CCR9 and acute lymphoblastic leukemia: While the functional relevance of CCR5 in T-ALL progression has yet to be determined in vivo [114], very recent studies have demonstrated that targeting of CCR9, which is expressed in >70% of cases of T-ALL, has potent anti-leukemic activity in vivo in human T-ALL xenografts and could be a highly effective therapeutic strategy for T-ALL [244,245] (Figure 3).