Development of a Chimeric Plasmodium berghei Strain Expressing the Repeat Region of the P. vivax Circumsporozoite Protein forIn VivoEvaluation of Vaccine Efficacy

Abstract

The development of vaccine candidates against Plasmodium vivax-the most geographically widespread human malaria species-is challenged by technical difficulties, such as the lack of in vitro culture systems and availability of animal models. Chimeric rodent Plasmodium parasites are safe and useful tools for the preclinical evaluation of new vaccine formulations. We report the successful development and characterization of chimeric Plasmodium berghei parasites bearing the type I repeat region of P. vivax circumsporozoite protein (CSP). The P. berghei-P. vivax chimeric strain develops normally in mosquitoes and produces highly infectious sporozoites that produce patent infection in mice that are exposed to the bites of as few as 3 P. berghei-P. vivax-infected mosquitoes. Using this transgenic parasite, we demonstrate that monoclonal and polyclonal antibodies against P. vivax CSP strongly inhibit parasite infection and thus support the notion that these antibodies play an important role in protective immunity. The chimeric parasites we developed represent a robust model for evaluating protective immune responses against P. vivax vaccines based on CSP.T he global burden of malaria due to Plasmodium vivax is approximately 70 to 390 million cases annually (1), with around 2.5 billion people living at risk of infection (2). Even though Plasmodium falciparum remains the leading cause of malaria in Africa, P. vivax malaria is the most geographically widespread of the human malarias (2, 3). It is extensively distributed throughout the tropics, in the Middle East, Asia, the western Pacific, and Latin America (1-4).P. vivax malaria was long considered a benign and non-lifethreatening disease; however, recent publications report an increasing number of severe, complicated cases due to P. vivax infections (5, 6). Efforts toward the development of antimalaria vaccines are still mainly focused on P. falciparum, although P. vivax malaria is "harder to prevent, diagnose, and treat, and both species are coendemic" (7). While the importance of a vaccine targeting P. vivax is recognized, the development of P. vivax malaria vaccines is hampered by insufficient funding and technical difficulties (2,8,9). The lack of in vitro culture systems and suitable animal models, for example, imposes a significant limitation on testing novel vaccine candidates (7, 10).The circumsporozoite protein (CSP) is the most abundant protein on the surfaces of sporozoites and is responsible for eliciting both T-cell and antibody responses. The plasmodial CSP is one of the best studied antigens and is considered to be a major malaria vaccine candidate. RTS,S, the most effective malaria vaccine candidate to date, is based on P. falciparum CSP, thus underscoring CSP's immunogenic properties. CSP is comprised of an immunodominant central repeat region, diverse among Plasmodium species, flanked by two conserved domains: region I at the N terminus of the repeats and a type I thrombospondin repeat (TSR) motif C terminal to the repeat region. Early studies in animal...

Rational development of a protective P. vivax vaccine evaluated with transgenic rodent parasite challenge models

“…The use of transgenic P. berghei parasites expressing P. vivax or P. falciparum antigens is a practical and affordable option, which can be used in laboratories with access to mouse models. Indeed, such models have been previously used to analyze protective immunity has been reported for several Plasmodium vaccine antigen candidates such as TRAP, CSP and a transmission-blocking vaccine (TBV)21223147. For example, transgenic P. berghei parasites expressing different forms of P. vivax CSP have been generated by Espinosa et al 21.…”

Immunogenicity of a Prime-Boost Vaccine Containing the Circumsporozoite Proteins of Plasmodium vivax in Rodents

“…However, the ability of these antibodies to neutralize sporozoites in vivo has yet to be evaluated with transgenic parasites (31).…”

Baculovirus-Vectored Multistage Plasmodium vivax Vaccine Induces Both Protective and Transmission-Blocking Immunities against Transgenic Rodent Malaria Parasites

“…Our strategy for evaluation of the BDES multistage vaccine used appropriately designed and phenotyped transgenic rodent malaria parasites for assessing murine immune responses to individual antigenic targets from a human malaria parasite. We and other groups have developed several transgenic rodent malaria parasites expressing human malaria antigens (e.g., PfCSP, PfMSP-1 19 , Pfs25, and Pvs25) to evaluate the immunogenicity and/or protective efficacy of vaccines (13,(15)(16)(17)(27)(28)(29)(30). Here, we describe the successful development of PvCSP [PvCSP(Sal)/Pb] transgenic P. berghei parasite expressing the full-length PvCSP-(Sal) in place of the natural P. berghei counterpart.…”

“…Recently, two groups have reported that passive immunization of the MAb-specific CSP repeat region was able to reduce liverstage burden when mice were challenged by the bites of infected mosquitoes using transgenic parasites (30,31), indicating that Abs provide effective protection against a natural infection. One potential reason why there was no significant correlation between the anti-PvCSP Ab titers and the protective efficacy among indi-FIG 7 TB efficacy against Pvs25DR3 by active immunization.…”