HIV-1 viral diversity and its implications for viral load testing: review of current platforms

IntroductionHuman immunodeficiency virus (HIV-1) plasma RNA viral load assays have become an essential tool, not only in HIV care, but also in understanding HIV pathogenesis.[1][2][3][4] Precision and reproducibility in the measurement of both plasma HIV-1 RNA levels and the absolute CD4 T-lymphocyte count are critical as these tests are the cornerstones of modern HIV care.1,2,5,6 HIV viral load levels are used to assess an individual's infectivity, 7 to gauge their risks for disease progression, 3 to monitor their response to antiretroviral therapy (ART), 8 and to assess the potential for emergence of viral resistance.6,9,10 Successful ART therapy is defined in most guidelines as suppression of plasma viremia, and is clinically documented by having two sequential quantitative HIV-1 plasma RNA measurements that are below the lower quantification limit of an approved viral load assay.6 Clinical trials of novel antiretroviral drugs or new regimens often use the difference between the pretreatment and endpoint HIV-1 plasma RNA level or the rate of decline of viral load to assess potency.[11][12][13][14] Although the North American and Western European experience has historically been with HIV-1 group M subtype B viral infections, this paradigm is changing rapidly.[15][16][17][18][19][20] In developed countries travelers may acquire non-B subtype infections abroad and present for care at home.Migrants and refugees from the developing world often now present for care in the developed world with strains reflective of the wide diversity of the global HIV pandemic.Secondary spread of non-B subtypes within the developed world is also recognized.Awareness of any clinical or laboratory differences between the common HIV-1 group M subtype B and the newer HIV-1 strains being seen in practice is increasingly important.The 2008 Recommendations for care of the International AIDS Society reaffirmed the importance of both accurate and sensitive viral load assessment, and by necessity, access to viral load assays.21 HIV-1 viral load testing is considered essential when initiating ART, when monitoring ART response, and when considering switching ART regimens.The demand for accurate, reproducible, and cost-effective viral load assays is therefore a global issue.[22][23][24] The potential value of a standardized genotype assignment for HIV-1 viral subtypes, regular monitoring of the performance of available commercial HIV viral load assays on emerging non-B HIV subtypes, circulating recombinant forms (CRFs) and unique recombinant forms (URFs), and the implications for resource-limited settings are discussed herein.

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