In the 1970s, June Kwon-Chung was characterizing the life cycle of Cryptococcus neoformans, a fungus that causes a rare disease called cryptococcosis, which results in a fatal brain infection if left untreated. Looking at the fungal sexual spores under the microscope, she noticed two distinct forms—one round, the other shaped as fingerlike projections. She had a hunch she was observing two different species.
“I thought, this has got to be two different species, genetically, but at the time we didn’t even know how to extract DNA since molecular techniques for Cryptococcus were not yet developed. So I was using classical methods to determine how they differed geographically, epidemiologically, and biologically,” said Kwon-Chung, chief of the Molecular Microbiology Section in the Laboratory of Clinical Infectious Disease at the National Institute of Allergy and Infectious Disease (NIAID) in Bethesda, Maryland.
In a study this week in mBio®, Kwon-Chung’s group reports on a risk factor that appears to make some patients susceptible to that second Cryptococcus species she has described.
Kwon-Chung, a medical mycologist, spent a good chunk of the 1980s and 1990s studying the two forms, which originally had been identified as C. neoformans variety neoformans and a sister variety called C. neoformans variety gattii. Found in the environment, the fungus gets inhaled into the lungs. In immunocompromised patients, it can multiply in the lungs and travel to the brain where it proliferates, causing headaches, memory loss, and swelling. Even with anti-fungal treatment, about one-quarter of patients still die. The advent of AIDS put a spotlight on C. neoformans, because it frequently attacked these immunocompromised patients. Today, it is a major cause of AIDS deaths worldwide, with an estimated 1 million new cases and 625,000 deaths annually.
Kwon-Chung’s research group showed that the C. neoformans variety gattii was biochemically quite different and that it was mostly found in patients from tropical and subtropical regions, including Australia, Brazil, Thailand, Hawaii, Mexico, and central and southern Africa. In 2002, molecular genetics proved what Kwon-Chung already knew—that C. neoformans variety gattii was actually a separate species, which she eventually named Cryptococcus gattii.
Soon after, it became clear that while C. neoformans mostly infected AIDS patients , C. gattii only rarely infected HIV patients and instead struck patients who were apparently healthy. At this same time, an epidemic of cryptococcal infections in temperate Vancouver, British Columbia was strangely found to be caused by C. gattii.
“People began opening their eyes and saying let’s identify whether [a patient has] C. gattii or C. neoformans,” said Kwon-Chung. The majority of C. gattii patients were so-called immunocompetent, the opposite profile of C. neoformans. “Why is C. gattii going after immunocompetent people?” she asks. “That is the last major question I want to solve before I retire.”
Clearly, it wasn’t attacking every healthy person breathing in the spores, so Kwon-Chung hypothesized that there might be a subtle immunological difference in these patients. “Since I’m not an immunologist, it was a little bit like shooting in the dark,” she said.
Then, in 2013, a study published by Steven Holland’s group also at NIAID gave her a huge hint. It showed that seven immunocompetent patients with cryptococcal infections had autoantibodies to granulocyte-macrophage colony-stimulating-factor (GM-CSF). Normally, the GM-CSF cytokine regulates growth and survival of immune cells, particularly macrophages and T cells.
In that study, one patient clearly had a C. gattii infection, three patients had infections by unspecified Cryptococcus and three were identified as having C. neoformans. Kwon-Chung’s team confirmed that the three unknown strains were C. gattii, and she strongly suspected that the other three were misidentified.
Working with colleagues in China and Australia, her group obtained numerous blood samples from immunocompetent patients with cryptococcosis and found that seven patients who had the GM-CSF antibodies in their blood were all infected by C. gattii. In the mBio® paper, the authors make the case that anti-GM-CSF autoantibodies are a risk factor for C. gattii infection and not necessarily for C. neoformans infection.
“It turns out that patients suffering a C. gattii infection are not exactly immunocompetent,” said Kwon-Chung. The team also found one healthy control patient from China with autoantibodies to GM-CSF in his blood who could be predisposed to C. gattii infection.
Although not proven yet, Kwon-Chung thinks it’s very likely that the autoantibodies make patients susceptible to infections, and not the other way around. If true, testing for anti-GM-CSF antibodies might be used in the future to find patients at risk for C. gattii infections, especially in areas where the fungus is endemic.
With a new hunch to chase, she is not considering retirement anytime soon: “I assume this will open up a huge immunological investigation. We have a lot to do. I can’t just stop here.”