Efficacy and safety of CAR-T therapy targeting CLL1 in patients with extramedullary diseases of acute myeloid leukemia

Abstract

Backgrounds

The incidence of extramedullary diseases (EMDs) in patients diagnosed with acute myeloid leukemia (AML) is approximately 10–20%. These patients exhibit a significantly distinct etiology, therapeutic response, and prognosis compared to patients without EMDs. CLL1 CAR-T therapy has been demonstrated satisfactory efficacy and safety in the treatment of refractory and relapsed AML patients. However, concerns have been raised regarding the potential impact of extramedullary niduses on the effectiveness of CLL1 CAR-T therapy.

Methods

A total of 47 patients were enrolled in this study, including 27 patients with isolated AML tumor bone marrow infiltration and 20 patients with both extramedullary and bone marrow infiltration of AML. CLL1 CAR-T cells were manufactured and subjected to rigorous quality control in the hematology laboratory of Tianjin First Central Hospital. The efficacy and adverse reactions were assessed following CAR-T cell infusion, while expansion of CAR-T cells, levels of cytokines releasing, and other indicators were closely monitored.

Results

Among the 20 patients with EMDs and the 27 individuals without EMDs, complete remission in bone marrow was achieved by 65.00% and 81.48% of patients, respectively. Meanwhile, among the patients with EMDs, 55.00% achieved complete remission while 10.00% achieved partial remission when assessing the efficacy of CLL1 CAR-T cells against extramedullary niduses. Although the overall survival, progression-free survival, and duration of remission period appeared to be shorter for patients with EMDs compared to those without EMDs, this difference did not reach statistical significance. The incidence rates of complications were comparable between both groups. Meanwhile, there were no significant differences observed in the levels of CAR-T cell expansion and accompanying cytokines release between patients with and without EMDs.

Conclusions

Our study findings have demonstrated the efficacy of CLL1 CAR-T therapy in the treatment of AML patients with EMDs, while also indicating manageable occurrence rates of complications within a tolerable range. The CLL1 CAR-T therapy, serving as an ideal strategy for AML patients irrespective of the presence of EMDs, effectively ameliorates the conditions of AML patients and provides them with an opportunity to undergo curative hematopoietic stem cell transplantation while significantly enhancing their prognosis.

Introduction

Acute myeloid leukemia (AML) is a hematologic cancer that displays the rapid growth of abnormal myeloid cells within the bone marrow, resulting in compromised generation of healthy blood cells.

Approximately 10–20% of AML patients exhibit extramedullary infiltration, characterized by a diverse range of manifestations including cutaneous ecchymosis, lymphadenopathy, central nervous system (CNS) symptoms such as headaches and visual disturbances, hepatosplenomegaly, and potential involvement of other organs such as the lungs, kidneys, or gastrointestinal tract [1, 2]. The prognosis for AML patients is frequently worse and the disease course more aggressive when extramedullary infiltration is present [3]. Treatment of AML patients with extramedullary diseases (EMDs) poses challenges due to the advanced disease stage and may require a comprehensive approach involving chemotherapy, radiation therapy, and potentially hematopoietic stem cell transplantation (HSCT) [4]. Despite the significant advancements in such therapeutic approaches, which have greatly improved the prognosis of AML patients with EMDs, there remains a subset of patients with relapsed or refractory disease who fail to achieve long-term survival [5].

The Chimeric Antigen Receptor T-cell therapy (CAR-T) has emerged as a promising approach in recent years for the treatment of hematologic malignancies. By genetically modifying patients’ T cells to express the chimeric antigen receptor targeting specific antigens on cancer cells, CAR-T therapy harnesses the immune system’s power to recognize and eliminate malignant cells [6]. The human C-type lectin-like molecule 1 (CLL1) is a cell surface antigen expressed on leukemic stem cells and myeloid blasts in AML, but it is not significantly expressed on hematopoietic stem cells. This characteristic has attracted attention as CLL1 could potentially serve as a target for CAR-T therapy in AML [7]. Compared to control T cells, CLL1 CAR-T cells effectively eradicated CLL1-positive AML cell lines and primary tumor cells in vitro. Additionally, CLL1 CAR-T cells exhibited significant anti-tumor activity in human xenograft mouse models [8].

