An antibody-based assay developed by Humabs BioMed was able to detect Zika virus infections and differentiate them from dengue and other flaviviruses, according to data published today by researchers from the Swiss company and University of California (UC), Berkeley.
The researchers previously applied Humabs’ proprietary CellClone discovery technology to generate a Zika virus nonstructural protein 1 (NS1)-specific human monoclonal antibody, which they used to develop an NS1-based competition enzyme-linked immunosorbent assay (ELISA). The assay is designed to measure the presence of plasma or serum antibodies in immune individuals that can block the binding of a labeled monoclonal antibody to coated Zika virus NS1.
In the just-published study, the scientists sought to determine the sensitivity and specificity of the NS1 blockade-of-binding (BOB) assay by studying well-characterized samples confirmed with Zika through reverse transcription polymerase chain reaction from travelers and other individuals with a high level of exposure to other flavivirus infections or vaccination.
Eva Harris, Ph.D., a professor at UC Berkeley’s School of Public Health, and Humabs CSO Davide Corti, Ph.D., were co-senior authors for the study, which used laboratories in five countries—Brazil, Italy, Nicaragua, Switzerland, and the U.K.—to study Humabs’ assay.
Of 158 sera/plasma patients studied, 145 (91.8%) yielded greater than 50% inhibition. Of 171 patients with primary or secondary dengue virus infections, 152 (88.9%) scored negative. When the control group was extended to patients infected by other flaviviruses, other viruses, or healthy donors, expanding the group’s number to 540 patients, specificity rose to 95.9%.
“These results support that the antibody-based assay that we have developed is highly effective in detecting both recent and past Zika virus infections and in discriminating Zika from other flavivirus infections,” Dr. Corti said in a statement.
Researchers also analyzed longitudinal samples from dengue-immune and dengue-naïve patients with Zika infections and found inhibition was achieved within 10 days after the onset of illness and maintained over time.
“We have demonstrated the high sensitivity and specificity of a low-cost, accessible ZIKV NS1 serological assay,” the researchers reported in “Antibody-Based Assay Discriminates Zika Virus Infection from Other Flaviviruses,” published in Proceedings of the National Academy of Sciences. “The NS1 BOB assay is thus a timely solution for Zika surveillance, seroprevalence studies, and intervention trials.”
NS1 BOB is also a “broadly accessible, low-cost solution,” the researchers added, citing initial calculations estimating the cost per well in reagents and materials as approximately 25 cents—as well as the fact that the assay is based on an ELISA platform, widely available worldwide.
“Other important features of the NS1 BOB assay are its simplicity, its single-assay format, and its requirement for only one dilution of the samples compared with other tests requiring several dilutions and/or more complex and lengthy procedures (such as neutralization tests or Luminex-based assays),” the researchers added.
However, they acknowledged the study was limited by their inability to test samples from patients recovering from dengue virus 4 infections, since the sample set did not include DENV4. An assay using a BOB approach to study monoclonal antibody reaction with dengue viruses 1–4 NS1 antigen could also be developed to identify previous dengue infections as well as define the dengue-immune status of Zika-infected patients, the researchers stated.
Additional studies are ongoing to further simplify the Zika NS1 BOB assay protocol, including direct conjugation of the Zika-spacific anti-NS1 monoclonal antibody to peroxidase and the development of a lateral flow format.
Last year, the researchers illustrated the use of Zika-specific antibodies in a BOB assay that they said could be used as a highly-specific blood-based diagnostic tool in large cohort clinical and epidemiological studies to investigate the risk of Zika virus disease enhancement and the real incidence rate of Zika virus congenital infection in areas endemic for other flaviviruses. That study, “Specificity, Cross-Reactivity and Function of Antibodies Elicited by Zika Virus Infection,” was published in Science.
Humabs BioMed is a spin-off of the Institute for Research in Biomedicine, which is affiliated with the Università della Svizzera Italiana. The company has a portfolio of more than a dozen immunotherapy product candidates and has partnered with MedImmune and Novartis on several of its programs—two of which are now in clinical development by the companies.