CRISPR may help in kidney-transplants by detecting viruses

CRISPR may help in kidney-transplants by detecting viruses

By Dr. Liji Thomas, MD Apr 13 2020 An exciting new study published in the journal Nature Biomedical Engineering in April 2020 reports excellent results with a new test for two common viruses that infect kidney transplant patients. The levels of these viruses shoot up during the acute phase of rejection. Why are immunosuppressives necessary? A kidney transplant is a lifesaving but complicated procedure. There are many different points at which it can fail. Of these, the most dreaded complication following a successful surgery has to be organ rejection – when the patient’s body rejects the new kidney as a foreign object. The immune system starts producing antibodies to try and kill the new kidney. This not only wastes a precious donor kidney but can lead to the patient’s death. To prevent this, doctors usually prescribe medications that reduce the strength of the immune response, called immunosuppressives. This decreases the probability of rejection. There’s a downside, though. The problem with immunosuppressive drugs The disadvantage of such drugs is that it disarms the very system that enables us to function normally even while exposed to millions of bacteria, viruses, and other germs that, if allowed, would enter the body and harm or even kill the organism. What keeps them at bay is the immune system – the finely tuned natural defenses of the body. Sometimes it fails, as when the body is exposed to a new and unknown threat (like COVID-19), or it’s taxed beyond its strength. With the immune system no longer operating at full strength, the drawbridge is down – we are much more susceptible to external threats. This is why transplant doctors have to toe a fine line between too little dampening (resulting in organ rejection), and too much (which allows the infection to gain a hold in the body). Moreover, the infections which occur in immunosuppressed patients are just ordinary ones for the most part, which in a healthy person would have been dispelled with ease. Doctors have to monitor their patients exceptionally closely to ensure that the drug is at the right concentration to prevent either of these things from happening. Such monitoring is usually done via kidney biopsies and blood tests – both expensive, invasive, and time-consuming. A new way Urine testing is much simpler and less expensive than blood and kidney tests. And now, scientists have combined this modality with the powerful technology called CRISPR to sense the presence of molecules that signal infection. CRISPR is more usually associated with gene editing. Still, the current use could result in a highly sensitive diagnostic tool to detect early signs of rejection, just like the more common urine tests that screen for urine sugar, pregnancy hormones, and the like. 3d illustration of CRISPR-Cas9 genome editing system. Illustration Credit: Meletios Verras / Shutterstock To adapt a urine test for this purpose, it has to be able to detect nucleic acids – DNA or RNA. And this is why CRISPR becomes so useful because it is able to find tiny segments of nucleic acid with a particular sequence if there is a complementary piece of guide RNA to help it out. It is coupled with an enzyme called Cas, which occurs in several forms, and makes cuts to isolate the sequence being sought. It is also bound to a fluorescent molecule called a reporter, because it lights up when the target sequence is cleaved. The lateral flow strips show three patient samples that are negative for BK virus (13,14,15) and three patient samples that are positive (16,17,18). Presence of the upper band indicates a positive test result. Image Credit: Michael Kaminski, MDC Many researchers have proved that CRISPR can pick up diagnostically useful information on man-made samples, but real-world clinical testing is rare. This involves achieving sufficient sensitivity to detect extremely low concentrations, which are typically what is found in biological samples. Researcher Michael Kaminski comments: “The challenge is getting down to concentrations that are clinically meaningful. It really makes a huge difference if you are aiming for a ton of synthetic target in your test tube, versus if you want to get to the single-molecule level in a patient fluid.” How is CRISPR-aided urine testing done? Related Stories



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