Editing Progressive multifocal leukoencephalopathy (section)

===Immunosuppression===
PML is most common in people with HIV1 infection; prior to the advent of effective [[HAART|antiretroviral therapy]], as many as 5% of people with AIDS eventually developed PML.<ref name="NIH">{{cite web|date=14 February 2014|title=Progressive Multifocal Leukoencephalopathy Information Page|url=https://www.ninds.nih.gov/disorders/all-disorders/progressive-multifocal-leukoencephalopathy-information-page|access-date=11 September 2020|work=National Institute of Neurological Disorders and Stroke|publisher=National Institutes of Health|df=dmy-all}}</ref> Why PML occurs more frequently in people with AIDS than in other immunosuppressive conditions is unclear; some research suggests the effects of HIV on brain tissue, or on JCV itself, make JCV more likely to become active in the brain and increase its damaging inflammatory effects.<ref name="pmid12709870">{{cite journal |title=Progressive multifocal leukoencephalopathy in acquired immunodeficiency syndrome: explaining the high incidence and disproportionate frequency of the illness relative to other immunosuppressive conditions |journal=[[J. Neurovirol.]] |volume=9 Suppl 1 |issue= 2|pages=38–41 |year=2003 |pmid=12709870 |doi=10.1080/13550280390195261 |last1=Berger |first1=Joseph|s2cid=17171153 }}</ref>

PML can still occur in people on immunosuppressive therapy, such as [[efalizumab]], [[belatacept]], and various transplant drugs, which are meant to weaken the immune system.<ref name="pmid21777829" />