Integrated genomic and single-cell transcriptomic analyses reveal clonal evolution and immune signature in donor cell leukemia after haploidentical allogeneic hematopoietic stem cell transplantation.

The pathogenesis of donor cell leukemia (DCL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is unclear and likely multifactorial. Leukemic transformation of healthy donor HSCs in recipient's bone marrow microenvironment provides a useful in vivo model for investigating the mechanisms involved in leukemogenesis. Here, we report a rare case of late-onset DCL developing in a recipient. Whole-genome sequencing indicates that donor-derived cells harboring clonal hematopoiesis of indeterminate potential (CHIP)-associated genetic alterations expand and eventually transform to full-blown AML via acquisition of additional somatic mutations within the recipient's bone marrow microenvironment. The 10× single-cell RNA sequencing reveals the abundance of GMP-like cells with a specific transcriptional signature in DCL. Moreover, impaired immune surveillance, including dysfunction of cytotoxic T lymphocytes (CTLs) and decreased number of canonical NK cells, is discovered in DCL. Our data add valuable information to the current understanding of the mechanisms of DCL.