A subset of primed CD4+ and CD8+ T cells differentiates into long-acting memory cells after the infection subsides. TCR-p: MHCII signaling helps in CD4+ T memory cell formation along with presence of cytokines like IL-2, IL-21 and interaction via CD40R-CD40L (Jaigirdar and MacLeod, 2015). Similarly, This CD8+ T cell transition to memory cells take place under the influence of CD8+ TREG cells via secreted IL-10 (Laidlaw et al., 2015). Long lasting CD4+ and CD8+ T memory cells were detected in the recovered SARS-CoV infected patients (Peng et al., 2006; Li et al., 2008).