Graph of the kinetics of the T cell response to antigenic stimulation in vivo. Following stimulation with antigen, antigen-specific T cells proliferate vigorously to reach peak numbers during the expansion phase. They then decline in number rapidly, a process referred to as the contraction phase. Importantly, both the peak-expansion phase and the contraction phase can be independently modulated by stimulators of innate immunity (adjuvants) (53, 54).