB virus C (GBV-C), a positive-strand RNA virus, currently infects approximately one-sixth of the world's population. This virus exists as a collection of genotypes whose global distribution correlates with geographical origin. Genotyping of GBV-C isolates by phylogenetic analysis has relied upon the use of 5'-untranslated region (5'-UTR) sequences, however, complete genome sequences are used to demonstrate definitively their existence and geographical correlation. Initial identification of the fifth genotype from South Africa was based upon phylogenetic analysis of the 5'-UTR. It was sought to confirm this classification by analysis of full-length E2 genes from South African isolates and by analysis of a complete genotype 5 genome. Analysis of full-length E2 genes from 28 GBV-C-infected South African individuals revealed the existence of a unique group of 18 isolates, distinct from the other four genotypes. Bootstrap analysis provided strong support (95 %) for this fifth group. The remaining isolates were either genotype 1 (n=8) or 2 (n=2). Analysis of human E2 gene sequences, with the E2 gene from the chimpanzee variant GBV-Ctro included as the outgroup, produced a tree rooted on the genotype 1 branch. The complete genome nucleotide sequence of South African genotype 5 isolate D50 was determined. Phylogenetic analysis of the 5'-UTR and open reading frame produced congruent trees that grouped the sequences into five major genotypes. Inclusion of the corresponding region of the chimpanzee isolate GBV-Ctro in the analysis produced trees rooted on the branch leading to the genotype 5 isolate D50, suggesting an ancient African origin of GBV-C.

GB virus C genotype determination in GB virus-C/HIV co-infected individuals.

Several recent studies have indicated that patients infected with human immunodeficiency virus (HIV) exhibit a beneficial effect of co-infection with GB virus C (GBV-C). The benefit is demonstrated by slower progression to acquired immunodeficiency syndrome (AIDS) and prolonged survival time after the development of AIDS. In some but not all studies, a significant association between GBV-C/HIV co-infection and increased CD4(+) cell counts has been reported. To understand further the possible role that GBV-C might play in the reduced morbidity and mortality among HIV-infected patients, we sought to examine the presence of different GBV-C genotypes in a cohort of co-infected patients. PCR products derived from the 5'-untranslated region (5'-UTR) and the second envelope gene (E2) were sequenced directly and genotyped by phylogenetic analysis. While 5'-UTR analysis delineated the major type, analysis of the complete E2 gene was required for identification of group 2 subtypes, designated 2a and 2b. Among 35 patients tested, GBV-C genotype was determined for 33: two patients were infected with genotype 1, 12 with type 2a, and 19 with type 2b. Clinical data were available for 25 genotyped patients: one infected with genotype 1, nine with genotype 2a, and 15 with type 2b. CD4 cell counts tended to be lower in patients infected with genotype 2a compared with those with genotype 2b (310 +/- 136 vs 430 +/- 199, P = 0.054). Additional studies with larger cohorts from separate geographical regions are needed to determine whether a particular GBV-C genotype is associated with reduced morbidity or mortality among HIV co-infected patients.

Selectively primed adaptive driver RDA (SPAD-RDA): an improved method for subtractive hybridization.

A modification of the Representational Difference Analysis (RDA) method for subtractive hybridization, termed Selectively Primed Adaptive Driver (SPAD) RDA, is described. It differs from conventional RDA primarily in the manner by which initial driver (D) and tester (T) amplicon complexities are determined, and by optimizing the composition of D with respect to T for each round of subtraction. Total nucleic acid is extracted from serum or plasma and converted to double-stranded DNA/cDNA. A polymerase chain reaction (PCR) primer containing a selective nucleotide(s) at its 3'-end is used to generate amplicons of reduced complexity. Parallel subtractions are carried out, D vs. T (DT) for enrichment of tester-unique sequences and D vs. D (Driver Control or DC) to generate an optimized driver for use in the subsequent round. Following each round, agarose gel electrophoresis is used to visually identify any DT-unique bands through a side-by-side comparison of DT and DC subtraction products. In comparison to conventional RDA, SPAD-RDA achieved greater enrichment of viral sequences from an HCV infected chimpanzee, resulting in isolation of 13.7% of the viral genome, and an overall enrichment for HCV sequences of 239-fold. Virus fragments were also obtained from an HCV-infected human sample subtracted against non-paired human driver sequences. J. Med. Virol. 71:150-159, 2003.

Detection of HCV core antigen in human serum and plasma with an automated chemiluminescent immunoassay.

BACKGROUND: Currently, the detection of HCV infection in blood donors relies on the ability of immunoassays to detect circulating HCV antibodies. However, a significant delay exists between the time of infection and the development of antibodies. This delay (window period) can last up to 70 days. The introduction of NAT for the detection of HCV RNA has reduced this window period dramatically. However, NAT is labor intensive, prone to contamination, and expensive as compared with standard serologic tests. STUDY DESIGN AND METHODS: An automated, microparticle-based chemiluminescent assay for the detection of HCV core antigen in human serum and plasma was developed. The specificity and sensitivity of this prototype assay were evaluated by testing a population of normal blood donors and commercially available seroconversion panels. RESULTS: The HCV core antigen assay exhibited a 99.9-percent specificity by detecting a single repeatably reactive sample out of 1004 normal donors tested. Assay sensitivity was determined by comparing the HCV core antigen detection rate with the antibody seroconversion profile and the rate of HCV RNA detection. Among 15 seroconversion panels examined, core antigen was detected in 69 of 70 antibody-negative and/or RNA-positive samples for a sensitivity relative to NAT of 98.6 percent. CONCLUSION: These data indicate that the automated, microparticle-based chemiluminescent HCV core antigen assay can reduce the window period for detection of potentially infected blood donors by 32.7 days, and it represents a viable alternative to HCV RNA testing.