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Hologic Hepatitis C Viral Load Test Fares Well in German Validation

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NEW YORK (GenomeWeb) – Researchers in a clinical lab in Germany have validated the Hologic Aptima hepatitis C virus assay on the firm's Panther system, showing it provides superior performance at low viral loads when compared to a widely used HCV assay from Roche.

The investigator-initiated study, published online earlier this month in the Journal of Clinical Microbiology, used reagents provided by Hologic and the data was convincing enough that the lab will now switch to the Aptima HCV test from the Roche test it had been using for decades, Gunnar Schalasta, lead author on the study and a microbiologist at the Labor Enders diagnostics lab, told GenomeWeb.

Labor Enders is a private clinical lab in Stuttgart, Germany, accredited according to European standards as well as those of CAP and CLIA. It offers a broad range of medical services to physicians, hospitals, and university hospitals in the fields of virology, molecular biology, clinical chemistry, and bacteriology, Schalasta said.

The lab was also an early adopter of a previous generation of the Hologic Panther system, the Tigris system originally developed by Gen-Probe, Scott Hauenstein, senior manager of scientific affairs for virology at Hologic told GenomeWeb in an interview.

"Labor Enders was one of the first Aptima Panther customers in Germany and Europe; they had a Tigris a long time ago, and now have two Panthers on site for routine use," Hauenstein said.

The lab had been using systems to perform Aptima women's health assays, which rely on end point transcription mediated amplification (TMA).

Hologic has been building a menu of virology assays, with a test for HIV diagnosis and treatment monitoring CE-marked in December of 2014, and the HCV test CE-marked in October of last year.

"When we heard about the new HIV and HCV Aptima tests, we were very curious to learn something about the performance of these new real-time TMA tests," Schalasta said in an email.

Schalasta's group chose the Roche Cobas TaqMan HCV Test for use with the High Pure System (HPS/CTM) as the reference assay. Notably, it has been used in a number of phase III clinical trials for HCV drugs. 

Bob Purcell, vice president of communications for Roche Molecular Systems noted that the HPS/CTM "is a highly successful, but early generation HCV viral load test." Over the past several years, Roche has launched two other HCV tests that are now CE-marked as well as approved by the US Food and Drug Administration — the Cobas AmpliPrep/Cobas TaqMan HCV Test, v2  and the Cobas HCV for the Cobas 6800/8000 Systems. The firm also has a CE-IVD HCV test for the Cobas 4800 System.

Drug therapies for HCV aim to cure infection, but viral load must be carefully monitored over the course of several months to determine if a patient is responding, requiring tests with a lower limit of quantitation under 25 IU/ml.

Compared to the HPS/CTM, the Hologic Aptima HCV Quant Dx assay showed high agreement on one commercially available reference panel and two External Quality Assessment panels.

A set of 267 samples collected from HCV-positive patients was then tested using the Hologic and Roche tests in parallel. One sample was excluded because of an invalid Aptima result. For the remaining 266 samples, however, concordance between the tests in discriminating between negative and positive samples was 92 percent. 

Aptima detected 20 samples that were not detected with the HPS/CTM. Fifteen of these were below the lower limit of quantitation on the HPS/CTM system. There was also one sample detected with HPS/CTM at a low but quantifiable level that was negative in the Aptima test. In addition, two samples were detected by both assays that were below the limit of quantitation, and 17 were detected and quantifiable by Aptima that were detected but below the limit of quantitation of the HPS/CTM test.

The authors also analyzed the linearity of quantitation by HCV genotype, as well as variability within and between assays, and analytical sensitivity.

Hologic's Hauenstein noted that the study "demonstrated Aptima HCV had equal or superior performance, especially at the low viral loads, compared to the HPS/CTM, and this was especially evident with a few different genotypes." At the low end at the clinical cutoff of 25 IU/ml, Aptima showed "a little bit better precision and sensitivity," he said. There was also high correlation and agreement between the two tests, providing "strong evidence for the clinical usefulness" of the Aptima HCV assay.

