Juliane Mietz, University Of Zurich, Zurich, Switzerland, provides an overview of mouse models currently in use for the pre-clinical study of immunotherapies, including cell line-derived xenografts (CDX) and patient-derived xenografts (PDX). CDX models are derived from established and easily accessible cell lines, which is beneficial for monitoring tumor growth and assessing chimeric antigen receptor (CAR) T-cell efficacy. PDX models consist of tissue from the patient’s tumor and will retain the pathophysiology of the patient. However the aforementioned models are modelled in immunocompromised mice and humanized mice models consisting of hematopoietic progenitor cells (HPCs) derived from fetal liver tissue or cord blood represent an alternative. This interview took place at the International Conference on Lymphocyte Engineering (ICLE) 2022.