Luigi Naldini, MD, PhD, San Raffaele Telethon Institute for Gene Therapy, Milano, Italy, talks on the toxicity associated with chemotherapy or radiotherapy-based conditioning prior to hematopoietic stem cell (HSC) gene therapy in hematological diseases. Prof. Naldini underlines the importance of exploring strategies to reduce the short-term and long-term toxicity of these regimens, as well as to assess milder conditioning strategies. This interview took place at the Transplantation & Cellular Therapy (TCT) Meetings of ASTCT™ and CIBMTR® 2022 in Salt Lake City, Utah.