Selective Modification of Variable Loops Alters Tropism and Enhances Immunogenicity of Human Immunodeficiency Virus Type 1 Envelope

Abstract

Although the B clade of human immunodeficiency virus type 1 (HIV-1) envelopes (Env) includes five highly variable regions, each of these domains contains a subset of sequences that remain conserved. The V3 loop has been much studied for its ability to elicit neutralizing antibodies, which are often restricted to a limited number of closely related strains, likely because a large number of antigenic structures are generated from the diverse amino acid sequences in this region. Despite these strain-specific determinants, subregions of V3 are highly conserved, and the effects of different portions of the V3 loop on Env tropism and immunogenicity have not been well delineated. For this report, selective deletions in V3 were introduced by shortening of the stem of the V3 loop. These mutations were explored in combination with deletions of selected V regions. Progressive shortening of the stem of V3 abolished the immunogenicity as well as the functional activity of HIV Env; however, two small deletions on both arms of the V3 stem altered the tropism of the dualtropic 89.6P viral strain so that it infected only CXCR4 ؉ cells. When this smaller deletion was combined with removal of the V1 and V2 loops and used as an immunogen in guinea pigs, the antisera were able to neutralize multiple independent clade B isolates with a higher potency. These findings suggest that highly conserved subregions within V3 may be relevant targets for eliciting neutralizing antibody responses, affecting HIV tropism, and increasing the immunogenicity of AIDS vaccines.

Type-Specific Epitopes Targeted by Monoclonal Antibodies with Exceptionally Potent Neutralizing Activities for Selected Strains of Human Immunodeficiency Virus Type 1 Map to a Common Region of the V2 Domain of gp120 and Differ Only at Single Positions from the Clade B Consensus Sequence

“…One approach being investigated to overcome the effects of this masking is to delete the V2 domain from Env-based immunogens. Oligomeric V2-deleted forms of gp140 have been reported to possess enhanced immunogenicity over the wild-type molecule and to produce increased titers of neutralizing antibodies (8,21,33,43). However, these effects are only modest, and recent studies indicate that this approach involves the induction of type-specific neutralizing antibodies directed mostly toward highly variable epitopes in V1 that possess limited neutralizing activities for heterologous isolates (10, 42).…”

Replication-Competent Variants of Human Immunodeficiency Virus Type 2 Lacking the V3 Loop Exhibit Resistance to Chemokine Receptor Antagonists

“…Envs with partial or complete deletions of V1/V2 are more neutralization sensitive (25,50,56,70) and in the case of SIV are less dependent on CD4 (43). Not surprisingly, given the importance of V3 for interacting with CCR5 and CXCR4, Envs lacking V3 function poorly in fusion assays and infectious viruses without V3 have not been described (50).…”

“…The structure, function, and immunogenicity of the HIV (or simian immunodeficiency virus [SIV]) Env have been explored by deriving replication-competent viruses with functional Envs that lack variable loops (25,50,56,65,67,70). Envs with partial or complete deletions of V1/V2 are more neutralization sensitive (25,50,56,70) and in the case of SIV are less dependent on CD4 (43).…”

“…The recently solved V3 structure on a CD4-bound gp120 core shows that its base is contiguous with the surface formed by the bridging sheet while its more distal region projects toward the cell membrane, where it has been proposed to contact the coreceptor's extracellular loops (ECLs) (22). However, despite extensive data from mutagenesis, the precise nature of these interactions is unknown, as are their contributions to Env function (18).The structure, function, and immunogenicity of the HIV (or simian immunodeficiency virus [SIV]) Env have been explored by deriving replication-competent viruses with functional Envs that lack variable loops (25,50,56,65,67,70). Envs with partial or complete deletions of V1/V2 are more neutralization sensitive (25,50,56,70) and in the case of SIV are less dependent on CD4 (43).…”

Comparative Immunogenicity of Human Immunodeficiency Virus Particles and Corresponding Polypeptides in a DNA Vaccine

“…A hybrid CCR5-tropic Env protein gp160 modified by deletion of the cleavage site (C), the fusion peptide (F), and the interspace (I) between the two heptad repeats (⌬CFI) to stimulate high levels of antibody production without compromising the cytotoxic T-lymphocyte response (7,24) was further altered by deletion of V1 and V2 (⌬V 1 V 2 ) loop regions to expose core conserved determinants (Fig. 1A, gp145⌬CFI⌬V 1 V 2 ).…”