The purpose of this guidance is to provide recommendations to sponsors interested in studying multiple versions of a cellular or gene therapy  product in an early-phase clinical trial  for a single disease.  Sponsors have expressed interest in gathering preliminary evidence of safety and activity using multiple versions of a cellular or gene therapy product in a single clinical trial.  Although multiple versions of a product can be studied together in a single clinical trial, each version is a distinct product that is generally submitted to FDA in a separate investigational new drug application (IND).  The objective of these early-phase clinical studies is to guide which version(s) of the product to pursue for further development in later-phase studies.  Thus, these studies are not intended to provide primary evidence of effectiveness to support a marketing application and generally are not adequately powered to demonstrate a statistically significant difference in efficacy between the study arms.  In this guidance, we, FDA, provide recommendations for studies that evaluate multiple versions of a cellular or gene therapy product, including how to organize and structure the INDs, submit new information, and report adverse events.