Hyperplexing Approaches for up to 45-Plex Quantitative Proteomic Analysis.

Isobaric labeling has emerged as an indispensable quantitative proteomic approach for its unprecedented multiplexing capacity in a single analysis. Currently, different hyperplexing approaches have been developed to meet the demand for the increasing sample size in large-scale cohort analysis. In this report, we present a tribrid hyperplexing approach by the combinatorial use of three types of isobaric reagents, a novel isobaric tag 16-plex (IBT16) reagent and the widely used tandem mass tag (TMT; TMT11) and TMTpro (TMT18) reagents. After the determination of labeling efficiency and the optimization of testing conditions, we systematically evaluated the identification and quantification performance of the three labeling reagents in both independent and combinatorial manners using the mixtures of E. coli and HeLa peptides with different ratios. Our results reveal that the three reagents are quite similar in all testing aspects despite some differences, and the combination use of the three reagents could expand the multiplexing capacity to up to 45-plex. Furthermore, we conclude the advantages of IBT16 in the combination use and the preferred combinations for different practical applications. Data are available via ProteomeXchange with identifier PXD037498.

Reduction of Pre-Existing Adaptive Immune Responses Against SaCas9 in Humans Using Epitope Mapping and Identification.

The CRISPR-Cas9 system is increasingly being used as a gene editing therapeutic technique in complex diseases but concerns remain regarding the clinical risks of Cas9 immunogenicity. In this study, we detected antibodies against Staphylococcus aureus Cas9 (SaCas9) and anti-SaCas9 T cells in 4.8% and 70% of Chinese donors, respectively. We predicted 135 SaCas9-derived B cell epitopes and 50 SaCas9-derived CD8+ T cell epitopes for HLA-A*24:02, HLA-A*11:01, and HLA-A*02:01. We identified R338 as an immunodominant SaCas9 B cell epitope and SaCas9_200-208 as an immunodominant CD8+ T cell epitope for the three human leukocyte antigen allotypes through immunological assays using sera positive for SaCas9-specific antibodies and peripheral blood mononuclear cells positive for SaCas9-reactive T cells, respectively. We also demonstrated that an SaCas9 variant bearing an R338G substitution reduces B cell immunogenicity and retains its gene-editing function. Our study highlights the immunological risks of the CRISPR-Cas9 system and provides a solution to mitigate pre-existing adaptive immune responses against Cas9 in humans.