Filter assemblies are processing biological fluid, such as blood or a blood component containing leukocytes. The filter assemblies include a flexible housing with first and second walls. A filtration medium and a support member are at least partially positioned between the walls of the housing, with a seal joining the walls of the housing, the filtration medium, and the support member. The filter assemblies may further include a pre-filter and/or a post-filter positioned between the walls of the housing. If provided, the pre- and post-filter may be positioned on opposite walls of the filtration medium, with the post-filter being a mesh positioned between the filtration medium and one of the walls of the housing or within an opening defined by the support member. A seal of the filter assembly may pass through the filtration medium, with the filtration medium being substantially omitted in a section of the seal.
