Measles Virus (MV) as Vaccine-vectors

The attenuated measles virus (MV) vaccine strain has become a promising oncolytic vector platform due to its many good characteristics. Reverse genetics technology using a helper-cell-based rescue system allowed the production of a variety of live recombinant MV (rMV) that are capable of stably expressing heterologous proteins. The rMV vector is highly safe, induces humoral and cellular immune responses against transgenes, and provides lasting protection, making it an attractive candidate to prevent infectious diseases.

Structure of Measles Virus

Measles virus (MV), the causative agent of measles, is a negative-sense RNA virus with a nonsegmented genome and a lipid envelope that belongs to the morbillivirus genus of the family Paramyxoviridae. The MV has a genome size of 16 kb and encodes eight proteins, six of which are present in virions. The envelope has surface protrusions composed of viral hemagglutinin (H) and fusion (F) glycoproteins. H interacts with viral receptors on susceptible cells for attachment, and F interacts with H and cell membranes for fusion and entry. The helical ribonucleocapsid is formed from the genomic RNA wrapped by the nucleoprotein (N) with attached phosphoprotein (P) and large polymerase (L) proteins. The matrix (M) protein interacts with the ribonucleocapsid and the tail of the glycoprotein for the assembly of virions. C and V are non-structural proteins encoded within the P gene that regulate cellular responses to infection and modulate IFN signaling.

Fig.1 Schematic diagram of the measles virus and its genome. (Brandler. 2008)

Measles Virus as Vaccine-vectors

In 1954, Enders and Peebles produced the attenuated Edmonston A and B, Zagreb (EZ), and AIK-C seeds in a variety of cell lines. The Edmonston B vaccine was licensed in 1963 but frequently caused fever and rash. Further passages of Edmonston A and B on chick embryo fibroblasts produced the more attenuated Schwarz and Moraten vaccines. Therefore, the currently used attenuated strains mainly include Schwarz/Moraten, AIK-C, and Zagreb (EZ). Attenuated MV have acquired the ability to use the complement regulator CD46 as a major receptor to mediate virus entry and intercellular fusion. Therefore, attenuated MV strains preferentially infect and destroy a wide variety of cancer cells making them attractive oncolytic vectors.

Production of Recombinant Measles Virus Vector

Expression systems have been designed to rescue replicated MVs from cloned DNA expression constructs. Reverse genetics allows rescue of recombinant measles virus in the HEK293 helper cell line, where the foreign gene can be inserted between the P and M protein in the measles virus genome or H and L proteins respectively. The helper cell line is co-transfected with the recombinant MV construct and the plasmid expressing the MV polymerase L gene, followed by transfer of the syncytia to a specific cell culture after several days, and the recombinant MV particles are harvested when the 80%-90% cytopathic effect is reached.

Fig.2 The schematic shows the cloning location of the exogenous transgenes into the measles virus (MV) genome. The measles virus structural proteins are flanked by T7 RNA polymerase promoter and the T7 RNA polymerase terminator. N=nucleoprotein; P=phosphoprotein; M=matrix protein; F=fusion protein; H=hemagglutinin; L=large polymerase protein; T7=T7 RNA polymerase promoter; T7 term=T7 RNA polymerase terminator.

Features of Measles Virus as Vaccine-vectors

• Can stably express heterologous genes singly or in combination
• Lack of genomic integration in the host cell due to cytoplasmic replication
• Recombinant MV induces a quantitative immune response against itself and the cloned gene products
• Large foreign gene insertion capacity (> 6 kb)
• Large-scale production in most countries at low cost
• Selectivity to tumor cells in case of virotherapy applications

Attenuated measles virus vaccine represents a number of essential features for the development of candidate prophylactic and therapeutic vaccines. Creative Biolabs rescues this negative-strand RNA virus from cloned DNA by using reverse genetics techniques without affecting the viral structure, reproduction, and cell targeting. The recombinant virus rescued from the cloned cDNA induces a strong immune response against the measles virus and the cloned antigen.

Reference

1. Brandler S and Tangy F. (2008). Recombinant vector derived from live attenuated measles virus: potential for flavivirus vaccines. Comp Immunol Microbiol Infect Dis, 31(2): 271-291.

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