A SIMPLE PROCEDURE TO GENERATE CHIMERIC PR55GAG VIRUS-LIKE PARTICLES EXPRESSING THE PRINCIPAL NEUTRALIZATION DOMAIN OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1

The Pr55gag human immunodeficiency virus type 1 (HIV-1) precursor prot ein that is capable of auto-assembling was used as a carrier for a con sensus sequence of the principal neutralization domain (PND) of the HI V-1 envelope. For this purpose, a modified HIV-1 gag gene with deletio n of the sequence encoding a previously described p24 epitope (amino a cids 196-228 of Pr55gag) was first obtained using PCR with degenerate primers, and then cloned. This deleted gag gene allowed in a second ti me the insertion of a synthetic oligonucleotide cassette encoding the North American/European consensus PND precisely in place of the p24 ep itope. The chimeric gene was then inserted into a baculovirus transfer vector and expressed in insect cells. The construct formed 100-140 nm virus-like particles that were released into the extracellular medium . The use of a serum-free medium that supports growth of insect cells facilitated the downstream purification of the extracellular particles . The chimeric particles were recognized by monoclonal antibodies dire cted to V3 by Western blot but not by immune electron microscopy, sugg esting that, although the inserted sequence was still antigenic it was not exposed at the surface of the particles. The results show the abi lity of Pr55gag to serve as a carrier for easy insertion, in a precise ly defined region, of selected epitopes of gp120 surface envelope prot ein, and to still auto-assemble in virus-like particles. However, the data indicate that exposed epitopes of the mature p24 protein are not presented similarly in the Pr55 precursor, and therefore that differen t constructs with various insertions in different places must be gener ated. Such constructs offer an attractive approach for HIV vaccine dev elopment and will need evaluation for both antigenicity and immunogeni city.