A bypass air filter is provided for attachment to the return air duct of an existing forced air conditioning system. In particular, the present invention provides devices capable of delivering cells or clusters of cells, such as islets of Langerhans, in combination with a therapeutic compound, such as an angiogenic growth factor, for the purpose of transplantation. In an embodiment, the enclosure can comprise a shell with a base end having an opening therein forming a cavity within the shell and a base cap for covering the opening of the base end.