Subsequently, several clinical trials have demonstrated the efficacy and safety of CLL1 CAR-T treatment in patients with AML [9,10,11,12]. Furthermore, our center’s latest findings indicate that over 70% of patients achieved complete remission through CAR-T therapy, leading to long-term survival after subsequent bridged HSCT [13]. However, the application of CAR-T therapy in AML cases complicated by extramedullary infiltration poses distinct challenges compared to patients with solely bone marrow invasion and has not been comprehensively documented thus far.

Here, we initially presented the report to evaluate the efficacy and safety of CLL1 CAR-T therapy in treating AML patients with extramedullary diseases, focusing on both bone marrow remission rate and extramedullary nidus. Additionally, we assessed the occurrence and severity of side effects associated with CAR-T therapy. This study aims to summarize the value of CLL1 CAR-T therapy in AML patients with EMDs and provide an optimal therapeutic option for them.

Materials and methods

Study design and population

The CLL1 CAR-T therapy trial enrolled a total of 51 patients, with 4 patients being excluded due to CAR-T cells dysfunction, disease progression, or severe infection. Ultimately, a prospective cohort of 47 patients was enrolled in our study conducted from July 2020 to February 2024. Among them, bone marrow infiltration was exclusively observed in AML tumors for 27 patients, while the simultaneous presence of EMDs and bone marrow involvement was noted in another 20 patients (Fig. 1). The diagnosis of all patients was conducted in accordance with the diagnostic criteria established by the World Health Organization. This study has obtained approval from the institutional review board of Tianjin First Center Hospital and has been duly registered with the China Clinical Trial Registration Center (Clinical Trial Number: ChiCTR2000041054). The patients participating in this study have all completed informed consent forms in accordance with the principles outlined in the Declaration of Helsinki.

Fig. 1

Identification of EMDs among patients with AML treated with CLL1 CAR T-cell therapy

CAR-T cell manufacturing and management

The CAR-T cells were produced in the laboratory of the Department of Hematology at Tianjin First Center Hospital. The preparation process of the CAR-T cell involved T cell isolation and activation, lentivirus transfection, expansion and culturing, quality control, cellular infusion, monitoring, and follow-up. Moreover, all patients underwent lymphodepletion chemotherapy with a 3-day regimen of fludarabine (25 mg/m²/day) and cyclophosphamide (300 mg/m²/day) prior to the infusion of CAR-T cells. All patients received comprehensive inpatient care throughout the CAR-T therapy process.

Assessment of efficiency

The response of patients to CAR-T therapy was categorized into bone marrow response and EMDs response. Flow cytometry was employed to assess the level of minimal residual diseases (MRD) in the bone marrow or cerebrospinal fluid, while the EMDs response was evaluated through imaging examinations such as B-mode ultrasound, computerized tomography, magnetic resonance imaging, and positron emission tomography-computed tomography (PET-CT). The assessment of response to therapy was determined based on the criteria established by the guidelines of the National Comprehensive Cancer Network for AML [14].

Evaluation of side effects

Cytokine release syndrome (CRS) should be taken into consideration if any of the following indications are observed: body temperature ≥ 38℃; hypotension (systolic blood pressure < 90mmHg); inadequate arterial oxygen saturation (< 90%); compromised organ function, which was classified into 5 grades. The immune effector cell-associated neurotoxicity syndrome (ICANS) was categorized into grades 1 to 4 based on the assessment of patients’ neurological function, presence or absence of elevated intracranial pressure, and occurrence of seizures or limb weakness. Furthermore, the evaluation of other hematologic toxicities and organ damages related to CAR-T therapy was conducted using the grading criteria specified in NCICTCAE 4.0 [15].

