Enhancement of the viability of T cells electroporated with DNA via osmotic dampening of the DNA-sensing cGAS-STING pathway.

Viral delivery of DNA for the targeted reprogramming of human T cells can lead to random genomic integration, and electroporation is inefficient and can be toxic. Here we show that electroporation-induced toxicity in primary human T cells is mediated by the cytosolic pathway cGAS-STING (cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) synthase-stimulator of interferon genes). We also show that an isotonic buffer, identified by screening electroporation conditions, that reduces cGAS-STING surveillance allowed for the production of chimaeric antigen receptor (CAR) T cells with up to 20-fold higher CAR T cell numbers than standard electroporation and with higher antitumour activity in vivo than lentivirally generated CAR T cells. The osmotic pressure of the electroporation buffer dampened cGAS-DNA interactions, affecting the production of the STING activator 2'3'-cGAMP. The buffer also led to superior efficiencies in the transfection of therapeutically relevant primary T cells and human haematopoietic stem cells. Our findings may facilitate the optimization of electroporation-mediated DNA delivery for the production of genome-engineered T cells.

Base editing of the HBG promoter induces potent fetal hemoglobin expression with no detectable off-target mutations in human HSCs.

Reactivating silenced γ-globin expression through the disruption of repressive regulatory domains offers a therapeutic strategy for treating ß-hemoglobinopathies. Here, we used transformer base editor (tBE), a recently developed cytosine base editor with no detectable off-target mutations, to disrupt transcription-factor-binding motifs in hematopoietic stem cells. By performing functional screening of six motifs with tBE, we found that directly disrupting the BCL11A-binding motif in HBG1/2 promoters triggered the highest γ-globin expression. Via a side-by-side comparison with other clinical and preclinical strategies using Cas9 nuclease or conventional BEs (ABE8e and hA3A-BE3), we found that tBE-mediated disruption of the BCL11A-binding motif at the HBG1/2 promoters triggered the highest fetal hemoglobin in healthy and ß-thalassemia patient hematopoietic stem/progenitor cells while exhibiting no detectable DNA or RNA off-target mutations. Durable therapeutic editing by tBE persisted in repopulating hematopoietic stem cells, demonstrating that tBE-mediated editing in HBG1/2 promoters is a safe and effective strategy for treating ß-hemoglobinopathies.