Blood processing systems and methods convey blood cells from a blood cell source into a blood component collection flow channel that includes a blood cell storage container and an in-line filter to remove leukocytes from blood cells before entering the blood cell storage container. The systems and methods also convey additive solution from an additive solution source into the blood component collection flow channel. The systems and methods alternate the conveyance of blood cells through the filter with the conveyance of additive solution through the filter.