Preliminary Results of Balli-01: A Phase I Study of UCART22 (allogeneic engineered T-cells expressing anti-CD22 Chimeric Antigen Receptor) in Adult Patients with Relapsed or Refractory (R/R) CD22+ B-Cell Acute Lymphoblastic Leukemia (B-ALL)

Introduction: UCART22 is a genetically modified T-cell product manufactured from non-HLA matched healthy donor cells. Donor derived T-cells are transduced using a lentiviral vector to express anti-CD22 CAR (anti-CD22 scFv-41BB-CD3ζ) and are further modified using Cellectis' TALEN® technology to disrupt the T-cell receptor alpha constant (TRAC) and CD52 genes. These modifications minimize the risk of graft versus host disease (GvHD) and allow the use of anti-CD52 directed drugs in the lymphodepletion (LD). UCART22 demonstrated antigen-specific cytotoxic activity against B-ALL cell lines and primary human samples in vitro. In a preclinical in vivo model, immune compromised mice engrafted with Daudi cells, a CD22(+) expressing Burkitt's lymphoma cell line, treated with UCART22 cells demonstrated extended survival in a dose-dependent fashion compared to controls (Wells et al, Blood 2017, abstr. 208).

Methods: BALLI-01 (NCT04150497) is a Phase I open-label dose-escalation study designed to assess the safety, the maximum tolerated dose (MTD), and preliminary anti-leukemia activity of UCART22 in patients (pts) with R/R B-ALL. Additional endpoints include characterization of the expansion, trafficking and persistence of UCART22. Eligible pts include adults (18-65 years) with adequate organ function, ECOG PS ≤1, and B-ALL blast CD22 expression ≥ 90% by flow cytometry. Pts must have received at least one standard chemotherapy regimen and one salvage regimen. Protocol therapy includes LD regimens of cyclophosphamide and fludarabine (FC) or FC with alemtuzumab (FCA), followed by a single dose of UCART22 at 1 of 4 dose levels (DL). DLT is assessed at the end of the 28-day DLT observation period. Anti-leukemia activity is based on investigator assessment using NCCN ALL response criteria. UCART22 expansion and persistence are assessed in blood and bone marrow (BM) by flow cytometry, vector copy number and chimerism analysis by qPCR. Immune reconstitution is assessed by flow cytometry.

Results: As of 01 July, 2020, 7 pts signed consent, 1 pt failed screening, and 6 pts (4 male; median age 24 [22-52]) were enrolled. Five pts received UCART22 infusion [DL1: 1X10⁵ cells/kg (n=3), DL2: 1x10⁶ cells/kg (n=2)] after FC LD (cyclophosphamide 1g/m² x 3 days and fludarabine 30 mg/m² x 4 days). 1 pt discontinued prior to UCART22 administration due to AE (hypoxia due to pneumonitis related to LD). Median number of prior therapies was 3 [2-4]. Median baseline BM blasts % prior to LD was 35% [5-78.4%].

Among 5 pts treated, 4 pts experienced 10 treatment-related treatment-emergent AEs (TEAEs): bilirubin increased (n=1, G4); ALP increased (n=1, G2); hypotension (n=1, G2); CRS (n=2, G2; n=1, G1); headache (n=1, G1); lymph node pain (n=1, G1); fever (n=1, G1); transaminitis (n=1, G1). Two pts experienced serious TEAEs: 1 pt had G3 febrile neutropenia and G3 peri-hepatic hematoma; 1 pt had G4 bleeding and G5 sepsis in the context of PD. No pts had treatment-related serious TEAE, GvHD, ICANS, protocol-defined DLT nor AE of special interest.

2 pts at DL1 achieved best response at day 28 of CR with incomplete hematologic recovery (CRi); and 1 pt at DL2 had initial significant reduction in BM blasts [40% (D -1) to 13% (D 28)] and then progressed.

Host T cells recovery was observed in all pts within the DLT period (range D17-D28). Correlative analysis of UCART22 expansion and persistence is ongoing.

Conclusion:

UCART22 demonstrated no unexpected toxicities at doses of 1x10⁵/kg and 1x10⁶/kg with FC LD regimen. CRS was observed in 3 patients, all grade 1-2, and was manageable. No pts had DLT, GvHD nor ICANS. Two pts achieved CRi. As host immune recovery was observed early, the addition of alemtuzumab to FC LD is now being explored in ongoing treatment cohorts to potentially achieve a deeper and more sustained T-cell depletion and promote expansion and persistence of UCART22. Enrollment is ongoing.