CD4 and AIDS: We keep the b = 3.5x10-5 and decrease the T ̄ number to i) T ̄ = 5x105 cells per ml, corresponding to average chronic HIV CD4+ T cell numbers [47]; ii) T ̄ = 3.3x105 cells per ml as in the HIV/HPV co-infection study [41]; and iii) T ̄ = 2x105 cells per ml, corresponding to AIDS.