A Linear Peptide Containing Minimal T- and B-Cell Epitopes ofPlasmodium falciparumCircumsporozoite Protein Elicits Protection against Transgenic Sporozoite Challenge

Abstract

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...

Preclinical Vaccine Study of Plasmodium vivax Circumsporozoite Protein Derived-Synthetic Polypeptides Formulated in Montanide ISA 720 and Montanide ISA 51 Adjuvants

“…The P. falciparum RTS,S vaccine candidate has been constructed with sequences representing the R and the C region of the P. falciparum CS 2 known to contain strong B-and T-cell epitopes, respectively. 33 Apparently, for the RTS,S construct the N region of that protein was not considered important; however, in the case of P. vivax we have evidence to believe that the N fragment has greater vaccine potential. 34 The high immunogenicity displayed by the N region of the CS here, is in agreement with previous serological studies performed before, not only with P. vivax 35 but more recently also with P. falciparum , 36 where the N region induced better immunogenicity under natural conditions.…”

Replacing adenoviral vector HVR1 with a malaria B cell epitope improves immunogenicity and circumvents preexisting immunity to adenovirus in mice

“…In order to measure PfCSP-specific humoral immune response, ELISA assay was done as described above, except that ELISA plates were coated with 1 μg/ml (T1B)4 peptide that contains NANP repeat sequence (31). (T1B)4 peptide was provided by Elizabeth Nardin, New York University School of Medicine, New York, New York, USA.…”

Transgenic Rodent Plasmodium berghei Parasites as Tools for Assessment of Functional Immunogenicity and Optimization of Human Malaria Vaccines

“…Through the use of transgenic rodent parasites, it has become possible to quantify infectivity, as well as delineate humoral and cellular immune responses that are critical in anti-CS immunity (10,17). The use of the CS(Pf) transgenic parasites has also demonstrated that linear peptides such as those described above need to be further explored for their potential as vaccines (6). Further vaccine immunogenicity and CS(Pf) sporozoite challenge studies can also help in dissecting the potential roles of various arms of cellular immune responses.…”

“…The findings from this in vivo assay further substantiate the potential of CS-based target antigens to induce either sterile or protective immunity against sporozoite challenge. Other formulations of CS vaccines have also been tested and protective epitopes from linear synthetic peptides containing minimal B-and T-cell epitopes of PfCS have been examined using CS(Pf) in a murine model (6). Peptides containing CS B-and T-cell epitopes were immunogenic in mice and elicited antibodies neutralizing sporozoites of the CS(Pf) parasites (6), suggesting that preerythrocytic vaccine development can benefit from transgenic parasites in murine models.…”

“…Other formulations of CS vaccines have also been tested and protective epitopes from linear synthetic peptides containing minimal B-and T-cell epitopes of PfCS have been examined using CS(Pf) in a murine model (6). Peptides containing CS B-and T-cell epitopes were immunogenic in mice and elicited antibodies neutralizing sporozoites of the CS(Pf) parasites (6), suggesting that preerythrocytic vaccine development can benefit from transgenic parasites in murine models. Furthermore, the neutralization potential of human sera from phase I clinical trials of a CS-based vaccine was assessed using the CS(Pf) parasite (27).…”