Modeling the effects of tetanus vaccination on chronically infected HIV patients

T-cell activation plays a critical role in the initiation and propagation of HIV-1 infection and yet transient activation of the immune system is a normal response to immunization. In this study we extend a simple of model of HIV infection to include T cell activation by vaccination. We then show that the model can reproduce many but not all of the features of the post-tetanus immunization rise in viral load observed and reported on by Stanley et al., [N. Engl. J. Med., 334:1222--1230 (1996)]. Amplitudes and approximate timing of post-immunization maximum viremia were matched in nine of twelve cases; in patients with double peaks of nearly equal amplitude the later peaks were matched. Patients with single early peaks in their viremia were best fit with relatively high antigen clearance rate constants, while patients with early and late peaks in viremia of equal or nearly equal amplitude were best-fit with much lower clearance rates. The rate of clearance may depend on the level of pre-existing antibody, which in turn would be expected to depend on the time since the individual under study received a previous tetanus vaccination.