I recently installed a new, full bath in my basement featuring a WC, lavatory, shower and bar sink. My inspector approved one two inch vent which served each fixture (although the WC and bar sink is combined). This two inch vent ran up through the floor of the main level where it tied into a revent for the main floor shower and tub. The tie in from the 2 inch basement fixture vent had to be above the highest fixture on the main floor (generally 48 inches according to my inspector). This combined revent then ran up into the attic where it wrapped around skylights, etc. and then tied into the 3 inch stack through the roof.
My inspector signed off on this arrangement, although he did some figuring on how many fixtures these revents could serve. Hope it helps.