Sterile Protective Immunity to Malaria is Associated with a Panel of Novel P. falciparum Antigens

Abstract

The development of an effective malaria vaccine remains a global public health priority. Less than 0.5% of the Plasmodium falciparum genome has been assessed as potential vaccine targets and candidate vaccines have been based almost exclusively on single antigens. It is possible that the failure to develop a malaria vaccine despite decades of effort might be attributed to this historic focus. To advance malaria vaccine development, we have fabricated protein microarrays representing 23% of the entire P. falciparum proteome and have probed these arrays with plasma from subjects with sterile protection or no protection after experimental immunization with radiation attenuated P. falciparum sporozoites. A panel of 19 pre-erythrocytic stage antigens was identified as strongly associated with sporozoite-induced protective immunity; 16 of these antigens were novel and 85% have been independently identified in sporozoite and/or liver stage proteomic or transcriptomic data sets. Reactivity to any individual antigen did not correlate with protection but there was a highly significant difference in the cumulative signal intensity between protected and not protected individuals. Functional annotation indicates that most of these signature proteins are involved in cell cycle/DNA processing and protein synthesis. In addition, 21 novel blood-stage specific antigens were identified. Our data provide the first evidence that sterile protective immunity against malaria is directed against a panel of novel P. falciparum antigens rather than one antigen in isolation. These results have important implications for vaccine development, suggesting that an efficacious malaria vaccine should be multivalent and targeted at a select panel of key antigens, many of which have not been previously

RTS,S Vaccination Is Associated With Serologic Evidence of Decreased Exposure to Plasmodium falciparum Liver- and Blood-Stage Parasites*

“…Each pad contains 824 peptide fragments expressed from Pf ORFs representing 702 unique proteins and three concentrations of 14 full-length proteins expressed using clinicalgrade manufacturing procedures. The protein targets on the array were selected from published studies done on a larger microarray containing 2,323 protein features after interrogating specimens from naturally exposed individuals (18), and specimens from sporozoite vaccine trials (19). The top 824 most immunoreactive antigens from these studies were printed on this down-selected array.…”

Plasmodium vivax Pre-Erythrocytic–Stage Antigen Discovery: Exploiting Naturally Acquired Humoral Responses

“…Using the ELISA assay, 20-31 donors displayed reactivity to CSP depending on the peptide used. Previous protein microarray serology results from our group showed that, although high levels of anti-PfCSP reactivity are seen in irradiated sporozoite-immunized volunteers, 34,50 antiPfCSP reactivity is much lower in naturally exposed individuals. 32 Reactivity to IVTT-produced P. falciparum CSP (PfCSP) and purified recombinant PfCSP was compared on the same chip; although good correlation was observed between the proteins, the magnitude of the response to the IVTT-produced PfCSP was five times lower than reactivity to the purified PfCSP.…”

Immunization of Mice with Live-Attenuated Late Liver Stage-Arresting Plasmodium yoelii Parasites Generates Protective Antibody Responses to Preerythrocytic Stages of Malaria

“…Finally, it is also possible that both the type and the specificity of antibodies elicited by the two strains of mice in response to malaria infection contribute to the differential levels of protection observed. Studies in human malaria have shown that acquisition of antibodies against non-CSP antigens such as TRAP and LSA1 as well as against other less extensively characterized antigens is associated with the level of protection against malaria (52)(53)(54). Thus, it will be important to identify which antigens are recognized by the antibodies that result from Pyfabb/f Ϫ immunization of the different mouse strains as well as to characterize whether differences in their functional activities correlated with protection.…”