IMMUNOGENIC TARGETING OF RECOMBINANT PEPTIDE VACCINES TO HUMAN ANTIGEN-PRESENTING CELLS BY CHIMERIC ANTI-HLA-DR AND ANTISURFACE IMMUNOGLOBULIN-D ANTIBODY FAB FRAGMENTS IN-VITRO

To increase the inherently weak immunogenicity of synthetic peptide va ccines, we used recombinant DNA techniques to generate chimeras betwee n immunogenic determinants of human immunodeficiency virus type 1 (HIV -1) gp120 and antibody Fab fragments reactive with surface structures displayed specifically on human antigen-presenting cells (APCs), inclu ding surface immunoglobulin D (sIgD) and class II major histocompatibi lity complex (MHC) molecules. Hybridomas producing anti-human MHC clas s II (HLA-DR) or surface immunoglobulin D monoclonal antibodies (MAbs) that recognize nonpolymorphic determinants were used to clone chimeri c Fab gene fragments by employing an established procedure to generate antigen-binding Fab libraries in phagemid vector pComb3. Molecular an d immunochemical analysis indicated that the expected chimeric Fab fra gments expressing the HIV-1 epitopes were correctly cloned and express ed in Escherichia call and retained the binding specificity of the nat ive (hybridoma-derived) MAb. The chimeric Fab fragments targeted the l inked HIV-1-derived antigenic determinants to the surface of human APC s in vitro, as evidenced by fluorescence-activated cell sorter analysi s. Furthermore, such recombinant immunotargeted HIV-1 peptide antigens demonstrated improved immunogenicity over equivalent nonimmunotargete d control antigens, as shown by their ability to stimulate interleukin -2 production by CD4(+) T-he!per cells from human donors exposed to HI V-1 antigens. These data suggest that immunotargeting of recombinant p eptide antigens via the attached Fab fragments facilitates uptake by h uman APCs with subsequent access to the MHC class II processing pathwa y, thereby validating the immunotargeting concept for such recombinant subunit vaccines in an in vitro human system.