[Establishment and Application of Efficient Gene Editing Method for Classical HLA-I Molecules].

Objective: To establish an efficient gene editing method of HLA-I gene to prepare HLA-I universal hematopoietic stem cells.

Methods: The easyedit small guide RNA(sgRNA) was designed according to the sequences of β2 microglobulin gene and synthesized by GenScript company. RNP complexes were formed by NLS-Cas9-NLS nuclease and Easyedit sgRNA according to different molar ratios (1∶1~1∶4). Control group and four transfection groups were performed respectively. HEK-293 cells and CD34⁺ hematopoietic stem cells were nucleotransfected with RNP complex by Lonza 4D Nucleofector system. The expression of HLA-I on the surface of HEK-293 cells was detected by flow cytometry after transfection for 72 hours, the cleavage effect was determined by T7E1 enzyme digestion reaction and the presence of nested peak in the DNA sequence was identified by direct sequencing.

Results: The transfection groups had different levels of HLA-I negative expression cell populations by flow cytometry after transient transfection of HEK-293 cells and CD34⁺ hematopoietic stem cells with different molar concentrations of RNP complex for 72 hours. There were nested peaks proximal to the sgRNA PAM sequence in the transfection groups by direct DNA sequencing, indicating that sgRNA had obvious editing effect. In the transfection of HEK-293 cells, the highest proportion of HLA-I negative expression cells was (87.69±0.83)% when the molar ratio of NLS-Cas9-NLS nuclease to Easyedit sgRNA was 1∶4. The cutting efficiency of T7E1 was the highest up to (38±2.0)% when the molar ratio was 1∶3. In the transfection of CD34⁺ hematopoietic stem cells, the proportion of HLA-I negative expression cells was (91.56±3.39)% when the molar ratio was 1∶2, and the cutting efficiency of T7E1 was (64±8.45)% when the molar ratio was 1∶1.

Conclusion: This study provides an efficient gene editing method for classical HLA-I molecules, which can effectively silence the expression of class HLA-I molecules on the cell surface, and is suitable for stem cell system with difficult transfection.