A study on the efficacy, safety and mechanism of venetoclax combined with CAR-T targeting CLL1 in the treatment of Acute Myeloid Leukemia

Abstract Objective: Venetoclax (VEN) monotherapy exhibits limited clinical benefits in refractory/relapsed acute myeloid leukemia (r/r AML). The aim of this study is to investigate the potential synergistic effect of VEN in combination with CLL1-targeting chimeric antigen receptort cells (CLL1 CART) in r/r AML patients and the mechanisms of VEN resistance. Methods: A total of 63 r/r AML patients were enrolled, with 33 receiving one week of VEN treatment prior to CLL1 CART cell preconditioning, while the remaining 30 were treated with alternative regimens without VEN. CLL1 CART cells were manufactured and rigorously quality-controlled by the Hematology Laboratory at Tianjin First Central Hospital. Efficacy and adverse reactions were assessed following CLL1 CART cell infusion, while expansion of CLL1 CART cells, cytokine release levels, and other indicators were closely monitored. In vitro, we employed CLL1-knockdown AML cell lines to evaluate VEN sensitivity. CLL1 expression levels were verified via PCR. The apoptosis and activity of the knockdown group and the control group were compared. To further explore the mechanism, transcriptomics analysis was conducted on both groups. Results: In the VEN+CLL1 CART cohort, 26 patients (78.8%) achieved complete remission / partial response (CR/PR), compared to 20 (66.7%) in the non-VEN group, with no statistically significant difference in response rates (P = 0.279). However, the VEN+CLL1 CART group exhibited significantly prolonged overall survival (OS) (P < 0.0001). For progression-free survival (PFS), there was no statistically significant difference between patients who had received VEN and those who had not (P = 0.188). In vitro studies revealed that CLL1 expression increased dose-dependently with VEN treatment but remained stable post-withdrawal. Notably, CLL1-knockdown cells demonstrated enhanced VEN sensitivity, evidenced by a reduced IC50 and elevated apoptosis rates (P<0.05). Transcriptomic analysis further identified significant downregulation of MCL-1 in CLL1-deficient cells, suggesting a potential mechanistic link to VEN susceptibility. Conclusion: The results of clinical retrospective studies show that the combination of VEN and CLL1 CART therapy can improve the OS of r/r AML patients. The results of cell experiments showed that CLL1-knockdown AML cells were more sensitive to VEN. These results support the hypothesis that VEN kills CLL1-negative AML, resulting in an increased CLL1 positive rate in the AML cell population and a better targeting effect of CLL1 CART.