Donor-derived CD19-CAR-T therapy in combination with TKI cure uncommon CRLF2r- Mixed Phenotype Acute Leukemia lineage switch to Ph+ Acute Lymphoblastic Leukemia

Mixed phenotype acute leukemia (MPAL) is a rare hematologic malignancy characterized by the presence of a single population of cells expressing antigens of two or more lineages or by two or more populations of blast cells with different lineage features. Lineage transformation was seen in the patients diagnosed as MPAL with BCR::ABL1 (Philadelphia chromosome) or KMT2A rearrangements (KMT2Ar) occasionally. The Philadelphia chromosome-like (Ph-like) MPAL is rarely reported, existing literature mostly consists of case reports of CRLF2r -MPAL. The characteristics have not been studied in MPAL. Here, we report a rase case with refractory CRLF2r - MPAL who relapsed early post-transplant developed lineage switch to Ph+ B-ALL. Insights P2RY8::CRLF2r leukemia may lineage switch because of CRLF2 gene associated plasticity escaping therapy-related immune pressure. The Ph- like leukemia and Ph+ leukemia probably do share a possibility of transition.