{Reference Type}: Journal Article {Title}: Eμ-TCL1 adoptive transfer mouse model of chronic lymphocytic leukemia. {Author}: Fernandez Botana I;Gonder S;Klapp V;Moussay E;Paggetti J; {Journal}: Methods Cell Biol {Volume}: 188 {Issue}: 0 {Year}: 2024 {Factor}: 1.829 {DOI}: 10.1016/bs.mcb.2024.03.012 {Abstract}: Despite being the most common adult leukemia in the western world, Chronic Lymphocytic Leukemia (CLL) remains a life-threatening and incurable disease. Efforts to develop new treatments are highly dependent on the availability of appropriate mouse models for pre-clinical testing. The Eμ-TCL1 mouse model is the most established pre-clinical approach to study CLL pathobiology and response to treatment, backed by numerous studies highlighting its resemblance to the most aggressive form of this malignancy. In contrast to the transgenic Eμ-TCL1 model, employing the adoptive transfer of Eμ-TCL1-derived splenocytes in immunocompetent C57BL/6 mice results in a comparably rapid (e.g., leukemic development within weeks compared to months in the transgenic model) and reliable model mimicking CLL. In this chapter, we would like to provide readers with a thoroughly optimized, detailed, and comprehensive protocol to use the adoptive transfer Eμ-TCL1 model in their research.