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ProteinLogic Developing Blood-Based Test to Screen for Active TB


NEW YORK – ProteinLogic has developed an immune system biomarker signature and predictive models that are part of a blood-based diagnostic test the firm anticipates launching to screen for active tuberculosis at the point of need.

The test, ImmiPrint-TB, conducts quantitative measurements of selected proteins and uses those values as inputs for predictive models derived using machine learning. The models, in turn, produce a diagnosis that reflects the presence or absence of TB.

The test rules out the presence of TB when infection has progressed beyond the latent stage and a patient is presenting clinically with TB symptoms, ProteinLogic CEO Nicolas Huber said in an interview.

The Cambridge UK-based company has integrated its TB assay with an ELISA platform from an undisclosed collaborator. In addition to its potential use in the future at the point of need, the assay is ready for deployment as an ELISA-based laboratory-developed test, Huber said, adding that its TB assay has thus far been demonstrated on both chemiluminescence and fluorescence detection systems.

If the firm is successful in its commercialization efforts, the TB assay may become one of the first blood-based tests on the market used to rule-out active TB. The firm believes it can obtain CE marking or an IVDR approval in Europe in about two years and make the test available for screening, Huber said. 

The blood test for active TB is different from those currently used to diagnose latent TB infection. To detect latent TB, when a person is infected with Mycobacterium tuberculosis but does not have active TB, clinicians are increasingly switching to blood-based interferon-gamma release-based assays (IGRAs), driving sales growth for Qiagen and Oxford Immunotec, who lead the market in that testing category. About 75 percent of all testing for latent TB infection involves use of tuberculin skin tests conducted in clinics.

Testing for active TB, on the other hand, is usually done using smear microscopy or molecular diagnostic assays that analyze sputum samples. If sputum has enough bacteria in it, techniques such as culture and use of molecular diagnostic platforms "are excellent at finding TB," Huber said.

Cepheid's sputum-based GeneXpert molecular diagnostic platform has the largest global footprint of any test for active TB on the market.

However, getting a sputum sample that is adequate for testing can be challenging, Huber noted.

Sick patients are sometimes unable to produce sputum. Further, TB isn't detectable in the sputum of patients who have extra pulmonary TB, a condition in which bacteria are not present in the lungs and which accounts for up to 20 percent of all cases of active disease.

Diagnostic markets for tuberculosis testing have seen "great improvements" in tests for both latent infection and active disease over the last decade, said Jeff Fischer, co-founder and president of Bethesda, Maryland-based Longhorn Vaccines and Diagnostics.

"More than one billion people worldwide have latent tuberculosis and approximately 10 percent will develop active infection in their lifetime," said Fischer, whose company is developing PrimeScreenTB, an oral TB screening kit that detects the presence of TB DNA in the mouth. 

Treating all patients with latent TB is not cost effective and can lead to unnecessary side effects from TB drugs, and there has been a focus among diagnostic test developers on identifying biomarkers and tests that can predict or identify patients that are progressing to active disease for further clinical evaluation, which is often referred to as sub-clinical or incipient TB.

Among these are the approaches developed by Longhorn Vaccines and Diagnostics and ProteinLogic, Fischer said.  "Both approaches, as well as use of other biomarker screening tests, are likely necessary for the TB community to meet their goals of significantly reducing or eliminating TB infection over the next decade," Fischer added.

Test validation

"[The ProteinLogic ImmiPrint-TB assay] is a promising community-based test for ruling out active TB, including for persons living with HIV and those unable to provide sputum samples or that are smear-negative," said Marcelo Cordeiro-Santos, an infectious diseases specialist at Fundação de Medicina Tropical Dr. Heitor Vieira Dourado, in Manaus, Brazil.

Cordeiro-Santos has provided samples for studies commissioned by ProteinLogic to validate the test.

In an observational study involving collaboration among researchers from South Africa, Spain, and the United Kingdom, Cordeiro-Santos' group "showed that by testing on complex platforms, a posteriori," the ProteinLogic serum-based biomarker assay had 90 percent sensitivity and 70 percent specificity.

That study was part of a larger project involving an international consortium of investigators and funded by a European Union Horizon 2020 grant worth €3.5 million ($3.9 million) to develop and validate the ProteinLogic TB assay. 

In a presentation of the results at the 50th Union World Conference on Lung Health in Delhi, India, in October, Cordeiro-Santos and his colleagues said that the clinical investigators' findings associated with the test's results met the World Health Organization and Foundation for Innovative New Diagnostics' minimal requirements for non-sputum screening tests to rule out tuberculosis.

In the study, ProteinLogic's collaborating clinicians evaluated the ImmiPrint-TB assay using a point-of-need ELISA platform. Clinical blood samples were collected from patients suspected of having TB who had presented at medical clinics. The patient population included those with active pulmonary TB and extra-pulmonary TB, including subjects co-infected with HIV, as well as people without TB.

Including samples from patients co-infected with HIV was important because their samples usually "confound" TB diagnostic tests, and the patients may not be able to produce sputum for diagnosis, Huber said.

According to the WHO, people living with HIV are up to 22 times more likely to develop TB than persons without HIV. It’s the most common presenting illness among people living with HIV and the major cause of HIV-related deaths.

A screening test must have a high negative predictive value above 90 percent to rule out active TB in clinical practice and "be confident that the individual with a negative result does not really need to undergo additional testing," Cordeiro-Santos said.

Huber noted that in recent studies, ProteinLogic's TB rule-out test has demonstrated a negative predictive value of 94 percent.

A Nobel Prize foundation

At the foundation of the company's ImmiPrint diagnostic technology is work on monoclonal antibodies for which César Milstein received the Nobel Prize in Physiology or Medicine in 1984. Milstein and his colleague Adrian Woolfson developed the technology at the MRC Laboratory of Molecular Biology in Cambridge, UK.

Their idea was that "soluble versions of CD antigens could be used as a fingerprint of disease," Huber said. "Because of a number of limitations, it had not been possible for several years to validate this idea and determine whether it could be effective enough to be applied for diagnostic purposes."

In December 2003, the University of Cambridge UK granted ProteinLogic a worldwide and exclusive license to commercialize the intellectual property, which was then owned by the university, Addenbrooke’s NHS Trust, and the UK Medical Research Council.

Around 2010, the firm began investigating immune system proteins and comparing their levels in samples from healthy patients with levels in samples from patients with TB.

A few years ago, the firm also sourced antibodies that enabled it to measure the biomarkers it was interested in with enough sensitivity, Huber said, adding that the antibodies enabled ProteinLogic to develop "unique combinations of immune system markers to diagnose specific diseases."

As part of the EU Horizon 2020 project, the firm worked with a third-party company that provided it with a platform "that could potentially be used at the point of care, and we hope to move forward with them" to develop a commercial test, Huber said.

In addition to developing the TB diagnostic test, ProteinLogic anticipates advancing its early-stage product development pipeline by continuing to validate biomarker signatures, with a focus on biomarkers for the diagnosis of infectious, autoimmune, and inflammatory diseases.

Huber said that for the TB assay, he is looking to forge partnerships with a view to executing out-license agreements with larger diagnostic companies. "We are also looking at a laboratory developed test avenue in the US through CLIA labs and currently talking to a few that have shown an interest," he said.

The firm, backed thus far by angel investments as well as EU grants, is focusing its current funding on commercial rather than development activities. It is also seeking capital to the tune of about $5 million to drive additional development and commercial initiatives, Huber said.