A method for separating a volume of whole blood contained in a separation bag (1) into at least three components comprises: - Centrifuging the separation bag (1) so as to separate therein a first inner layer comprising plasma, a second intermediate layer comprising platelets, a third intermediate layer comprising lymphocytes, monocytes and granulocytes and a fourth outer layer comprising red blood cells, wherein at least the third and fourth layers partially overlap - Transferring, into a plasma component bag (2) connected to the separation bag (1), a plasma component substantially comprising a first fraction of the first layer and - Transferring, into a mononuclear cell component bag (3a) connected to the separation bag (1), a mononuclear cell component comprising at least a fraction of the third layer comprising lymphocytes and monocytes.