Assessments of laboratory indices

Flow cytometry was utilized to assess the ratios of CAR-T cells within CD3-positive T lymphocytes present in peripheral blood. The levels of cytokines, including interleukin-2 (IL-2), IL-4, IL-6, IL-10, tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), C-reactive protein (CRP), and ferritin were quantified in accordance with the manufacturer’s instructions to evaluate the severity of cytokine storm observed in patients undergoing CAR-T therapy.

Statistical analysis

The characteristics of patients and diseases were primarily summarized through descriptive statistics. The utilization of differentiation analysis was employed to illustrate the significance of characteristics among patients with and without EMDs. We conducted an analysis using a modified Levene test to evaluate the equality of variances. Subsequently, appropriate statistical tests were chosen based on whether group variances were equal or unequal - either employing a T-test with equal variances or an Aspin-Welch unequal-variance T-test. In instances where data did not follow a normal distribution, we prioritized utilization of the Mann-Whitney test. Overall survival (OS) denoted the period commencing from the infusion of CAR-T cells until the date of decease, or last follow-up. Progression-free survival (PFS) was determined as the period of time between the start of treatment and the onset of disease progression or death. Duration of remission (DOR) referred to the time between achieving complete remission and experiencing relapse or death without any documented relapse. Non-recurrent mortality (NRM) referred to the occurrence of deaths caused by factors unrelated to disease recurrence or progression. The estimation of medians for OS, PFS, DOR, and NRM was conducted using the Kaplan-Meier methodology. The statistical analysis was performed utilizing GraphPad Prism V.9, with a significance level set at P < 0.05 to determine statistical significance.

Results

Characteristics of AML patients with and without EMDs

The study recruited a total of 47 patients diagnosed with AML between January 2021 and March 2024. This cohort comprised of 20 patients presenting EMDs, while the remaining 27 patients exhibited localized disease within the bone marrow. Among these individuals, CNS involvement was observed in 12 cases, extensive skin involvement in two cases, and liver and spleen infiltration in 3 cases. Additionally, other organs such as the ovary, kidney, and breast infiltration were also observed. The cohort comprised of 24 males and 23 females, with a median age of 35 years (range: 17–73). In comparison to the 30 patients who experienced relapsed disease once or multiple times, a total of 17 patients have never achieved disease remission. The identification of 20 patients with a complex karyotype was based on the presence of three or more chromosomal abnormalities at the time of diagnosis. 13 patients had a medical history of myelodysplastic syndrome (MDS) or myeloproliferative neoplasm (MPN). At the time of disease diagnosis, patients were classified into high-risk group (n = 23), intermediate-risk group (n = 15), and low-risk group (n = 9) based on the AML risk stratification classified by National Comprehensive Cancer Network. 14 patients had a history of undergoing allo-HSCT treatment, while one patient had a previous experience with auto-HSCT treatment. The median number of prior lines of therapy was 4, ranging from 2 to 13. The Eastern Cooperative Oncology Group (ECOG) score was employed to evaluate the physical condition of patients, with 37 patients presenting an ECOG score of 0–2, while 10 patients exhibited a score of 3–4. The median percentage of tumor burden observed in the bone marrow among participants included in this study was 27.00%, with a range spanning from 2.32 to 95.02%. Meanwhile, the median CNS tumor cells percentage detected through flow cytometry among patients with CNS involvement was 21.07%, ranging from 8.24 to 39.56%. In addition, the proportion of CLL1-positive cells among all tumor cells in patients ranged from 50.20 to 99.48%, with a median rate of 89.60%. Furthermore, the dosage of CLL1 CAR-T cells administered ranged from 0.5 to 3.0 × 10⁶/kg, with a median value of 1.5 × 10⁶/kg. The baseline characteristics data of the patients were comprehensively presented in Table 1, encompassing a comparison between patients with and without EMDs. The findings indicated that there was no statistically significant disparity in fundamental characteristics between patients belonging to these two groups.

