An effective malaria vaccine is needed to address the public health tragedy resulting from the high levels of morbidity and mortality caused by Plasmodium parasites. The first protective immune mechanism identified in the irradiated sporozoite vaccine, the "gold standard" for malaria preerythrocytic vaccines, was sporozoiteneutralizing antibody specific for the repeat region of the surface circumsporozoite ( There is a critical need for an effective malaria vaccine, as standard public health measures have been eroded by drug resistance of the parasite and insecticide resistance of the mosquito vector. Moreover, traditional control measures have failed to prevent Plasmodium infections in 300 to 600 million people worldwide, resulting in over 1 million deaths each year (55). Vaccines remain the most cost-effective means for control of infectious diseases. Over the past 30 years, an effective malaria vaccine, based on attenuated sporozoites delivered by the bites of irradiated infected mosquitoes, has been shown to elicit sterile immunity in experimental animal models and human volunteers (11,25,27,45). However, large-scale production of an attenuated parasite vaccine faces significant practical limitations and logistical and regulatory hurdles that must be overcome. Sporozoites cannot be grown in culture and must be dissected from the salivary glands of infected mosquitoes that have fed on blood-stage parasites cultivated in human red blood cells. Additional challenges for attenuated sporozoite vaccines relate to cost, scale-up production, sterility, cold-chain storage, and route of immunization, which in humans has thus far been obtained only by exposure to the bites of irradiated infected mosquitoes. Nevertheless, the ability to elicit sterile protection following immunization with attenuated sporozoites provides a gold standard for development of subunit malaria vaccines that target the preerythrocytic stages of the parasite and effectively prevent initiation of the blood-stage infection responsible for clinical disease.In contrast to whole parasites, peptide vaccines can be readily synthesized from inexpensive, well-defined amino acid components and lyophilized for storage and transport. In recent years, peptide immunotherapeutics have been developed for human autoimmune diseases and allergies (21, 31), and peptide subunit vaccines for infectious diseases and treatment of cancer have been tested in clinical trials (3,24,32,33,52). The first phase I/II trial of a malaria synthetic peptide vaccine was carried out over 20 years ago to assess the efficacy of a peptide-protein conjugate vaccine, termed (NANP) 3 -TT, comprised of the immunodominant B-cell repeat epitope (NANP) 3 from the Plasmodium falciparum major surface circumsporozoite (CS) protein linked to tetanus toxoid (TT) as the protein carrier (26). Exposure of a small number of (NANP) 3 -TTimmunized volunteers to the bites of P. falciparum-infected mosquitoes demonstrated that the vaccine could elicit protective antibody responses against P. falciparum s...