CLL-1-Targeted In Vivo CAR-T Cell Immunotherapy for Relapsed/Refractory Acute Myeloid Leukemia

This is a single-center, single-arm, open-label, phase 1 dose-escalation study of SL1CC Injection in adults with R/R AML. SL1CC is an in vivo CAR-T product in which a lentiviral vector (LVV) encoding a CLL-1-specific chimeric antigen receptor is administered intravenously to transduce the patient's endogenous T cells in situ; no leukapheresis, ex vivo manufacturing, or lymphodepleting conditioning is required. Three dose levels are planned (1 × 10^9, 3 × 10^9, and 6 × 10^9 TU) using a traditional 3+3 escalation design, and dose-limiting toxicity (DLT) is assessed during the first 28 days after a single infusion. Anticipated enrollment is 12 participants (range 9-18, depending on the number of dose levels requiring expansion). The study includes a screening period, a treatment (infusion) period, and a follow-up period of up to 24 months. Safety assessments include adverse events and serious adverse events graded per NCI CTCAE v6.0, with CRS and ICANS graded per the ASTCT consensus criteria; hematologic recovery, infection, organ toxicity, and viral shedding (blood, saliva, and urine; qPCR) are also monitored. Disease response is assessed by bone marrow morphology according to the ELN 2022 criteria (CR, CRi, MLFS, and PR), together with MRD measured by multiparameter flow cytometry. Exploratory cellular kinetics include peripheral blood CAR transgene copies (qPCR), CAR-positive T-cell counts, Cmax, Tmax, and AUC0-28d. Long-term safety monitoring for potential insertional mutagenesis associated with integrating lentiviral vectors is planned in accordance with applicable gene therapy guidance.

Inclusion criteria

• Voluntarily agrees to participate in the study, has signed the informed consent form, and is willing and able to comply with scheduled visits, study treatment, laboratory tests, and other study procedures.
• Diagnosis of relapsed or refractory acute myeloid leukemia (AML), excluding acute promyelocytic leukemia (APL), according to the 2022 World Health Organization (WHO) classification, meeting at least one of the following:
• Relapsed AML: Reappearance of leukemic cells in the peripheral blood after achieving complete remission (CR), bone marrow blasts ≥5% (excluding bone marrow regeneration after consolidation chemotherapy or other non-leukemic causes), or the presence of extramedullary leukemic infiltration.
• Refractory AML: Newly diagnosed AML with no response after two courses of standard induction therapy; relapse within 12 months after achieving CR followed by consolidation/intensification therapy; relapse more than 12 months after CR with failure to respond to conventional chemotherapy; two or more relapses; or persistent extramedullary leukemia.
• CLL-1 expression ≥50% on AML blasts, confirmed by flow cytometry on bone marrow or peripheral blood samples at the local certified laboratory.
• Patients with targetable mutations (e.g., FLT3, IDH1/2, NPM1, or KMT2A rearrangement) must have received, be intolerant to, or be ineligible for the corresponding approved targeted therapy.
• Recovered from acute toxicities of prior antileukemic therapy to ≤ Grade 1 (CTCAE v6.0) before SL1CC infusion, except for alopecia and hematologic abnormalities attributable to the underlying disease.
• Male or female participants aged 18 to 75 years, inclusive.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
• Estimated life expectancy of more than 3 months from the date of signing the informed consent form.
• Adequate renal, hepatic, cardiac, and pulmonary function, defined as follows:
• Creatinine clearance (estimated by the Cockcroft-Gault formula) ≥60 mL/min or serum creatinine ≤1.5 × the upper limit of normal (ULN);
• Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST)≤2.5×upper limit of normal (ULN), total bilirubin≤1.5×ULN;
• Cardiac ejection fraction≥50%, no pericardial effusion on echocardiography, and no significant abnormalities on electrocardiogram (ECG);
• No clinically significant pleural effusion, and oxygen saturation >92% on room air at baseline.
• Participants of reproductive potential must agree to use highly effective contraception before enrollment and for at least 12 months after SL1CC infusion. A negative serum pregnancy test is required for women of childbearing potential at screening. Participants must immediately notify the investigator if pregnancy occurs or is suspected.

Exclusion criteria

• The patient has severe cardiac dysfunction, or left ventricular ejection fraction (LVEF) <50%, or a history within the 12 months prior to enrollment of myocardial infarction, coronary angioplasty or coronary stent implantation, unstable angina, clinically significant arrhythmia, or other severe cardiovascular diseases.
• A history of severe pulmonary disease associated with impaired lung function.
• Concurrent progressive malignancy other than acute myeloid leukemia.
• Severe active infection that cannot be effectively controlled.
• Severe autoimmune disease or congenital immunodeficiency.
• Active hepatitis B or hepatitis C infection, defined as hepatitis B virus DNA (HBV DNA) or hepatitis C virus RNA (HCV RNA) levels above the lower limit of detection.
• Human immunodeficiency virus (HIV) infection, known acquired immunodeficiency syndrome (AIDS), or syphilis infection; has received a live vaccine within 4 weeks, or is anticipated to require a live vaccine during the study period.
• A history of severe allergic reactions to biological products, including antibiotics.
• Prior allogeneic hematopoietic stem cell transplantation with persistent acute graft-versus-host disease (GVHD) after discontinuation of immunosuppressive therapy for at least 1 month.
• Prior treatment with any gene therapy product or any in vivo CAR-T therapy, or known pre-existing neutralizing immunity to the lentiviral vector.
• Active central nervous system (CNS) leukemia or leptomeningeal involvement not controlled after adequate intrathecal therapy; cerebrospinal fluid examination is required during screening.
• The patient has severe autoimmune disease, congenital immunodeficiency or active autoimmune disease requiring ongoing systemic immunosuppressive treatment, or is currently within the washout period after having received medications that may affect CAR-T cell immunotherapy, or is anticipated to require medications during the study period that may affect CAR-T cell immunotherapy treatment, or active GVHD requiring systemic therapy.
• Pregnancy or breastfeeding (lactation).
• The patient has other significant uncontrolled comorbidities that may affect protocol compliance or interpretation of results.
• The investigator judges that the patient is unlikely to complete all visits and procedures required by the study protocol (including medium- and long-term follow-up visits), such as insufficient willingness of the patient and their family members to participate in the study, refusal to participate, inability of the patient to fully cooperate with the study arrangements, or inadequate compliance on the part of the patient and their family members.
• Any other severe physical or psychiatric disorder or clinically significant laboratory abnormality that may increase the risk associated with study participation, interfere with the interpretation of study results, or, in the investigator's judgment, make the participant unsuitable for participation in the study.

Note:

• Severe infection is defined as sepsis or an infection with an uncontrolled infectious focus. Participants may be enrolled after the infection has been adequately controlled.