Table 1 The characteristics of patients enrolled and the comparison between patients with and without EMDs

Response comparison of patients with and without EMDs to CLL1 CAR-T cells

The systemic assessment was conducted on all patients between Day 12–16, which included the evaluation of CNS and bone marrow tumor burden using flow cytometry. However, imaging examinations for patients with EMDs may be postponed until the patients’ physical condition has improved. In terms of bone marrow assessment of patients, complete remission (CR) was achieved in 35 out of 47 patients (Table 2). In detail, the remission rate of patients without EMDs was 81.48% (22/27), with 15 showing minimal residual disease (MRD) negativity and 7 showing MRD positivity in CR. In contrast, the bone marrow remission rate of patients with EMDs was 65.00% (13/20), with 6 exhibiting MRD negativity and 7 displaying MRD positivity in CR. Furthermore, extramedullary nidus regression was achieved in 11 out of the total of 20 patients. Two patients achieved CR in bone marrow but only partial remission in EMDs, therefore, they were not included in the group that achieved complete alleviation. The findings indicated that CLL1 CAR-T cells effectively mitigate the tumor burden in the bone marrow of patients, while exhibiting a comparatively lower remission rate for extramedullary nidus. The PET-CT imaging comparison presented in Fig. 2 demonstrates the remission of extramedullary nidus in 2 patients before and after CLL1 CAR-T cell therapy, indicating a significant efficacy of CAR-T therapy in alleviating extramedullary infiltration of AML. After achieving remission from CLL1 CAR-T therapy, 28 patients underwent bridge HSCT treatment, while salvage HSCT treatment was administered to 2 patients who did not respond to CAR-T therapy. Meanwhile, the subsequent chemotherapy was administered to 7 and 5 patients, while only supportive care was provided to 3 and 2 cases following CLL1 CAR-T therapy in groups with EMDs and without EMDs respectively (Table 2).

Table 2 Patients’ response to CLL1 CAR-T therapy and the subsequent therapy they received

Fig. 2

The PET-CT imaging comparison in 2 patients before and after CLL1 CAR-T cell therapy. The red circles indicate the most representative sites of extramedullary disease, which were nearly eradicated following CLL1 CAR-T therapy. MTV, metabolic tumor volume; CMR, complete metabolic response

Long-term survival and outcomes of patients with and without EMDs

The median follow-up duration for this cohort is 272 days, ranging from 58 to 911 days. The patients enrolled in this study had a median OS of 466 days and a median PFS of 282 days. Specifically, the OS of patients with EMDs was comparable to those with isolated bone marrow involvement (301 vs. 586 days, P = 0.31), Similarly, the PFS of patients with EMDs was also shorter but without statistics difference (258 vs. 341 days, P = 0.25). Meanwhile, we observed that the OS rates at 6 months and 1 year for patients with EMDs were 63.09% and 45.17%, respectively, whereas those for patients without EMDs were 82.60% and 66.72%. Additionally, patients with EMDs had significantly lower PFS rates at 6 months and 1 year compared to those without EMDs (74.29% vs. 85.64%, 37.14% vs. 44.86%). Similarly, the median DOR time of patients with EMDs were shorter than patients without EMDs (176 vs. 327 days, P = 0.06). The DOR was 6 months for 85.64% patients without EMDs, as well as for 47.17% patients with EMDs. Meanwhile, the DOR was 1 year for 47.17%for patients without EMDs and 23.58% with EMDs. The NRM rates of patients without and with EMDs were respectively 12.81% and 24.41% at 6 months, and 17.39% and 31.96% at 1 year (P = 0.52). Although there was no statistically significant difference in the analysis of these survival rates between the two groups, it appeared that patients with EMDs may have had a more unfavorable prognosis following CLL1 CAR-T therapy (Fig. 3).

Fig. 3

Long-term survival and outcomes of patients enrolled in this study, with the comparisons between EMDs patients and non-EMDs patients. (A, E) overall survival; (B, F) progression-free survival; (C, G) duration of remission; (D, H) non-recurrent mortality. The comparisons revealed no statistically significant differences in long-term survival and outcomes between the two groups

Side effects occurred during CLL1 CAR-T therapy

The most frequently observed adverse events associated with CLL1 CAR-T therapy are summarized in Table 3. The incidence of CRS was observed in 45 out of the total 47 patients, with severe CRS (Grade 3/4) being reported in 25 individuals. The incidence rate of CRS in patients with EMDs is comparable to that of patients without EMDs. Another significant complication is the occurrence of ICANS, which was observed in 10 out of 47 patients, with severe ICANS being observed in 3 patients. ICANS was respectively detected in 5 patients without EMDs and in 5 patients with EMDs, particularly among the subset of individuals with CNS involvement where ICANS was experienced by 4 out of 12 patients.

