Based on the HAEC system, we constructed a series of novel "pop-in" vectors, which can be inserted into current BAC/PAC/ P1 clones via loxP-Cre site-specific integration. This "loxP-Cre" mediated system has been used to establish BAC/PAC/P1 clones up to 250 kb in size in human cells as HAECs. Several functional studies are currently ongoing.