Whole-blood agglutination assay for on-site detection of human immunodeficiency virus infection

Diagnostic Tools for Rapid Screening and Detection of SARS-CoV-2 Infection

The novel coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has severely impacted human health and the health management system globally. The ongoing pandemic has required the development of more effective diagnostic strategies for restricting deadly disease. For appropriate disease management, accurate and rapid screening and isolation of the affected population is an efficient means of containment and the decimation of the disease. Therefore, considerable efforts are being directed toward the development of rapid and robust diagnostic techniques for respiratory infections, including SARS-CoV-2. In this article, we have summarized the origin, transmission, and various diagnostic techniques utilized for the detection of the SARS-CoV-2 virus. These higher-end techniques can also detect the virus copy number in asymptomatic samples. Furthermore, emerging rapid, cost-effective, and point-of-care diagnostic devices capable of large-scale population screening for COVID-19 are discussed. Finally, some breakthrough developments based on spectroscopic diagnosis that could revolutionize the field of rapid diagnosis are discussed.

A rapid and affordable point of care test for antibodies against SARS-CoV-2 based on hemagglutination and artificial intelligence interpretation

Diagnostic tests that detect antibodies (AB) against SARS-CoV-2 for evaluation of seroprevalence and guidance of health care measures are important tools for managing the COVID-19 pandemic. Current tests have certain limitations with regard to turnaround time, costs and availability, particularly in point-of-care (POC) settings. We established a hemagglutination-based AB test that is based on bi-specific proteins which contain a dromedary-derived antibody (nanobody) binding red blood cells (RBD) and a SARS-CoV-2-derived antigen, such as the receptor-binding domain of the Spike protein (Spike-RBD). While the nanobody mediates swift binding to RBC, the antigen moiety directs instantaneous, visually apparent hemagglutination in the presence of SARS-CoV-2-specific AB generated in COVID-19 patients or vaccinated individuals. Method comparison studies with assays cleared by emergency use authorization demonstrate high specificity and sensitivity. To further increase objectivity of test interpretation, we developed an image analysis tool based on digital image acquisition (via a cell phone) and a machine learning algorithm based on defined sample-training and -validation datasets. Preliminary data, including a small clinical study, provides proof of principle for test performance in a POC setting. Together, the data support the interpretation that this AB test format, which we refer to as 'NanoSpot.ai', is suitable for POC testing, can be manufactured at very low costs and, based on its generic mode of action, can likely be adapted to a variety of other pathogens.

A Rapid and Affordable Point-of-care Test for Detection of SARS-Cov-2-Specific Antibodies Based on Hemagglutination and Artificial Intelligence-Based Image Interpretation

Diagnostic tests that detect antibodies (AB) against SARS-CoV-2 for evaluation of seroprevalence and guidance of health care measures are important tools for managing the COVID-19 pandemic. Current tests have certain limitations with regard to turnaround time, costs and availability, particularly in point-of-care (POC) settings. We established a hemagglutination-based AB test (HAT) that is based on bi-specific proteins which contain a dromedary-derived antibody (nanobody) binding red blood cells (RBD) and a SARS-CoV-2-derived antigen, such as the receptor-binding domain of the Spike protein (Spike-RBD). While the nanobody mediates swift binding to RBC, the antigen moiety directs instantaneous, visually apparent hemagglutination in the presence of SARS-CoV-2-specific AB generated in COVID-19 patients or vaccinated individuals. Method comparison studies with assays cleared by emergency use authorization (EUA) demonstrate high specificity and sensitivity. To further increase objectivity of test interpretation, we developed an image analysis tool based on digital image acquisition (via a cell phone) and a machine learning algorithm based on defined sample-training and –validation datasets.

Preliminary data, including a small clinical study, provides proof of principle for test performance in a POC setting. Together, the data support the interpretation that this AB test format, which we refer to as ‘NanoSpot.ai’, is suitable for POC testing, can be manufactured at very low costs and, based on its generic mode of action, can likely be adapted to a variety of other pathogens.

