Long-term efficacy and immune responses following immunization with the RTS,S malaria vaccine.
The malaria sporozoite vaccine candidate RTS,S, formulated with an oil-in-water emulsion plus the immunostimulants monophosphoryl lipid A and the saponin derivative QS21 (vaccine 3), recently showed superior efficacy over two other experimental formulations. Immunized volunteers were followed to determine the duration of protective immune responses. Antibody levels decreased to between one-third and one-half of peak values 6 months after the last dose of vaccine. T cell proliferation and interferon-gamma production in vitro were observed in response to RTS,S or hepatitis B surface antigen. Seven previously protected volunteers received sporozoite challenge, and 2 remained protected (1/1 for vaccine 1, 0/1 for vaccine 2, and 1/5 for vaccine 3). The prepatent period was 10.8 days for the control group and 13.2 days for the vaccinees (P < .01). Immune responses did not correlate with protection. Further optimization in vaccine composition and/or immunization schedule will be required to induce longer-lasting protective immunity.
Stoute
J A
JA
Department of Immunology, Walter Reed Army Institute of Research, Washington, DC, USA. stoutej@wrsmtp-ccmail.army.mil
Kester
K E
KE
Krzych
U
U
Wellde
B T
BT
Hall
T
T
White
K
K
Glenn
G
G
Ockenhouse
C F
CF
Garcon
N
N
Schwenk
R
R
Lanar
D E
DE
Sun
P
P
Momin
P
P
Wirtz
R A
RA
Golenda
C
C
Slaoui
M
M
Wortmann
G
G
Holland
C
C
Dowler
M
M
Cohen
J
J
Ballou
W R
WR
D000293:Adolescent; D000328:Adult; D000913:Antibodies, Protozoan / Q000097:blood; D018572:Disease-Free Survival; D006801:Humans; D007371:Interferon-gamma; D017780:Malaria Vaccines / Q000276:immunology*; D016778:Malaria, Falciparum / Q000517:prevention & control*; D008875:Middle Aged; D015800:Protozoan Proteins / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology; D014611:Vaccination; D014614:Vaccines, Synthetic / Q000276:immunology
D000913:Antibodies, Protozoan; D017780:Malaria Vaccines; D015800:Protozoan Proteins; D014614:Vaccines, Synthetic; C041595:circumsporozoite protein, Protozoan; D007371:Interferon-gamma