Bruce Irvine

Rapid and precise quantification of HIV-1 RNA in plasma using a branched DNA signal amplification assay.

The level of human immunodeficiency virus type 1 (HIV-1) RNA in human plasma has been quantitated directly with use of a solid-phase nucleic acid hybridization assay, based on branched DNA (bDNA) signal amplification technology with chemiluminescent detection. Signal amplification is accomplished by the incorporation of sites for 1,755 alkaline phosphatase-labeled probes per genome of HIV-1, after successive hybridization of target-specific oligonucleotides and bDNA amplifier molecules. The assay is performed in microwells, much like an immunoassay, and is amenable to routine laboratory use. Reproducibility and specificity studies indicated that the bDNA method was precise and showed no reactivity with seronegative donors. HIV-1 RNA levels were quantitated for 348 seropositive specimens, with a detection rate of 83% for those specimens from patients with < 500 CD4+ T-cell counts. Plasma RNA levels were found to change with disease stage, and in response to antiviral therapy. Quantitation of HIV-1 RNA in the plasma of HIV-1-infected patients, with use of the bDNA assay, may be a useful method for monitoring HIV-1 disease progression and therapeutic response.

Short and long‐term effects of interferon on serum markers of hepatitis C virus replication

Abstract Hepatitis C virus RNA (HCV‐RNA) and serological markers of HCV infection were measured in 30 patients with chronic hepatitis C who had been treated with interferon (IFN). Patients were classified into four groups according to serum alanine aminotransferase (ALT) levels after treatment. These were: as complete responders (CR); partial responders (PR); transient responders (TR); and non‐responders (NR). In all 11 patients in the CR group, HCV‐RNA disappeared from serum for at least 24 months and anti‐c100‐3 decreased progressively during this time. In the PR group, four of five patients were positive for HCV‐RNA in spite of the improvement of ALT levels and decline of anti‐c100‐3. In the TR and NR groups, HCV‐RNA disappeared transiently or remained persistently positive. The results indicate that IFN‐mediated improvement of ALT and decrease of anti‐HCV (anti‐c100‐3) were not always related to the disappearance of HCV‐RNA from serum. On the other hand, sustained disappearance of HCV‐RNA from serum was demonstrated in the patients who did not have post‐treatment ALT relapse. This indicates that IFN can eradicate HCV from serum in some patients and provide a clinical remission of chronic hepatitis C.

Derivation of a rational nomenclature for hepatitis C virus by phylogenetic analysis of the NS-5 region.

Different isolates of hepatitis C virus (HCV) are highly polymorphic throughout the genome. Phylogenetic analysis of nucleotide sequences derived from part of the gene encoding a nonstructural protein (NS-5) has provided evidence for six major genotypes of HCV among a worldwide collection of 76 samples from HCV-infected blood donors and patients with chronic hepatitis. Many of these HCV types comprised a number of more closely related subtypes, leading to a current total of 11 genetically distinct viral populations. Analysis of other regions of the viral genome produced equivalent relationships between published sequences to those found in NS-5, apart from the more highly conserved 5′ noncoding region where only the six major HCV types, but not subtypes, could be differentiated. A new nomenclature for HCV variants is proposed in this communication that reflects the two-tiered nature of sequence differences between different viral isolates.