Immunogenicity of HILDA/LIF either in a Soluble or in a Membrane Anchored Form expressed In Vivo by Recombinant Vaccinia Viruses

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Abstract
Insertion of various cDN As in the genome of the vaccinia virus (VV) enables the in vivo and in vitro study of the functional role and/or the immunogenicity of the virally encoded recombinant proteins. We have prepared a recombinant VV expressing the cDNA of the human cytokine HILDA/LTF (human interleukin for DA cells/leukaemia inhibitory factor), and used this virus to immunize mice against this protein, which is very homologous to its murine counterpart (∼80% homology). We also constructed and expressed by the same system a chimeric gene encoding the HILDA/LIF protein fused to the 37 COOH‐terminal amino‐acids of the human decay accelerating factor (DAF). This sequence proved to be sufficient for the targeting of the fusion protein to the cell membrane, where it is linked to the phosphatidylinositols. Both recombinant VVs induced cytokine‐specific antibodies in mice as analysed with an FLISA where the recombinant HILDA/LIF was plastic‐coated and a cytofluorometric assay where the LIF‐DAF molecule was present at the cell surface of stably transfected PS15. In the latter case HILDA/LIF remained biologically active suggesting that it was expressed in its native form. The LIF‐DAF fusion protein was found to exhibit a better capacity to elicit an antibody response against the native form of the cytokine as detected in cytofluorometric assays. Whatever the recombinant virus used to immunize the mice, the MoAbs obtained were positive either in the ELISA or in the cytofluorometric assays but one, which suggested that the plastic coating induced a conformationa1 change of HILDA/LIF.