T cell Immune Escape in Blast Crisis Transformation of Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) may transform from a chronic phase (CP) into blast crisis (BC), which is often incurable. Herein, we report that miR-142 deficit acquired by T lymphocytes contributes to BC transformation by promoting immune escape. We observe that T cells of BC patients lack miR-142 and are fewer and exhausted compared with CP patients. Similarly, BC miR-142−/−/BCR/ABL+/+ mouse presents with T lymphopenia compared with the CP miR-142+/+/BCR/ABL+/+ mouse. In the BC mouse, miR-142 deficit impairs thymic differentiation of lymphoid-primed multipotent progenitors (LMPP) into mature T cells and redirects them toward myeloid lineage. The fewer mature T cells in the BC mouse are enriched with exhausted T effectors. MiR-142 deficit, driven by leukemic blasts-secreted inflammatory cytokines (i.e., IL-6), induces T cell hypofunction by preventing the metabolic reprogramming that allows activated T cells to thrive and expand. This ultimately results in an increase in T cell spontaneous apoptosis and BC immune escape. In fact, NSG mice transplanted with BC CML LSKs and miR-142 KO T cells had shorter survival than mice transplanted with BC CML LSKs and miR-142 wild-typewt T cells. Conversely, BC patient-derived xenograft (PDX) mice receiving autologous T cells and synthetic miR-142 lived longer than those receiving autologous T cells and scramble RNA. Combination of tyrosine kinase inhibitors (TKI) plus synthetic miR-142 and/or PD-1 antibody induced a prolonged survival compared to TKI alone, suggesting that harnessing the host immune system with synthetic miR-142 and immunocheckpoint inhibitors along with BCR/ABL inhibition may provide novel therapeutic opportunities. Bone marrow (BM) LMPPs from miR-142+/+, miR-142−/−, miR-142+/+BCR-ABL (CP CML), and miR-142−/−BCR-ABL (BC CML) mice (BCR-ABL was induced for two week by tet-off) were sorted for scRNA-seq.