Notably, quiescent CD4+ T cells, which are metabolically and transcriptionally silent (Yusuf and Fruman 2003; Tzachanis et al. 2004), were originally thought to be refractory to HIV infection; however, evidence suggests that partially activated cells can support infection, especially with subsequent stimulation (Stevenson et al. 1990; Zack et al. 1990, 1992; Korin and Zack, 1998; Unutmaz et al. 1999; Manganaro et al. 2018). This evidence concerns the gene CD4 and infection.