Naturally selected CD7 CAR-T therapy without genetic editing demonstrates significant antitumour efficacy against relapsed and refractory acute myeloid leukaemia (R/R-AML)

BACKGROUND: The survival rate for patients with relapsed and refractory acute myeloid leukaemia (R/R-AML) remains poor, and treatment is challenging. Chimeric antigen receptor T cells (CAR-T cells) have been widely used for haematologic malignancies. Current CAR-T therapies for acute myeloid leukaemia mostly target myeloid-lineage antigens, such as CD123 and CD33, which may be associated with potential haematopoietic toxicity. As a lineage-specific receptor, CD7 is expressed in acute myeloid leukaemia cells and T cells but is not expressed in myeloid cells. Therefore, the use of CD7 CAR-T cells for R/R-AML needs to be further explored. METHODS: In this report, immunohistochemistry and flow cytometry were used to analyse CD7 expression in clinical samples from R/R-AML patients and healthy donors (HDs). We designed naturally selected CD7 CAR-T cells to analyse various functions and in vitro antileukaemic efficacy based on flow cytometry, and xenograft models were used to validate in vivo tumour dynamics. RESULTS: We calculated the percentage of cells with CD7 expression in R/R-AML patients with minimal residual disease (MRD) (5/16, 31.25%) from our institution and assessed CD7 expression in myeloid and lymphoid lineage cells of R/R-AML patients, concluding that CD7 is expressed in T cells but not in myeloid cells. Subsequently, we designed and constructed naturally selected CD7 CAR-T cells (CD7 CAR). We did not perform CD7 antigen knockdown on CD7 CAR-T cells because CD7 molecule expression is naturally eliminated at Day 12 post transduction. We then evaluated the ability to target and kill CD7(+) acute myeloid leukaemia cells in vitro and in vivo. Naturally selected CD7 CAR-T cells efficiently killed CD7(+) acute myeloid leukaemia cells and CD7(+) primary blasts of R/R-AML patients in vitro and significantly inhibited leukaemia cell growth in a xenograft mouse model. CONCLUSION: Naturally selected CD7 CAR-T cells represent an effective treatment strategy for relapsed and refractory acute myeloid leukaemia patients in preclinical studies.