Laboratory markers of antiviral activity

Quantitative assays for viral nucleic acids have been instrumental in monitoring the response of patients to various antiviral therapies. The level of viraemia is predictive of clinical outcome in that a reduced risk of progression to AIDS or death was observed with lower plasma human immunodeficiency virus (HIV) RNA levels. Rebound in viral levels often signals therapeutic failures, some of which are associated with the development of drug resistance. Quantitative plasma assays for HIV, hepatitis C virus (HCV), cytomegalovirus (CMV) and hepatitis B virus (HBV) have been developed. Over time, modifications to these assays have been required to meet new demands. For example, as antiviral therapies have become more effective, HIV and HCV assays of greater sensitivity are required in order to follow patients for longer periods of time and to fully assess the extent of viral suppression. For HIV-1, a large percentage of patients treated with combination therapies had viral loads that were below the detection limit of the ultrasensitive assay (50 copies/ml). To assess the residual viral burden in this patient population an assay to quantify HIV-1 proviral DNA in peripheral blood mononuclear cells was developed. Studies to date indicate that proviral DNA remains easily detectable despite undetectable plasma RNA and may be useful in monitoring this patient population. To increase assay throughput, a new generation of quantitative assays that will provide real-time detection and a 6 log10 detection range from a single amplification is under development.