Title

Mucosal immune responses to HIV-1 C4/V3 epitopes following genetic or peptide immunizations of rabbits

Date of Completion

January 1997

Keywords

Biology, Molecular|Health Sciences, Immunology

Degree

Ph.D.

Abstract

The studies reported herein were designed to elicit secretory IgA (S-IgA) responses to specific epitopes of the HIV-1 envelope protein gp120. Since HIV is most often acquired after sexual contact at mucosal surfaces, a S-IgA response may reduce transmission rates. The synthetic peptide T1- SP10MN(A) is derived from the V3 loop and C4 domains of gp120 and contains T-helper, B-cell, and CTL epitopes. This 40 amino acid peptide was first tested for its ability to induce immunity after systemic immunizations and generated high titered antibody responses. The mucosal immunogenicity of this peptide was subsequently examined using the Thiry-Vella loop model in rabbits. Groups of five rabbits were intestinally immunized with either T1-SP10MN(A) alone, T1-SP10MN(A) plus the mucosal adjuvant cholera toxin (CT), or T1-SP10MN(A) linked to the mucosal carrier protein LT-B and admixed with CT. Intestinal secretions and sera demonstrated specific S-IgA and serum IgG responses, respectively. These results indicated that T1-SP10MN(A) was immunogenic upon mucosal administration and allowed for additional studies intended to induce specific S-IgA antibody responses in vaginal and fecal secretions.^ The first vaccine strategy consisted of intranasal peptide immunizations where five rabbits received T1-SP10MN(A) co-administered with CT. Three animals generated specific S-IgA in nasal and vaginal secretions, while all five contained serum anti-T1-SP10MN(A) IgG. This study further establishes the correlation between nasal immunizations and vaginal immunity.^ The second study focused on a novel technique known as DNA vaccination. A mammalian-based plasmid containing the sequence encoding T1-SP10MN(A) was delivered to the Peyer's patches (PP) of five rabbits using the helium-driven gene gun. Two of five animals received intradermal boosts of plasmid at week 6. The PP was chosen as a target because it is the principal inductive site found in the intestine. Following immunization, high titered S-IgA responses were observed in specific vaginal and fecal samples and serum IgG was detected in two animals. The two boosted animals displayed an augmentation of S-IgA responses in both vaginal and fecal samples. This study establishes the PP as a promising mucosal target tissue for DNA immunization.^ These studies may assist in future HIV vaccine research, especially those focusing on eliciting mucosal immunity. ^