HIV dynamics and immunosenescence.

Three differential equations modelling HIV virion, and infected and uninfected immune-cell densities during acute and chronic phases of infection underlie in-vivo HIV viral dynamics models. Adding a fourth equation that simulates immunosenesence through the drawdown of a stem-cell reservoir permits the phase of full-blown AIDS to be incorporated in the model. This greatly enhances the utility of the model in designing interventions and explains why time-to-full-blown AIDS decreases with age at infection.