The aim of this study was to establish the performance characteristics of a nonradioisotopic branched DNA (bDNA) signal amplification assay for quantitation of hepatitis B virus (HBV) DNA in human serum. Quantitation was determined from a standard curve and expressed as HBV DNA equivalents/mL (Eq/mL; 285,000 Eq = 1 pg of double stranded HBV DNA). The bDNA assay exhibited a nearly four log dynamic range of quantitation and an analytical detection limit of approximately 100,000 Eq/mL. To ensure a specificity of 99.7%, the quantitation limit was set at 700,000 Eq/mL. The interassay percent coefficient of variance for quantification values ranged from 10% to 15% when performed by novice users with different sets of reagents. Using the bDNA assay, HBV DNA was detected in 94% to 100% of hepatitis B e antigen-positive specimens and 27% to 31% of hepatitis B e antigen-negative specimens from chronic HBV-infected patients. The bDNA assay may be useful as a prognostic and therapy monitoring tool for the management of HBV-infected patients undergoing antiviral treatment.

SUMMARYWe examined the antigenic reactivities and virion associations of glycoproteins that were released into the culture fluids of cells infected with respiratory syncytial (RS) virus. Culture fluids and cell extracts were obtained from cells 24 to 30 h after they were infected with the Long strain of RS virus. Radioimmune precipitation of [3H]glucosamine-labelled glycoproteins by large glycoprotein (G)-specific or fusion protein (F)-specific monoclonal antibodies (MAbs) revealed that the G, F1 and F2 proteins were present in cell extracts but only the G protein was clearly evident in culture fluids. A glycoprotein (Mr 43K) which may be a precursor or a breakdown product of the G protein was also precipitated by the G-specific MAb from cell extracts and culture fluids. The G protein in culture fluids was slightly smaller (Mr 82K) than the G protein in cell extracts (Mr 88K). An abundant or heavily labelled, 18K glycoprotein in the fluids of virus-infected but not of mock-infected cells was weakly precipitated by the Fspecific MAb; this suggested that the 18K protein shares epitopes with the fusion protein of RS virus. The absence of F1 and F 2 polypeptides from culture fluids is evidence that the cells, which contained an abundance of these proteins, were intact. To determine whether any of the viral glycoproteins released by infected cells were soluble (non-virion-associated), culture fluid was subjected to rate zonal centrifugation in a 10 to 50~ sucrose gradient. An assay of fractions using a MAb-capture ELISA for the nucleocapsid (N) and F proteins revealed a peak of activity, due to virions, in the centre of the gradient, and a strong signal for the N protein at the top of the gradient suggesting that N protein was released from intact cells. Radioimmune precipitation of glycoproteins from the fractions at the top of the gradient using a hyperimmune guineapig serum revealed the G protein and a heterogeneous band which had the electrophoretic mobility of the 43K protein. Neither the F~ nor the F 2 protein was present in these fractions thus suggesting that virions had remained intact. These results showed that a soluble form of the G protein of RS virus is released into the culture fluids of intact, infected cells. Several theories concerning viral and non-viral origins for the 18K protein are discussed.

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Transcription-mediated amplification (TMA) is an isothermal, autocatalytic target amplification method which has the potential to detect less than 50 hepatitis C virus (HCV) RNA copies/ml (10 IU/ml). The TMA assay was used to assess the presence of residual HCV RNA in plasma from patients treated with polyethylene glycol-modified interferon ␣-2a (peginterferon ␣-2a) who showed a virologic relapse after the end of therapy. Chronic hepatitis C virus (HCV) infection is one of the major causes of the development of cirrhosis and hepatocellular carcinoma (3, 18). The current standard treatment of HCV infection with alpha interferon (IFN-␣) in combination with ribavirin leads to virologic end-of-treatment response in approximately 50% of cases. At the end of a 24-week follow-up period after completion of therapy, approximately 40% of patients achieve a sustained virologic response (13, 17). Thus, in about one of five patients who achieve an end-of-treatment response, a virologic relapse occurs. Rates of virologic relapse are even higher for IFN-␣ monotherapy than for combination therapy with IFN-␣ plus ribavirin. In patients treated with IFN-␣ alone, HCV RNA cannot be detected by reverse transcription-PCR (RT-PCR) at the end of treatment and the end of follow-up in approximately 30 and 15% of cases, respectively (4,6,7,11,12). Thus, ribavirin in the current standard combination treatment enhances virologic end-of-treatment response and reduces relapse rates (13, 16). Recently, treatment of patients with chronic hepatitis C with long-acting polyethylene glycol-modified IFN (peginterferon) resulted in an increase in virologic response rates (24,25). In patients treated for 48 weeks with 180 g of peginterferon ␣-2a, HCV RNA was undetectable by RT-PCR in 69 and 39% of patients at the end of treatment and the end of a 24-week follow-up period, respectively (25).Determination of virologic response is currently based on RT-PCR methods for measurement of HCV RNA in serum or plasma with a lower detection limit of about 100 HCV RNA copies/ml (ϳ50 IU/ml). Transcription-mediated amplification (TMA) is an isothermal, autocatalytic target amplification method, which has the potential to detect less than 50 HCV RNA copies/ml (Ͻ10 IU/ml) (21). The high sensitivity of the TMAbased assay may allow for the detection of low HCV RNA levels in end-of-treatment specimens from patients with subsequent virologic relapse. In a recent pilot study, residual HCV RNA was detected by TMA at the end of treatment in 36% of patients with virologic relapse after standard therapy using IFN-␣ with or without ribavirin (20). In the present study, end-of-treatment and end-of-follow-up plasma samples were investigated by the TMA-based assay to test for residual HCV RNA in a large cohort of patients who were chronically infected with HCV and were treated with standard IFN ␣-2a or peginterferon ␣-2a.

Residual serum HCV RNA was detected by the TMA-based assay in EOT samples from 34.6% of patients that had achieved apparent viral clearance by PCR. The detection of HCV RNA by the TMA-based assay could help redefine EOT response and assist in the antiviral management of HCV infection.