NEW YORK – A new low-cost tuberculosis (TB) test that requires no lab facilities and little specialist training might be able to help fill healthcare gaps in remote and low-resource settings.
The Lab-in-a-Tube TB (LIT-TB) test is being developed by scientists at Tulane University, who published the results of a pilot study of the device Wednesday in Science Translational Medicine.
To run the LIT-TB test, blood, saliva, or sputum is collected in an assay tube, which is then transferred to the incubator port of a portable device for solubilization and inactivation. A plunger loads the lysate onto a DNA capture membrane and initiates a recombinase polymerase amplification (RPA) reaction involving a CRISPR-Cas12a system. Once this reaction is complete, the tube is transferred to a readout port where a fluorescent signal indicating the presence of the TB bacterium is detected and analyzed.
The assay was tested in serum samples from a cohort of 27 children from the Dominican Republic, diagnosed with either pulmonary or extrapulmonary TB (PTB and EPTB, respectively), and 35 children who were close contacts of the others but had no evidence of infection.
The investigators compared LIT-TB's performance to traditional lab culture and to Cepheid's GeneXpert MTB/RIF assay. Although specimen culture is often considered the gold standard for diagnosing TB, GeneXpert is more sensitive and faster than culture and is recognized as a valid TB diagnostic platform by both the World Health Organization and the US Food and Drug Administration, said Tony Hu, a molecular biologist at Tulane University and the senior author of the study.
In Hu's study, LIT-TB demonstrated an overall better sensitivity than the comparators in this cohort: 81 percent for LIT-TB, 55 percent for lab culture, and 68 percent for the GeneXpert MTB/RIF.
The researchers tested the children over the course of their treatments and observed the LIT-TB signal decrease in both types of TB as the children's health improved, suggesting that the test can also be used to monitor treatment.
Hu added that another key finding in this cohort was that LIT-TB successfully identified six of the eight children with EPTB.
"This is quite important for pediatric TB management," he said, as EPTB is generally harder to diagnose than PTB, owing to its more diverse clinical presentations and greater difficulty in obtaining samples.
As an added measure, Hu and his colleagues also tested saliva samples from a case-control cohort of 15 adults diagnosed with TB and 15 healthy controls. The LIT-TB assay identified 11 true positives and no false positives among this group.
Similar results also came from an analysis of 71 sputum samples obtained from 36 adults with suspected TB. Here, LIT-TB demonstrated 100 percent sensitivity across the board, with specificities between approximately 87 and 91 percent for individuals with TB, nontuberculous mycobacteria infections, and no evidence of TB infection.
Mikashmi Kohli, senior scientist for evidence and policy at global nonprofit research organization FIND, whose research has focused on TB diagnostics, called the LIT-TB findings "very interesting" with respect to both diagnostic performance and treatment response monitoring, while also drawing attention to the study's small size and single geographical site.
"I think this is a great start for something very innovative, and I am happy to see the design and use cases of this test," Kohli said via email. She cautioned, however, that the LIT-TB technology should be evaluated in more presumptive cases of PTB and EPTB, both for diagnostic performance and for monitoring treatment response, and the evidence should come from larger and more diverse cohorts from different regions.
Hu acknowledged the study's small size and homogeneous cohort, saying that larger and more diverse studies are currently being planned. "Ultimately we need a better cohort to validate," he said.
The LIT-TB assay is designed to be simple, stable to a broad range of temperature changes, and cheap. Hu said that the entire process from sample to result takes approximately 45 minutes to run. The reader costs roughly between $700 and $800 in components, all of which can be ordered via Amazon, and it costs approximately $2.70 to run each sample. Hu estimates that this price will drop further when the test can be made at scale.
By comparison, prices for the GeneXpert MTB/RIF benchtop device range from approximately $9,000 to $72,000, with costs per cartridge ranging between roughly $10 to $25, although reduced pricing options are available for low-income regions through the Global Fund.
Tulane University holds the LIT-TB patent and IntelliGenome, a diagnostics company cofounded by Hu, is currently negotiating with the university for the right to license it.
Hu said that the goal is to acquire a nonexclusive license, since the LIT-TB technology is essentially a platform technology with a wide range of potential applications and should be made available to all who can use it.
"You can really [apply] this to many tests," he said, adding that his own lab at Tulane is currently exploring its uses in syphilis and pneumonia.
Although the licensing negotiations have not yet finished, Hu said that IntelliGenome has been making plans for the clinical trials that would be needed for regulatory submission.
"[IntelliGenome] is having a very active conversation with the FDA, and it will start a clinical trial very soon," Hu said, noting that the company has identified three trial sites in Germany, Mexico, and the US.
In addition to TB testing, IntelliGenome is also developing RPA-CRISPR-based diagnostic assays for nontuberculous mycobacteria infection and mycobacterium avium complex and is exploring possibilities in the oncology space. The company currently markets a benchtop version of the LIT-TB test that Hu developed previously.
Hu said that such low-cost and simple-to-use tests are crucial for TB testing in remote areas and those with limited infrastructure and resources.
Most current technology on the market, Hu said, relies on benchtop handling and in many low- to middle-income countries (LMICs), these are often placed in central lab facilities in urban areas, making it more expensive and logistically complicated to gather and analyze samples.
The World Health Organization estimates that globally, TB is the leading cause of death from a single infectious disease. It also estimates that the vast majority of cases occur in LMICs, with some two-thirds of global cases coming from just eight countries: India, Indonesia, China, the Philippines, Pakistan, Nigeria, Bangladesh, and the Democratic Republic of Congo.
Even higher-income countries stand to benefit from the availability of a rapid and low-cost TB test. The US, for instance, recently cut funding to several programs that supported TB testing. The WHO has previously said that the US has funded nearly a quarter of global TB testing and treatment programs over the past 20 years.
In addition to advancing the development of LIT-TB, Hu has been designing a self-powered microfluidic chip for detecting TB infection. A paper detailing that device, Hu said, was just accepted to Nature Biomedical Engineering.
"This test is going to make TB testing more convenient," Hu said, "especially for people living in resource-limited areas where a central lab is not available to them. I think that's going to hopefully change the landscape."