 If 75 of volunteers in group 1 are protected against the homologous Pf CHMI, volunteers in groups 3 and 4 will receive an additional immunization immunization 4, which will consist of six ID injections on the same day of 75,000 PfSPZ Challenge and NS respectively, at day 162. In this fourth immunization period chloroquine will be administered for another 6 weeks starting at day 154. Finally, 33 days after the last dose of chloroquine, volunteers in groups 3 and 4 will have homologous Pf CHMI by the bites of five PfSPZ-infected mosquitoes. 