Proteins that normally reside inside cell nuclei have never been found in the blood, until 

now. A new blood test developed at the Johns Hopkins University by Shih-Chin Wang and 

Chih-Ping Mao—graduate students in Jie Xiao's lab in the Department of Biophysics and 

Chien-Fu Hung's lab in the Department of Pathology—can identify individual molecules in 

human blood samples with minimal detection errors. Among the molecules that they used 

their new test to find was a mutated protein thought to be restricted to the inside of cells, 

mostly within the nucleus. It is the first time that single-molecule imaging has been applied to 

visualize disease-causing molecules in blood. They will present their research at the 63rd 

Biophysical Society Annual Meeting, to be held March 2—6, 2019 in Baltimore, Maryland.

Wang and colleagues call their new approach Single-Molecule Augmented Capture (SMAC). 

They used this new technique to detect molecules commonly screened for in standard blood 

tests, like prostate-specific antigen. And they were also able to detect rare intracellular 

proteins, secreted proteins and membrane proteins, including the cancer-associated proteins 

mutant p53, anti-p53 autoantibodies and programmed death-ligand 1 (PD-L1).

Mutant p53 is a well-known tumor-specific nuclear protein and has never before been 

detected in the blood, likely because current tests cannot detect its extremely low blood 

concentrations. Wang and colleagues found mutant p53 or anti-p53 autoantibodies in 

samples from patients with ovarian cancer, but not in patients without cancer. PD-L1 is also 

found on the surface of some cancer cells and has recently been effectively targeted with 

immunotherapy to combat cancer. Knowing whether or not a patient's tumor expresses PD-L1 

is a crucial first step in this treatment—and SMAC may be able to identify cancers that have 

PD-L1 at low levels that are undetectable by standard blood tests.