Cellectis Reports Preliminary Results from its Phase 1 BALLI-01 Study of UCART22 in R/R Adult B-ALL at American Society of Hematology (ASH) Annual Meeting Published on December 05, 2020 in New York, NY BACK TO ALL PRESS RELEASES Cellectis’ Proprietary Program UCART22 was Safely Administered in BALLI-01 Phase 1 Study with No Dose-Limiting Toxicity or Evidence of Graft-Vs-Host Disease 2 out of 3 Patients at DL1 Achieved CR/CRi and 1 out of 2 Patients at DL2 Achieved a Significant Reduction in Bone Marrow Blasts BALLI-01 Currently Enrolling at DL2 with Addition of Alemtuzumab to the FC Lymphodepletion Regimen; Next Data Update Expected in 2021 December 5, 2020 – New York (N.Y.) – Cellectis (Euronext Growth: ALCLS - Nasdaq: CLLS), a clinical-stage biopharmaceutical company focused on developing immunotherapies based on gene-edited allogeneic CAR T-cells (UCART), announced preliminary results from Cellectis’ dose escalation Phase 1 BALLI-01 study of UCART22 product candidate in relapsed/refractory B-cell Acute Lymphoblastic Leukemia (B-ALL) were presented at the American Society of Hematology (ASH) Annual Meeting. This is the first publicly released data from Cellectis’ BALLI-01 clinical trial. The BALLI-01 clinical trial presentation released at the ASH Annual Meeting is available on Cellectis website: https://bit.ly/CellectisASH2020 We are encouraged by the promising preliminary data obtained from the first two lower dose levels of UCART22 following a standard fludarabine and cyclophosphamide lymphodepletion regimenfrom the BALLI-01 trial. The anti-leukemia activity observed in these patients with B-ALL who had been previously heavily pre-treated speaks to the validity of CD22 as a target in the CAR T-cell space, and demonstrates the promise of allogeneic cellular therapies to leapfrog the autologous CAR-T products. We have now started enrolling cohorts that include alemtuzumab, an anti-CD52 monoclonal antibody, in the lymphodepletion regimen, as we anticipate this may extend the window of persistence of our TALEN® gene-edited allogeneic CAR T-cells,” said Carrie Brownstein, MD, Chief Medical Officer, Cellectis. Based on the strong progress of our partnered- and proprietary product candidate portfolio, which was presented at ASH, we are looking forward to presenting additional clinical data in 2021.” Characteristics As of the November 2, 2020 data cutoff, 7 patients were enrolled and 5 patients received UCART22 cells. One patient failed screening and one patient was discontinued prior to the administration of UCART22 cells due to an adverse event related to the lymphodepletion. Safety No patient experienced a DLT, ICANS, GvHD, AESI[1], nor UCART22-related Grade ≥3 adverse event (AE) nor serious adverse event (SAE). No patient discontinued treatment due to a UCART22-related treatment-emergent adverse event. Anti-leukemic Activity Two patients in Dose Level 1 achieved an objective response of complete remission with incomplete hematologic recovery (CRi) at Day 28, one of which attained a complete remission (CR) at Day 42 and received a transplant after subsequent therapy with inotuzumab. One patient in Dose Level 2 with refractory disease did achieve a noteworthy reduction in bone marrow blasts (60% at screening down to 13% at Day 28) after treatment with UCART22 product candidate and then progressed. Host lymphocyte reconstitution was observed in all patients within the DLT period (range Day 9-Day 28). Correlative analysis of UCART cell expansion and persistence is ongoing. UCART22 demonstrated preliminary signs of activity at low dose levels with fludarabine/cyclophosphamide (FC) lymphodepletion regimen, without unexpected nor significant treatment-related toxicities. Host immune recovery was observed early, supporting the addition of alemtuzumab to the FC lymphodepletion regimen which is expected to result in a deeper and more sustained T-cell depletion and thereby promote expansion and persistence of UCART22 cells. Enrollment into the Dose Level 2 cohorts with alemtuzumab is ongoing. Treatment-emergent adverse events of interest with DL1 and DL2 Grade 1 Grade 2 Grade 3 Grade 4 Grade 5 Graft-versus-host disease (GvHD) 0 0 0 0 0 Cytokine release syndrome (CRS) 2 1 0 0 0 ICANS 0 0 0 0 0 SAEs2 3 1 1 [1] DLT: Dose Limiting Toxicity; GvHD: Graft versus Host Disease; AESI: adverse event of special interest; ICANS: immune effector cell-associated neurotoxicity syndrome; AE: Adverse Event; SAE: Serious Adverse Event 2 SAEs that are not related to UCART22 cells About UCART22 UCART22 is one of Cellectis’ wholly owned, allogeneic, off-the-shelf gene-edited T-cell product candidates, designed for the treatment of relapsed and refractory B-cell acute lymphoblastic leukemia (R/R B-ALL). Like CD19, CD22 is a cell surface antigen expressed from the pre-B-cell stage of development through mature B-cells. CD22 expression occurs in more than 90% of patients with B-ALL. 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