Cellectis to Present Pre-Clinical Data on HSPC Gene Therapy Program and Comprehensive Analysis of TALE-BE at the ESGCT 30th Annual Congress

New York, NY – October 24, 2023 - Cellectis (the “Company”) (Euronext Growth: ALCLS - NASDAQ: CLLS), a clinical-stage biotechnology company using its pioneering gene-editing platform to develop life-saving cell and gene therapies, announced today that they will be showcasing pre-clinical data on its program of gene therapy for HSPC as well as comprehensive analysis of TALE-BE editing determinants at the European Society of Gene and Cell Therapy (ESGCT) 30^th annual congress that will take place on October 24-27, 2023 in Brussels, Belgium.

The data will be presented in three posters:

Intronic editing enables lineage specific expression of therapeutics relevant for HSPC gene therapy (Poster N°646)

Presenter: Eduardo Seclen, Senior Scientist & Team Leader, Gene Editing

Date/Time: Wednesday October 25^th from 18:15 to 19:30 and Thursday October 26^th from 19:30 to 20:30

• Intronic editing enables lineage specific expression of therapeutics relevant for HSPC gene therapy.
• TALEN®-mediated intron editing of the CD11b locus results in the lineage-specific expression of a reporter transgene in myeloid cells, with negligible expression in HSPC or other cellular subsets in vitro and in vivo.
• We believe this intron editing approach could be disruptive in HSPC gene therapy and brain delivery of multiple therapeutics.

TALEN editing coupled to non-viral DNA delivery enables efficient correction of sickle cell mutation with minimal transcriptional changes and low level of HBB KO (Poster N°380)

Presenter: Julien Valton, VP, Gene Therapy

Date/Time: Wednesday October 25^th from 18:15 to 19:30 and Thursday October 26^th from 19:30 to 20:30

• Using a combination of scRNA sequencing and multiple genomic read out methodologies, we demonstrate that the mutant HBB gene can be efficiently corrected in HSPCs by TALEN®-mediated gene editing coupled to non-viral gene delivery (ssODN) with a low risk of generating β-thalassemic RBCs.
• TALEN®-mediated HBB editing coupled to non-viral gene delivery (ssODN) in SCD patients’ HSPCs led to a lower activation of p53 response compared to viral gene delivery (AAV), preserves the transcriptomic profile of edited HSPCs in vitro and their engraftment capacity in vivo.

Comprehensive analysis of TALE-BE editing determinant (Poster N°667)

Presenter: Maria Feola, Scientist III, Manager, Gene Editing

Date/Time: Wednesday October 25^th from 17:00 to 18:15 and Thursday October 26^th from 20:30 to 21:30

• The robustness and versatility of genome engineering strategies we developed allowed us to gain in-depth insight of TALE-BE editing rules in cellulo and further highlighted that the composition surrounding the TC to be edited could strongly impact editing efficiencies. Therefore, educated choice of the TALE-BE architecture and positioning on DNA could either prevent target sequence limitations (increasing targetable sequence space) or decrease, if not eliminate, bystander editing within the editing window, allowing for more precise genome editing outcomes.
• We believe that the knowledge presented will help ensure that genome editing-based strategies are skillfully designed to minimize the risk of potential genotoxic events, overall expanding the potential of TALE-BE for nuclear and mitochondrial therapeutic cell engineering.