Preemptive immunotherapy for KMT2A rearranged acute leukemias post-allogeneic stem cell transplantation

To the Editor: Rearrangements involving lysine methyltransferase 2A (KMT2A) represent recurrent genetic abnormalities in acute leukemia (AL), which are commonly associated with poor clinical outcomes.[1] Allogeneic hematopoietic stem cell transplantation (allo-HSCT) can improve long-term survival of KMT2A-rearranged (r) AL, but relapse remains the most important cause of transplant failure.[2] Measurable residual disease (MRD) can predict post-HSCT relapse, and MRD-directed therapies improve clinical outcomes.[3,4] Studies from our center indicate that monitoring the KMT2A level with real-time quantitative polymerase chain reaction (RT-qPCR) can predict relapse and survival post-allo-HSCT.[5,6] Patients positive for KMT2A have a significantly higher cumulative incidence of relapse (93.5% vs. 12.5%, P <0.001), a worse overall survival (OS: 12.5% vs. 77.8%, P <0.001), and a worse leukemia-free survival (LFS, 0 vs. 72.2%, P <0.001) compared with those continuously negative for KMT2A.[6] A previous study demonstrated that MRD-directed immunotherapy (i.e., preemptive immunotherapy), including donor lymphocyte infusion (DLI, with or without chemotherapy) or interferon (IFN)-α treatment, can prevent relapse and improve the long-term survival post-allo-HSCT.[3] Our pilot study enrolled 27 patients with KMT2A-r AL who received allo-HSCT in 2021; 21 received preemptive IFN-α treatment, and six received preemptive DLI treatment. The rates of KMT2A negativity were 33.3% and 66.7% for the two groups, respectively, but only eight patients (29.6%) achieved long-term LFS.[5] Due to the small number of patients, the efficacy of preemptive immunotherapy in patients with KMT2A-r AL remains uncertain. Therefore, we designed a cohort study to evaluate the efficacy of preemptive immunotherapy directed by KMT2A monitoring using RT-qPCR in patients with KMT2A-r AL post-allo-HSCT. From July 1, 2018, to March 15, 2024, 49 patients with KMT2A-r AL who had a positive MRD status post-allo-HSCT were enrolled. This study followed the principles of the Declaration of Helsinki and was approved by the Ethics Committee of Peking University People’s Hospital (No. 2018PHB103-01). Informed consent was obtained from all patients or their guardians. The final follow-up was conducted on May 31, 2024. The patients were primarily allocated to the immunotherapy group. Initially, patients were offered IFN-α treatment according to the protocol of the clinical trail (No. ChiCTR1800016741). Those who were either unsuitable for, or declined, IFN-α treatment, were administered DLI. Immunosuppressive agents were tapered or discontinued based on clinical indications. Patients in the control group had tapered or discontinued immunosuppressive agents. Patients who relapsed, had persisting or increasing MRD (e.g., KMT2A-r transcripts increased by 1-log) or regained a positive MRD status post-IFN-α treatment, could receive salvage DLI or vice versa [Supplementary Figure 1, https://links.lww.com/CM9/C524]. Detailed information on the immunotherapy is provided in the Supplementary Methods, https://links.lww.com/CM9/C524. MRD status was monitored at 1, 2, 3, 4.5, 6, 9, and 12 months post-intervention (in the immunotherapy group) or enrolment (in the control group) and then every six months thereafter. KMT2A levels were measured using real-time quantitative polymerase chain reaction (RQ-qPCR). KMT2A positivity was defined as detectable by RQ-qPCR. All of the samples with an undetectable fusion transcript had ≥100,000 copies of ABL to guarantee that at least a 10−5 transcript level could be detected. A KMT2A/ABL level <0.1% indicates a low-level MRD status, whereas a level ≥0.1% indicates a high-level MRD status.