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White Paper on Antibody Testing
April 27, 2021
Challenged in public management post-COVID-19
The COVID-19 pandemic has drastically changed our lives, from causing about 2.9 million deaths worldwide to severe illnesses to our loved ones. Furthermore, travel and other restrictions have resulted in high unemployment rates, business closures, and financial loss, especially those who work in sectors that are most impacted by the restrictions. Since the start of the COVID-19 pandemic, individuals who suspect they have been infected with the SARS-CoV-2 virus would take a COVID-19 test, which is a molecular diagnostic test that uses swab samples from the nasopharyngeal area. These tests employ reverse transcription polymerase chain reaction (RT-PCR) to determine whether one has an active, current infection by testing for the presence of SARS-CoV-2 virus. With the ramping up of the vaccination program around the world, there is now finally a light at the end of the tunnel in terms of returning to some sort of normalcy. As we attempt to reopen the economy, the question shifts from how we can rapidly detect an infection case to how to stop outbreaks at workplaces. Contact tracing is effective, but it heavily relies on individuals volunteering information regarding their recent contacts. Thus, there is an urgent need to complement PCR tests with immunity screening to actively monitor and prevent the spread of COVID-19, even amongst asymptomatic individuals. The combination of these strategies will help drive more effective and economically feasible public health decisions.
Importance of Immunity Testing
Immunity screening involves the detection of antibodies (IgM and IgG) in blood samples. The presence of antibodies can be due to a prior infection or vaccination. When the virus is present in the body, the immune system, specifically B cells (lymphocytes), produces IgM and IgG antibodies which target viral proteins on the outer shell (i.e. spike (S) protein) or nucleic acid binding sites (i.e. the nucleocapsid (N) protein). These antibodies are normally not present at the onset of a viral infection. However, they can indicate whether someone has had an infection in the past or has been vaccinated. Furthermore, antibodies are known to persist in the blood for months, so they can be useful long-term indicators of immunity resistance compared to PCR tests. As the pandemic evolves into an endemic, having reliable and fast antibody tests will be essential for proactive surveillance of the immunity status of a population.
Currently, antibody tests are carried out by using immunoassays such as enzyme-linked immunosorbent assays (ELISA) and lateral flow immunoassays (LFI). ELISA is a sensitive method but requires centralized laboratory instruments and can take hours to days. The cost to perform an ELISA test can range from $100 - $200 per test, thus it is not economically feasible as a screening tool for a large population. LFI, on the other hand, can be produced economically and hence, be distributed to a wider population. However, commercial LFIs are known to produce unreliable results, partially since it is self-administered. There is a pilot study in the United Kingdom where LFI missed over half of PCR-positive COVID-19 cases.
SPR-based Antibody Tests
An immunity screening platform that combines the best of both ELISA and LFI, and suitable in point-of-care (PoC) settings can be found through the deployment of portable surface plasmon resonance (SPR) devices. Traditionally, SPR is a reliable label-free optical technique for drug screening purposes employed by the pharmaceutical industry. Affinité Instruments has miniaturized SPR as a portable biosensor to detect large biomolecules such as antibodies (Figure 1). Antibodies are excellent candidates for SPR detection since their surface binding causes a shift in refractive index, hence changing the surface plasmon conditions. This results in a shift of the surface plasmon dip, which can be detected and correlated to the concentration of the antibodies.
Figure 1. Schematic diagram of a SPR setup using immobilized SARS-CoV-2 nucleocapsid protein to detect anti-nucleocapsid antibodies.
Using Portable SPR for Immunity Screening
Figure 2. Photo of a lab personnel injecting a sample into Affinité’s P4SPR.
In a recent publication by Djaileb et al., scientists from research centres across Québec and Manitoba have demonstrated antibody detection for nucleocapsid and spike protein in serum and plasma using Affinité's portable SPR (P4SPR) (Figure 2). The results are also cross-validated to both in-house and commercial ELISA. Dried blood spots (DBS) are used as an alternate type of sample which can potentially simplify collection, storage, and transportation of blood samples. In this study, the sensor chip from P4SPR could be regenerated 9 times, and yielded results for 4 biological samples within 30 min, highlighting its cost-effectiveness and rapid speed of analysis as a point-of-care test (POCT). In addition, statistical study indicated that the magnitude of the response for all three platforms were proportional and quantitative and correlated 100% with ELISA over 20 clinical samples.
In another academic-industry project between the Université de Montréal, Université Laval, and Affinité Instruments, it was successfully demonstrated that the portable P4SPR from Affinité Instruments can detect antibodies associated with SARS-CoV-2, with recombinant nucleocapsid protein immobilized on the sensor chip to detect anti-SARS-CoV-2 antibodies in undiluted serum in the nanomolar range. Most importantly, the results were obtained within 15 min of sensor exposure to the sample. Both studies show the potential of using portable SPR as a POCT that can be deployed easily in public places such as workplace entrance, walk-in clinics, and pharmacies etc.
Future Direction
COVID-19 Immunity Task Force (CITF) is an initiative from the Government of Canada to support a study involving the tracking of immune responses of front-line food industry workers in Québec such as those who work in grocery stores, restaurants, and pubs. This major collaboration is being coordinated between researchers at Université de Montréal and Université Laval, and Affinité Instruments will provide the POCT SPR instruments. Blood samples will be collected initially as well as after 12 and 24 weeks to determine how many individuals become exposed to the virus in a 6-month study period. This study will shed light on immune response of these front-line workers. Factors that determine the severity of COVID-19 will also be investigated.
Portable SPR has been shown to be a promising platform for immunity screening using actual SARS-CoV-2 clinical samples. Affinité Instruments is at the forefront to develop POCT SPR platform for antibody testing. There is a tremendous benefit for public health surveillance through the deployment of portable SPR in the field outside of centralized labs and hospitals. Places like rural areas, meat packing plants, movie production sets, long-term care homes, and even households can benefit from having a simple way to collect samples (e.g. dried blood spots). The samples can be sent, not just for screening but also for confirmation, in local pharmacies or even on-site with a portable SPR. Obtaining crucial epidemiological information will aid in public health to make informed and proactive decisions, not just for the current pandemic, but also for other infectious diseases and influenza epidemics.