Adeno-associated virus serotype 2 capsids with proteolytic cuts by trypsin remain intact and potent

Recombinant adeno-associated viral (AAV) vectors have emerged as prominent gene delivery vehicles for gene therapy. In the journey of an AAV vector, AAV vectors can be exposed to different proteolytic environments inside the production cells, during the cell lysis step, within the endosome, and finally inside the cell nucleus. The stability of a modified AAV serotype 2 (AAV2) capsid was evaluated via a proteolytic approach using trypsin and other proteases and both denaturing and non-denaturing analytical methods. Trypsin digestion of the AAV2 capsids resulted in clips of the capsid proteins at the C-terminus as confirmed by denaturing methods including SDS-PAGE, CE-SDS, Western blot, and RPLC-MS. It was found that the AAV2 capsid with clips not only remains structurally intact, as confirmed by non-denaturing methods including SEC, thermostability testing, and cryo-EM, but also remains potent, as confirmed in a cell-based potency assay. This finding reveals that AAV2 capsid with proteolytic cuts remains intact and potent since the icosahedral three-dimensional structural arrangement of AAV capsid proteins can protect the clipped fragment from being released from the capsid, such that the AAV capsid remains intact allowing for the functionality to be maintained to deliver the DNA in the host cell. Evaluation of AAV stability using a proteolytic approach and multiple denaturing and non-denaturing analytical methods can provide valuable information for engineering AAV capsids to develop AAV-based gene therapy.