[5,6] The primary endpoint was relapse after enrolment. Secondary endpoints included achieving negative MRD status, LFS, OS, and nonrelapse mortality (NRM). There were 40 patients in the immunotherapy group and nine in the control group. The patient characteristics are summarized in Supplementary Table 1, https://links.lww.com/CM9/C524. In the immunotherapy group, 29 patients received IFN-α as initial therapy with a median of two cycles (range, 1–7 cycles), and eight received salvage DLI during follow-up. Eleven patients received DLI as initial therapy, and four received salvage IFN-α during follow-up. Four patients in the control group discontinued immunosuppressive therapy post-enrolment [Supplementary Figure 1, https://links.lww.com/CM9/C524]. The rate of achieving negative MRD status was 47.5% (95% confidence interval [CI], 32.5–62.5%) for the immunotherapy group vs. 11.1% (95% CI, 0–33.3%) for the control group (P = 0.047). The median time to achieving a negative MRD status post-immunotherapy was 32 days (range, 13–190 days), and the median duration of a negative MRD status was 104 days (range, 14–1430 days). In the control group, only one patient achieved a persistently negative MRD status 60 days post-enrolment. For the IFN-α and DLI groups, the rates of a negative MRD status were 48.3% and 45.5%, respectively (P = 0.554), with median times from treatment to achieving a negative MRD status of 32 days (range, 13–190 days) and 29 days (range, 21–212 days), respectively (P = 0.769). Among 29 patients who received IFN-α as initial therapy, 13 (59.1%) achieved a negative MRD status. The median time from IFN-α treatment to achieving a negative MRD status was 32 days (range, 13–190 days), and the median duration of a negative MRD status was 101 days (range, 14–1206 days). Six patients who relapsed or had a persistently positive MRD status underwent salvage DLI, but all had relapsed at the final follow-up. For the 11 patients who received DLI as the initial therapy, four (36.3%) achieved a negative MRD status. The median time from DLI to a negative MRD status was 38.5 days (range, 29–48 days), and the median duration of a negative MRD status was 300.5 days (range, 32–569 days) [Supplementary Figure 2, https://links.lww.com/CM9/C524]. For 19 patients with high-level KMT2A (≥0.1%), the rates of achieving a negative MRD status were 28.6% (95% CI: 7.1–50.0%) in the immunotherapy group and 0% in the control group (P = 0.252). For the seven patients with high-level KMT2A and receiving IFN-α as initial treatment, only one (14.3%) achieved a negative MRD status. Of the six patients with high-level KMT2A who received DLI as initial treatment, three (50.0%) achieved a negative MRD status within a median of 28 days (range, 21–32 days), and the median duration of a negative MRD status was 1000 days (range, 914–1430 days). Two patients with persistently positive MRD status achieved a negative MRD status post-salvage IFN-α therapy following DLI [Supplementary Figure 2, https://links.lww.com/CM9/C524]. The one-year cumulative incidence of relapse and LFS in the immunotherapy group was significantly higher than that in the control group, particularly for patients with high-level KMT2A [Supplementary Table 2, Supplementary Figures 3A–D, https://links.lww.com/CM9/C524]. For the patients receiving IFN-α or DLI as initial therapy, the one-year probability of relapse, NRM, LFS, and OS were all comparable between the two groups in patients with low-level KMT2A [Supplementary Table 2, Supplementary Figures 3E–H, https://links.lww.com/CM9/C524]. However, the DLI group had a significantly lower one-year relapse rate (16.7% vs. 100%, P = 0.006), a higher one-year LFS rate (83.3% vs. 0%, P <0.001), and a higher one-year OS rate (83.3% vs. 28.6%, P = 0.021) compared with those in the IFN-α group in patients with high-level KMT2A [Supplementary Table 2, Supplementary Figures 3J–K, https://links.lww.com/CM9/C524]. A total of 12 patients received IFN-α and DLI, that is, eight patients received salvage DLI post-IFN-α (IFN-DLI group) and four patients received salvage IFN-α post-DLI (DLI-IFN group) The one-year probability of relapse and LFS of the DLI-IFN group was lower than that