Editors' ChoiceGenome Editing

Immunity to CRISPR-Cas9

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Science Translational Medicine  20 Feb 2019:
Vol. 11, Issue 480, eaaw5328
DOI: 10.1126/scitranslmed.aaw5328

Abstract

Evaluation of patient serum samples commonly reveals preexisting anti-Cas9 antibodies and T cells.

The relative ease of applying clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR-Cas9) to precisely edit DNA loci has led to the rapid development of CRISPR-Cas9–based therapies for disease. Therapies for sickle cell disease, muscular dystrophy, and retinitis pigmentosa will likely be the first of many using this system. The most common orthologs of Cas9, however, are derived from bacteria—specifically Staphylococcus aureus (SaCas9) and Streptococcus pyogenes (SpCas9), two of the most common pathogens that humans encounter. Charlesworth and colleagues thus astutely evaluated whether adults may harbor a preexisting adaptive immune response to Cas9 by evaluating serum for anti-Cas9 antibodies and T cells.

Using enzyme-linked immunosorbent assay (ELISA) on 125 blood donors, the authors noted preexisting immunoglobulin G (IgG) antibodies against SaCas9 and SpCas9 in 78% and 58%, respectively. To evaluate preexisting T cell responses, the authors used parallel methods of enzyme-linked immunospot (for interferon-γ), intracellular cytokine staining, and detection of CD137 and CD154 activation markers. Integrating these results showed antigen-reactive T cells to SaCas9 and SpCas9 in 78% and 67% of samples. Importantly, the authors demonstrated T cell responses to be specific to the Cas9 by isolating activated T cells (CD137+ and/or CD144+) by flow cytometry, expanding sorted cells, and rechallenging cells with Cas9. T cells only showed response when rechallenged with the appropriate Cas9 ortholog but not with a tetanus positive control.

These data suggest that a large percentage of humans possess preexisting adaptive immune responses to Cas9. Further studies are required, as recent reports on degree of immune response from other groups vary. In addition, these early data do not address the effect of this immune response on CRISPR therapy efficacy and host safety. However, with the enthusiasm for CRISPR-Cas9 therapies, these data raise crucial considerations that should be addressed as these therapies advance to clinical trials.

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