ASSEMBLY AND EXTRACELLULAR RELEASE OF CHIMERIC HIV-1 PR55(GAG) RETROVIRUS-LIKE PARTICLES

The HIV-1 Pr55(gag) precursors were previously shown to assemble and b ud from a variety of different cell types as noninfectious virus-like particles (VLPs) resembling immature HIV virions. The use of these VLP s as an immunogenic and autologous carrier component may allow the pre sentation of defined epitopes deduced from reading frames other than g ag to the immune system, thereby avoiding the induction of adverse imm une responses. In order to identify domains within Pr55(gag) that can be replaced by immunologically relevant epitopes without affecting its capacity to assemble into VLPs, we deleted three domains of a predict ed high surface probability. Deletion of amino acids 211-241 within p2 4CA and amino acids 436-471 within the p6LI portion of Pr55(gag) had n o effect on the assembly, ultrastructure, biophysical properties, and yields of mutant VLPs when expressed via recombinant vaccinia viruses in mammalian cells. Deletion of amino acids 99-154 overlapping the p17 MA/p24CA cleavage site completely abolished the capacity of the gag po lyprotein to form VLPs and led to a reduction of immature Pr55 VLPs re leased into the cell-culture supernatants when coexpressed with wild-t ype Pr55(gag). In contrast, assembly and budding of chimeric VLPs coul d be demonstrated after replacing amino acids 211-241 and 436-471 by i mmunologically relevant epitopes derived from reading frames other tha n pr55(gag) (e.g., vs loop; CD4-binding-domain; nef-CTL epitope) or af ter fusion of these sequences to the carboxy terminus of Pr55(gag). Th e importance of these data for the development of novel HIV candidate vaccines is discussed. (C) 1994 Academic Press, Inc.