Immunogenic properties of synthetic peptides copying the V3 loop of HIV-1 gp120 envelope protein: effects of various administration routes and poly(I:C) immunoadjvant use

Synthetic peptides provide a promising basis for HIV vaccine development. Following their administration, the immune response is focused only on a specific epitope. Moreover, they are able to activate both humoral and cellular pathways of immune response, being safe and well tolerated. Due to low molecular weight, the synthetic peptides exhibit low immunogenicity, therefore requiring usage of various immunoadjuvants in immunogenic compositions. The V3 loops of gp120 envelope protein are among the main protective epitopes, with a number of monoclonal antibodies with broad neutralizing activity having been obtained to this antigen. We have studied the immunogenicity of peptides copying the V3 loop of the group M HIV-1 virus consensus sequence, and the Russian viral isolate RUA022a2. We have also assessed the possible impact of its administration route (subcutaneously versus intraperitoneally) and usage of an immunoadjuvant. poly(I:C), a synthetic analogue of double-stranded RNA, being a ligand of TLR3 innate immunity receptors, was used as an adjuvant. The studies were conducted on Balb/c mice. It has been shown that the route of administration did not affect an immune response development to the tested peptides. However, earlier production of specific IgG antibodies was observed in the groups treated with immunoadjuvant. At the same time, the antibody titer was slightly higher in the groups where peptides were administered with the adjuvant after the 3 rd (last) administration. No differences have been revealed in the isotypes of induced antibodies. IgG1 antibodies were predominantly induced in all groups. Specific IgM antibodies were detected only after 3 rd injection of the antigens. The antibody titer did not depend on the administration route, being slightly higher in the groups where peptides were administered with the poly(I:C) adjuvant. The induced antibodies did not exhibit neutralizing activity against the QF495.23.M.EnvA1 isolate. When studying antigen-specific cellular immune activation, the production of IFNγ, the Th1 response marker was detected only in poly(I:С)-treated groups. In addition, a low level of anti-inflammatory cytokine IL-10 was determined in groups where poly(I:С) was included in the immunogenic composition. Moreover, the highest IL-10 level was detected in groups with intraperitoneal administration. Our studies have shown that the use of poly(I:С) adjuvant promotes immune response to the synthetic peptides, thus contributing to earlier induction of specific antibodies as well as switching to the Th1 pathway. The data obtained may be used for development of vaccines against HIV and other viral infections, in order to increase their immunogenicity and ability of inducing a protective immune response.