Open label dose-escalation and dose-expansion study to evaluate the safety, expansion, persistence and clinical activity of UCART22 (allogeneic engineered T-cells expressing Anti-CD22 Chimeric Antigen Receptor) in patients with relapsed or refractory CD22+ B-cell Acute Lymphoblastic Leukemia (B-ALL)

The primary objective of this study is to evaluate the **safety** and tolerability of UCART22, an allogeneic engineered T-cell therapy expressing Anti-CD22 Chimeric Antigen Receptor, in patients with relapsed or refractory B-cell Acute Lymphoblastic Leukemia (R/R B-ALL). The study aims to determine the Maximum Tolerated Dose (MTD) and/or Recommended Phase 2 Dose (RP2D) during the dose-escalation phase. In the dose-expansion phase, the objective is to confirm the MTD and/or RP2D in patients who have failed a CD19 directed therapy. This is clinically relevant as it seeks to establish a safe and effective dosing regimen for UCART22, potentially offering a new therapeutic option for patients with limited treatment alternatives.

Secondary objectives include: - Assessing the anti-leukemic activity of UCART22 in patients with R/R B-ALL. - Identifying the optimal lymphodepletion regimen to evaluate with UCART22 RP2D. - Measuring the development of a potential immune response to **alemtuzumab**. - Determining the pharmacokinetic (PK) profile and exposure levels of alemtuzumab. - Determining the pharmacodynamics (PD) of alemtuzumab. - Assessing minimal residual disease (MRD) negativity by an approved genomic assay in a central laboratory. - Evaluating the safety and tolerability of UCART22 in R/R B-ALL subjects who have failed a CD19 directed therapy.

The clinical trial involves a total of **73 participants** diagnosed with **relapsed or refractory B-cell Acute Lymphoblastic Leukemia**. The study population includes both male and female subjects, with an age range of 12 to 70 years. Participants were selected based on specific criteria, including a history of prior therapy with at least one standard chemotherapy regimen and one salvage regimen. Additionally, participants must have measurable or evaluable disease in the bone marrow and a significant expression of CD22 on B-ALL blast cells. The trial excludes vulnerable populations and requires participants to have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 for those aged 18 and above, or a Lansky/Karnofsky score of 70 or higher for those under 18. Adequate organ function, including renal and hepatic function, is necessary, and women of childbearing potential must have a negative pregnancy test prior to enrollment. The trial does not impose specific lifestyle considerations such as diet or physical activity.

The clinical trial is designed to evaluate the safety, expansion, persistence, and clinical activity of **UCART22**, an allogeneic engineered T-cell therapy, in patients with relapsed or refractory B-cell Acute Lymphoblastic Leukemia (B-ALL). This study is structured as an open-label, dose-escalation, and dose-expansion trial. The trial aims to determine the maximum tolerated dose (MTD) and/or recommended phase 2 dose (RP2D) of UCART22. The trial is expected to conclude by January 12, 2039, with recruitment having started on November 12, 2019.

Participants will undergo a series of study visits, beginning with a screening visit to assess eligibility based on criteria such as age, prior therapy, disease burden, and organ function. The inclusion criteria specify that patients must have relapsed or refractory B-ALL, with no available alternative curative therapies, and must be ineligible for or have refused hematopoietic stem cell transplantation (HSCT). The trial includes both a dose-escalation phase, where the incidence and severity of adverse events will be monitored, and a dose-expansion phase to confirm the MTD and/or RP2D.

Study visits will include regular follow-up assessments to monitor the incidence, nature, and severity of adverse events, as well as the overall response rate and progression-free survival. The end-of-study visit will evaluate the long-term safety and efficacy of the treatment. Participants are expected to be involved in the study for the duration of the trial unless they experience dose-limiting toxicity, withdraw consent, or meet other criteria for early termination.

The trial employs a randomized, controlled design, with a focus on ensuring the reliability and validity of the results. The primary endpoints include the incidence of adverse events and serious adverse events, while secondary endpoints focus on response rates and survival outcomes. The study is not classified as a low-intervention trial, given its adaptive design and the novel nature of the therapy being investigated.

The clinical trial involves the administration of several experimental and non-experimental treatments. **LEMTRADA** (alemtuzumab) is provided as a 12 mg concentrate for solution for infusion. It is administered intravenously. Alemtuzumab is a protein-based substance, and its administration is intended to be part of the experimental treatment regimen. The frequency and specific dosing schedule are determined by the study protocol, and participant compliance is monitored throughout the trial.

**MabThera** (rituximab) is supplied as a 1400 mg solution for subcutaneous injection, although in this trial, it is administered intravenously. Rituximab is also a protein-based substance. The administration schedule is defined by the study protocol, and adherence to the dosing regimen is closely monitored.

**CLLS52** is another experimental treatment in the form of a solution for infusion, containing alemtuzumab as the active substance. It is administered intravenously. The dosing regimen and frequency are specified in the study protocol, with compliance monitoring in place to ensure adherence.

**ENDOXAN** (cyclophosphamide) is provided as a 1000 mg powder for solution injectable, administered intravenously. Cyclophosphamide is a chemical-based substance. The administration schedule is outlined in the study protocol, and participant compliance is monitored.

**Fludara** (fludarabine phosphate) is available as a 50 mg powder for solution injectable or for infusion, administered intravenously. Fludarabine phosphate is a chemical-based substance. The dosing schedule is determined by the study protocol, with compliance monitoring to ensure adherence.

**UCART22** is a cell suspension for injection, containing engineered T-cells targeting CD22. It is administered intravenously. UCART22 is a structurally diverse substance used in cell therapy. The administration and dosing schedule are specified in the study protocol, with participant compliance being closely monitored.

Efficacy in this clinical trial will be assessed through a series of primary and secondary endpoints. The primary endpoints for the dose escalation phase include the incidence, nature, and severity of adverse events and serious adverse events (SAEs), as well as the proportion of patients in each dose level cohort experiencing dose-limiting toxicity during the dose-limiting toxicity (DLT) observation period. For the dose expansion phase, the primary endpoints remain focused on the incidence, nature, and severity of adverse events and SAEs, particularly those associated with lymphodepletion.

Secondary endpoints for the dose escalation phase include the investigator-assessed overall response rate (ORR), which encompasses complete response, complete response with incomplete hematologic recovery, and complete response with partial hematologic recovery, according to the Response criteria for Acute Lymphoblastic Leukemia (ALL). Additionally, the rate of minimal residual disease (MRD) negativity, defined as bone marrow ALL blasts less than 0.01% by flow cytometry, will be evaluated. Time-to-event endpoints such as progression-free survival (PFS), overall survival (OS), and duration of response (DoR) will also be measured. The proportion of patients achieving an adequate response and proceeding to hematopoietic stem cell transplant (HSCT) will be recorded, along with the incidence, nature, and severity of adverse events and SAEs associated with lymphodepletion, anti-leukemic activity, and corresponding host T-cell recovery and CAR+ T-cell expansion.

For the dose expansion phase, secondary endpoints include the investigator-assessed ORR according to the Response criteria for ALL, time-to-event endpoints (PFS, OS, and DoR), and the proportion of subjects achieving an adequate response and proceeding to HSCT without additional antileukemia therapy. The MRD negative rate will be measured on bone marrow by the ClonoSeq MRD assay at a central laboratory. Monitoring of anti-CD52 (alemtuzumab) antibodies in serum pre- and post-administration, quantitation of alemtuzumab levels in serum post-administration, and quantitation of T, B, and NK cells and total lymphocytes in peripheral blood post-administration will also be conducted.