Status in the development of ASFV live
attenuated vaccinesManuel V. Borca
Plum Island Animal Disease Center, ARS, USDA, USA
African swine fever: Call for action | Series of webinars | 26-30 October 2020
Attenuated isolates were produced by:
• Low virulence field isolates
• Viruses attenuated by tissue culture passages
• Viruses with genetically engineered deletions
Live attenuated virus strains are effective
protecting against the challenge with
homologous virulent virus
Attenuated isolates were produced by:
• Low virulence field isolates
Low virulent field isolates
retain residual virulence
Live attenuated virus strains are effective
protecting against the challenge with
homologous virulent virus
Live attenuated virus strains are effective
protecting against the challenge with
homologous virulent virus
Attenuated isolates were produced by:
• Viruses with genetically engineered deletions
Infection
ASFV
Macrophages/Vero
Transfection
Recombination
xSelection
P72 GUS
Virus Stock
Purity
assessmentSequencing
Test for attenuation
Developing recombinant viruses from virulent field isolates
Discovering determinant of virulenceAllowed the identification of the
role of specific genes in virus
virulence
Set the bases for the rationally
development of experimental
vaccines
African swine fever virus genome
• Double-stranded DNA virus (genome 170-190kb)
• Contains more than 150 genes
• Most of the genes have been characterized by
functional genomics
• Very few genes (30%) have been experimentally
studied.
19 different genes tested
8 genes associated with
virulence: (9GL, NL, UK, MGF,
DP148R, TK, CD2, I177L)
ASFV-G-Δ9GL
9GL gene deletion does not
attenuate Georgia strain as
efficiently as it does in either
Malawi or Pretoria isolates
ASFV-G 9GL/UK
1 189340p72-GUS
ASFV-G ΔB119L
95104 95278 184331184621
P96R
1 189340P96R ASFV sequencesASFV sequencesp72-GUS
95104 95278
1 189340p72-GUS p72-mCherry
184331 184586
ASFV-G ΔB119L/DP96R
95104 95278
1 189340B119L
94949 95308
1 189340B119L ASFV sequencesASFV sequences
184331184621
P96RASFV-G
184331184621
P96RASFV-G-9GL/UK:
• Deletion of UK in the ASFV-G-9GL genome
increases virus attenuation at least hundred times
Several naturally attenuated isolates present deletions in this area
These genes have been involved in modulation of the innate immune response
These genes was shown to revert to virulence virus attenuated strains having
deletions in this area of the genome
The MGF360/MGF505 area
and virus attenuation
HLJ/18-7GD
INIM
HLJ/18-7GD remains attenuated after 5
passages in pigs and was innocuous in
pregnant sows
Several laboratories showed that deletion of
MGF360/505 genes efficiently attenuate virus virulence
Virus having deleted these genes produce protection
against disease caused by homologous virus challenge
MGF360/505 genes area is inclined to participate in
recombination events. Problems with genetic stability?
BA71CD2
BA71CD2 induced protection against challenge
with homologous and heterologous virus
BA71CD2 can be growth in a stable cell line
BeninDP148R
Deletion of DP148R produced attenuation of
Benin virus
ASFV-G-I177L
ASFV-G-I177L
• Induces protection even at a dose of 102 HAD50
• Lacks residual virulence even at a dose of 106 HAD50
• Does not induce virus shedding
• Induces sterile immunity
Gaps
Study critical aspects of vaccine candidates (onset and duration of
immunity, genetic stability, attenuation stability, minimal protection
doses, possible routes of inoculation)
• Standardization of methodologies to test efficacy of vaccine candidates
(vaccine doses, route of inoculation, challenge dose)
• Develop vaccine candidates with DIVA capability
• Investigate the bases of the differential effect in virus virulence of
deleting the same genes among different virus isolates (9GL, NL, UK,
TK, DP148R)
• Continue the discovery and characterization of virulence associate genes
Thank You
