Clonal Evolution Dissection Reveals High MSI2 Level Promotes Chemo-resistance in T-cell Acute Lymphoblastic Leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive cancer with resistant clonal propagation in recurrence. We performed high-throughput droplet-based 5'-single-cell RNA with paired T-cell receptor (scTCR) sequencing of paired diagnosis-relapse (Dx_Rel) T-ALL samples to dissect the clonal diversities. Two leukemic evolutionary patterns, "clonal shift" and "clonal drift" were unveiled. Targeted single-cell DNA sequencing of paired Dx_Rel T-ALL samples further corroborated the existence of the two contrasting clonal evolution patterns, revealing that dynamic transcriptional variation might cause the mutationally static clones to evolve chemo-resistance. Analysis of commonly enriched drifted gene signatures showed expression of the RNA-binding protein MSI2 was significantly upregulated in the persistent TCR clonotypes at relapse. Integrated in vitro and in vivo functional studies suggested that MSI2 contributed to the proliferation of T-ALL and promoted chemo-resistance through the posttranscriptional regulation of MYC, pinpointing MSI2 as an informative biomarker and novel therapeutic target in T-ALL.