 Whole genome sequencing of "C. elegans" modified with a pair of 5-finger ZFNs found only the intended modification and a deletion at a site "unrelated to the ZFN site" indicating this pair of ZFNs was capable of targeting a unique site in the "C. elegans" genome.As with many foreign proteins inserted into the human body, there is a risk of an immunological response against the therapeutic agent and the cells in which it is active.Since the protein must be expressed only transiently, however, the time over which a response may develop is short.