Antibody Responses Induced In Balb/C Mice Vaccinated With Malaria Dna Vaccine Candidate, Psebcgtt, Co-Expressing Ccl5 Or Ccl20 As Adjuvants

ABSTRACT

Malaria is a leading cause of morbidity and mortality in sub-Saharan Africa. Parasite resistance to current antimalarials and resistance of Anopheline mosquitoes to insecticides have hampered control and elimination of malaria. Over the past twenty years, many vaccine candidates have been under development but none has advanced to clinical trials due to lack of appropriate adjuvant for human use. A vaccine inducing high levels of Immunoglobulin M (IgM), total IgG (or IgG1, IgG2, and or IgG3) would be important for effective control of malaria. DNA vaccines are safer and easy to mass produce and store, but they are less immunogenic and require an adjuvant to boost their immunogenicity. Although the adjuvants CCL5 and CCL20 have chemotactic properties and can immunopotentiate DNA vaccines, no previous study had evaluated their potential use as effective strain transcending blood-stage malaria DNA-adjuvant antibody-inducing vaccine. The present study sought to determine antibody immunity induced in mice vaccinated with malaria DNA vaccine candidate, pSeBCGTT, expressing CCL5 or CCL20 as an adjuvant. Mice in groups of 18 animals each were treated as follows: Group I was vaccinated with pSeBCG/TT/CCL5; Group II was immunized with pSeBCG/TT/CCL20; Group III was injected with pSe/BCG/TT alone while Group IV was inoculated with pIRES plasmid and Group V was a non-vaccinated control. All vaccinations were done intramuscularly with 100 μg of the inoculants per dose on days 0, 21, and 42. Blood samples for sera preparation were collected at day 0, 21, 42 and 63 post-vaccination for determination of antibody levels including IgM, total IgG, and IgG sub-classes. Data were analyzed using one-way analysis of variance (ANOVA) and where applicable, Bonferroni test was used as a post hoc. A P value ≤ 0.05 was considered statistically significant. Results indicated that the mice group vaccinated with pSeBCGTT/CCL20 induced significantly higher IgM antibody levels as compared to pSeBCGTT/CCL5 or pSeBCGTT alone (P < 0.01). Similarly, vaccination with pSeBCGTT/CCL20 produced significantly higher IgG levels as opposed to pSeBCGTT/CCL5 or pSeBCGTT alone (P < 0.01). Further analysis indicated a significant difference in IgG subclasses in vaccinated mice groups with the pSeBCGTT/CCL20 inducing the highest levels of IgG1, IgG2b and IgG3 compared to vaccination with either pSeBCGTT/CCL5 or pSeBCGTT (P < 0.05) while pSeBCGTT/CCL5 induced the highest IgG2a antibody levels as compared to either pSeBCGTT/CCL20 or pSeBCGTT alone (P < 0.05). Comparison between antibody isotype levels showed that IgG levels were significantly higher than IgM (P