Current drug development research is generating many new approaches for using biologics in diverse therapeutic areas. However, the TeGenero disaster spurred a fundamental rethinking by regulators. Special rules have been developed for pre-clinical and first-in-human clinical trials. However, due to the complexity of these drugs, the severity of their potential side-effects, and their therapeutical areas, it is often difficult to plan first-in-human clinical trials. Defining relevant animal models for in vivo pre-clinical studies, calculating the initial start dose and maximal dose in human trials, and implementing appropriate safety-monitoring assessments remain a challenge. These factors should be considered in planning any first-in-human clinical trials.