Background: Relapse post hematopoietic cell transplant (HCT) still remains a major challenge in patients with relapsed/refractory (R/R) leukemia. Chimeric antigen receptor modified T cell (CAR-T) reducing leukemia burden and unrelated cord blood (UCB) having better anti-tumor effect than adult lymphocytes have well been recognized. It has also been proven, meanwhile, that antileukemia capacity based on NK allo-reactivity is potent in TCRab-depleted haploidentical HCT (TDH) because of high dose of NK cell infusion and reduced use of anti-GVHD medicines. Thus, we hypothesized that integration of multipronged approach including CAR-T, T/NK alloreactivity of UCB, and haplo-NK alloreactivity of TDH can synergistically eradicate leukemia cells by multiple cellular mechanisms in peri-graft period to prevent relapse. Hence, we developed a novel CAR-T-UCB-TDH protocol.

Objective: To evaluate the effect of preventing relapse and safety of CAR-T-UCB-TDH triple cellular therapy.

Methods: A total of 25 R/R leukemia patients who were enrolled in the current study in our center from August 2020 to July 2024 were analyzed, with M:F of 15:10 and median age of 8 years (22 children/adolescents, 3 adults). Radiation-free conditioning regimen consisted of regular Busulfan, Cyclophosphamide, Fludarabine and Thiotepa. TCRab T cells were depleted by Miltenyi system. CAR-T cells were infused first for induction of deep leukemia remission before TDH. UCB was infused before and/or after TDH. No GVHD prophylaxis was given. Patients' characteristic and treatment details were included in Table. Briefly, 18 patients had B-ALL, 3 T-ALL, and 4 AML; with 10 CR1, 11 CR2 and 4≥CR3 or disease progress; 23 patients received 1st HCT, one 2nd HCT, and one 3rd HCT.

Results: 22 patients received CAR-T as planned. 3 patients did not receive CAR-T due to economic factors or no suitable antigen targets. 7 of 12 patients with positive molecular MRD (Mol-MRD) test prior to CAR-T achieved negative Mol-MRD test after CAR-T. Following CAR-T, 12 patients received UCB on a median of 16 (14-46) days before TDH (pre-UCB), 7 patients received UCB 3 day after TDH (post-UCB), and 6 patients received both pre- and post-UCB. Low grade fever and grade II skin GVHD-like rash occurred in two patients 6-10 days after pre-UCB, which resolved with low-dose steroid, and one of whom had 12.1% UCB chimerism detected in blood 7 days after pre-UCB. Among 6 patients with positive Mol-MRD before pre-UCB, 4 patients had decreased MRD after pre-UCB. 3 patients still had positive Mol-MRD after TDH conditioning, and all 3 had negative Mol-MRD after post-UCB. One month after TDH, all 25 patients were Mol-MRD negative (except patient #23 of whom Mol-MRD test was unavailable but flow-MRD negative). Only one 3rd HCT patient died of severe VOD. No patient had leukemia relapse. With 293 median follow-up days (range 31-1345 days), all patients maintained full donor chimerism, with excellent overall survival (OS) equal to disease-free survive (DFS) at 96% (Figure 1).

Conclusion: Our preliminary results showed that triple cellular therapy consisting of CAR-T, UCB and TDH markedly prevented early post-HCT relapse. We believe that the promising early outcomes were a result of the three-pronged anti-leukemia force in peri-graft period. Further follow up will elucidate the long-term antileukemic effect and will be presented at the ASH meeting.

Disclosures

No relevant conflicts of interest to declare.

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2024
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