Researchers from the Center for Regenerative Medicine of Boston University and Boston Medical Center, as well as Beam Therapeutics, have demonstrated single-base editing to correct the most common mutation that causes alpha-1 antitrypsin deficiency (AATD). The results, which are published in Molecular Therapy, show that adenine base editors (ABEs) could be used to correct the disease-causing guanine to adenine (G to A) mutation (referred to as the Z mutation) of the SERPINA1 gene that leads to misfolded alpha-1-antitrypsin(AAT) proteins (Z-AAT) and ultimately AATD.
The researchers found that the use of ABE was efficient at correcting the Z mutation in iPSCs and iHeps while not producing off-target genomic mutations. The authors stated, “These results reveal the feasibility and utility of base-editing to correct the Z mutation in AATD patient cells.”
The research was conducted in the PiZZ1 cell line of patient-induced pluripotent stem cells (iPSC) and subsequently derived hepatocytes (iHeps). The PiZZ1 cell line was collected from an AATD patient homozygous for the Z mutation (ZZ). iPSCs were nucleofectors with ABEs and resulted in cells both heterozygous (MZ) and homozygous (MM) for the corrected SERPINA1 gene. These base-edited cells were further differentiated into iHeps.
Base-editing was also successfully performed directly in ZZ iHeps during the study. Both iHeps differentiated from base-edited iPSCs and those which were directly base-edited showed lower accumulation of AAT inside the cell and higher levels of secreted AAT while not affecting other cell functions including albumin secretion and cytochrome (CYP) expression. Immunostaining of the iHeps also revealed that base-edited cells were rescued from endoplasmic reticulum (ER) stress, which is commonly seen in ZZ cells.
The Z mutation of the SERPINA1 gene is the most common AATD-causing mutation. The single substitution of G to A results in a glutamic acid to lysine substitution (Glu342Lys) that produces the aberrant Z-AAT protein. This protein tends to misfold and aggregate inside of cells. The accumulation of Z-AAT inside of cells leads to a lack of circulating AAT causing imbalances between protease and antiproteases in the lungs, cell damage, and emphysema. Accumulation of Z-AAT also leads to toxicity in hepatocytes and ultimately liver disease in AATD patients.
Werder RB, Kaserman JE, Packer MS, et al. Adenine base editing reduces misfolded protein accumulation and toxicity in alpha-1 antitrypsin deficient patient iPSC-hepatocytes. Mol Ther. Published online ahead of print 2021. doi:10.1016/j.ymthe.2021.06.021