Iwasaki Lab/International Research Center for Infectious Diseases  Laboratory of Emerging Viral Diseases

Mammarenaviruses include highly pathogenic agents, like Lassa (West Africa) and Junin (South America) viruses that cause viral hemorrhagic fever in humans and pose serious public health concerns in their endemic regions. In addition, worldwide-distributed lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen with clinical significance. Nonetheless, current therapeutic options against mammarenaviruses are very limited. To develop novel antivirals and vaccines, our research focuses on better understanding of molecular and cellular biology of mammarenaviruses utilizing reverse genetics technologies.


Mammarenaviruses are simple enveloped viruses with four genes encoded in bi-segmented ambisense RNA genomes (Fig 1A). Each RNA segment, small (S) and large (L), directs the synthesis of two viral proteins from two open reading frames separated by non-cording intergenic region (IGR). Despite their simple genome structure, we know very little about mechanistically how they multiply and cause disease in infected hosts. To understand their complex biology and develop antiviral strategies to combat mammarenaviruses, we take advantage of reverse genetics systems for mammarenaviruses, which allow us to generate from cloned cDNAs recombinant mammarenaviruses containing pre-determined mutations or additional foreign genes like enhanced green fluorescence protein (eGFP) or both. Using these technologies, we have generated a recombinant LCMV having synthetic LCMV S-IGR-like IGR instead of L-IGR [rLCMV(IGR/S-Ssyn)] (Fig 1B). rLCMV(IGR/S-Ssyn) grew to high titer in culture cells but severely attenuated in vivo. This strategy can be applicable for the generation of live-attenuated vaccines for currently known, as well as potentially future emerging hemorrhagic fever mammarenaviruses without incorporating amino acid changes. In addition, we have generated rLCMV expressing eGFP or an affinity-tagged viral protein to facilitate genetic and pharmacological screenings and proteome analysis for identification of virus-host interactions required for efficient multiplication of mammarenaviruses that can be exploited as drugable targets (Fig 2).

  • Fig 1.
    (A) Schematic diagram of mammarenavirus genome organization. (B) Predicted RNA secondary structures of the LCMV S-IGR (left) and synthetic LCMV S-IGR-like IGR (right).
    (Iwasaki M. et al., J Virol. (2016) 90(6):3187-97)

  • Fig 2.
    Summary of our findings on each step of the viral life cycle.


  • SA Assoc. Prof.: Masaharu Iwasaki
  • Postdoc.: Mei Hashizume



  • (1)A Lassa Virus Live-Attenuated Vaccine Candidate Based on Rearrangement of the Intergenic Region.Cai Y. et al., mBio (2020) 11(2):e00186-20.
    (2) Interactome analysis of the lymphocytic choriomeningitis virus nucleoprotein in infected cells reveals ATPase Na+/K+ transporting subunit Alpha 1 and prohibitin as host-cell factors involved in the life cycle of mammarenaviruses. Iwasaki M. et al., PLoS Pathog. (2018) 20;14(2):e1006892.
    (3) Resistance of human plasmacytoid dendritic CAL-1 cells to infection with lymphocytic choriomeningitis virus (LCMV) is caused by restricted virus cell entry, which is overcome by contact of CAL-1 cells with LCMV-infected cells. Iwasaki M. et al., Virology. (2017) 511:106-113.
    (4) Residues K465 and G467 Within The Cytoplasmic Domain of GP2 Critically Contribute To LCMV Persistence In Mice. Iwasaki M. et al., J Virol. (2016) 28;90(22):10102-10112.
    (5) The High Degree of Sequence Plasticity of the Arenavirus Noncoding Intergenic Region (IGR) Enables the Use of a Nonviral Universal Synthetic IGR To Attenuate Arenaviruses. Iwasaki M. et al., J Virol. (2016) 90(6):3187-97.
    (6) General Molecular Strategy for Development of Arenavirus Live-Attenuated Vaccines. Iwasaki M. et al., J Virol. (2015) 89(23):12166-77.
    (7) Efficient Interaction between Arenavirus Nucleoprotein (NP) and RNA-Dependent RNA Polymerase (L) Is Mediated by the Virus Nucleocapsid (NP-RNA) Template. Iwasaki M. et al., J Virol. (2015) 89(10):5734-8.
    (8) Cell Entry of Lymphocytic Choriomeningitis Virus Is Restricted In Myotubes. Iwasaki M. et al., Virology. (2014) 458-459:22-32.
    (9) Sodium Hydrogen Exchangers Contribute to Arenavirus Cell Entry. Iwasaki M. et al., J Virol. (2014) 88(1):643-54.