SECRETION OF HUMAN INTERLEUKIN-2 BY RECOMBINANT MYCOBACTERIUM-BOVIS BCG

The human interleukin 2 (huIL-2) gene was introduced into Mycobacteriu m bovis BCG by using the integrative vector pMV306. To express and sec rete huIL-2 from BCG, two different plasmids, CI and CII, were made. I n CI, the huIL-2-encoding region was under the control of the alpha-an tigen promoter of BCG; in CII, the expression of huIL-2 was regulated by the heat shock protein 60 promoter. A signal peptide sequence isola ted from the naturally secreted alpha-antigen of BCG was inserted betw een the promoter and huIL-2-encoding region to facilitate secretion. B oth huIL-2 expression plasmids were integrated into the BCG genome whe n introduced into the BCG Pasteur strain by electroporation. Approxima tely 150 U of huIL-2 was secreted into the medium of a BCG CII culture , while the BCG-CI cells secreted approximately one-sixth of that amou nt. When the IL-2-expressing BCG strain BCG-CII was injected intraveno usly into BALB/c mice. the number of BCG cells in the spleens of these mice was significantly less than the number in the control mice. The decreased number of IL-2-expressing BCG cells is likely due to the aug mentation of the host immune response by the secreted huIL-2, although the exact mechanism is not known.