Comparable Antigenicity and Immunogenicity of Oligomeric Forms of a Novel, Acute HIV-1 Subtype C gp145 Envelope for Use in Preclinical and Clinical Vaccine Research

Abstract

Eliciting broadly reactive functional antibodies remains a challenge in human immunodeficiency virus type 1 (HIV-1) vaccine development that is complicated by variations in envelope (Env) subtype and structure. The majority of new global HIV-1 infections are subtype C, and novel antigenic properties have been described for subtype C Env proteins. Thus, an HIV-1 subtype C Env protein (CO6980v0c22) from an infected person in the acute phase (Fiebig stage I/II) was developed as a research reagent and candidate immunogen. The gp145 envelope is a novel immunogen with a fully intact membrane-proximal external region (MPER), extended by a polylysine tail. Soluble gp145 was enriched for trimers that yielded the expected "fan blade" motifs when visualized by cryoelectron microscopy. CO6980v0c22 gp145 reacts with the 4E10, PG9, PG16, and VRC01 HIV-1 neutralizing monoclonal antibodies (MAbs), as well as the V1/V2-specific PGT121, 697, 2158, and 2297 MAbs. Different gp145 oligomers were tested for immunogenicity in rabbits, and purified dimers, trimers, and larger multimers elicited similar levels of crosssubtype binding and neutralizing antibodies to tier 1 and some tier 2 viruses. Immunized rabbit sera did not neutralize the highly resistant CO6980v0c22 pseudovirus but did inhibit the homologous infectious molecular clone in a peripheral blood mononuclear cell (PBMC) assay. This Env is currently in good manufacturing practice (GMP) production to be made available for use as a clinical research tool and further evaluation as a candidate vaccine. IMPORTANCEAt present, the product pipeline for HIV vaccines is insufficient and is limited by inadequate capacity to produce large quantities of vaccine to standards required for human clinical trials. Such products are required to evaluate critical questions of vaccine formulation, route, dosing, and schedule, as well as to establish vaccine efficacy. The gp145 Env protein presented in this study forms physical trimers, binds to many of the well-characterized broad neutralizing MAbs that target conserved Env epitopes, and induce cross-subtype neutralizing antibodies as measured in both cell line and primary cell assays. This subtype C Env gp145 protein is currently undergoing good manufacturing practice production for use as a reagent for preclinical studies and for human clinical research. This product will serve as a reagent for comparative studies and may represent a next-generation candidate HIV immunogen. Human immunodeficiency virus (HIV) vaccine candidates capable of eliciting broad, protective humoral immune responses would significantly advance prevention strategies to control the AIDS pandemic. The diversity of circulating HIV type 1 (HIV-1) envelope (Env) sequences and structures has complicated HIV-1 immunogen design and has impaired the development of a globally efficacious vaccine. Env diversity of up to 20% within a subtype and up to 35% between subtypes has been reported (1), leading vaccine developers to focus on common antigenic features most frequently r...

Influences on the Design and Purification of Soluble, Recombinant Native-Like HIV-1 Envelope Glycoprotein Trimers

“…4B). Such disulfide bond-linked aggregates are routinely seen in uncleaved gp140 preparations (32,36,57). How they arise is discussed further below.…”

“…Whether or not uncleaved gp140 proteins such as those based on the CZA97.012 and 92UG037.8 genotypes are pursued as immunogens in human clinical trials, claims that these proteins have a native-like structure and, by inference, may be able to induce trimerization-influenced NAbs to tier 2 viruses, are clearly not verifiable. The same concerns apply to other uncleaved gp140s of comparable designs that are also being produced for clinical trials, again on the basis that they mimic the native structure of virion-associated Env (36,82). A more appropriate rationale for the use of uncleaved gp140s may be their induction of non-NAbs that are partially protective in a macaque challenge model (83).…”

“…The various defects present in the 92UG037.8 and CZA97.012 gp140 UNC -Fd-His gp140s are in no way unique to these genotypes, as they have been found in similar assays using several other uncleaved gp140s and/or can be inferred from the general biochemical properties of such proteins (e.g., the propensity to form disulfide-linked aggregates or the limited reactivity with trimer-specific bNAbs). As various uncleaved gp140s are being tested in or produced for human clinical trials, including proteins based on the 92UG037.8 and CO6980v0c22 genotypes, there are obvious and serious concerns about at least some of the underlying hypotheses (2,4,5,34,36,42).…”

“…Often, a trimerization domain is added to the C terminus of gp41 ECTO , most commonly a Foldon (Fd) moiety (2,4,14,15,(30)(31)(32)(33)(34). The resulting uncleaved gp140 (gp140 UNC ) proteins can be purified as entities that contain three gp120 subunits and three gp41 ECTO subunits (2,4,14,15,(32)(33)(34)(35)(36). However, a variety of assays show that these gp140 UNC proteins do not adopt or retain a native-like structure (19,30,33,(37)(38)(39).…”

New developments in an old strategy: heterologous vector primes and envelope protein boosts in HIV vaccine design

“…In comparison to monomeric gp120 immunogens, trimer constructs have elicited more potent nAb responses [117,118]. Recently, a clade C trimer, of interest due to the global prevalence of clade C HIV, was shown to elicit nAb activity against some tier-2 viruses [119]. Moreover, in guinea pigs, a quadrivalent mixture of clade C trimers elicited higher nAb responses against a panel of tier-1A and B viruses compared to a single trimer alone [120].…”