Delayed-Type Hypersensitivity Response to High Doses of Adenoviral Vectors

Abstract

The present study evaluates the hypothesis that delayed-type hypersensitivity (DTH) contributes to the inflammatory reaction observed when high-dose adenoviral (Ad) vectors are administered to a previously immunized animal. Immunocompetent C57BL/6 mice immunized intraperitoneally with 10⁹ pfu AdCMV.Null [an E1¯, E3¯ Ad vector with a cytomegalovirus (CMV) promoter but no transgene] and challenged intradermally to the footpad with the same vector demonstrated significant footpad swelling 24 hr after challenge with 10⁹ pfu, but not with a lower dose. Footpad histology revealed a mononuclear-granulocytic cellular infiltrate typical of that seen in DTH. Evaluation of the same doses of vector in immunodeficient mice nu/nu and RAG-2¯ on the C57BL/6 background, and nu/nu and severe combined immunodeficiency (SCID) on the BALB/c background demonstrated suppression of footpad swelling. However, the footpad response remained intact inβ ₂-microglobulin deficient (β ₂-m¯) mice, suggesting minimal or no role of major histocompatibility complex (MHC) class I-mediated mechanisms for the region of localized inflammation. Challenge with an Ad expressing the interleukin-2 cDNA to immunized C57BL/6 mice demonstrated augmented footpad swelling response. Finally, pretreatment with cyclosporin resulted in a 69% inhibition of the response compared to controls, whereas other immunosuppressants (cyclophosphamide, methotrexate, and hydrocortisone) had no inhibitory effect. These findings provide further insight into the dynamic interplay of immune processes ultimately leading to inflammation when high-dose Ad vectors are administered to a target organ.

Overview summary

Recombinant adenoviruses (Ad) are efficient vectors for in vivo gene transfer in humans. However, inflammation of the target organ presents a challenge as higher doses of this vector are administered. By using the mouse footpad as a target for Ad infection, we have demonstrated a response that, by quantitative measurements and histologic evaluation, resembles delayed-type hypersensitivity (DTH) when AdCMV.Null 10⁹ pfu is administered to mice previously sensitized to the virus. Challenge with AdCMV.IL-2 to the footpads of immunocompetent mice demonstrated an augmented response. The DTH response to the Ad vectors was suppressed in nude (both C57BL/6 and BALB/c strains), RAG-2¯, and severe combined immunodeficiency disease (SCID) mice, but not β ₂-microglobulin deficient (β ₂m¯) mice. Pretreatment with cyclosporin, but not other conventional immunosuppressants, also inhibited the response. The results of these studies indicate that a DTH response may contribute to the inflammation observed after the administration of high dose Ad and that immunological manipulation of the immune reaction is possible.