Acute myeloid leukemia (AML) is a heterogeneous malignancy characterized by clonal expansion of myeloid progenitor cells that are arrested in differentiation. Allogeneic stem cell transplantation (alloSCT) is a potentially curative treatment of AML. In allogeneic stem cell transplantation (alloSCT), patients receive hematopoietic stem cells from a healthy donor to establish a new immune system. Despite the anti-tumor effect, relapses still occur in about half of all patients. AlloSCT can also lead to severe side effects. To reduce these side effects, patients are preferably transplanted with an HLA-matched donor. After HLA-matched alloSCT, donor T cells recognize minor histocompatibility antigens (MiHAs). MiHAs are polymorphic HLA-binding peptides on patient cells that are created by genetic differences between the patient and donor. The tissue distribution of MiHAs plays an important role in the type of clinical responses that are induced after alloSCT. While donor T cells directed against MiHAs on the patient’s malignant cells trigger anti-tumor responses, side effects occur when MiHAs on healthy non-hematopoietic tissues are attacked. MiHAs with hematopoietic-restricted expression are attractive targets for immunotherapy, as donor T cells against these antigens eliminate patient hematopoietic cells, including the malignant cells, while sparing patient’s non-hematopoietic tissues as well as healthy hematopoietic cells, which are of donor origin after alloSCT.
Using isolated T-cell clones from transplanted patients, we recently identified eleven new MiHAs with selective hematopoietic expression. Here, we sequenced and cloned T-cell receptors (TCRs) for four of these MiHAs, including LB-MYO1G-2M (HLA-C*03:03/C*03:04), LB-LILRB4-1G (HLA-B*07:02), LB-IL10RA-1R (HLA-B*07:02), and LB-ITGB2-1 (HLA-B*15:01). We isolated CD8 T cells from healthy donors, we knocked-out the endogenous TCRαβ genes by CRISPR/Cas9 and introduced the MiHA-specific TCRs by retroviral transduction.
T cells engineered with these TCRs bound cognate peptide-HLA tetramers and recognized patient EBV-B cells, while no reactivity was observed against donor EBV-B cells and skin fibroblasts. Furthermore, using a large panel of antibodies against early stem cell and myeloid progenitor markers, we demonstrated that TCR-T cells against LB-MYO1G-2M, LB-IL10RA-1R, and LB-ITGB2-1 induced specific lysis of patient-derived AML cells arrested at different stages in myeloid differentiation, while TCR-T cells for LB-LILRB4-1G specifically killed AML cells with more mature phenotypes.
These results highlight the therapeutic potential of TCR-T cells targeting hematopoietic-restricted MiHAs, supporting their development as novel immunotherapies to treat AML patients after HLA-matched alloSCT.