The CRISPR-Cas9 system has proven to be a powerful tool for genome editing allowing for the precise modification of specific DNA sequences within a cell. Many efforts are currently underway to use the CRISPR-Cas9 system for the therapeutic correction of human genetic diseases. The most widely used homologs of the Cas9 protein are derived from the bacteria Staphylococcus aureus (S. aureus) and Streptococcus pyogenes (S. pyogenes). Based on the fact that these two bacterial species cause infections in the human population at high frequencies, we looked for the presence of pre-existing adaptive immune responses to their respective Cas9 homologs, SaCas9 (S. aureus homolog of Cas9) and SpCas9 (S. pyogenes homolog of Cas9). We have identified the presence of pre-existing humoral immune responses to SaCas9 and SpCas9 by both Western Blot and ELISA. In addition we have also identified pre-existing cellular responses to Cas9 by intracellular cytokine staining and ELISPOT. 

Learning Objectives: 

1. Pre-existing adaptive immunity to the most commonly used homologous of Cas9 is prevalent
2. Potential immune responses to any new therapeutic should be considered when considering any kind of in-vivo therapy