INTRACELLULAR INTERFERENCE OF TICK-BORNE FLAVIVIRUS INFECTION BY USING A SINGLE-CHAIN ANTIBODY FRAGMENT DELIVERED BY RECOMBINANT SINDBIS VIRUS

A single-chain antibody fragment that identifies a neutralizing epitop e on the envelope protein of louping ill and some other tick-borne fla viviruses was previously expressed in soluble form from bacteria and s hown to be functionally active in vitro. To see whether or not the sin gle chain antibody could bind and inactivate infectious virus in vivo, we have used recombinant Sindbis virus as a delivery vehicle for intr acellular expression of the antibody fragment. The variable genes and interchain linker encoding the single chain antibody were cloned into a double subgenomic Sindbis virus expression vector to generate recomb inant Sindbis virus. Infection with this recombinant Sindbis virus pro vided high-level cytoplasmic expression of the antibody fragment in ma mmalian cells. We demonstrate (i) that the antibody fragment was antig en binding and (ii) that louping ill virus infectivity was significant ly reduced in the presence of intracellular antibody expressed by the superinfecting recombinant Sindbis virus.