The principle of delivery of T cell epitopes to antigen-presenting cells applied to peptides from influenza virus, ovalbumin, and hen egg lysozyme: Implications for peptide vaccination

Abstract

Targeting of antigens to antigen-presenting cells (APCs) increases CD4 ؉ T cell activation, and this observation can be exploited in the development of new vaccines. We have chosen an antigen-targeting approach in which we make recombinant antibodies (Abs) with T cell epitopes in their constant region and APC-specific variable regions. Three commonly used model epitopes, amino acids 110 -120 of hemagglutinin, 323-339 of ovalbumin, and 46 -61 of hen egg lysozyme, were introduced as loops in the C H1 domain of human IgG3. For all three epitopes, we show that the recombinant molecules are secreted from transfected cells. The epitopes are presented to specific T cells, and targeting to IgD on B cells in vitro enhances the presentation efficiency by 10 4 to 10 5 compared with the free peptide. After i.v. injection, the epitopes targeted to IgD are presented by splenic APCs to activate specific T cells, whereas little or no activation could be detected without targeting, even after the amount of antigen injected was increased 100-fold or more. Because a wide variety of T cell epitopes, in terms of both length and secondary structure, can be tolerated in loops in constant domains of Abs, the Ab constant region seems to have the intrinsic stability that is needed for this fusion molecule strategy. It might thus be possible to load the Ab with several different epitopes in loops in different domains and thereby make a targeted multisubunit vaccine.O ver recent years, considerable efforts have been directed toward the development of efficient vaccines aimed to stimulate T cells. Effector CD4 ϩ T cells are central in this regard because they regulate B cells and are essential for induction of CD8 ϩ CTL responses through both cytokine secretion (1) and dendritic cell sensitization (2). CD4 ϩ T cells mainly recognize peptides derived from the processing of extracellular antigens by antigen-presenting cells (APCs), presented in association with MHC class II molecules. Targeting of antigen to APCs by coupling to APC-specific Abs increases CD4 ϩ T cell activation, probably because of increased uptake of antigen (3, 4).Several new prospects for preparation of T cell vaccines have been suggested based on the identification and characterization of MHC-associated peptides. Synthetic peptides that correspond to these T cell epitopes may represent ideal subunits for safe vaccines. However, synthetic peptides are poor immunogens because of their small molecular size and very short serum half-life. To circumvent these disadvantages, a variety of recombinant proteins that carry short immunogenic epitopes have been described, and these so-called antigenized molecules represent a new generation of subunit vaccines (5-9). Genetically engineered Ab molecules can function as such delivery systems for T cell peptides (10, 11) and have the advantage of being self-proteins devoid of the side effects sometimes associated with microbial vaccines and, moreover, have a long half-life compared with synthetic peptides.Abs are processed by APCs, and s...

Efficient Delivery of T Cell Epitopes to APC by Use of MHC Class II-Specific Troybodies

“…Previous results have shown that IgD-specific Troybodies efficiently prime B cells (14,24). The present class II-specific Troybodies should target other professional APC as well, such as DC and macrophages.…”

“…The different T cell epitopes were introduced into the C H 1 domain of a human IgG3 H chain by site-specific in vitro mutagenesis, as previously described (23,24). The epitopes were introduced into the loop of C H 1 that corresponds to the CDR3 loop of V domains.…”

“…Each T cell epitope was added by replacing the 12 nt encoding the 4-aa-long loop with nucleotides encoding the epitope. Initially, four different 5 iodo-4 hydroxy-3 nitrophenacetyl (NIP)-specific Ab were made (Table I): L6-2 315 contain the 91-101 epitope from the 2 315 Ig L chain (23), whereas the L6-HA, L6-HEL, and L6-OVA Ab contain the 110-120 HA (25), the 46-61 HEL (26), and the 323-339 OVA (27) T cell epitopes, respectively (24). These nontargeting Ab with peptide are denoted peptide Ab.…”

“…Because V domains can accommodate large sequence variation in their CDR3 loops, the L6 loop was chosen as the site for peptide introduction. Indeed, by analogy to CDR3 (10,11), the L6 loop appears to accept engraftment of new peptide sequences (14,24).…”

Antibody‐mediated delivery of antigen to chemokine receptors on antigen‐presenting cells results in enhanced CD4+ T cell responses

“…In one strategy, T cell epitopes have been added to the C terminus of the Fc-region [23,24]. In another strategy, T cell epitopes have been introduced as loops between g -strands in constant domains of the H chain [25,26]. The latter strategy has the advantage that it maintains Ig structure and in vivo stability (K. W. Schjetne, unpublished).…”