Epitope-specific antibody responses differentiate COVID-19 outcomes and variants of concern

BACKGROUNDThe role of humoral immunity in COVID-19 is not fully understood, owing, in large part, to the complexity of antibodies produced in response to the SARS-CoV-2 infection. There is a pressing need for serology tests to assess patient-specific antibody response and predict clinical outcome.METHODSUsing SARS-CoV-2 proteome and peptide microarrays, we screened 146 COVID-19 patients' plasma samples to identify antigens and epitopes. This enabled us to develop a master epitope array and an epitope-specific agglutination assay to gauge antibody responses systematically and with high resolution.RESULTSWe identified linear epitopes from the spike (S) and nucleocapsid (N) proteins and showed that the epitopes enabled higher resolution antibody profiling than the S or N protein antigen. Specifically, we found that antibody responses to the S-811-825, S-881-895, and N-156-170 epitopes negatively or positively correlated with clinical severity or patient survival. Moreover, we found that the P681H and S235F mutations associated with the coronavirus variant of concern B.1.1.7 altered the specificity of the corresponding epitopes.CONCLUSIONEpitope-resolved antibody testing not only affords a high-resolution alternative to conventional immunoassays to delineate the complex humoral immunity to SARS-CoV-2 and differentiate between neutralizing and non-neutralizing antibodies, but it also may potentially be used to predict clinical outcome. The epitope peptides can be readily modified to detect antibodies against variants of concern in both the peptide array and latex agglutination formats.FUNDINGOntario Research Fund (ORF) COVID-19 Rapid Research Fund, Toronto COVID-19 Action Fund, Western University, Lawson Health Research Institute, London Health Sciences Foundation, and Academic Medical Organization of Southwestern Ontario (AMOSO) Innovation Fund.

Rapid and accurate agglutination-based testing for SARS-CoV-2 antibodies

We have developed a rapid, accurate, and cost-effective serologic test for SARS-CoV-2 virus, which caused the COVID-19 pandemic, on the basis of antibody-dependent agglutination of antigen-coated latex particles. When validated using plasma samples that are positive or negative for SARS-CoV-2, the agglutination assay detected antibodies against the receptor-binding domain of the spike (S-RBD) or the nucleocapsid protein of SARS-CoV-2 with 100% specificity and ∼98% sensitivity. Furthermore, we found that the strength of the S-RBD antibody response measured by the agglutination assay correlated with the efficiency of the plasma in blocking RBD binding to the angiotensin-converting enzyme 2 in a surrogate neutralization assay, suggesting that the agglutination assay might be used to identify individuals with virus-neutralizing antibodies. Intriguingly, we found that >92% of patients had detectable antibodies on the day of a positive viral RNA test, suggesting that the agglutination antibody test might complement RNA testing for the diagnosis of SARS-CoV-2 infection.

A rapid, point-of-care red blood cell agglutination assay detecting antibodies against SARS-CoV-2

The COVID-19 pandemic has caused significant morbidity and mortality. There is an urgent need for serological tests to detect antibodies against SARS-CoV-2, which could be used to assess past infection, evaluate responses to vaccines in development, and determine individuals who may be protected from future infection. Current serological tests developed for SARS-CoV-2 rely on traditional technologies such as enzyme-linked immunosorbent assays (ELISA) and lateral flow assays, which have not scaled to meet the demand of hundreds of millions of antibody tests so far. Herein, we present an alternative method of antibody testing that depends on one protein reagent being added to patient serum/plasma or whole blood with direct, visual readout. Two novel fusion proteins, RBD-2E8 and B6-CH1-RBD, were designed to bind red blood cells (RBCs) via a single-chain variable fragment (scFv), thereby displaying the receptor-binding domain (RBD) of SARS-CoV-2 spike protein on the surface of RBCs. Mixing mammalian-derived RBD-2E8 and B6-CH1-RBD with convalescent COVID-19 patient serum and RBCs led to visible hemagglutination, indicating the presence of antibodies against SARS-CoV-2 RBD. B6-CH1-RBD made in bacteria was not as effective in inducing agglutination, indicating better recognition of RBD epitopes from mammalian cells. Given that our hemagglutination test uses methods routinely used in hospital clinical labs across the world for blood typing, we anticipate the test can be rapidly deployed at minimal cost. We anticipate our hemagglutination assay may find extensive use in low-resource settings for detecting SARS-CoV-2 antibodies.

