Adeno-Associated Virus as an Effective Malaria Booster Vaccine Following Adenovirus Priming

Abstract

An ideal malaria vaccine platform should potently induce protective immune responses and block parasite transmission from mosquito to human, and it should maintain these effects for an extended period. Here, we have focused on vaccine development based on adeno-associated virus serotype 1 (AAV1), a viral vector widely studied in the field of clinical gene therapy that is able to induce long-term transgene expression without causing toxicity in vivo . Our results show the potential utility of AAV1 vectors as an extremely potent booster vaccine to induce durable immunity when combined with an adenovirus-priming vaccine in a rodent malaria model. We generated a series of recombinant AAV1s and human adenovirus type 5 (AdHu5) expressing either Plasmodium falciparum circumsporozoite protein (PfCSP) or P25 (Pfs25) protein. Heterologous two-dose immunization with an AdHu5-prime and AAV1-boost (AdHu5-AAV1) elicited robust and durable PfCSP- or Pfs25-specific functional antibodies over 280 days. Regarding protective efficacy, AdHu5-AAV1 PfCSP achieved high sterile protection (up to 80% protection rate) against challenge with transgenic Plasmodium berghei sporozoites expressing PfCSP. When examining transmission-blocking (TB) efficacy, we found that immunization with AdHu5-AAV1 Pfs25 maintained TB activity in vivo against transgenic P. berghei expressing Pfs25 for 287 days (99% reduction in oocyst intensity, 85% reduction in oocyst prevalence). Our data indicate that AAV1-based malaria vaccines can confer potent and durable protection as well as TB efficacy when administered following an AdHu5 priming vaccine, supporting the further evaluation of this regimen in clinical trials as a next-generation malaria vaccine platform.

A Viral-Vectored Multi-Stage Malaria Vaccine Regimen With Protective and Transmission-Blocking Efficacies

“…The transgenic P. berghei Pfs25DR3 ( Pb Pfs25DR3) that was used for TB assays and the ookinete immunofluorescence assays (IFAs) was kindly donated by A. Blagborough from Imperial College London (22). The transgenic P. berghei expressing PfCSP (PfCSP-Tc/Pb) that was used for the IFAs and the protective efficacy study was described previously (21–23). Both transgenic parasites were maintained in the Laboratory of Vaccinology and Applied Immunology, Kanazawa University.…”

“…For the generation of AdHu5-Pfs25-PfCSP, the gene encoding Pfs25 and the Gly6Ser hinge was excised from pUC57-Simple-sPfs25-hinge (21) by digestion with EcoRI/MefI and then inserted into the EcoRI site of pENTR-D-sPfCSP2-G2-sWPRE (23) to construct pENTR-D-fusion. Pfs25-PfCSP was excised by digestion of pENTR-D-sPfs25-sPfCSP-WPRE with EcoRI/XmaI and then inserted into the EcoRI/XmaI sites of pENTR-CAG-sPfCSP2-G2-sWPRE (21) to construct pENTR-CAG-sPfs25-sPfCSP2-G2-sWPRE, which was subsequently cloned into the shuttle vector pAd/PL-DEST (Invitrogen, Carlsbad, CA, USA) using a Gateway cloning technology. The adenovirus was purified and titrated as described previously (24).…”

“…The adenovirus was purified and titrated as described previously (24). For the generation of AAV1-Pfs25-PfCSP, the gene cassette encoding the fusion Pfs25-PfCSP was excised from pENTR-CAG-sPfs25-sPfCSP2-G2-sWPRE by digestion with KpnI and XhoI and then inserted into the KpnI and XhoI sites of pAAV-CMV-sPfs25 (21). The resulting plasmid, pAAV-CMV-sPfs25-sPfCSP2, was used to generate AAV1-Pfs25-PfCSP in HEK293 cells as described previously (25).…”

“…Very recently, our group generated a series of human adenovirus 5 (AdHu5) and adeno-associated virus serotype 1 (AAV1) expressing either P. falciparum pre-erythrocytic PfCSP or sexual stage Pfs25 antigen. Heterologous two-dose immunization with an AdHu5-prime and AAV1-boost elicited a high level of protection against sporozoite challenge and excellent TB activity with sustained high-titer antibody responses (21). Using the same platform, the present study aimed to develop a potent multi-stage malaria vaccine to effectively induce durable immunity for both protection and TB, which lasts for at least one transmission season (~6 months).…”

In vivo Characterization of Plasmodium berghei P47 (Pbs47) as a Malaria Transmission-Blocking Vaccine Target

“…Most TBVs rely on host antibodies ingested during blood feeding, along with Plasmodium parasites, that bind to proteins on the surface of the parasite and block transmission by inhibiting parasite development ( Sauerwein and Bousema, 2015 ; Schorderet-Weber et al, 2017 ). Over the last 20 years, a number of antigens, including Pfs230 ( MacDonald et al, 2016 ; Marin-Mogollon et al, 2018 ; Scaria et al, 2019 ), Pfs48/45 ( Theisen et al, 2014 ; Singh et al, 2017 , 2019 ; Cao et al, 2018 ; Lennartz et al, 2018 ), and Pfs25 in Plasmodium falciparum as well as its ortholog Pvs25 in Plasmodium vivax ( Miura et al, 2007 ; Lee et al, 2016 ; Blagborough et al, 2016 ; Brune et al, 2016 ; Leneghan et al, 2017 ; Parzych et al, 2018 ; Thompson et al, 2018 ; McLeod et al, 2019 ; Yusuf et al, 2019 ), have been identified as potential vaccine targets. Preclinical and clinical studies have shown that TBVs hold the promise to reduce malaria transmission and raise the prospect of providing an additional effective tool toward malaria eradication ( Chichester et al, 2018 ; Sagara et al, 2018 ).…”