CD4 and malaria: T cells against liver-stage malaria parasites in mice and nonhuman primates immunized with radiation-attenuated SPZ mediate protection9,29–31 and it is likely this is the case in humans.12 CD8 and CD4 T-cell responses generally peak after the first vaccination with PfSPZ Vaccine.13 In this trial, T-cell responses were measured before immunization, 2 weeks after the first and 2 weeks after the final immunization in Group 2 (1.35 × 105 PfSPZ).