Infectivity in bone marrow from sporadic CJD patients

Prion infectivity was recently identified in the blood of both sporadic and variant Creutzfeldt-Jakob disease (CJD) patients. In variant CJD (vCJD) the widespread distribution of prions in peripheral tissues of both asymptomatic and symptomatic patients is likely to explain the occurrence of the observed prionaemia. However, in sporadic CJD (sCJD) prion infectivity is described to be located principally in the central nervous system. In this study, we investigated the presence of prion infectivity in bone marrow collected after death in patients affected with different sCJD agents. Bioassays in transgenic mice expressing the human prion protein revealed the presence of unexpectedly high levels of infectivity in the bone marrow from seven out of eight sCJD cases. These findings may explain the presence of blood-borne infectivity in sCJD patients. They also suggest that the distribution of prion infectivity in peripheral tissues in sCJD patients could be wider than currently believed, with potential implications for the iatrogenic transmission risk of this disease.