Heterologous prime-boost immunization in rhesus macaques by two, optimally spaced particle-mediated epidermal deliveries of Plasmodium falciparum circumsporozoite protein-encoding DNA, followed by intramuscular RTS,S/AS02A.
BACKGROUND
RTS,S/AS02A, a recombinant Plasmodium falciparum vaccine based on the circumsporozoite protein (CSP) repeat and C-terminus regions, elicits strong humoral and Th1 cell-mediated immunity. In field studies, RTS,S/AS02A reduced malaria infection, clinical episodes, and disease severity. Heterologous prime-boost immunization regimens, optimally spaced, might improve the protective immunity of RTS,S/AS02A.


METHODS
DNA plasmid encoding P. falciparum CSP (3D7) was administered to six experimental groups of rhesus monkeys (N = 5) by gene gun (coded as D), followed by a 1/5th human dose of RTS,S/AS02A (coded as R). Immunization regimens, including a numeral to denote weeks between immunizations, were D-4-R, D-16-R, D-4-D-4-R, D-4-D-16-R, D-16-D-4-R and D-16-D-16-R. A control group (N = 5) received a single 1/5th dose of RTS,S/AS02A. Endpoints were antibody (Ab) to homologous CSP repeat and C-terminus regions and delayed-type hypersensitivity (DTH) to CSP peptides.


RESULTS
Monkeys immunized twice with DNA, 16 weeks apart (D-16-D-4-R and D-16-D-16-R), developed higher levels of anti-C-terminus Abs than control monkeys (p<0.02). No CSP DNA priming regimen increased RTS,S/AS02A-induced Ab to CSP repeats. At 16 months after first immunization, D-R and D-D-R, but not control, monkeys had histologically confirmed DTH reactions against CSP C-terminus, which persisted at repeat testing 12 months later.


CONCLUSIONS
Two optimally spaced, particle-mediated epidermal deliveries of CSP DNA improved the humoral immunogenicity of a single dose of RTS,S/AS02A. Further, CSP DNA prime followed by one dose of RTS,S/AS02A gave biopsy proven DTH reactions against CSP C-terminus of up to 2 years duration, implying the induction of CD4+ memory T cells. Heterologous prime-boost strategies for malaria involving gene gun delivered DNA or more potent vectors, administered at optimal intervals, warrant further investigation.
Department of Immunology & Medicine, US Army Medical Component, Armed Forces Research Institute of Medical Sciences (AFRIMS), Bangkok, Thailand. douglas.walsh@na.amedd.army.mil
Douglas S
DS
Walsh
Montip
M
Gettayacamin
Wolfgang W
WW
Leitner
Jeffrey A
JA
Lyon
V Ann
VA
Stewart
Gary
G
Marit
Sathit
S
Pichyangkul
Panita
P
Gosi
Pongsri
P
Tongtawe
Kent E
KE
Kester
Carolyn A
CA
Holland
Nelly
N
Kolodny
Joe
J
Cohen
Gerald
G
Voss
W Ripley
WR
Ballou
D Gray
DG
Heppner
D000818:Animals; D000913:Antibodies, Protozoan / Q000096:biosynthesis; D000953:Antigens, Protozoan / Q000235:genetics; D019470:Biolistics; D005260:Female; D006801:Humans; D006968:Hypersensitivity, Delayed; D007115:Immunization Schedule; D007117:Immunization, Secondary; D007273:Injections, Intramuscular; D008253:Macaca mulatta; D017780:Malaria Vaccines / Q000008:administration & dosage* / Q000235:genetics; D016778:Malaria, Falciparum / Q000276:immunology / Q000517:prevention & control; D008297:Male; D010963:Plasmodium falciparum / Q000235:genetics / Q000276:immunology*; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology; D012449:Safety; D019444:Vaccines, DNA / Q000008:administration & dosage / Q000235:genetics
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D017780:Malaria Vaccines; D015800:Protozoan Proteins; C493155:RTS,S-AS02A vaccine; D019444:Vaccines, DNA; C041595:circumsporozoite protein, Protozoan