These observations suggest that CCR1-, CXCR4-, and possibly CCR3-mediated signaling is important for the regulation of MSC proliferation in cocultures, and these results further illustrate that this bidirectional cytokine-mediated crosstalk between MSCs and AML cells affect not only the AML cells but also the MSCs. Here, CXCR4 is linked to acute myeloid leukemia.