Background: Probable interhuman transmission of vCJD through blood and derived products has been reported in several cases in Great Britain, highlighting the necessity to secure transfusion against prion risk. Experimental models suggest an equal distribution of infectivity among plasma and white cells, but the cellular populations supporting infectivity remain to be clearly identified. Objectives: Experimental BSE/vCJD infection of cynomolgus macaque constitutes a model of choice to better assess the distribution of prion infectivity among the different blood cell populations. Methods: Monkeys were experimentally infected with BSE by the oral route, or with primate-adapted BSE by the intravenous route (secondary and tertiary passages). In the context of the PrionBloodPrimate project funded by Alliance BioSecure Foundation, blood was sampled and fractionated according to an adapted protocol to concentrate white cells. Different cell populations were then sorted with the Foundation’s secured cell sorter (Influx). Infectivity of whole blood, plasma and the different cell fractions will be assessed by inoculation of transgenic mice overexpressing human PrPMet129 (tg650). Results: Primates were selected for their presence of peripheral infectivity according to the presence of PrPres in biopsied inguinal lymph nodes. Corresponding granulocytes, monocytes, lymphocytes and dendritic cells fractions were separated and enriched with purity around 90%. tg650 mice that demonstrate a high susceptibility to vCJD and allow endpoint titration of infectivity within relatively short delays, have been inoculated with these samples and the first results will be available for the congress Prion 2009. Discussion: With detailed information about donor primates (incubation period, presence of peripheral replication or clinical signs), the efficient actors are now gathered to evaluate the distribution of infectivity among the different components of these unique samples, to better assess the risk of transmission of prion by blood transfusion.