CD33 and leukemia: As an example of the latter, Biondi et al recently showed that although anti-CD33 CAR equipped cytokine-induced killer (CIK) cells permanently expressing CXCR4R334X displayed enhanced retainment in the BM, these cells had inferior ability to reduce leukemia burden in vivo and prolong survival of KG-1 inoculated mice compared with anti-CD33 CAR CIK cells engineered to express CXCR4WT.