Defective interfering influenza virus RNAs: time to reevaluate their clinical potential as broad-spectrum antivirals?

Abstract

Defective interfering (DI) RNAs are highly deleted forms of the infectious genome that are made by most families of RNA viruses. DI RNAs retain replication and packaging signals, are synthesized preferentially over infectious genomes, and are packaged as DI virus particles which can be transmitted to susceptible cells. Their ability to interfere with the replication of infectious virus in cell culture and their potential as antivirals in the clinic have long been known. However, until now, no realistic formulation has been described. In this review, we consider the early evidence of antiviral activity by DI viruses and, using the example of DI influenza A virus, outline developments that have led to the production of a cloned DI RNA that is highly active in preclinical studies not only against different subtypes of influenza A virus but also against heterologous respiratory viruses. These data suggest the timeliness of reassessing the potential of DI viruses as a novel class of antivirals that may have general applicability.

FIG 1

Schematic of the different types of DI RNA (not to scale). The virus genome is shown at the top with terminal sequences containing the replication signals labeled at the 5′ end (a) and at the 3′ end (g). The remainder of the genome is arbitrarily divided into sections to indicate the possible origin of some of the DI RNA sequences. See the text for explanations of sections i to iv.

FIG 2

Schematic diagram of the structure of influenza 244 DI RNA. This 395-nucleotide RNA was derived by a single central deletion from the full-length genomic segment 1 (2,341 nucleotides) of A/PR/8/34 (H1N1) (42). Numbers indicate the nucleotide positions of the breakpoints in the genomic segment 1 RNA (negative sense, 3′ to 5′). The sequence is in GenBank under accession number FB718012.

FIG 3

Comparison of prophylactic (a, b) and therapeutic (c, d) protection of mice mediated by a single dose of intranasal 244 DI virus. (a, c) Homologous protection from clinical disease caused by intranasal influenza A virus (A/WSN, H1N1); (b, d) heterologous protection from clinical disease caused by intranasal pneumonia virus of mice (PVM). Mice were 5-week-old C3H/He-mg. The filled and open arrows indicate the delivery of the DI virus and the challenge virus (10 50% lethal doses [LD₅₀]), respectively. Mice were anesthetized before inoculation. DI virus was administered at a time that gives optimum protection in each virus system. On the y axis, a score of 1 indicates a normal healthy mouse and 5 is a dead mouse; a score of 2 to 4 refers to increasingly severe clinical disease estimated on a formal scale (42). In parentheses is the percentage survival at the end of the study. Helper virus infectivity was removed from the DI virus preparation by UV irradiation for 40 s. For the prophylaxis studies depicted in panels a and b, the symbols indicate: ◼, 1.2 μg DI virus protein; ◆, 0.12 μg DI virus; ▲, 0.012 μg DI virus (PVM only); ◻, 1.2 μg DI virus inactivated by extensive UV irradiation (8 min) for influenza and PVM challenges, respectively; ○, a control group inoculated with diluent—these all had a value of 1. For the therapeutic studies (panels c and d), influenza and PVM infections were treated with optimally effective amounts of DI virus (12 μg and 1.2 μg protein, respectively). Mice were treated with DI virus after infection at the following times: 1 day (◼), 2 days (◆), or 3 days (▲; PVM only); with inactivated DI virus at 1 day (◻); or with diluent (○)—these all had a value of 1. Data are from references and .

FIG 4

Decay of 244 DI RNA in the lungs of mice inoculated with 12 μg 244 DI virus protein. The amount of 244 RNA associated with the lung was determined by quantitative PCR (89). Also shown is the amount of 244 RNA administered initially (inoculum) and the lack of signal at 1 and 6 weeks in the lungs of mice inoculated with diluent (mock) (B. Meng, A. J. Easton, and N. J. Dimmock, unpublished data).