Introduction and Background of the Project

Introduction

Schistosomiasis elimination programs urgently require new tests. Recognizing this, WHO issued two TPPs in 2021. Schistosomiasis is a WHO top-priority, surpassed in worldwide case numbers only by malaria. More than 200 million people are estimated to be affected, with 90% of cases occurring in Africa, caused by Schistosoma mansoni (intestinal disease) and Schistosoma haematobium (urogenital disease). None of the current diagnostics meets all TPP criteria. The reference test for S. haematobium is urine filtration and microscopy, which requires skilled personnel and underestimates infection prevalence due to low sensitivity, especially in low-infection-intensity areas. The CCA antigen test does not work for S. haematobium, and the CAA test is still in development. A promising molecular test has been developed which is, however, expensive and remains restricted to laboratory use. Key opinion leaders agree that serological testing of preschool-age children offers a viable and cost-effective solution to monitor progress of schistosomiasis elimination programs, particularly in low-prevalence settings. In previous work, we have developed fully TPP-compliant serological RDT prototypes for S. mansoni, the pathogen causing around 50% of global schistosomiasis cases. Herein, we propose to address the remaining 50% of cases by developing equally TPP-compliant RDT prototypes for S. haematobium based on promising biomarkers independently developed at the Centers for Disease Control and Prevention CDC and NEKKEN, and evaluating their diagnostic performance.

Project objective

The overarching objective of this project is to deliver a fully TPP-compliant, easy-to-use, low-cost point-of-care test able to detect antibodies raised by the human host against selected S. haematobium antigens as an indicator for current or prior infection. The RDT delivered at the end of G2024-203 will have the required sensitivity and specificity to support decisions for Schistosomiasis Transmission Interruption and subsequent Surveillance in hypo-endemic areas post-MDA where other diagnostic methods struggle to accurately determine disease prevalence. Targeting young children as sentinel groups, the RDT will mainly be used with fingerstick blood but will be designed to also work with dried blood spots, which will facilitate integration with other NTD programs conducting seroprevalence studies. Our test will come with a complete set of laboratory validation data generated jointly by the Nagasaki University Institute of Tropical Medicine (NEKKEN) and the Kenya Medical Research Institute (KEMRI).

Project design

We will pursue the following 4 specific objectives:

- Objective 1: Define the most appropriate use case(s) for a serological S. haematobium test and present the proposed rationale and justification to the Schisto DTAG for endorsement.

- Objective 2: We will express the 5-10 most promising S. haematobium biomarkers from the literature and from previous work at CDC and NEKKEN, and evaluate their performance in an S. haematobium ELISA. The goal is to select up to 4 antigen candidates based on sensitivity, specificity, and biophysical properties (such as solubility, stability) for the subsequent Objective.

- Objective 3: We will generate RDT prototypes for each of the biomarker candidates down-selected in the preceding Objective, and evaluate the performance of the resulting singleplex LFAs in comparison with ELISA based on LOD, sensitivity, and specificity (non-specific binding). The 1-2 best-performing antigens and RDT prototypes will be fully optimized until all TPP criteria are met, including thermal stability, compatibility with blood samples and DBS, time-to-result, as well as result stability and reproducibility.

- Objective 4: NEKKEN and KEMRI will independently evaluate the diagnostic performance of the prototype RDT(s) delivered in the preceding Objective using extended patient sample panels, and compare the results with those from laboratory-based serological tests (ELISA/MBA) as well as with other, non-serological diagnostic methods (microscopy, PCR, CAA-test) wherever available. At the end of G2024-203, all team members and key stakeholders (donors, WHO Schisto-DTAG) will convene to review all data collected on the S. haematobium candidate RDT and decide on whether the test characteristics warrant initiation of field evaluation and manufacturing process development in a subsequent project.

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

We propose to develop a first-in-class serological point-of-care test for S. haematobium by leveraging prior biomarker work at CDC and NEKKEN for the diagnosis of urogenital schistosomiasis. Based on a growing body of evidence gathered in schistosomiasis and other NTD programs, we believe that our serological RDT will be complementary to the CAA antigen test currently in development by allowing to better detect the disease in low-prevalence settings where infections will be of low-intensity, as will be the case when approaching interruption of transmission. Part of the purpose of this grant is to explore when one test will be more useful than the other, and when the combination of both tests will provide the most useful information. Our test may also have applications in detecting Female Genital Schistosomiasis (FGS). Having already developed a TPP-compliant serological test for S. mansoni in a previous project, we are confident that we will achieve the same for S. haematobium in this project. We respectfully submit that our test will address a major global health problem, insofar as it will help improve the lives of hundreds of millions of people living mostly in neglected, underprivileged regions of the world with patent schistosomiasis or the threat of newly contracting the disease.

What sort of innovation are you bringing in your project?

- Innovation 1: In prior work, CDC and NEKKEN have independently identified completely novel biomarker candidates showing promise for S. haematobium in various laboratory studies in the US, Japan, and Kenya. Evaluating these biomarker candidates for their amenability to a lateral flow assay format in this project adds another layer of innovation.

- Innovation 2: DDTD has introduced a novel test architecture combined with a proprietary sample pad material to further increase the sensitivity of our tests and ensure flawless behavior with blood samples (no red streaking).

- Innovation 3: Following the successful precedent of our GHIT-funded S. mansoni project, MBL will again develop novel monoclonal antibodies against the two best S. haematobium antigens identified in Objective 2, to be used as positive controls in future field work involving our point-of-care test.

Role and Responsibility of Each Partner

- Drugs & Diagnostics for Tropical Diseases (DDTD): as the Designated Development Partner, will provide management of the project and the Collaboration Partners to ensure that the deliverables and Milestones set forth in Section 3 above are met. Furthermore, DDTD will contribute to selecting the best S. haematobium biomarkers, and will then develop and optimize the corresponding prototype RDTs. All experimental procedures, as well as diagnostic and biophysical data generated during the project will be recorded by DDTD in its ISO13845-certified quality management system.

- Medical & Biological Laboratories Co., Ltd. (MBL): will be responsible for producing up to 4 S. haematobium antigens and up to 2 monoclonal positive control antibodies in R&D-grade quality, and for maintaining any records necessary to reproduce the expression and purification of these key biological resources in view of future ISO13485-compliant test manufacturing.

- Nagasaki University Institute of Tropical Medicine (NEKKEN): will be involved in defining the optimal use case(s) for a serological S. haematobium point-of-care test, for laboratory evaluation and down-selection of biomarker candidates, and for laboratory evaluation of the diagnostic performance of the optimized S. haematobium test(s) using its well-characterized collections of patient sera and/or dried blood spots (DBS).

- Kenya Medical Research Institute (KEMRI): will also be involved in defining the optimal use case(s) for a serological S. haematobium point-of-care test and for independent laboratory evaluation of the diagnostic performance of the optimized S. haematobium test(s) using well-characterized collections of patient sera and/or dried blood spots (DBS).