To engineer T-cells, scientists need to introduce specific molecules inside the cell to modify its DNA. To make its off-the-shelf UCART product candidates, Cellectis implements two separate steps of T-cell engineering.

In the first engineering step, genes are added to the T-cell genome. Delivering genes is a key step. Because T-cells are naturally refractory to the entry of foreign DNA, scientists need a very efficient gene transfer tool: lentiviral vectors.

Lentiviruses are a subclass of retroviruses. These viruses are made of an envelope, a capsid and, inside, a RNA genome. Lentiviruses have evolved to deliver their genome efficiently to their target cells (including T-cells), where this RNA is reverse-transcribed into a DNA molecule and is then very efficiently integrated into the genome of the cell thanks to the viral integrase enzyme.

Lentivectors utilize these interesting natural biological properties of lentiviruses to serve as an efficient gene transfer tool. Lentiviral vector is a crucial technology for CAR T-cell therapies. 

In the second T-cell engineering step implemented in Cellectis’ manufacturing process, vectorization is also used to introduce its gene editing technology TALEN®. A transfection is needed to introduce TALEN®-enconding messenger RNA (or mRNA). To do so, Cellectis uses its patented PulseAgile electroporation technology.

Electroporation consists of the delivery of controlled short electric impulses to allow the introduction of molecules into cells. PulseAgile is thus used to allow introducing TALEN®-encoding mRNA into T-cells, where they are translated into TALEN® that perform the required gene editing.