A Recombinant Chimeric Ad5/3 Vector Expressing a Multistage Plasmodium Antigen Induces Protective Immunity in Mice Using Heterologous Prime-Boost Immunization Regimens

Abstract

An ideal malaria vaccine should target several stages of the parasite life cycle and induce anti-parasite and anti-disease immunity. We have reported a Plasmodium yoelii chimeric multi-stage recombinant protein (PyLPC/RMC), engineered to express several autologous T cell epitopes and sequences derived from the circumsporozoite protein (CSP) and the merozoite surface protein 1 (MSP-1). This chimeric protein elicits protective immunity, mediated by CD4+ T cells and neutralizing antibodies. However, experimental evidence from pre-erythrocytic vaccine candidates and irradiated sporozoites has shown that CD8+ T cells play a significant role in protection. Recombinant viral vectors have been used as a vaccine platform to elicit effective CD8+ T cell responses. The human adenovirus serotype 5 (Ad5) has been tested in malaria vaccine clinical trials with excellent safety profile. Nevertheless, a major concern for the use of Ad5 is the high prevalence of anti-vector neutralizing antibodies in humans, hampering its immunogenicity. To minimize the impact of anti-vector pre-existing immunity we developed a chimeric Ad5/3 vector in which the knob region of Ad5 was replaced with that of Ad3, conferring partial resistance to anti-Ad5 neutralizing antibodies. Furthermore, we implemented heterologous adenovirus/protein immunization regimens which include a single immunization with recombinant Ad vectors. Our data show that immunization with the recombinant Ad5/3 vector induces protective efficacy indistinguishable from that elicited by Ad5. Our study also demonstrate that the dose of the Ad vectors has an impact on the memory profile and protective efficacy. The results support further studies with Ad5/3 for malaria vaccine development.

A prime-boost immunization regimen based on a simian adenovirus 36 vectored multi-stage malaria vaccine induces protective immunity in mice

“…We previously determined that heterologous adenoviral prime-protein boost regimens are the most efficacious where the combination of adenovirus and protein is used [15, 30]. We, therefore, used one of three doses of the recombinant simian adenoviral vector at either 10 6 , 10 7 , or 10 10 v.p for priming to determine the optimal dose to induce protective efficacy.…”

“…To induce an optimal cellular response against Plasmodium , viral vectors have been used to increase the numbers of CD8 + T cells capable of recognizing Plasmodium antigens [15, 24–26, 30, 44, 45]. Adenoviral vectors are easily adaptable to vaccine studies because of their ability to incorporate large transgene inserts, high levels of transgene expression for periods up to one year [46], and their ability to be mass-produced at vaccine quality under good manufacturing practice [47, 48].…”

“…The replication incompetent Ad5 PyCMP vector was constructed using the E1-deleted Ad5 backbone as we previously described [15, 27]. To construct the genome of simian adenovirus 36 SAdV-36 from species E containing the PyCMP transgene cassette in place of the deleted E1A/B genes we used the strategy originally described by Roy et al [19].…”

“…(High dose), or the previously protective recombinant Ad5 10 7 v.p. dose [15, 30]. All mice received two boosting immunizations with 20 μg of PyCMP emulsified in Montanide ISA 51 (Seppic, Fairfield, NJ) at days 30 and 60.…”

“…This vaccine protected mice from experimental challenge through induction of CD4 + T cells and antibodies [14]. However, the lack of induction of protective CD8 + T cells led us to pursue an adenovirus-vectored malaria vaccine, and we reported that an Ad5 prime and two proteins boosts significantly increased the PyCMP protective effect [15]. …”