Introduction and Background of the Project

Introduction

Schistosomiasis control programs urgently require new tests, and a WHO target product profile (TPP) exists. The current-best technique is stool examination. Other groups are working towards a urinary antigen rapid test (Circulating Anodic Antigen; CAA) and isothermal DNA amplification techniques.

Serological testing using children as sentinel groups offers a simple and cost-effective alternative. Literature data suggests that the importance of a serological test as a measure of transmission will increase as the disease prevalence decreases. Hence, a serological test will benefit programs, and could be used either in conjunction with other tests (pre-screen or confirmation) or as a standalone tool.

Therefore, we propose a sensitive and specific lateral flow immunoassay (LFIA) which will meet the WHO TPP, poised for routine screening of school-aged children. An antibody test for schistosomiasis represents a shift from the current M&E strategies, but consultation with Dr. Secor, Chair of the WHO Schistosomiasis DTAG Subgroup, led to the conclusion that an antibody test for M&E is not only a viable approach, but also constitutes a very pragmatic and cost-effective strategy.

Our team’s experience in LFIAs (DDTD), antigen and antibody production (MBL), and biomarker identification (CDC) will allow us to produce a prototype LFIA in only one year. Given the above-mentioned paradigm shift, Operational Research (OR) will be of utmost importance. We therefore propose to deliver 5’000 tests to support initial OR. Several field sites are already set up where the resulting RDT could immediately be evaluated, with funding from independent sources.

We are thankful and excited to have been awarded funding from GHIT to develop a first-in-class serological RDT that will comply with the TPP released by WHO and be ready to support OR field studies at the end of this project.

Project objective

The overarching project goal is to deliver a Rapid Diagnostic Test (RDT) to detect exposure to Schistosoma mansoni, one of the main pathogens responsible for schistosomiasis. The RDT will meet the sensitivity and specificity requirements of the WHO TPP. At the end of this project, the test will be ready to be evaluated in the field. This test could be a standalone solution, or could be part of a total solution, in which people would be prescreened with the RDT at the point of contact, and positive results would later be confirmed in a laboratory using stool examination or molecular techniques.

Objective 1 (MBL): Generate critical reagents (Schistosoma antigens, with up to 2 positive control antibodies)

Objective 2a (DDTD): Develop serological RDT with >75% sensitivity and >96.5% specificity.

Objective 2b (CDC): Iterative performance assessment (sensitivity/specificity) of the RDT prototypes using schistosomiasis and other patient sample collections. To this end, the CDC will be able to leverage a preexisting research collaboration agreement with DDTD under which the CDC will not receive any funds from GHIT

Objective 3 (DDTD): Demonstrate equal performance with both plasma/serum and blood samples.

Objective 4 (DDTD): Produce 5’000 tests to be delivered to stakeholders in support of OR.

Project design

We propose a low-cost, easy-to-use serological RDT to detect exposure to Schistosoma mansoni, one of the pathogens responsible for schistosomiasis. The test will be able to detect human IgG1 antibody responses to one or several S. mansoni antigens (Sm25, Sm29, and/or Calumenin B).

Different assay formats will be generated and compared in terms of their performance. Great care will be given to demonstrating matrix equivalence between serum and whole blood, given that the test will be developed and validated with serum/plasma samples but eventually used with fingerstick blood, as required by the TPP. In addition to this, the TPP calls for a shelf life of minimally 18 months, and ideally 24 months, at 2–40°C and a relative humidity of 75%. Since stability studies are inherently long and intricate, we will commence them already at this very early stage and dedicate a significant amount of work to them. The antigen(s), or antigen combination, providing the best overall test performance in terms of sensitivity and specificity, as well as matrix equivalence and thermal stability, will be selected for further development.

One key factor ensuring a reproducible product quality is to have access to a constant, reliable source of the biological components of the test, notably the S. mansoni antigens. These antigens will be produced in recombinant form by MBL, in research grade for this proposal, and in ISO13485 grade for future commercialization. Secondly, for the assay optimization and fine-tuning, positive controls are needed. Recombinant, humanized IgG1-antibodies against the S. mansoni antigen(s) having proven to give the best assay performance will be produced by MBL, again in research grade quality at this stage of the project.

