Ultra-sensitive test for cancers, HIV

When a disease - whether it's a cancer or a virus like HIV - begins growing in the body, the immune system responds by producing antibodies. Fishing these antibodies or related biomarkers out of the blood is one way that scientists infer the presence of a disease. This involves designing a molecule that the biomarker will bind to, and which is adorned with an identifying "flag." Through a series of specialized chemical reactions, known as an immunoassay, researchers can isolate that flag, and the biomarker bound to it, to provide a proxy measurement of the disease.

A new technique developed by a team of chemists at Stanford has shown promise to be thousands of times more sensitive than current techniques in lab experiments, and it is now being put to test in real-world clinical trials.

The new technique augments this standard procedure with powerful DNA screening technology. In this case, the chemists have replaced the standard flag with a short strand of DNA, which can then be teased out of the sample using DNA isolation technologies that are far more sensitive than those possible for traditional antibody detections.

The technique termed antibody detection by agglutination-PCR (ADAP). Antibodies bind to and agglutinate synthetic antigen–DNA conjugates, enabling ligation of the DNA strands and subsequent quantification by qPCR. ADAP detects zepto- to attomoles of antibodies in 2 μL of sample with a dynamic range spanning 5–6 orders of magnitude.

The researchers tested their ADAP technique, with its signature DNA flag, against four commercially available, FDA-approved tests for a biomarker for thyroid cancer. Anti-thyroglobulin autoantibodies from human patient plasma with a 1000-fold increased sensitivity over an FDA-approved radioimmunoassay.

Authors also demonstrate the multiplexability of ADAP by simultaneously detecting multiple antibodies in one experiment. y detecting the biomarkers of disease at lower concentrations, physicians could theoretically catch diseases far earlier in their progression.

"The thyroid cancer test has historically been a fairly challenging immunoassay, because it produces a lot of false positives and false negatives, so it wasn't clear if our test would have an advantage," author said. "We suspected ours would be more sensitive, but we were pleasantly surprised by the magnitude."

Based on the success of the thyroid screening, the group has won a few grants to advance the technique into clinical trials. One trial underway in collaboration with the nearby Alameda County Public Health Laboratory will help evaluate the technique as a screening tool for HIV. Early detection and treatment of the virus can help ensure that its effects on the patient are minimized and reduce the chance that it is transmitted to others.

The researchers are also pursuing tests for Type 1 diabetes, for which early detection could help patients manage the disease with fewer side effects.