CXCR4 and HIV infectious disease: Exploiting CRISPR-Cas9 system can overwhelm this hurdle, because this system has the potential to disrupt CXCR4 without affecting the cell propagation.19 Introduction of the homozygous CCR5∆32 mutation in induced pluripotent stem cells (iPSCs) using the combination of CRISPR-Cas9 system and a PiggyBac transposon caused a significant resistance to HIV infection.