The harmonization of World Health Organization International Nonproprietary Names definitions for cell and cell-based gene therapy substances: when a name is not enough.

The World Health Organization (WHO) assigns International Nonproprietary Names (INN) to pharmaceutical substances, including advanced therapy medicinal products, to ensure that each substance is globally recognized by a unique name. The majority of INN are published in the WHO Drug Information in accordance with the nomenclature rules of the International Union of Pure and Applied Chemistry. However, advanced therapy medicinal products, and in particular cell therapy and cell-based gene therapy substances, cannot be defined by such chemical nomenclature. Instead, they are published together with a textual definition paragraph to unambiguously describe their characteristics. These definitions are an integral part of the INN nomenclature system, and their presence contributes to pharmacovigilance and patient safety, as they help to distinguish regulated substances from cell-based interventions that have no INN and are marketed without regulatory oversight. Particular attention is therefore allocated to these descriptive paragraphs, as they form the basis for defining the uniqueness of a particular cell substance. This review describes the INN nomenclature system for cell-based substances and focuses on the progress made by the WHO INN Programme to develop and harmonize these definition paragraphs, which is reflected in a newly revised INN application form for cell therapy substances.