CCR9 and acute lymphoblastic leukemia: These studies have confirmed that various factors lead to the upregulation of CCR9, such as TNF-α, which promotes CCR9 expression in human breast cancer MCF-7 cells [6], Notch signaling has been observed to induce CCR9 upregulation, which plays a vital role in T-lineage acute lymphoblastic leukemia (T-ALL) [7].