British doctors who spent 102 days treating a cancer survivor for Covid-19 documented how the virus mutated after the man was treated with convalescent plasma.
The case study suggests the use of blood plasma donated from Covid-19 survivors may have put enough pressure on the virus to force it to evolve. The result: Less susceptibility to immune system antibodies that normally fight off infection, according to the report published Friday in the journal Nature.
While the convalescent plasma didn't seem to harm the patient, it offered no clear benefit, said senior author Ravindra Gupta, a professor of clinical microbiology at the Cambridge Institute of Therapeutic Immunology and Infectious Disease. It should be used cautiously in people with chronic immune conditions, he said, preferably in clinical trials or carefully controlled settings.
The report also suggests that numerous mutations may be emerging among patients who have both compromised immune systems and chronic infections.
"When the virus has a chance to sit in one person for a long time and replicates for weeks and months, it learns how to fight the immune system," Gupta said. It's all about "pressure on the virus."
The patient didn't develop the exact variant that's now become the dominant form of the virus circulating in the U.K., the report said, but it did have certain elements in common. "It just illustrates that someone like him is probably patient zero," Gupta said.
Overall, Covid-19 is mutating relatively slowly. That's because it is a fast-moving virus giving it little time to evolve. In this case, however, the patient and his doctors fought the virus for 102 days from the time he was diagnosed until he died, Gupta said.
The patient was diagnosed with Covid-19 at a local hospital in the spring of 2020, when the first wave of the virus was reaching crisis levels in the U.K. He was subsequently brought to Cambridge University Hospitals for more intensive care.
The team there tested him twice a week to see if the treatments he was receiving, including Gilead Sciences Inc.'s remdesivir, were reducing his viral load. They were not.
At the same time, the samples were being sent for genetic profiling. That resulted in a snapshot of the virus mutating over time, allowed the researchers to hone in on where, how and when the pathogen changed as the months progressed.
There were few changes in the virus after he received two courses of remdesivir in the first two months, according to the researchers. However, after convalescent plasma was administered, there were large, dynamic virus population shifts, including in the key spike protein, which the virus uses to latch on to and infect healthy cells.
The variants then presented evidence of reduced susceptibility to neutralizing antibodies that normally control the virus.
The case study comes almost a month after a large, national study in the U.K. examining convalescent plasma as a therapy was ended after a finding that the treatment touted by U.S. President Donald Trump doesn't work.
The University of Oxford research was part of a clinical trial named Recovery that's investigating different Covid-19 treatments. The study's other arms are ongoing.
The results come after more than 100,000 Americans have been treated with convalescent plasma after its use was authorized by U.S. regulators on an emergency basis.