The use of peptides for studying molecular events in HIV- and HSV-infections

Abstract

Synthetic peptides were used as tools in order to study various characteristicsof human immunodeficiency virus (HIV) and herpes simplex virus (HSV). Peptides weredesigned as multiple antigenic peptides (MAPs) and used as HIV vaccines in experimentalanimals. The included HIV epitopes were more immunogenic when immunized as MAPs thanas a protein. This was probably due to the fork-like MAP structure which gave aneffective multimeric epitope delivery to the immune cells. The anti-peptide anbbodiesalso bound to the protein and showed biological activity.

An accurate antibody population profile is crucial in order to evaluate differentvaccine candidates. Specific antibody populations in HIV envelope protein gpl60-vaccinatedanimals, HIV infected patients or untreated infected patients from Sweden and Argentina,were analyzed. A broad vaccine-induced antibody production in immunized animals anda slight expansion of the existing immunity in vaccinated HIV-infected humans. Anew immunodominant region of the HIV envelope was identified, against which the majorityof HIV seropositive Swedish and Argentinian patients showed reactivity. By usingpeptides the HIV-specific antibody pool could be mapped in detail which was not possibleby using the entire gpl60 protein. A comparison of different adjuvants revealed thatthe muramyl dipeptide (MDP) and proteosome adjuvants were potent enhancers of immunityagainst the HIV envelope protein gpl60.

A mini antibody was designed, corresponding to a complementarity determining region(CDR) in the antigen-binding domain of an HIV-specific antibody with neutralizingcapacity. The CDR peptide competed with the whole antibody for its epitope, locatedin the third variable loop (V3) of the HIV envelope protein gpl20. The mini antibodyalso showed broad neutralization of both laboratory-adapted virus and primary isolates.This CDR peptide appeared to cross cellular membranes and may be capable of inactivatingviral envelopes intracellularly. It might be used to treat HIV-infected individualsand should induce less side effects and spread more effeciently than whole antibodies.

The interaction between the HIV envelope protein gpl20 and its cellular co-receptorCCR5 was analyzed. CCR5 mediates a which is a post-binding interaction necessaryfor cellular fusion. Strong binding of gpl20 was seen against peptides representingthe N-terminal and first extracellular loop regions in CCR5. In addition, the N-terminalCCR5 domain peptide bound strongly to the V3 loop of gpl20, which is the major neutralizationdeterminant of HIV. Both the N-terminal CCR5 peptide and peptide-induced rabbit immunesera showed specific inhibition of viral replication. This indicates a possibilityto treat HIV-infected patients with CCR5 peptides that block the post binding fusionstep.

Discrimination between herpes simplex virus type 1 (HSV-I) and type 2 (HSV-2)infection is important in prevention of virus transmission. Sites of HSV glycoproteinswere analyzed for their potency for serodiagnosis of latent HSV infection. Peptidesfrom the glycoproteins G (gG) and D (gD) proteins showed promise as HSV-2 specificand HSV type-common antigens respectively. Interestingly, the most homologous regionof HSV-1 / HSV-2 gG was highly discriminating and with sensitivities and specificitiessimilar to native antigens. These peptides may be developed into HSV diagnostic tests.

ISBN 91-628-2784-7