Fundamentals of affinity cell separations

Cell separations using affinity methods continue to be an enabling science for a wide variety of applications. In this review, we discuss the fundamental aspects of affinity separation, including the competing forces for cell capture and elution, cell-surface interactions, and models for cell adhesion. Factors affecting separation performance such as bond affinity, contact area, and temperature are presented. We also discuss and demonstrate the effects of nonspecific binding on separation performance. Metrics for evaluating cell separations are presented, along with methods of comparing separation techniques for cell isolation using affinity capture.

Expression of recombinant antibody (single chain antibody fragment) in transgenic plant Nicotiana tabacum cv. Xanthi

Plants offer an alternative inexpensive and convenient technology for large scale production of recombinant proteins especially recombinant antibodies (plantibodies). In this paper, we describe the expression of a model single chain antibody fragment (B6scFv) in transgenic tobacco. Four different gene constructs of B6scFv with different target signals for expression in different compartments of a tobacco plant cell with and without endoplasmic reticulum (ER) retention signal were used. Agrobacterium mediated plant transformation of B6scFv gene was performed with tobacco leaf explants and the gene in regenerated plants was detected using histochemical GUS assay and PCR. The expression of B6scFv gene was detected by western blotting and the recombinant protein was purified from putative transgenic tobacco plants using metal affinity chromatography. The expression level of recombinant protein was determined by indirect enzyme-linked immunosorbent assay. The highest accumulation of protein was found up to 3.28 % of the total soluble protein (TSP) in plants expressing B6scFv 1003 targeted to the ER, and subsequently expression of 2.9 % of TSP in plants expressing B6scFv 1004 (with target to apoplast with ER retention signal). In contrast, lower expression of 0.78 and 0.58 % of TSP was found in plants expressing antibody fragment in cytosol and apoplast, without ER retention signal. The described method/system could be used in the future for diverse applications including expression of other recombinant molecules in plants for immunomodulation, obtaining pathogen resistance against plant pathogens, altering metabolic pathways and also for the expression of different antibodies of therapeutic and diagnostic uses.

Approaches for the development of rapid serological assays for surveillance and diagnosis of infections caused by zoonotic flaviviruses of the Japanese encephalitis virus serocomplex

Flaviviruses are responsible for a number of important mosquito-borne diseases of man and animals globally. The short vireamic period in infected hosts means that serological assays are often the diagnostic method of choice. This paper will focus on the traditional methods to diagnose flaviviral infections as well as describing the modern rapid platforms and approaches for diagnostic antigen preparation.

Directed evolution of an anti-human red blood cell antibody

We have earlier described a haemagglutination-based assay for on-site detection of antibodies to HIV using whole blood. The reagent in this assay comprises of monovalent Fab fragment of an anti-human RBC antibody fused to immunodominant antigens of HIV-1 and HIV-2. In the present work, we describe a rational and systematic method for directed evolution of scFv and Fab antihuman RBC antibody fragments. Based on homology modeling and germline sequence alignments of antibodies, target residues in the anti-RBC MAb B6 sequence were identified for mutagenesis.A combinatorial library of 107 clones was constructed and subjected to selection on whole RBC under competitive binding conditions to identify several phage-displayed B6 scFv clones with improved binding as determined in an agglutination assay.Selected VL and VH sequences were shuffled to generate a second generation phage-displayed Fab library which on panning yielded Fab clones with several fold better binding than wild type. The mutants with better binding also displayed more Fab molecules per phage particle indicating improved in vivo folding which was also confirmed by their increased periplasmic secretion compared to the wild type. The mutant Fab molecules also showed superior characteristics in large scale production by in vitro folding of LC and Fd. The biophysical measurements involving thermal and chemical denaturation and renaturation kinetics clearly showed that two of the mutant Fab molecules possessed significantly improved characteristics as compared to the wild type B6 Fab.Structural modelling revealed that B6 Fab mutants had increased hydrogen bonding resulting in increased stability. Our approach provides a novel and useful strategy to obtain recombinant antibodies with improved characteristics.

