Anti-TRAP/SSP2 monoclonal antibodies can inhibit sporozoite infection and enhance protection of anti-CSP monoclonal antibodies

Vaccine-induced sterilizing protection from infection by Plasmodium parasites, the pathogens that cause malaria, will be essential in the fight against malaria as it would prevent both malaria-related disease and transmission. Stopping the relatively small number of parasites injected by the mosquito before they can migrate from the skin to the liver is an attractive means to this goal. Antibody-eliciting vaccines have been used to pursue this objective by targeting the major parasite surface protein present during this stage, the circumsporozoite protein (CSP). While CSP-based vaccines have recently had encouraging success in disease reduction, this was only achieved with extremely high antibody titers and appeared less effective for a complete block of infection (i.e. sterile protection). While such disease reduction is important, these and other results indicate that strategies focusing on CSP alone may not achieve the high levels of sterile protection needed for malaria eradication. Here, we show that monoclonal antibodies (mAbs) recognizing another sporozoite protein, TRAP/SSP2, exhibit a range of inhibitory activity and that these mAbs can augment CSP-based protection despite conferring no sterile protection on their own. Therefore, pursuing a multivalent subunit vaccine immunization is a promising strategy for improving infection-blocking malaria vaccines.