Localization of CD4⁺T cell epitope hotspots to exposed strands of HIV envelope glycoprotein suggests structural influences on antigen processing

Abstract

The spectrum of immunogenic epitopes presented by the H2-IA b MHC class II molecule to CD4 ؉ T cells has been defined for two different (clade B and clade D) HIV envelope (gp140) glycoproteins. Hybridoma T cell lines were generated from mice immunized by a sequential prime and boost regime with DNA, recombinant vaccinia viruses, and protein. The epitopes recognized by reactive T cell hybridomas then were characterized with overlapping peptides synthesized to span the entire gp140 sequence. Evidence of clonality also was assessed with antibodies to T cell receptor V␣ and V␤ chains. A total of 80 unique clonotypes were characterized from six individual mice. Immunogenic peptides were identified within only four regions of the HIV envelope. These epitope hotspots comprised relatively short sequences (Ϸ20-80 aa in length) that were generally bordered by regions of heavy glycosylation. Analysis in the context of the gp120 crystal structure showed a pattern of uniform distribution to exposed, nonhelical strands of the protein. A likely explanation is that the physical location of the peptide within the native protein leads to differential antigen processing and consequent epitope selection.T he primary role of any vaccine is to generate sustained immune memory to antigenic epitopes that are expressed on, or by, the pathogen in question. Vaccines designed to prevent the development of virus-induced pathology must promote the clonal expansion of CD4 ϩ T cells specific for those complexes of nonself peptide and self MHC class II glycoprotein that will be encountered again as a consequence of natural virus challenge. Experiments in a variety of mouse model systems have established that the virus-specific CD4 ϩ (T h ) subset functions both to enhance antibody production by cognate interaction with B cells (1, 2) and to promote the development of effector CD8 ϩ T cells (3, 4). Studies of readily eliminated viruses further indicate that the development of long-term memory in both lymphocyte compartments depends substantially on a concurrent T h response (5), and CD8 ϩ T cell-mediated control of persistent infections requires the continued presence of virus-specific CD4 ϩ T cells (6, 7). This CD4 ϩ T h for the CD8 ϩ subset is thought to operate via the intermediary of the activated dendritic cell (8).In some infections, particularly with the large DNA viruses, INF-␥-producing CD4 ϩ T cells are also important effectors of immunity (9-11). An ongoing CD4 ϩ T cell response also is thought to be important for the CD8 ϩ T cell-mediated control of HIV infection (12). Effective priming of the CD4 ϩ T cell response would thus seem to be a priority for any HIV vaccine.What is known about the antigenic epitopes recognized by HIV-specific CD4 ϩ T cells? Previous studies have sought to characterize immunogenic peptides from the HIV envelope (env) protein (13-20) for a variety of mammalian species expressing a spectrum of MHC class II phenotypes. Much of the available information was generated by scoring heterogeneous CD4 ϩ T cell respons...

Long-Term Maintenance of gp120-Specific Immune Responses by Genetic Vaccination with the HIV-1 Envelope Genes Linked to the Gene Encoding Flt-3 Ligand

“…The poor immunogenicity of HIV envelope protein gp120 could be partly due to its inherent biological properties (71,72,73). Covalent attachment of FLex to gp120 could have converted gp120 to a better immunogen for induction of robust immune responses in mice.…”

WT1 in acute leukemia, chronic myelogenous leukemia and myelodysplastic syndrome: therapeutic potential of WT1 targeted therapies

“…Data obtained in small animal models, as well as in primates, indicate a higher efficacy of prime-boost strategies over single-agent immunizations, such as DNA, protein or viral delivery systems, alone. [100][101][102][103][104][105] Which system will be most effective in human WT1 vaccines needs to be the subject of preclinical murine studies using murine WT1 vaccines and Phase 1 trials.…”

Cutting Edge: Culture with High Doses of Viral Peptide Induces Previously Unprimed CD8+ T Cells to Produce Cytokine

“…Primed mice were boosted i.p. 30 -60 days later with 10 7 PFU of a Vacc construct (Vacc-gp140) encoding the same HIV gp140 (7,8). Influenza memory mice had been infected intranasally (i.n.)…”

“…The HIV-1 envelope peptide sequences are LPCRIKQIINMWQEV for the 208 epitope and REKRAIGLGALFLGF for the 388 epitope. The full-length envelope sequences have been previously described (8). Control experiments were done using the influenza A virus nucleoprotein 366 -374 peptide (ASNENMETM; NP 366 ) (9) and the influenza acid polymerase PA 224 -233 peptide (SSLENFRAYV; PA 224 ) (5).…”

“…4 -6). The present experiments started with efforts to define the CD8 ϩ T cell response in H-2 b mice primed and boosted with HIV-1 envelope glycoproteins in the form of a DNA vaccine, followed by infection with a recombinant vaccinia virus (Vacc) (7,8). To identify candidate epitopes, we used a 6-day in vitro culture system that was intended to expand any epitope-specific CD8 ϩ T cells before screening our panel of HIV-1 envelope peptides with the Pep␥ assay.…”