A fungus that can cause severe pneumonia in people with weaker or weakened immune systems appears to have become resistant to a drug that never intended to kill it, according to the findings of a study by researchers from around the world published in Science Translational Medicine .
The study focused on mycophenolic acid (MPA), an immunosuppressive drug used with people who have received solid-organ transplants. MPA helps keep the immune system from rejecting the organ — but it was also found to affect Pneumocystis jirovecii fungi. The researchers have acknowledged that they have only established resistance at the enzyme level, rather than in infected patients, and that their cohort sizes and clinical data were limited. Nonetheless, researchers understand antimicrobial resistance as microorganisms evolving to resist antibiotics, antifungals or other medicines. But in the study, a drug intended to act on the human body was found unintentionally exerting pressure on a pathogen as well. And mutant fungi that could better tolerate MPA may have enjoyed an advantage among transplant recipients taking the drug, allowing them to survive and spread.
The “results challenge the current status quo on P. jirovecii ’s unknown resistance,” the study authors wrote, “calling for reevaluating immunosuppressive strategies and infection control measures and highlighting the broader potential for other pathogens to evolve under selective pressures imposed by human-targeted therapies.”
