This presents several problems in vectors , particularly those in which additional genes , either a co-stimulatory gene or a selectable marker , are inserted .
this presents several problems in vectors , particularly those in which additional genes , either a co-stimulatory gene or a selectable marker , are inserted .
O O O O O O O O O O O O O O O O B-DNA_family_or_group I-DNA_family_or_group O O O O O O O O