of the IFN-DLI group [Supplementary Table 3, https://links.lww.com/CM9/C524]. For patients receiving IFN-α or DLI alone, the one-year relapse, NRM, LFS, and OS rates were similar [Supplementary Table S3, https://links.lww.com/CM9/C524]. In the multivariate analysis using the Cox proportional hazards model, immunotherapy were associated with a lower risk of relapse and superior LFS. Acute lymphoblastic leukemia (ALL) was associated with a higher risk of relapse, worse LFS and OS [Supplementary Table 4, https://links.lww.com/CM9/C524]. This study demonstrates that KMT2A-directed preemptive immunotherapy, including IFN-α and DLI, can reduce the risk of relapse in patients with KMT2A-r AL who received allo-HSCT. Our results showed that preemptive immunotherapy decreased the one-year relapse rate from 88.9% to 60.1% and improved LFS from 0 to 34.3% without increasing NRM or severe graft-versus-host disease (GVHD). In our previous study, 27 patients with KMT2A-r AL were enrolled and the rates of achieving a negative MRD status and LFS were 33.1% vs. 47.1% and 9.5% vs. 21.1%, respectively, for the IFN-α and DLI groups.[5] In this larger cohort, the immunotherapy group, particularly the IFN-α subgroup, had a significantly higher rate of MRD clearance and a superior LFS rate compared with those of the historical cohort. These improvements may be due to the dynamic KMT2A monitoring and wide use of IFN-α treatment in patients with a lower KMT2A level. However, despite current immunotherapeutic interventions, the relapse rate of patients with KMT2A-r AL and a positive MRD status post-allo-HSCT remains as high as 60%, which is significantly higher than that of KMT2A negative patients. Therefore, these patients should receive more effective interventions to prevent relapse. Recently, emerging targeted therapies, particularly menin inhibitors, have demonstrated efficacy in refractory and relapsed KMT2A-r acute myeloid leukemia, and may potentially prevent post-transplantation relapse.[7] However, advances in understanding the immune mechanisms for relapse of leukemia post-transplantation suggest that targeting and modulating immune cells can enhance the efficacy of immunotherapy.[8,9] In addition, for patients with ALL, alternative immunotherapies, such as bispecific T-cell engager or chimeric antigen receptor T-cell therapy may also improve clinical outcomes.[10,11] The graft-versus-leukemia (GVL) effect, closely associated with chronic GVHD, represents a primary mechanism through which IFN-α assists in the elimination of MRD.[8] In our study, the incidence of chronic GVHD was comparable between the DLI and IFN-α groups, suggesting that they had similar capacities to induce the GVL effect. In our study, the rate of severe chronic GVHD was only 6.5%, indicating that preemptive immunotherapy is safe for these patients. Nevertheless, this study has limitations. As this was a single-center, nonrandomized cohort study with limited sample size, the generalizability of the findings may be limited. Consequently, to further confirm the efficacy of IFN-α and DLI as preemptive immunotherapies for patients with KMT2A-r AL, larger, multi-center, randomized controlled trials are required. Thus, our study suggests that IFN-α and DLI are effective for patients with KMT2A-r AL and a positive MRD status post-allo-HSCT. However, more effective methods should be identified for these patients, particularly those with a high-level positive MRD status. Funding This work was supported by grants from the National Key Research and Development Program of China (No. 2017YFA0104500), CAMS Innovation Fund for Medical Sciences (CIFMS) (No. 2019-I2M-5-034), the Capital’s Funds for Health Improvement and Research (No. 2018-4-4089), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No. 81621001), the Program of the National Natural Science Foundation of China (Nos. 81900173 and 82170208), the Key Program of the National Natural Science Foundation of China (No. 81930004). Conflicts of interest None.