CD4 and infection: While control RBCs had no effect, CD4-GpA-RBCs lowered infection rates by 50% and 70%, respectively, demonstrating that RBC viral traps can effectively prevent infection of HIV-1 target cells at RBC/T cell ratios that are ∼1,000-fold lower than typically found in human blood (∼5,000:1)22 (Figure 4B).