COVID-19 and graft-versus-host disease: a tale of two diseases (and why age matters)
Disorders involving injury to tissue stem cells may show unusually devastating clinical consequences. In acute graft-versus-host disease (aGVHD) relatively few cytotoxic immune cells target skin stem cells to produce significant morbidity and mortality. By analogy, SARS-CoV-2 initially homes to pulmonary stem cells that preferentially express the ACE2 receptor, thus potentially incurring similarly robust pathological consequences. As with aGVHD, lung stem cell targeting is a potential co-factor in explaining age-related severity of COVID-19 infection.