“…In the literature, CTL immune response has been incorporated into mathematical models of different pathogen infections (see e.g. [18,24,25,27,32,33,37,38,48]). The function φ(y, x) has been chosen in different forms such as: (i) constant, φ(y, x) = c 1 [31]; (ii) linear, φ(y, x) = ρy [1,23,44]; (iii) nonlinear φ(y, x) = c 2 yx (see e.g [27,30]).…”