The 6108A1-500 study is an ongoing, double-blind, ascending-dose, randomized, placebo-controlled trial to assess the safety and tolerability of ascending doses of rLP2086 with aluminum phosphate (AlPO4) adjuvant, in healthy adults aged 18 to 25 years. Upon completion of participation in the 6108A1-500 study, subjects will be approached to participate in this blood sampling study. The sites participating in this blood sampling study are the same sites participating in the 6108A1-500 study.