TB Diagnostics at the Point of Care

ABSTRACT Tuberculosis ranks in the top ten worldwide cause of death and now ranks ahead of HIV, making it the number one infectious disease killer. Perhaps, most alarming is the global prevalence of multidrug-resistant TB (MDR- TB) and extensively drug-resistant TB (XDR-TB): more than 5% of new TB cases are MDR-TB and 10% of these have XDR-TB. And, the number of enrolled XDR-TB cases has grown from 58 countries in 2010 to 105 in 2015. The concern to prevent the spread of TB has fueled a TB diagnostics market that is expected to reach $3.1 billion by 2024. The predominant method for diagnosing XDR-TB is still culture. And, culture for XDR-TB detection requires 6 to 16 weeks. The only commercially-available alternative is a test that requires a skilled technician to perform 20 manual steps, which often include an upfront culture step and PCR to improve sensitivity. One of these steps is to transfer amplified DNA from a PCR tube to a line probe strip that requires visual interpretation. The transfer step is susceptible to PCR contamination; the visual interpretation is susceptible to incorrect readings; and the complex workflow is susceptible to mistakes. Developing molecular tests for XDR-TB are inherently complex for primarily three reasons: (1) the sample type (typically sputum) is highly viscous and heterogenous, and thus extracting and purifying microbial DNA presents significant challenges, (2) there are hundreds of genetic mutations that confer TB-drug resistance, and (3) the market is cost sensitive because those infected are often impoverished. This year, Akonni received a 2017 North American New Product Innovation Award from Frost and Sullivan. The test that we are developing includes an automated method of extracting DNA from sputum and a Lab-on- a-Film diagnostic, which consists of hundreds of molecular gel drops printed on a conventional film. This film costs 350X less than standard microarray glass. We laminate this film to additional layers of flexible films and pressure-sensitive adhesives that form chambers and channels – without need for pumps, valves, or special coatings. The resulting Lab-on-a-Film assembly is then used for integrated PCR/hybridization and includes a waste chamber absorbent for eventual confinement of all liquids in order to prevent PCR contamination. The promise of this assembly strategy is that manufacturing throughput can increase from one part per minute using robotics to one part per second using the newspaper printing production method: reel-to-reel manufacturing. During Phases 1 and 2 of this SBIR project, we developed and delivered a fully-automated sample-to-answer system, which included the Lab-on-a-Film consumable, to our collaborator in Mexico and demonstrated sample-to-answer genotyping of both isoniazid and rifampin resistant strains of Mycobacterium tuberculosis. Under a separate R01 project with University of California, San Diego Medical School, we developed a modular (non-automated) system and an XDR-TB assay using our gel drop arrays on glass. For Phase 2B, we propose to: (1) further the development of the Lab-on-a-Film assembly so that it can be produced with reel-to- reel manufacturing, (2) transfer the XDR-TB assay to our Lab-on-a-Film device, and (3) couple it with our sample-to-answer instrument for a fully-automated workflow. We propose to evaluate this system with retrospective XDR-TB sputa specimens collected under the R01 project.NARRATIVE Diagnosis and treatment of drug resistant tuberculosis is currently limited by its reliance on slow-growing, culture-based drug susceptibility testing. The goal of this project is to advance a Lab-on-a-Film (low cost) consumable test with a companion sample-to-answer instrument in order to detect extensively drug-resistant tuberculosis (XDR-TB) in sputum.