• Vaccine Name: ML29
• Target Pathogen: Lassa Fever Virus
• Target Disease: Lassa fever
• Vaccine Ontology ID: VO_0004085
• Type: Attenuated
• Preparation: Clone ML29 is selected and triple plaque purified. The viruses are grown on Vero E6 cells cultured in Dulbecco's modified minimum Eagle's medium with 2% fetal calf serum, 1% penicillin-streptomycin, and l-glutamine (2 mM) at 37°C in 5% CO2. Cells and virus stocks were free of mycoplasma contamination (Lukashevich et al., 2005).
• Description: ML29 is a clone that has been isolated from a Mopeia virus (MOPV) and Lassa virus (LASV) reassortant. It contains the L RNA from MOPV and the S RNA segment from LASV (Lukashevich et al., 2005).

Guinea pig Response

• Host Strain: 13
• Vaccination Protocol: Ten animals were inoculated subcutaneously (s.c.) with the ML29 clone, and 10 guinea pigs received the same dose of MOPV. Eight animals were used as negative controls. At day 30 after vaccination, the animals were s.c. challenged with 10^3 PFU of LASV (Josiah) and followed for 70 days. Liver enzymes were measured in plasma. Vaccinated animals were euthanized on day 70 after challenge, and tissues were removed (Lukashevich et al., 2005).
• Persistence: None noted
• Side Effects: In vaccinated animals, LASV infection did not induce alterations in target tissues. The lungs and livers of vaccinated animals looked essentially like normal tissues. There were also no lesions in other major organs (Lukashevich et al., 2005).
• Efficacy: All strain 13 guinea pigs vaccinated with clone ML29 survived at least 70 days after LASV challenge without either disease signs or histological lesions (Lukashevich et al., 2005).
• Description: Infection of strain 13 guinea pigs with MOPV or with the ML29 reassortant was not lethal for the animals and did not induce clinical or biochemical signs of the disease. All animals survived after challenge and had no clinical manifestations. All measured parameters were in normal ranges in ML29-vaccinated guinea pigs. In MOPV-vaccinated animals, a transient elevation of AST and AlkPh in plasma was observed at week 3 after challenge (Lukashevich et al., 2005).

Monkey Response

• Host Strain: Rhesus macaques
• Vaccination Protocol: Two adult rhesus macaques were s.c. injected with 10^3 PFU of ML29. Blood samples were taken weekly and submitted to the clinical laboratory for complete blood counts and standard 20-assay chemistry panels. At days 14 and 28, the monkeys were euthanized and total blood and tissues were collected. A portion of each tissue was submerged in MEM with 10% FCS (for plaque titration) and in RNAlater (for RNA isolation). The remaining tissue portions were fixed in 10% neutral formalin for the preparation of standard histological sections and stained with hematoxylin-eosin (Lukashevich et al., 2005).
• Efficacy: This data indicates that ML29 vaccination of rhesus macaques results in a short, inapparent, self-limited infection (Lukashevich et al., 2005).
• Description: The ML29-vaccinated animals were afebrile throughout the experiment and had no clinical manifestations. Hematological and chemical parameters were in the normal ranges, as was gross appearance at necropsy. Detailed histological examination of rhesus macaques infected with the ML29 reassortant revealed no tissue lesions. The ML29 virus replicated poorly in monkeys and was not detectable in the plasma and tissues by conventional infectious plaque assay. The only organ from which the virus was recovered was the spleen. RT/PCR with LASV GPC-derived primers was transiently positive with RNA plasma and tissue samples (Lukashevich et al., 2005).