Development of an adenovirus vector lacking the expression of virus-associated RNAs

A major limitation of the use of adenovirus (Ad) vectors is the innate immune response, which causes inflammatory cytokine production and tissue damages. To overcome this limitation, it is necessary to develop safer Ad vectors that are less likely to induce innate immunity. The Ad genome encodes two non-coding small RNAs, virus-associated (VA)-RNA I and VA-RNA II, which are transcribed by RNA polymerase III and promote Ad replication. Recently, we reported that VA-RNAs are produced in the cells transduced with a conventional first-generation (E1-deleted) Ad vector (FG-Ad) and trigger innate immune responses through intracellular nucleic acid sensors. In the present study, we have developed a VA-RNA-deleted Ad (AdΔVR) vector, in which the transcriptional control elements of the VA-RNA-expression were deleted. Although conventional HEK293 cells did not support the propagation of the AdΔVR vectors, HEK293 transformants inducibly expressing VA-RNA I (VR293 cells) with appropriate induction of VA-RNA I expression allowed the propagation of the AdΔVR vector. The AdΔVR vector showed high transduction efficiency comparable to that of the conventional FG-Ad vector in the cultured cells. The AdΔVR vector may be a safer alternative to the FG-Ad vector.