Dose optimization phase A: 9x10^5 PfSPZ on Days 0, 7 and 28 (n = 6) B1: 1.35x10^6 PfSPZ on Days 0 and 7 (n = 6) B2: 1.35x10^6 PfSPZ on Days 0, 7, and 28 (n = 6) C1: 2.7x10^6 PfSPZ on Day 0 (n = 6) C2: 2.7x10^6 PfSPZ on Day 0 and 7 (n = 6) C3: 2.7x10^6 PfSPZ on Days 0, 7 and 28 (n = 6)