How can your partnership (project) address global health challenges?

Schistosomiasis is one of WHO’s top-priority programs, surpassed in worldwide case numbers only by malaria. Disease control today relies on mass drug administration (MDA) which, in turn, critically depends on field-deployable diagnostic tools to guide decisions on MDA initiation and cessation. As a result, in 2021, WHO called for new diagnostic tests to support programs aimed at controlling schistosomiasis and defined the desired performance characteristics in a TPP. Releasing a TPP is the strongest signal WHO can give regarding the urgency to develop such new diagnostic tests.

Our new RDT will fill a clear unmet need by enabling schistosomiasis monitoring and evaluation (M&E):

- None of the existing tests meets the TPP criteria, and here is where we see our novel RDT being able to make a significant impact on a major global health problem.

- Key opinion leaders agree that a serological RDT (i.e., an RDT designed to detect antibody responses in the host) represents not only a viable concept but may also be the most pragmatic and cost-effective approach today.

- In areas where disease prevalence approaches 0%, our RDT will be able to support M&E activities by selecting children as sentinel groups, and it will also have value in supporting decisions to stop MDA.

- All downstream activities are already financed, insofar as the CDC has set up study sites with secured funding in Kenya, St. Lucia, and the Dominican Republic, where field testing of the RDT resulting from the GHIT project could immediately start after completion of the GHIT project.

In summary, we respectfully submit that our test will address a major global health problem, insofar as it will help improve the lives of an estimated 240 infected people and an estimated further 780 million people living at risk of contracting the disease.

What sort of innovation are you bringing in your project?

Lateral Flow Immunoassays (LFIAs) per se are not novel, but they represent a tried-and-true technology in the field of rapid diagnostic test development, particularly well adapted to field work in low-resource settings, which is why they are WHO’s preferred assay format. Our innovative contributions in the field of LFIAs have allowed us to deliver ultra-sensitive and specific tests for other indications (onchocerciasis, lymphatic filariasis, Buruli ulcer). The relevant innovative contributions for this project are:

- Use of novel S. mansoni biomarkers recently discovered at CDC, some of which are still unpublished.

- Use of novel plasmonic nanoparticles for optical detection, which improve test sensitivity by a factor of 2-10 (depending on the assay) compared to classical 40nm colloidal gold particles.

- Proprietary test strip architecture (confidential) allowing to build the assay strip in such a way that, upon addition of chase buffer, the sample reaches the test line first, and only then the nanoparticles are released, which leads to an increase in sensitivity.

- Proprietary cassette design (confidential).

Role and Responsibility of Each Partner

-Drugs & Diagnostics for Tropical Diseases (DDTD) is the Designated Development Partner and, as such, will provide management of the overall project and the Collaboration Partners. DDTD will also coordinate and ensure timely execution of the project and provide governance in terms of progress and finance reporting to the GHIT Fund. Furthermore, DDTD will design and develop all new prototype rapid diagnostic tests to detect exposure to Schistosoma mansoni. All experimental procedures, as well as chemical, biochemical, biophysical, and clinical data generated during the project will be captured by DDTD in a separate database under ISO-13845 quality standards.

-Medical & Biological Laboratories Co., Ltd. (MBL) will be responsible for producing three Schistosoma mansoni antigens and up to two positive control antibodies raised against selected Schistosoma mansoni antigens, in R&D grade quality, and for maintaining any records necessary to reproduce the expression of said antigens and antibodies, in view of ISO-13485 manufacturing (to be performed at a later stage, under a different grant).

-The Centers for Disease Control and Prevention (CDC), more specifically, the Elimination & Control Laboratory led by Dr. W. Evan Secor, who has been involved in the project since the beginning, will be responsible for providing an initial set of antigens while MBL develops procedures to generate them, and will be responsible for assessing the laboratory performance, more specifically the sensitivity and specificity, of the rapid diagnostic tests produced by DDTD using appropriate sample collections stored at CDC. Thereby, the CDC and DDTD will be able to leverage a separate Research Collaboration Agreement put in place in early 2022 under which the CDC will not receive any funds from the current GHIT Fund grant.