Human germline gene editing is often debated in hypothetical terms: if it were safe and efficient, on what further conditions would it then be ethically acceptable? This paper takes another course. The key question is: how can scientists reduce uncertainty about safety and efficiency to a level that may justify initiation of first-time clinical trials? The only way to proceed is by well-designed preclinical studies. However, what kinds of investigation should preclinical studies include and what specific conditions should they satisfy (...) in order to be considered well-designed? It is argued that multispecies and multigenerational animal studies are needed as well as human embryo editing without implantation. In order to be possible to translate to first-time clinical trials, animal studies need to satisfy strict conditions of validity. Moreover, embryo studies intended for translation to first-time clinical trials need to correspond to the animal studies in experimental design. Only in this way can uncertainty about risk for harm and prospect of benefit in first-time clinical trials be reduced to a modest level. If uncertainty is not reduced to such a level, first-time clinical trials in germline gene editing should not be initiated. (shrink)

BackgroundClustered Regularly Interspaced Short Palindromic Repeats-associated technology may allow for efficient and highly targeted gene editing in single-cell embryos. This possibility brings human germline editing into the focus of ethical and legal debates again.Main bodyAgainst this background, we explore essential ethical and legal questions of interventions into the human germline by means of CRISPR-Cas: How should issues of risk and uncertainty be handled? What responsibilities arise regarding future generations? Under which conditions can germline editing measures be therapeutically legitimized? For this (...) purpose, we refer to a scenario anticipating potential further development in CRISPR-Cas technology implying improved accuracy and exclusion of germline transmission to future generations. We show that, if certain concepts regarding germline editing are clarified, under such conditions a categorical prohibition of one-generation germline editing of single-cell embryos appears not to be ethically or legally justifiable.ConclusionThese findings are important prerequisites for the international debate on the ethical and legal justification of germline interventions in the human embryo as well as for the harmonization of international legal standards. (shrink)