"We want people to use our assay and get experience with it, and publish and get data out there so that people realize its potential and its utility for clinical monitoring — so, this is a very nice outcome for us," Hauenstein said.

Mike Watts, Hologic's vice president of investor relations and corporate communication, also noted that it is still early days in terms of the European launch of the HCV test.

Roche's Purcell pointed out that the results show the HPS/CTM test "continues to perform as expected with regard to agreement to several reference panels, sensitivity, accuracy, linearity, precision and reproducibility." The test also continues to fulfill the requirements of international HCV treatment guidelines, independently demonstrated by many publications in peer reviewed journals, and the product is used in the overwhelming majority of phase III clinical trials for new HCV treatments, he said.

At Labor Enders, Schalasta said other characteristics of the Panther system impacted the lab's decision to shift HCV testing away from the HPS/CTM test. That assay is "suitable for labs with lower or intermediate sample throughput and limited space," but Schalasta said the 6800/8000 systems were larger and challenging to fit into the lab's space. The Panther system, meanwhile, is "significantly smaller," Schalasta noted.

Panther is also fully automated, offers true random access, and its performance is "as good or better than the semi-automated HPS/CTM reference test," he said.

Random access, he noted, is "an important point for labs, because they can feed the Panther continuously with incoming samples," rather than batch processing.  

Hauenstein also noted that the Panther can run multiple different assays, which includes the firm's women's health menu and upcoming viral menu that includes the HCV assay.

"Panther is very unique in the molecular space," Watts said. "There's really no other instrument out there that can be used by such a wide range of customers with such a level of flexibility, throughput, workflow advantage, and walk-away time," he added.

"To be able to run the viral load assays on Panther in Europe, combined with the women's health assays that we already have approved, is a nice advantage for customers," Watts said.

The Panther system is FDA-approved with four tests — Aptima Combo 2 for chlamydia and gonorrhea, Aptima HPV and HPV genotyping, and Aptima Trichomonas.

In Europe, the firm offers all of these plus tests for HIV, HCV, as well as HBV viral load and Mycoplasma genitalium assays, both of which were CE-marked in December of 2015.

The firm plans to bring the CE-marked tests to the US. It has not disclosed a timeline, but Watts said, "We would expect to have the full menu available over the next couple years in the US, starting with HIV first, and then HCV and HBV."

This is a competitive market, with a number of firms such as Beckman Coulter, Cepheid, and Enzo Biochem also developing viral load monitoring menus for molecular diagnostics platforms.

Besides some of the aforementioned workflow advantages of Panther, its TMA technology — an isothermal RNA transcription-mediated amplification technique using RNA polymerase and reverse transcriptase to drive the reaction — provides a high level of sensitivity and differs from a lot of competitors who using more standard PCR, Hauenstein said.

Indeed, a recent economic model of human papillomavirus cervical cancer screening simulated co-testing with a test like Hologic's because of the specificity improvement, with the author noting that other commercial tests "would not give the benefit of the specificity parameter, and therefore benefits of co-testing would be eroded."

The TMA technology is also used in Hologic's blood screening assays. The legacy company, Gen-Probe, was a leader in that area for about 20 years, Watts said, and although the screenings tests are qualitative, there are foundational benefits to the TMA technology as it is adapted for the diagnostic assays.

The firm does not provide placement numbers, but the uptake of the Panther systems has been good, Watts said.

"We had communicated a goal several years ago to place more than 1,000 Panthers globally; a few quarters ago we achieved that goal, a little ahead of schedule," he said, such that the firm now has well over that number placed worldwide. This is a combination of clinical diagnostics and blood screening customers, with roughly two thirds of systems now placed in diagnostics labs.

"Panther is really the growth driver of our molecular diagnostics business," Watts said. The firm's molecular sales last quarter were up almost 10 percent on a constant currency basis, he said, "and that's really on the back of Panther, giving some indication of the strong uptake that we're seeing."

In Europe, lab customers tend to be based in hospitals, while in the US the firm is also selling to reference and public health labs. "There's significant overlap in terms of the customers who do women's health testing and those who do viral testing," Watts said.

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