COMPETING TECHNOLOGIESAs if drug development was not risky enough, Sangamo also faced the threat that its ZFN technol ogy would be rendered obsolete by other gene-editing alternatives. In early 2015, two alternatives were gain ing traction: TALENs (transcription activator-like effector nucleases), and CRISPRs (clustered regularly interspaced short palindromic repeats). TALENs are like ZFNs in that they are special nucleases that iden tify and bind to a specific part of the DNA and cut the genome at a desired spot. The main difference between the two is how they identify the right DNA binding location. By 2015, ZFN technology was more mature and better developed, but TALEN technology was considered more straightforward to design treatments with, and thus many considered it to have an advan tage in the longer term.' According to Stephen Ekker, director of the Mayo Addiction Research Center at the Mayo Clinic Cancer Center, while ZFNs had established the proof of principle for genome-editing technology, "TALENs ... do most of what ZFNs do, but cheaper, faster and better."® On the other hand, TALEN molecules were larger, which made them more difficult to deliver to certain regions of the body (a par ticular challenge was getting gene-editing nucleases past the blood-brain barrier for treatment of diseases such as Huntington's). Since both technologies had advantages and disadvantages, their sponsors would have to race to get effective treatments to market first.CRISPRs were somewhat different. CRISPR technology harnessed a natural defense system of bacteria that has evolved to recognize and eliminate foreign DNA, giving bacteria "adaptive immunity." CRISPRs were even more simple and efficient than TALENs, fueling enormous excitement over their potential. However, because CRISPRs used a very short RNA sequence to guide their activity, some people worried that their effects wouldn't be pre cise enough; that is, they could result in "off-target" cleavages—a highly undesirable result. As of early 2015, there remained great uncertainty about which gene-editing technology would pay off. This uncertainty, unfortunately, dampened investor support for all three technologies.