Targeting epitopes in prostate-specific membrane antigen for antibody therapy of prostate cancer.

Prostate-specific membrane antigen (PSMA) is a target for immunotherapy of prostate cancer. It has been shown that antibodies against PSMA inhibited the in vivo growth of LNCaP tumor. In the present study, monoclonal antibodies against four epitopes in PSMA were raised. MAb 24.4E6 (IgG1), specific for the epitope (residues 638-657) in PSMA, significantly reduced the growth rate of established LNCaP tumor in SCID mice. Mouse IgG was detected in the tumor of mice treated with 24.4E6, but not with an unrelated MAb. These results suggest that this epitope may be the main target in PSMA for antibody therapy of prostate cancer.

Therapeutic peptidomimetic strategies for autoimmune diseases: costimulation blockade.

Cognate interactions between immune effector cells and antigen-presenting cells (APCs) govern immune responses. Specific signals occur between the T-cell receptor peptide and APCs and nonspecific signals between pairs of costimulatory molecules. Costimulation signals are required for full T-cell activation and are assumed to regulate T-cell responses as well as other aspects of the immune system. As new discoveries are made, it is becoming clear how important these costimulation interactions are for immune responses. Costimulation requirements for T-cell regulation have been extensively studied as a way to control many autoimmune diseases and downregulate inflammatory reactions. The CD28:B7 and the CD40:CD40L families of molecules are considered to be critical costimulatory molecules and have been studied extensively. Blocking the interaction between these molecules results in a state of immune unresponsiveness termed 'anergy'. Several different strategies for blockade of these interactions are explored including monoclonal antibodies (mAbs), Fab fragments, chimeric, and/or fusion proteins. We developed novel, immune-specific approaches that interfere with these interactions. Using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis mediated by central nervous system (CNS)-specific T-cells, we developed a multi-targeted approach that utilizes peptides for blockade of costimulatory molecules. We designed blocking peptide mimics that retain the functional binding area of the parent protein while reducing the overall size and are thus capable of blocking signal transduction. In this paper, we review the role of costimulatory molecules in autoimmune diseases, two of the most well-studied costimulatory pathways (CD28/CTLA-4:B7 and CD40:CD40L), and the advantages of peptidomimetic approaches. We present data showing the ability of peptide mimics of costimulatory molecules to suppress autoimmune disease and propose a mechanism for disease suppression.

Intracellular delivery of a novel multiepitope peptide vaccine by an amphipathic peptide carrier enhances cytotoxic T-cell responses in HLA-A*201 mice.

Cytotoxic T lymphocytes (CTL) are key players in the neutralization of viruses and killing of tumor cells. However, for generating an optimal CTL response by vaccination, the antigen has to be delivered directly into the cytoplasm for presentation by the conventional MHC class I pathway. To mimic the presentation of multiple epitopes by a tumor or virus infected cell, we have designed a multiepitope peptide vaccine incorporating thee CTL epitopes in tandem with double arginine spacers to facilitate efficient cleavage of the individual epitopes. To deliver the multiepitope peptide vaccine into the cytoplasm of mature dendritic cells for presentation by the MHC class I pathway we made use of an amphipathic peptide carrier. Direct injection of a non-covalent complex of the multiepitope peptide vaccine and amphipathic peptide carrier in an aqueous formulation into HLA-A*0201 (HHD) transgenic mice enhanced the cytotoxic T-cell responses by two to sixfold compared with multiepitope peptide vaccination alone. This novel antigen delivery strategy may find general application in the development of more effective vaccines for the treatment of cancer and infectious disease.

Structural and immunogenicity analysis of chimeric B-cell epitope constructs derived from the gp46 and gp21 subunits of the envelope glycoproteins of HTLV-1.

B-cell epitopes were selected from the gp21 and gp46 subunits of the envelope glycoprotein of human T-cell lymphotropic virus type 1 (HTLV-1) by computer-aided analyses of protein antigenicity. Molecular modeling was used to design and synthesize the epitopes as chimeric constructs with promiscuous T-helper epitopes derived either from the tetanus toxoid (amino acids 947-967) or measles virus fusion protein (amino acids 288-302). Circular dichroism measurements revealed that the peptides had a secondary structure that correlated well with the crystal structure data or predicted structure. The chimeric peptides were then evaluated for their immunogenicity in rabbits or mice. Antibodies against one of the epitopes derived from the gp21 subunit were found to be neutralizing in its ability to inhibit the formation of virus-induced syncytia. These studies underscore the importance of the gp21 transmembrane region for the development of vaccine candidates. The applicability of a chimeric approach is discussed in the context of recent findings regarding the role of gp21 transmembrane region in the viral fusion process.