Infectious disease is one of the hottest areas of research today and researchers continue to seek ways to detect and diagnose infections earlier and more accurately.
In a groundbreaking paper published in the Journal of Virological Methods, researchers were able to demonstrate that Quanterix’ Simoa technology provided a 3000x improvement in sensitivity over conventional immunoassays for identifying acute HIV infection. In fact, the sensitivity achieved was equivalent to the gold standard of nucleic acid testing, but at the cost of a much less expensive immunoassay. This is particularly important for viruses such as HIV, as nucleic acid testing (NAT) can be cost prohibitive, especially in resource-constrained environments like those commonly found in many less developed countries where HIV prevalence is highest. Persons recently infected by HIV are 10 times more infectious than persons who have developed an immune response to the virus, but only NAT can reliably detect virus in the earliest stage of the infection prior to the immune response. Early detection of infection with a simple, cost-effective platform like Simoa can potentially have a significant impact in reducing the spread of the disease by making early stage detection more widely available.
The potential to replace nucleic acid testing for HIV screening has important implications for both HIV clinics globally as well as for donated blood screening. The door is now open to explore the application of Simoa to many other applications once thought to be only addressable with nucleic acid testing.
Simple diffusion-constrained immunoassay for p24 protein with the sensitivity of nucleic acid amplification for detecting acute HIV infection
Lei Chang, Linan Song, David R. Fournier, Cheuk W. Kan, Purvish P. Patel, Evan P. Ferrell, Brian A. Pink, Kaitlin A. Minnehan, David W. Hanlon, David C. Duffy, David H. Wilson
Nucleic acid amplification techniques have become the mainstay for ultimate sensitivity for detecting low levels of virus, including human immunodeficiency virus (HIV). As a sophisticated technology with relative expensive reagents and instrumentation, adoption of nucleic acid testing (NAT) can be cost inhibited in settings in which access to extreme sensitivity could be clinically advantageous for detection of acute infection. A simple low cost digital immunoassay was developed for the p24 capsid protein of HIV based on trapping enzyme-labeled immunocomplexes in high-density arrays of femtoliter microwells and constraining the diffusion of the enzyme–substrate reaction. The digital immunoassay was evaluated for analytical sensitivity for HIV capsid protein p24, and compared with commercially available NAT methods and immunoassays for p24, including 4th-generation antibody/antigen combo assays, for early detection of HIV in infected individuals. The digital immunoassay was found to exhibit 2000–3000-fold greater analytical sensitivity than conventional immunoassays reactive for p24, and comparable sensitivity to NAT methods. Assaying serial samples from 10 HIV-infected individuals, the digital immunoassay detected acute HIV infection as early as NAT methods, and 7–10 days earlier than conventional immunoassays. Comparison of assay results between the digital immunoassay and a quantitative NAT method from HIV infected serum exhibited a linear correlation R2 > 0.99. The data indicate that by constraining diffusion of the signal generation step of a simple sandwich immunoassay and enabling the digital counting of immunocomplexes, dramatic improvements in sensitivity to virus can be obtained to match the sensitivity of NAT at a fraction of the cost.