Induction of immune responses in mice and monkeys to Ebola virus after immunization with liposome-encapsulated irradiated Ebola virus: protection in mice requires CD4(+) T cells.
Ebola Zaire virus (EBO-Z) causes severe hemorrhagic fever in humans, with a high mortality rate. It is thought that a vaccine against EBO-Z may have to induce both humoral and cell-mediated immune responses to successfully confer protection. Because it is known that liposome-encapsulated antigens induce both antibody and cellular responses, we evaluated the protective efficacy of liposome-encapsulated irradiated EBO-Z [L(EV)], which contains all of the native EBO-Z proteins. In a series of experiments, mice immunized intravenously with L(EV) were completely protected (94/94 mice) against illness and death when they were challenged with a uniformly lethal mouse-adapted variant of EBO-Z. In contrast, only 55% of mice immunized intravenously with nonencapsulated irradiated virus (EV) survived challenge, and all became ill. Treatment with anti-CD4 antibodies before or during immunization with L(EV) eliminated protection, while treatment with anti-CD8 antibodies had no effect, thus indicating a requirement for CD4(+) T lymphocytes for successful immunization. On the other hand, treatment with either anti-CD4 or anti-CD8 antibodies after immunization did not abolish the protection. After immunization with L(EV), antigen-specific gamma interferon (IFN gamma)-secreting CD4(+) T lymphocytes were induced as analyzed by enzyme-linked immunospot assay. Anti-CD4 monoclonal antibody treatment abolished IFN gamma production (80 to 90% inhibition compared to that for untreated mice). Mice immunized with L(EV), but not EV, developed cytotoxic T lymphocytes specific to two peptides (amino acids [aa] 161 to 169 and aa 231 to 239) present in the amino-terminal end of the EBO-Z surface glycoprotein. Because of the highly successful results in the mouse model, L(EV) was also tested in three cynomolgus monkeys. Although immunization of the monkeys with L(EV)-induced virus-neutralizing antibodies against EBO-Z caused a slight delay in the onset of illness, it did not prevent death.
Rao
Mangala
M
Department of Membrane Biochemistry, Walter Reed Army Institute of Research, Silver Spring, Maryland 20910-7500, USA. Mangala.Rao@Na.Amedd.Army.Mil
Bray
Mike
M
Alving
Carl R
CR
Jahrling
Peter
P
Matyas
Gary R
GR
D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D004195:Disease Models, Animal; D029043:Ebolavirus / Q000276:immunology* / Q000528:radiation effects; D005260:Female; D019142:Hemorrhagic Fever, Ebola / Q000276:immunology / Q000517:prevention & control*; D006801:Humans; D007114:Immunization; D007371:Interferon-gamma / Q000096:biosynthesis; D008081:Liposomes; D008252:Macaca fascicularis; D051379:Mice; D008807:Mice, Inbred BALB C; D016176:T-Lymphocyte Subsets / Q000276:immunology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D014764:Viral Proteins / Q000008:administration & dosage / Q000276:immunology*; D014765:Viral Vaccines / Q000008:administration & dosage / Q000276:immunology*
D000914:Antibodies, Viral; D008081:Liposomes; D014764:Viral Proteins; D014765:Viral Vaccines; D007371:Interferon-gamma