Inexpensive designer antigen for anti-HIV antibody detection with high sensitivity and specificity

A novel recombinant multiepitope protein (MEP) has been designed that consists of four linear, immunodominant, and phylogenetically conserved epitopes, taken from human immunodeficiency virus (HIV)-encoded antigens that are used in many third-generation immunoassay kits. This HIV-MEP has been evaluated for its diagnostic potential in the detection of anti-HIV antibodies in human sera. A synthetic MEP gene encoding these epitopes, joined by flexible peptide linkers in a single open reading frame, was designed and overexpressed in Escherichia coli. The recombinant HIV-MEP was purified using a single affinity step, yielding >20 mg pure protein/liter culture, and used as the coating antigen in an in-house immunoassay. Bound anti-HIV antibodies were detected by highly sensitive time-resolved fluorometry, using europium(III) chelate-labeled anti-human antibody. The sensitivity and specificity of the HIV-MEP were evaluated using Boston Biomedica worldwide HIV performance, HIV seroconversion, and viral coinfection panels and were found to be comparable with those of commercially available anti-HIV enzyme immunoassay (EIA) kits. The careful choice of epitopes, high epitope density, and an E. coli-based expression system, coupled with a simple purification protocol and the use of europium(III) chelate-labeled tracer, provide the capability for the development of an inexpensive diagnostic test with high degrees of sensitivity and specificity.

Bifunctional recombinant fusion proteins for rapid detection of antibodies to both HIV-1 and HIV-2 in whole blood

BACKGROUND

Availability of accurate diagnostic tests has been helpful in curtailing the spread of HIV infection. Among these, simple, point of care, inexpensive tests which require only a drop of blood from finger-prick and give reliable results within minutes are a must for expansion of testing services and for reaching mobile and marginalized populations. Such tests will not only be a boon for the infrastructure-starved developing and underdeveloped countries but will also be extremely useful in developed countries where post-testing compliance is a major problem. Our laboratory has been involved in developing reagents for heamagglutination-based rapid detection of antibodies to HIV in whole blood using recombinant molecules specific for either HIV-1 or HIV-2. Since it is not required of a screening test to differentially detect HIV and HIV-2, it would useful to create a single molecule capable of simultaneous detection of both HIV-1 and HIV-2 in a drop of blood.

RESULTS

The present paper describes designing, high-level expression and large-scale purification of new molecules comprising recombinant anti-RBC Fab fused to immunodominant regions of envelope sequences from both gp41 of HIV-1 and gp36 of HIV-2. These immunodominant regions of HIV envelope contain cysteine residues, which make disulfide bond and can interfere with the assembly of light chain and heavy chain fragment to make Fab molecule in vitro. To circumvent this problem, a series of fusion proteins having different combinations of native and mutant envelope sequences were constructed, purified and evaluated for their efficacy in detecting antibodies to HIV-1 and HIV-2. A chimeric molecule comprising native envelope sequence of gp41 of HIV-1 and modified envelope sequence of gp36 of HIV-2 gave good production yield and also detected both HIV-1 and HIV-2 samples with high sensitivity and specificity.

CONCLUSION

The new bifunctional antibody fusion protein identified in this study detects both HIV-1 and HIV-2 infected samples efficiently and can be used in place of molecules that detect only HIV-1 or HIV-2. This will make reagent production more economical as only one molecule has to be produced in place of two molecules. Also, it will simplify the testing procedure allowing detection of both HIV-1 and HIV-2 infections in a single drop of blood.

Point-of-care immunotesting: Approaching the analytical performance of central laboratory methods

The use of point-of-care (POC) immunoassays has increased significantly and the menu of analytes continues to expand. Most of the rapid immunoassays are currently based on simple manual assay devices such as the immunochromatographic, agglutination, and immunofiltration assays. Although automated readers have recently been introduced at an increasing pace, the major benefit of these genuinely hand-portable assay devices is that they do not usually necessitate instrumentation but can be performed anywhere. Significant advances in assay and detection technologies have, however, recently facilitated the introduction of truly quantitative, sophisticated immunoassay methods to POC settings as well, with the analytical performance characteristics approaching those of conventional laboratory assays. Furthermore, innovative assay technologies such as those based on immunosensors have been introduced to POC testing (POCT) without ever being employed in clinical laboratories. However, further simplification of the assay procedures and analyzers is still feasible, and strong efforts are directed towards the development of miniaturized and simple, yet sensitive and quantitative, novel assay technologies to keep up with the increasing expectations set on future POC immunotesting.