Table 3 Adverse events associated with CLL1 CAR-T treatment

The occurrence of granulocytopenia was observed in all 47 patients enrolled in this study, and 46 out of them experienced severe agranulocytosis (Grade 3/4). Additionally, 43 out of 47 patients exhibited anemia, while thrombocytopenia was observed in 44 individuals. However, it has been observed that there were 31, 32, and 28 patients presenting with pre-existing complications of granulocytopenia, anemia, and thrombocytopenia prior to lymphodepletion, potentially attributed to the administration of multiple chemotherapy drugs. Furthermore, infections were observed in a total of 40 individuals undergoing CAR-T therapy. Among these cases, bacterial infections occurred in 37 patients, viral infections affected 9 patients, and fungal infections were detected in 10 patients. The incidence rate of these hematologic toxicities and infection complications were demonstrated no significant difference between patients with and without EMDs. Additionally, there were 6 patients who experienced hemorrhage, 5 patients with cardiac insufficiency, 13 patients with hepatic insufficiency, 6 patients with renal insufficiency, and 31 patients with electrolyte disturbance during the treatment. However, all of these adverse events were effectively managed through symptomatic treatment.

Expansion of CAR-T cells and levels of accompanying inflammatory cytokines

The expansion of CLL1 CAR-T cells has been detected at various time points during the course of CAR-T therapy. The details of CAR-T cell expansion and the accompanying cytokine storm during CAR-T therapy are illustrated in Fig. 4. The duration of CAR-T expansion discussed in this study refers to the period during which the proportion of CAR-T cells exceeds 1% among CD3-positive T cells in peripheral blood. Compared to patients without EMDs, the duration of CAR-T expansion was similar in patients with EMDs (P = 0.08). However, patients who achieved CR had a longer duration of CAR-T cell persistence compared to non-responders to CAR-T therapy (P < 0.01, Fig. 4A). Likewise, the peak of CAR-T cell expansion and the area under the curve (AUC) of CAR-T cell expansion levels during treatment were comparable between patients with and without EMDs (P = 0.73,P = 0.93), while both were higher in patients who achieved CR compared to those who did not experience remission (P = 0.03,P = 0.02, Fig. 4B.C). The flow cytometry diagrams depicting the expansion of CAR-T cells in three patients with EMDs and three patients without EMDs are presented in Fig. 5. Meanwhile, we evaluated the peripheral blood for elevated levels of classical cytokines, including CRP, IL-2, IL-4, IL-6, IL-10, TNF-α, IFN-γ and Ferritin to demonstrate the severity of inflammatory storm associated with CAR-T therapy in patients’ bodies. Subsequently, a comparative analysis was carried out, revealing no significant differences in the aforementioned indexes between the two groups (Fig. 4D).

Fig. 4

Comparative analysis of expansion of CLL1 CAR-T cells and levels of accompanying inflammatory cytokines. (A) The duration of CAR-T cell expansion in a diverse patient population, including those with and without EMDs, as well as individuals experiencing remission or no response to CLL1 CAR-T therapy; (B) Comparison of CAR-T cell expansion levels during treatment as assessed by the area under the curve (AUC); (C) Comparative analysis of CAR-T cell expansion peak in diverse individuals; (D) Comparison of the peak levels of multiple cytokines, including IL2, IL4, IL6, IL10, TNF-α, IFN-γ, CRP, and Ferritin in peripheral blood serum. Our findings indicated that there were no statistically significant differences in CAR-T cell expansion and the levels of accompanying inflammatory cytokines

