25 • the determination by the reviewing regulatory authority to require more costly or lengthy clinical trials than we currently anticipate; • delays in reaching agreement on acceptable terms with clinical trial sites or other third-party vendors, the terms of which can be subject to extensive negotiation and may vary significantly among different clinical trial sites or vendors; • delays in identifying, recruiting and training suitable clinical investigators; • delays in obtaining required Institutional Review Board, or IRB, approval at each clinical trial site; • imposition of a temporary or permanent clinical hold by regulatory agencies for a number of reasons, including after review of an IND or amendment, CTA or amendment, or equivalent application or amendment; as a result of a new safety finding that presents unreasonable risk to clinical trial participants; a negative finding from an inspection of our clinical trial operations or study sites; developments on trials conducted by competitors for related technology that raises FDA, EMA or any other regulatory authority concerns about risk to patients of the technology broadly; or if the FDA, EMA or any other regulatory authority finds that the investigational protocol or plan is clearly deficient to meet its stated objectives; • delays in identifying, recruiting and enrolling suitable patients to participate in our clinical trials, and delays caused by patients withdrawing from clinical trials or failing to return for post-treatment follow-up; • difficulty collaborating with patient groups and investigators; • failure by third parties or us to adhere to clinical trial requirements; • failure to perform in accordance with the FDA’s or any other regulatory authority’s good clinical practices, or GCPs, requirements, or applicable EMA or other regulatory guidelines in other countries; • occurrence of adverse events associated with the product candidate that are viewed to outweigh its potential benefits; • changes in regulatory requirements and guidance that require amending or submitting new clinical protocols; • changes in the standard of care on which a clinical development plan was based, which may require new or additional trials; • the cost of clinical trials of our product candidates being greater than we anticipate; • clinical trials of our product candidates producing negative or inconclusive results, which may result in our deciding, or regulators requiring us, to conduct additional clinical trials or abandon development of such product candidates; • transfer of manufacturing processes to larger-scale facilities operated by CMOs or by us, and delays or failure by our CMOs or us to make any necessary changes to such manufacturing process; and • delays in manufacturing, testing, releasing, validating, or importing/exporting sufficient stable quantities of our product candidates for use in clinical trials and for use in regulatory filings or the inability to do any of the foregoing. Any inability to successfully initiate or complete clinical trials could result in additional costs to us or impair our ability to generate revenue. In addition, if we make manufacturing or formulation changes to our product candidates, we may be required to or we may elect to conduct additional studies to bridge our modified product candidates to earlier versions. Clinical trial delays could also shorten any periods during which our products have patent protection and may allow our competitors to bring products to market before we do, which could impair our ability to successfully commercialize our product candidates and may harm our business and results of operations.