CCNT1 (cyclin T1) is a critical regulatory protein that serves as the cyclin subunit of the positive transcription elongation factor b (P-TEFb) complex, which promotes RNA polymerase II transcriptional elongation 12. The protein functions by forming the catalytic core of P-TEFb with CDK9, enabling transcription elongation through phosphorylation of RNA polymerase II 34. CCNT1 is regulated by 7SK snRNA, which sequesters P-TEFb in an inactive state until released by signaling events such as EGF-induced METTL3-mediated 7SK methylation 1. The protein forms multiple distinct complexes (CCAPs) that can negatively regulate its availability for transcriptional activation 2. In HIV-1 infection, CCNT1 serves as an essential cofactor for viral Tat protein, binding to Tat and enhancing its affinity for TAR RNA to promote viral gene transcription 5. CCNT1 shows species-specific differences, with a single amino acid change (C261Y) conferring resistance to HIV-1 in rodent cells, which has been exploited to engineer HIV-resistant human T cells 6. The protein is absolutely required for HIV latency reversal, making it a critical target for HIV cure strategies 34. Alternative splicing of CCNT1 during HIV infection affects its functional domains and viral transcription efficiency 7.