Nature 378, 779–783 (1995)

In this Letter we reported that transgenic mice expressing both human and mouse prion protein are no more susceptible to BSE than their wild-type counterparts. We also included the interim results of challenge of mice expressing only human prion protein (HuPrP+/+Prn-po/o) with BSE; these mice had remained disease-free 264 days post-inoculation. We have now found that from 489 days onwards, some of these HuPrP+/+ Prn-po/o mice developed a prion disease. More details appear on pages 448–450 of this issue.