Researchers from the Max Delbrück Centre for Molecular Medicine in Berlin, Germany and the Massachusetts Institute of Technology (MIT), have developed a urine test for the most common complications following a kidney transplant. Their finding are published in Nature Biomedical Engineering.
'Most people think of genome editing when they think of CRISPR, but this tool is also suitable for other applications, especially for cheaper and faster diagnostics,' said lead author Dr Michael Kaminski.
Kiidney transplant patients take immune suppressant medications to prevent organ rejection, placing them at higher risk of infection, including from viruses unlikely to harm a healthy person. To identify infection, time-consuming and expensive blood tests and kidney biopsies are performed.
The new test detects two viruses that often infect patients after a kidney transplant: Cytomegalovirus (CMV) and BK Polyomavirus (BKV). The method also detects CXCL9 mRNA, as an increase in the level of this protein can be an indicator of acute cellular rejection of kidney transplants.
First, the target nucleic acids (viral DNA or CXCL9 RNA) in the sample are amplified, meaning that even if there is only a tiny amount in the sample, it will get picked up by the test. The team used a specific CRISPR-Cas13 protocol called SHERLOCK to optimise the process. Then, a test strip is dipped into the prepared sample; if only one band appears on the strip, the sample is negative, two bands indicate that the virus or mRNA is present.
The team also developed a smartphone app, which analyses a photo taken of the strip to interpret the intensity of the second band, which can appear weak if the virus concentrations are very low. 'The challenge is to detect clinically relevant concentrations,' said Dr Kaminski. 'It makes a big difference whether you detect high concentrations of synthetic target molecules in a test tube or a single molecule in a patient sample.'
The assay was tested in over 100 patient samples and was able to detect BKV and CMV even at low concentrations, as well as accurately predicting graft rejection. The team now intends to compare the test to other conventional methods and is investigating ways to make it suitable for home testing by the patients themselves. The test may also be suitable for patients with other organ transplants that are similarly susceptible to viral infections.