Effect of anti-CD8 Mab treatment in monkeys protected by the irradiated sporozoite vaccine.

In the two Cohorts, a total of five monkeys vaccinated with irradiated Pk sporozoites were protected in their 1st Challenge with malaria sporozoites. Before their 2nd Challenge, Monkey A received control IgG while monkeys B–E received anti-CD8 Mab. Monkeys B, D, and E experienced a profound drop in circulating CD3+CD8+ T cells and became infected when given a 2nd Challenge with sporozoites. Monkey A was protected. Monkey C retained some CD3+CD8+ T cells and was also protected. After the 2nd Challenge, monkeys B, D, and E and control monkeys were drug treated and rested for 4 months before their 3rd Challenge. At the time of the 3rd Challenge circulating CD3+CD8+ T cells had returned, and all 5 vaccinated monkeys were again protected.*Control monkeys in the 1st and 2nd Challenges were malaria naïve.**Control monkeys in the 3rd Challenge had been infected once in the 2nd Challenge.