BCL2L1 and mantle cell lymphoma: To first evaluate whether antiapoptotic Bcl-xL rendered MCL cells apoptosis-resistant to BTZ, we introduced Bcl-xL transgene into parental Z/Parent cells using retroviral particles, hereafter designated as Z/Parent-Bcl-xL cells, and evaluated their apoptosis in response to BTZ in comparison to their counterpart control Z/Parent cells and the highly resistant Z/500R cells.