Induction of Primary Virus-Cross-Reactive Human Immunodeficiency Virus Type 1-Neutralizing Antibodies in Small Animals by Using an Alphavirus-Derived In Vivo Expression System

Abstract

We have studied the induction of neutralizing antibodies by in vivo expression of the human immunodeficiency virus type 1 (HIV-1) envelope by using a Venezuelan equine encephalitis virus (VEE) replicon system with mice and rabbits. The HIV-1 envelope, clone R2, has broad sensitivity to cross-reactive neutralization and was obtained from a donor with broadly cross-reactive, primary virus-neutralizing antibodies (donor of reference serum, HIV-1-neutralizing serum 2 [HNS2]). It was expressed as gp160, as secreted gp140, and as gp160⌬CT with the cytoplasmic tail deleted. gp140 was expressed in vitro at a high level and was predominantly uncleaved oligomer. gp160⌬CT was released by cells in the form of membrane-bound vesicles. gp160⌬CT induced stronger neutralizing responses than the other forms. Use of a helper plasmid for replicon particle packaging, in which the VEE envelope gene comprised a wild-type rather than a host range-adapted sequence, also enhanced immunogenicity. Neutralizing activity fractionated with immunoglobulin G. This activity was cross-reactive among a panel of five nonhomologous primary clade B strains and a Chinese clade C strain and minimally reactive against a Chinese clade E (circulating recombinant form 1) strain. The comparative neutralization of these strains by immune mouse sera was similar to the relative neutralizing effects of HNS2, and responses induced in rabbits were similar to those induced in mice. Together, these results demonstrate that neutralizing antibody responses can be induced in mice within 2 to 3 months that are similar in potency and cross-reactivity to those found in the chronically infected, long-term nonprogressive donor of HNS2. These findings support the expectation that induction of highly cross-reactive HIV-1 primary virusneutralizing activity by vaccination may be realized.

Modulation of disease, T cell responses, and measles virus clearance in monkeys vaccinated with H-encoding alphavirus replicon particles

“…Alphavirus replicon particle vaccines have been successfully used to induce immune responses in small animals to a variety of exogenous viral proteins and usually induce antibody and T cell responses that protect from virus challenge (22,28,(38)(39)(40)(41)(42)(43). For instance, SINV replicon particle vaccines protect mice from mucosal challenge with vaccinia virus expressing HIV gag (38) and from herpes simplex virus infection (28).…”

Protection of Rhesus Monkeys against Infection with Minimally Pathogenic Simian-Human Immunodeficiency Virus: Correlations with Neutralizing Antibodies and Cytotoxic T Cells

“…In vivo expression vectors. VEE-RP-HIV-1env R2 vectors were prepared as described previously, by using pRepX-R2gp160⌬CT, pCV, and pGPm as templates for in vitro transcription of RNA (19). VEE-RP-HIV-1env R2 was administered in doses of 10 6.5 focus forming units (FFU) at weeks 0, 1, 2, 10, 12, and 14 of the study.…”

“…However, induction of potent neutralizing antibody responses by means of candidate vaccines has been difficult (10). Previously, we described the induction of broadly cross-reactive neutralizing responses in small animals (19). It was of interest, therefore, to determine if similar responses could be induced in nonhuman primates and if they could protect against experimental challenge.…”

Unique V3 Loop Sequence Derived from the R2 Strain of HIV-Type 1 Elicits Broad Neutralizing Antibodies

“…14 A rare mutation found in the crown of the V3 loop, a proline (P) and methionine (M) (nucleotide position 313/314), appears responsible for the uncommon neutralization sensitivity phenotype and the capacity of this envelope to mediate CD4-independent infection. 14 Recently, Dong et al 15 expressed the Env R2 from a Venezuelan equine encephalitis (VEE) replicon and elicited high titer neutralizing antibodies in mice and rabbits following immunization. These properties are consistent with the possibility that the Env R2 expresses one or more neutralization epitopes that are responsible for induction of cross-reactive neutralizing antibodies in the donor of HNS2.…”