The present invention provides a method for expanding a pre-assembled closed, sterile container system used for the collection, transportation, storage and cryopreservation of biological fluids, such as, blood, bone marrow or umbilical cord blood. The closed sterile bag system comprises a plurality of parts including inlet and or outlet elements and regions for mixing and storing body fluids and cryopreservation liquids, wherein connecting lines provide sterile connection of each component, and wherein the parts are hermetically sealable and separable to maintain sterility system. The methods herein further provide a means for introducing fluids into and/or extracting fluids from a pre-assembled, closed, sterile container system, while maintaining a closed, sterile system without the need to operate under ultra-clean room conditions.