Enhanced Efficacy of a Codon-Optimized DNA Vaccine Encoding the Glycoprotein Precursor Gene of Lassa Virus in a Guinea Pig Disease Model When Delivered by Dermal Electroporation

Abstract

Lassa virus (LASV) causes a severe, often fatal, hemorrhagic fever endemic to West Africa. Presently, there are no FDA-licensed medical countermeasures for this disease. In a pilot study, we constructed a DNA vaccine (pLASV-GPC) that expressed the LASV glycoprotein precursor gene (GPC). This plasmid was used to vaccinate guinea pigs (GPs) using intramuscular electroporation as the delivery platform. Vaccinated GPs were protected from lethal infection (5/6) with LASV compared to the controls. However, vaccinated GPs experienced transient viremia after challenge, although lower than the mock-vaccinated controls. In a follow-on study, we developed a new device that allowed for both the vaccine and electroporation pulse to be delivered to the dermis. We also codon-optimized the GPC sequence of the vaccine to enhance expression in GPs. Together, these innovations resulted in enhanced efficacy of the vaccine. Unlike the pilot study where neutralizing titers were not detected until after virus challenge, modest neutralizing titers were detected in guinea pigs before challenge, with escalating titers detected after challenge. The vaccinated GPs were never ill and were not viremic at any timepoint. The combination of the codon-optimized vaccine and dermal electroporation delivery is a worthy candidate for further development.

Keywords: Lassa fever; Lassa virus; arenavirus; dermal electroporation; guinea pigs; vaccination; vaccine.

Figure 1

Plasmid Map and Immunoprecipitation and polyacrylamide gel electrophoresis (PAGE) of radiolabeled LASV strain Josiah glycoprotein precursor (GPC, 76 KD). (A) Map of pLASV-GPC cloned into the pWRG7077 vaccine plasmid. (B) Radioimmunoprecipitation and PAGE of LASV GPC and GP2 from COS-7 cell lysate. Expression products from COS-7 cells transfected with (Lane 1) empty vaccine plasmid pWRG7077 or (Lane 2) recombinant pLASV-GPC, and immunoprecipitated with LASV-immune guinea pig serum. The sizes of molecular weight markers M and the location of bands corresponding to GPC and GP2 are indicated.

Figure 2

Outcomes for IMEP study using the non-optimized LASV DNA construct. (A) Survival curve; (B) Serum viremia as measured by plaque assay; (C) Morbidity score based on observed disease signs.

Figure 3

Outcomes for dermal versus muscle electroporation using the codon-optimized LASV DNA construct. (A) Survival curve; (B) Serum viremia as measured by plaque assay; (C) Average body temperature changes as a function of time postinfection, and (D) Morbidity score based on observed disease signs. The grey bar indicates the normal body temperature range for guinea pigs.

Figure 4

Immunohistochemistry staining for LASV antigen in selected tissues of mock-vaccinated or ELGEN-MID-vaccinated guinea pigs. (A) Viral antigen staining of a mock-vaccinated lymph node (40×); (B) lymph node of a ELGEN-MID-vaccinated animal showing lymphoid hyperplasia and a lack of viral staining (20×); (C) Viral antigen staining of a mock-vaccinated spleen (40×); (D) Splenic white pulp hyperplasia in a ELGEN-MID-vaccinated guinea pig (40×); (E) Viral antigen staining of a mock-vaccinated adrenal gland (10×); (F) A lack of viral antigen staining of a ELGEN-MID-vaccinated adrenal gland (10×); (G) Viral antigen staining of a mock-vaccinated liver (20×); (H) A lack of viral antigen staining of a ELGEN-MID-vaccinated liver (10×); (I) Viral antigen staining of a mock-vaccinated kidney (20×); (J) A lack of viral antigen staining of a ELGEN-MID-vaccinated kidney (10×).

Figure 5

Outcome of backchallenge experiment. (A) Survival curve; (B) Average weights postchallenge; and (C) Average temperatures post-challenge for animals enrolled in the backchallenge experiment.