CD4 and lymphopenia: Although the scope of our pre-clinical study is to demonstrate the feasibility and efficacy of redirecting NK cells against CD4+ T-cell malignancies, the future case for a favorable safety profile of this novel immunotherapy is supported by the relatively short half-life of NK effector cells, the anticipated transient nature of treatment-induced CD4+ lymphopenia, the absence of CD4 on hematopoietic stem cells/progenitors, and previous studies with anti-CD4 monoclonal antibodies.