In Reply In our article,1 we described the systematic, sensitive, and specific identification of JC virus, the etiologic agent responsible for the development of progressive multifocal leukoencephalopathy (PML), within circulating immune cells. Notwithstanding results in contradistinction to those we reported, Warnke et al appropriately acknowledged in their letter concerning our report that their study was confounded by an analysis of a significantly lower number of peripherally circulating immune cells. Their application of validated analysis techniques to compromised or inadequate samples ultimately culminated in their corresponding lack of ability to coelucidate the anticipated JCV and cytomegalovirus from the same tissues samples.
Frohman EM, Douek D, Major EO. Relevance of CD34+ Cells as a Reservoir for JC Virus in Patients With Multiple Sclerosis—Reply. JAMA Neurol. 2014;71(9):1192-1193. doi:10.1001/jamaneurol.2014.1858