Ultrasensitive, High-Specificity Rapid Test to Support the End-Game of the Global Program to Eliminate Lymphatic Filariasis

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PROJECT SUMMARY / ABSTRACT Here we propose a rapid, field-deployable, cost-effective, highly sensitive and specific lateral flow assay (LFA) that meets all the requirements recently defined by the World Health Organization (WHO) in a target product profile (TPP) for surveillance activities of Lymphatic Filariasis (LF). LF is a disfiguring and debilitating neglected tropical disease that affects 40 million people in 72 countries and is due to the parasitic filarial worm Wuchereria bancrofti. To combat this disease, WHO has deployed mass drug administration (MDA) programs globally on an unprecedented scale. Today, WHO recommends repeating transmission assessment surveys (TAS) twice in 2- to 3-year intervals after MDA cessation, while acknowledging that more research is urgently required to improve diagnostic tests for TAS and post-treatment surveillance (PTS) until 2030, and beyond. In March 2021, WHO has published a TPP for the test it seeks, where the key requirements are that the test should be able to detect early infection, have >85% clinical sensitivity and > 98.8% specificity. The only proven field-deployable tests for LF are the immunochromatography testcard (ICT) and its subsequent, more stable version, the Filariasis Test Strip (FTS). These tests have been used for 2 decades to detect active infections. However, they are not suited for surveillance activities, as they detect the disease only 18 months after a person has been infected and lack sensitivity in post-MDA settings due to low parasite burden. According to the WHO TPP, LF surveillance requires an RDT indicative of early exposure to W. bancrofti infective larvae (L3 stage). Currently, the best biomarker to this effect are IgG4 antibodies specific for the Wb123 antigen expressed by infective larvae. A commercial IgG4/Wb123 ELISA exists (inBios) and is routinely used at the Centers for Disease Control and Prevention (CDC) but is not field-deployable. A portable rapid test was introduced by Standard Diagnostics, now part of Abbott, but fell short of the expected sensitivity and was abandoned (SD BIOLINE Wb123 IgG). We have recently succeeded in developing an LFA prototype for the detection of Wb123-specific IgG4 which is characterized by an analytical sensitivity 16-32 greater than that of the Abbott RDT and equal to the commercial Wb123 ELISA. We view this as a major achievement. This test is poised to meet the > 85% clinical sensitivity criterion. However, it is not clear if it will also meet the minimal (>98.8%) or ideal (>99.8%) specificity criterion. We now propose a biplex test allowing to simultaneously detect antibodies against two antigens, of which one will be Wb123, and the other one chosen from a series of five novel antigens, termed WbAg1-5 or WbAgX. The purpose of the dual test is to achieve a superior specificity by imposing the condition that both test lines must be visible to count the test as positive, and no line must be visible for the test to be counted as negative. We have been awarded a grant from the Task Force for Global Health (TFGH) and USAID to develop a prototype version of such a biplex assay. We are now requesting additional funding from the NIH to (1) optimize one or more biplex assays (2) establish a biorepository of 2000 clinical samples to demonstrate that the TPP meets the required sensitivity and specificity with > 95% statistical confidence and (3) progress one biplex to manufacturing and commercialization. By the end of this Phase I/II Fast-Track grant, a total of 100,000 assays will be available for testing by the TFGH, the CDC, and other stakeholders to generate the field data necessary to secure its international endorsement. The developed manufacturing process will be able to meet the estimated demand of 0.5-1 million assays/year at a cost point acceptable to the sponsoring agencies. It is noteworthy that USAID, which is the largest customer for LF tests worldwide, covering over 40% of the global demand, has already sponsored our initial research, showing their interest, and providing a clear path to commercialization. In short, our RDT will thus be poised for the surveillance of lymphatic filariasis, a disease that figures prominently on the WHO’s 2030 roadmap for Neglected Tropical Diseases, and which the international community, supported by major pharmaceutical companies and NGOs, has vowed to eliminate in the 2012 London Declaration.