Fig. 5

The representative CAR-T cell expansion figures of 3 patients with EMDs (A) and 3 patients without EMDs (B). The CAR-T cell expansion was demonstrated to patients 1, 2, and 3 on Day + 3 and + 10 who had EMDs, whereas patients 4, 5, and 6 did not have EMDs

Discussion

The tumor cells infiltrating extramedullary tissues demonstrated enhanced drug resistance in comparison to those confined within the bone marrow. The current literature suggests a potential correlation with specific cellular adhesion molecules, interactions between chemokine receptors and ligands [16]. For example, leukemia cells frequently exhibit upregulated expression of adhesive molecules such as CD56, which facilitates cancer cell adherence by binding to tissues expressing this molecule, including adipose tissue, the gastrointestinal tract, the brain, the testicular region, and skeletal muscle [17]. Another molecule involved in cell adhesion is CD11b, which facilitates interactions between cells and the extracellular matrix, potentially influencing extramedullary localization in cases of acute myeloid leukemia with monoblastic/myelomonocytic differentiation [18]. Meanwhile, a study involving 1273 AML patients has determined that the expression of CD36 significantly facilitates the extramedullary distribution of AML blasts, augments the incidence of relapse subsequent to intensive chemotherapy, and diminishes patients’ prognosis [19]. Furthermore, notable distinctions were observed in the fields of molecular biology and cytogenetics. The prevalence of NPM1, FLT3-ITD, and PTPN11 mutations is higher among patients with EMDs, while inv(16)(p13;q22), t(16;16)(p13;q22), t(8;21)(q22;q22), and translocations involving 11q23 are more commonly found in patients with EMDs [5, 20]. The incidence of EMDs in AML patients enrolled in this study was 42.55% (20/47), which exceeds the percentage observed among newly diagnosed AML patients, primarily due to the higher likelihood of EMDs in patients with relapsed or refractory disease.

Similarly, the clinical characteristics, therapeutic effect and prognosis of patients with and without EMDs also have difference. Patients diagnosed with AML and experiencing EMDs exhibited notably elevated levels of white blood cell count, peripheral blood blasts, bone marrow blasts, and lactic dehydrogenase. Limited by the number of enrolled patients, there were no statistically significant differences in clinical characteristics between patients with and without EMDs in our study. However, it can be primarily concluded that EMDs-patients had a weaker baseline physical condition compared to those without EMDs due to the impact of extramedullary nidus. Compared to AML patients without EMDs, those with EMDs face greater challenges in achieving remission following induction therapy and experience significantly higher rates of early mortality [2]. The use of involved-field radiotherapy was considered the preferred treatment for patients with isolated myeloid sarcoma, given its demonstrated sensitivity. Additionally, surgical decompression may be employed in cases with tumor-mass effects [21]. The analysis conducted by Tsimberidou and his colleagues revealed that AML patients with EMDs achieved a remission rate of 65% when treated with conventional therapeutic regimens based on anthracycline or cytarabine, resulting in a median overall survival of 20 months [22]. Moreover, there were additional targeted therapies available for patients who are not suitable candidates for intensive treatment, such as hypomethylating agents azacitidine and decitabine, B-cell lymphoma 2 inhibitors venetoclax, and IDH1/2 inhibitor enasidenib [23,24,25]. The utilization of HSCT was regarded as the exclusive approach to alleviate the detrimental impact of extramedullary infiltration, and the 5-year OS rates in AML patients with EMDs were comparable to those without EMDs who underwent HSCT [26]. However, the presence of extramedullary nidus has led to a reduction in the utilization rate of HSCT among patients with EMDs compared with those without EMDs included in our study. Therefore, it is imperative to develop innovative therapeutic strategies for individuals with EMDs, with the aim of further augmenting both remission rates and long-term survival outcomes.

