CRISPR/Cas originally evolved as a bacterial adaptive immune response that protects bacteria from infection by bacterial DNA viruses or phages. In Type II CRISPR/Cas systems, a single effector protein, called Cas9, is diverted to DNA targets by two small RNAs, the tracRNA and the crRNA, that serve as guide RNAs. These two RNAs can be combined into a single guide RNA (sgRNA) that can effectively direct Cas9 to DNA targets and induce its cleavage in not only bacterial but also mammalian cells as well. There have been many proposals about how CRISPR/Cas could be used to promote human health, including the destruction of pro-oncogenic genes, or the repair, by homologous recombination, of genes bearing inactivating mutations, such as is seen in muscular dystrophy.
Our focus has been on developing CRISPR/Cas as a means to target and destroy the genomic DNA of a range pathogenic human DNA viruses including HBV, HSV, HPV and HIV-1. To this end, we have been developing improved viral vectors, based on different Cas9 proteins, and have now demonstrated the highly effective cleavage and repression of several DNA viruses in cultured cells. Our recent research has extended these data to demonstrate a significant inhibitory effect on the growth of HPV-transformed cancer cells in mice. Currently, we are continuing to develop improved delivery strategies for Cas9 in vivo and we hope to extend our animal experiments to other viral induced diseases in the near future.