The Remission Status of AML Patients after Allo-Hct is Associated with a Distinct Single-Cell Bone Marrow T-cell Signature.

Acute myeloid leukemia (AML) is a hematologic malignancy for which allogeneic hematopoietic cell transplantation (allo-HCT) often remains the only curative therapeutic approach. However, incapability of T cells to recognize and eliminate residual leukemia stem cells might lead to an insuf fi cient graft-versus-leukemia (GVL) effect and relapse. Here, we performed single-cell RNA-sequencing (scRNA-seq) on bone marrow (BM) T lymphocytes and CD34 + cells of 6 patients with AML 100 days after allo-HCT to identify T-cell signatures associated with either imminent relapse (REL) or durable complete remission (CR). We observed a higher frequency of cytotoxic CD8 + effector and gamma delta ( gamma delta ) T cells in CR vs REL samples. Pseudotime and gene regulatory network analyses revealed that CR CD8 + T cells were more advanced in maturation and had a stronger cytotoxicity signature, whereas REL samples were characterized by in fl ammatory tumor necrosis factor/NF- kappa B signaling and an immunosuppressive milieu. We identi fi ed ADGRG1/GPR56 as a surface marker enriched in CR CD8 + T cells and con fi rmed in a CD33-directed chimeric antigen receptor T cell/AML coculture model that GPR56 becomes upregulated on T cells upon antigen encounter and elimination of AML cells. We show that GPR56 continuously increases at the protein level on CD8 + T cells after allo-HCT and con fi rm faster interferon gamma (IFN gamma ) secretion upon re-exposure to matched, but not unmatched, recipient AML cells in the GPR56 + vs GPR56 - CD8 + T-cell fraction. Together, our data provide a single-cell reference map of BM-derived T cells after allo-HCT and propose GPR56 expression dynamics as a surrogate for antigen encounter after allo-HCT.