Sp1 links CD46 to CD4 T cell metabolic fitness, survival, and retroviral control.

CD46, a human-specific complement receptor, regulates gene programs essential for T helper 1 (TH1) cell differentiation, yet how it exerts direct transcriptional control remains unclear. We show that the CD46 signaling domain cytoplasmic tail 1 (CYT-1) engages the transcription factor Sp1 in human CD4 T cells to dynamically modulate Sp1-DNA interactions. Beyond promoting TH1 cell induction, CD46-Sp1-controlled programs support naive CD4 T cell survival by maintaining nutrient transporter expression and suppressing the intrinsic caspase 9-caspase 3 apoptotic pathway. The CD46-Sp1 axis also restrains HIV transcription in infected CD4 T cells in vitro. Disruption of CYT-1-Sp1-regulated programs identifies T cells from individuals with HIV who exhibit incomplete viral suppression during antiretroviral therapy. Together, these findings define a human-specific transcriptional mechanism linking complement signaling to metabolic adaptation, apoptosis regulation, and antiviral defense, highlighting an unexpected role for CD46 in coordinating T cell homeostasis and host protection.