Novel Biopanning Strategy To Identify Epitopes Associated with Vaccine Protection

Abstract

cIdentifying immune correlates of protection is important to develop vaccines against infectious diseases. We designed a novel, universally applicable strategy to profile the antibody (Ab) repertoire of protected vaccine recipients, using recombinant phages encoding random peptide libraries. The new approach, termed "protection-linked (PL) biopanning," probes the Ab paratopes of protected vaccinees versus those with vaccine failure. As proof of concept, we screened plasma samples from vaccinated rhesus macaques (RMs) that had completely resisted multiple mucosal challenges with R5-tropic simian-human immunodeficiency viruses (SHIVs). The animals had been immunized with a multicomponent vaccine (multimeric HIV-1 gp160, HIV-1 Tat, and SIV Gag-Pol particles). After PL biopanning, we analyzed the phagotopes selected for amino acid homologies; in addition to the expected Env mimotopes, one recurring motif reflected the neutralizing Ab epitope at the N terminus (NT) of HIV-1 Tat. Subsequent binding and functional assays indicated that anti-Tat NT Abs were present only in completely or partially protected RMs; peak viremia of the latter was inversely correlated with anti-Tat NT Ab titers. In contrast, highly viremic, unvaccinated controls did not develop detectable Abs against the same epitope. Based upon the protective effect observed in vivo, we suggest that Tat should be included in multicomponent HIV-1 vaccines. Our data highlight the power of the new PL-biopanning strategy to identify Ab responses with significant association to vaccine protection, regardless of the mechanism(s) or targets of the protective Abs. PL biopanning is also unbiased with regard to pathogens or disease model, making it a universal tool.T he design of a safe, effective vaccine is desirable to control the AIDS pandemic. In order to improve future vaccine candidates, it is important to understand the protective mechanism(s) leading to reduced virus acquisition (1). Thus, correlates of infection risk for the recent RV144 vaccine efficacy trial (2) are the subject of intense study (3,4). However, additional information can be gained by dissecting immune responses in biologically relevant animal models where immunization induced complete protection from immunodeficiency virus challenge(s) (5, 6).Recent results of active (7,8) and passive (9) immunization trials in humans and in nonhuman primates suggested that antihuman immunodeficiency virus type 1 (HIV-1) Env antibodies (Abs) can have protective roles even in the absence of virus neutralization, implying that other Ab-mediated mechanisms may be involved in preventing mucosal virus acquisition. Thus, the ability to profile Ab epitopes associated with protection might help to identify potential targets for future HIV-1 vaccines.Random peptide phage display has been used to dissect Ab responses in the context of primate immunodeficiency virus infections, and several studies have identified HIV-1 or simian-human immunodeficiency virus (SHIV)-specific peptides (10-14). We developed a novel epitope...

Effects of different routes of administration on the immunogenicity of the Tat protein and a Tat-derived peptide

“…It has been recently shown that antibodies directed against the N-terminus region of Tat, which is the most immunogenic in terms of humoral responses, 32,33 protect monkeys from infection acquisition, 15 suggesting that the Tat 1-20 peptide constitutes an interesting candidate for a preventive vaccine. To assess how different routes of administration may affect humoral immunogenicity of peptide vaccines, mice were vaccinated 3 times (at days 1, 14 and 28), by ID or OM route, with Tat 1-20 peptide (EPVDPRLEPWKHPGSQPKT, synthesized by solid phase method and purified by HPLC to >98% purity by UF Peptides, University of Ferrara, Italy), encompassing an immunodominant Tat epitope, 32,33 at the dose of 7mg.…”

“…[5][6][7][8][9][10][11] Thus, the inclusion of Tat in preventive and therapeutic vaccines has been pursued by several groups showing promising results in nonhuman primates [12][13][14][15][16] and in phase I and II clinical trials. [16][17][18][19] However, the development of vaccines able to induce protective responses has to face some major challenges such as: i) the compliance requested for mass immunizations; ii) the induction of immune responses in mucosal tissues, which are the predominant sites of HIV acquisition; 20 and iii) the isotypes of antibodies elicited, which may influence the level of vaccine efficacy.…”

Identification of a Highly Conserved Surface on Tat Variants

“…A second successful heterologous SHIV challenge was reported with a Tat variant closely related to Tat OYI mixed with other active principles such as multimeric HIV-1 gp160 and SIV Gag-Pol particles (44). Interestingly, it was shown recently, using a biopanning strategy, that only anti-Tat neutralizing antibody were present in completely or partially protected macaques (45).…”

Paradigm Changes and the Future of HIV Vaccine Research: A Summary of a Workshop Held in Baltimore on 20 November 2013

“…One such approach called protection-linked biopanning, using recombinant phages encoding random peptide libraries, was found to be able to identify viral epitopes that bind to antibodies present only in vaccinated protected individuals [19]. Earlier paradigms unfortunately led investigators to concentrate on epitopes that only bind bnMabs (i.e.…”

“…Anti-Tat Abs, which are infrequently produced upon natural infection, are able to restore and increase HIV neutralization that would normally be impaired by extracellular Tat [24]. Since vaccination with Tat decreases the proviral DNA load (Ensoli et al submitted), slows down the progression to AIDS and can lead to complete or partial protection from infection [19,[24][25][26], the accumulated evidence supports a novel paradigm that views HIV-1 Tat as an important vaccine candidate either on its own or as part of a multicomponent vaccine [19,[24][25][26].…”