CD4 and infection: However, following the second infection with SARS-CoV-2, the IFN-γ response was significantly higher in the hACE2 transfected mice (average CD8+ response = 1.5% and average CD4+ response = 1.6%) as compared to GFP (average CD8+ response = 0.5% and average CD4+ response = 0.4%) (p = 0.025 and 0.0009, respectively).