FIG 4.

CD8⁺ T cell depletion at day zero is followed by ART at day three (11, 12). We start the model in the chronic states from Fig. 1 (using the same functions and parameters). The dashed line provides the rate of increase of the productively infected cells, dI₂/dt/I₂, and confirms that the initial rate at which the viral load increases reflects the steady-state killing rate in the late killing regime (K = 4.0) (b) but not in the early killing regime (a). In both regimes, the rate at which the viral load increases rapidly approaches the effective replication rate of ρ ≃ 1 day⁻¹, until the target cell numbers decline. Due to our design of the parameters d₁ and d₂, the downslope of the viral load during ART remains δ ≃ 1 day⁻¹ in both regimes (see Table 1).