NEW YORK – With an aim of making tuberculosis diagnosis more accurate and less labor-intensive, QuantuMDx is developing a sample preparation system that uses an electrical charge to enrich samples for easier identification of Mycobacteria tuberculosis.
Researchers from St. George's University of London, along with QuantuMDx, published their results on the system, called the Capture-XT, last week in the Journal of Molecular Diagnostics. Using 100 bio-banked sputum samples provided by FIND, the Capture-XT technology and qPCR testing together showed 87 percent sensitivity and 100 percent specificity compared to culture diagnosis, with higher false negatives in samples with lower bacterial burdens.
In the study, the authors flowed samples through parallel microfluidic channels of the prototype, immobilized M tuberculosis with electrode arrays, released them for concentration onto an electrode bed for visual confirmation by fluorescence microscopy, and released them again for molecular analysis by qPCR assay.
According to Philip Butcher, a microbiologist who has led research into the technology at St. George's University of London, the dielectrophoresis-based Capture-XT sample preparation system could help clinicians identify the "missing millions" of people who live with undiagnosed tuberculosis. Within 20 minutes, he said, the system can target and trap only the TB bacteria from among the hundreds of types of organisms in a solubilized sputum sample, aiding visual identification or molecular detection of infections even in patients who have low bacterial burden.
"Millions of people are not being properly diagnosed and treated, and that's a scandal," he said.
Butcher said each bacteria species or human cell type has specific dielectric properties. The Capture-XT enrichment method involves flowing samples through microfluidic channels containing probes that generate electrical charges tuned to capture specific targets based on those dielectric properties. The frequency used to target tuberculosis can accumulate all TB bacteria in a sample and release them together, enriching the sample for detection through a PCR test or microscopy.
QuantuMDX CEO Jonathan O'Halloran said the firm has also shown in testing that the technology can be used with blood samples to concentrate circulating tumor cells and sepsis-causing bacterial infections. The firm is developing its TB and circulating tumor cell applications first, followed by the enrichment of samples to detect bloodstream infections.
"It's really a sample prep system that would quickly and efficiently capture and then concentrate and release rare cells in large samples," he said.
Tuberculosis is the 13th leading cause of death worldwide and the second-highest killer among infectious diseases after COVID-19. According to the World Health Organization, more than 80 percent of deaths from TB occur in low- and middle-income countries. The organization said in its Global Tuberculosis Report 2022 in October that about 10.6 million people were sickened by TB in 2021 and 1.6 million died from the disease. Further, the COVID-19 pandemic continues to reduce access to TB diagnosis and treatment, illustrated through the declining number of people newly diagnosed with TB from a peak of 7.1 million in 2019 to 5.8 million in 2020 and 6.4 million in 2021.
In 2021, the Lancet Commission on Diagnostics estimated that 35 percent of people with tuberculosis are undiagnosed worldwide, largely due to a lack of access to diagnostics among almost half the global population.
According to Butcher, the standard sputum-based Cepheid GeneXpert PCR test performs very well with most samples yet even it can miss the low numbers of bacteria in some early-stage infections and incipient infections, the latter of which can become resurgent as a person becomes immunocompromised perhaps due to age, HIV infection, or cancer treatment.
"The problem with TB is finding people that have got very low levels of the organism and getting a correct diagnosis for those people," he said. "So, anything that would enrich the sample going into molecular detection would increase the ability to detect these low levels of bacteria in the sample."
Along with Cepheid, other tests for TB include MolBio Diagnostics' Truenat MTB, MTB Plus, and MTB-RIF Dx tests, Eiken Chemical's loop-mediated isothermal amplification TB-LAMP, Becton Dickinson's BD MAX MDR-TB assay, Bruker/Hain Lifescience's Hain FluoroType MTBDR assay, Roche's Cobas MTB and MTB-RIF/INH assays, and Abbott Laboratories' Abbott RealTime MTB and MTB RIF/INH.
Meanwhile, Qiagen and Revvity have interferon gamma-release assays for testing for TB, while Unitaid, FIND, and the Liverpool School of Tropical Medicine said in September they were partnering on the development of same-day assays for TB and improved access to testing for the underdiagnosed.
O'Halloran said he hopes QuantuMDx will increase the sensitivity of existing testing methods and, because the technology is low-cost, bring testing to more people and increase the rate of detection for TB. The disposable microfluidic cells used in each test cost less than $10 each in low-volume batches of 100, and he predicts further development and higher volume manufacturing will bring the cost of enrichment below $1 per sample.
"I've always had this bee in my bonnet about wanting to get a really low-cost diagnostic test with the sensitivity that's up there with PCR methodology, and I think that is possible," he said.
O'Halloran added the company continues its work to ensure the Capture-XT can differentiate between TB and non-tuberculosis mycobacteria and retain only TB in an enriched sample.
"We can get rid of some of them but not all of them," he said. "So, another thing we're able to use is TB-specific dye. We can bring that in and then only the TB will be fluorescing."
He also hopes to train the image analysis software well enough to distinguish TB from other mycobacteria without use of dyes.
QuantuMDx is working to incorporate the technology into a laboratory-use desktop instrument that could provide multiplex enrichment using the arrays of electrodes to select for multiple targets as well as an option to elute the concentrated cells for downstream analysis, O'Halloran said. The firm plans to make two versions of that instrument: One would include optics and automated image analysis software that could be used to confirm the identities of targets caught by the electrical fields and provide cell counts, and a second lower-cost version would exclude the optics.
In either version, the operator could use the enrichment step with downstream testing such as multiplex PCR, next-generation sequencing, or smear microscopy.
"The whole idea of it came from my frustration with TB diagnostics," O'Halloran said. "Sputum is a horrible sample type, and there's very few cells within it, and it involved a significant amount of analysis to get anything close to being a sensitive enough test, which means you miss millions of people with TB."
QuantuMDx plans to distribute its tuberculosis tests and enrichment instrument in India, China, and other regions of Asia and Africa with high TB burden. O'Halloran noted that the company has forged partnerships in China to help develop and manufacture the technology.
The US is the company's target market for its circulating tumor tests, he said.
O'Halloran said the company will pursue WHO prequalification for its TB application but has yet to decide which regulatory pathways to pursue for the circulating tumor cell or bloodstream infection applications.
The firm is currently trying to secure funding for further development of the Capture-XT technology and work with a manufacturer in China ahead of a commercial launch of its TB tests within the next two to three years. O'Halloran said the company is simultaneously working on a revamped, mass-multiplex version of its CE-marked, point-of-care Q-POC molecular testing platform and an expanded testing menu beyond the SARS-CoV-2 test and multiplex respiratory panel currently available on the instrument.
The firm plans to begin manufacturing the Q-POC 2.0 within nine to 12 months. The test development plans include a multiplex fever panel with simultaneous detection of mutations associated with antimicrobial resistance, O'Halloran said. Although he hinted that the company's technologies could be combined in some form, he declined to provide details.
"Imagine a world where you combine Capture-XT with Q-POC and how incredibly powerful that device will be," O'Halloran said.