CXCR4 and infection: In contrast to all other HIV-1 T/F viruses that use either CCR5 and/or CXCR4 coreceptors for entry, the T/F virus ZP6248 established the clinical infection most likely used the coreceptor GPR15 and the unique V3 crown GPEK in ZP6248 play a critical role in the GPR15 tropism [19].