Patients with extramedullary disease, especially those with CNS infiltration, were initially excluded from early clinical trials of CAR-T therapy due to the unpredictable toxicities and efficacy. However, with advancements in preparation technology and exciting therapeutic effects achieved, CAR-T therapy has gradually been utilized in patients with extramedullary lesions across various hematological malignancies. The small-scale retrospective study conducted across multiple centers aimed to assess the efficacy and adverse effects of CAR-T therapy on B-cell lymphoma complicated by CNS involvement. The findings indicated that 73.3% of patients achieved remission with CD19-specific CAR-T therapy, while the median OS and PFS were 9 and 4 months, respectively. Moreover, the incidence of CRS and ICANS primarily focused on grade 1–2 occurrences [27]. Similarly, the analysis of CD19 CAR-T therapy for B-ALL also revealed that extramedullary involvement is an independent risk factor associated with reduced long-term survival and increased incidence of severe CRS/ICANS [28]. Moreover, the Chinese multi-center clinical trial showed that CD19 CAR-T therapy achieved comparable high response rates in both bone marrow and CNS leukemia, with lower recurrence rates and longer durations of remission specifically in patients with isolated CNS involvement [29]. Additionally, a series of reports have also demonstrated the successful reduction of tumor burden in extramedullary blasts through BCMA-based CAR-T therapy, achieving remarkable remission when compared to traditional chemotherapy regimens [30,31,32]. However, the presence of extramedullary infiltration serves as a significant risk factor for predicting early relapse or progression of multiple myeloma [33]. The application of researches in hematological malignant diseases has revealed significant differences in the efficacy and safety of CAR-T therapy between patients with and without EMDs. Therefore, the evaluation of CLL1 CAR-T therapy’s potential value and side effects in AML patients with EMDs is crucial for its broader application in the treatment of diverse AML patient populations.

The current study has only reported two cases of AML patients with EMDs who received infusion of CLL1 CAR-T cells, both of which were previously published in the phase I study conducted by our team [13]. Fortunately, one patient achieved MRD-negative CR following CLL1 CAR-T therapy and obtained long-term survival after undergoing bridged HSCT. In addition, another patient achieved remission through salvage HSCT despite exhibiting no response to CAR-T therapy [13]. The present study presents an initial comparative analysis of the efficacy and safety profiles between patients with and without EMDs. A total of 47 patients were enrolled, including 20 with EMDs, while the remaining 27 patients exhibited isolated bone marrow involvement exclusively. The baseline characteristics of the patients did not demonstrate any significant differences between the two groups. The CR rate in bone marrow was achieved in 65.00% (13/20), whereas the CR rate for extramedullary lesions was observed in 55.00% (11/20) of EMDs patients following CLL1 CAR-T therapy, which did not exhibit a statistically significant difference compared to the CR rate observed in 81.48% (22/27) of non-EMDs patients. The OS and PFS of EMDs patients were recorded as 258 and 301 days, respectively, both shorter than those without EMDs, but this difference was not statistically significant. The incidence of CRS was observed in 45 out of 47 patients, with severe CRS occurring in 25 individuals. Additionally, ICANS was observed in 10 patients, among whom 3 experienced severe ICANS. The most prevalent complications observed were hematological toxicities, including granulocytopenia, anemia, and thrombocytopenia, all of which exhibited occurrence rates exceeding 90%. However, it is noteworthy that hemocytopenia was universally observed prior to lymphodepletion due to the patients’ primary disease. The aforementioned side effects were observed in both groups without any statistically significant differences. Furthermore, the levels of CAR-T cell expansion and concomitant release of cytokines were comparable between patients with and without EMDs.

Conclusion

The findings of our study demonstrated the effectiveness of CLL1 CAR-T therapy in treating AML patients with EMDs. Although CRS, ICANS, and hematological side effects occurred with high frequency, most patients were effectively managed through systemic treatment and subsequent bridged HSCT. Therefore, as an efficient and safe therapeutic option, we recommend CLL1 CAR-T therapy to serve as an ideal strategy for AML patients, regardless of the presence of EMDs. CLL1 CAR-T therapy successfully alleviates these patients’ conditions and offers them an opportunity to undergo curative HSCT while significantly improving their prognosis. Moreover, it is important to note that the limitation of our findings lies in the fact that this study was conducted at a single center and included only 47 patients. We anticipate expanding the sample size in future studies to validate these results.