Ken S. Rosenthal

Immunization with a LEAPS heteroconjugate containing a CTL epitope and a peptide from beta-2-microglobulin elicits a protective and DTH response to herpes simplex virus type 1.

A ligand epitope antigen presentation system (LEAPS) heteroconjugate vaccine containing a CTL epitope (H1) from the HSV-1 immediate early protein ICP27 (322-332) and a peptide sequence (J) from beta-2-microglobulin (35-50) elicited protection from intraperitoneal viral challenge and promoted DTH responses. The H1 peptide and other H1 containing heteroconjugates did not elicit protection or DTH responses. Antibody to the H1 peptide could not be detected by ELISA following vaccination with peptide, heteroconjugate or natural infection. The LEAPS heteroconjugate appears to prime a Thl-like response which is subsequently boosted by infection. These studies show that attachment of the J peptide can make a CTL epitope into a vaccine which is immunogenic and promotes a protective Th1 type of response.

Ligand epitope antigen presentation system vaccines against herpes simplex virus.

The Ligand Epitope Antigen Presentation System (L.E.A.P.S.) approach to vaccine development allowed construction of immunogens from defined T cell epitopes from herpes simplex virus (HSV) proteins that conferred protection against lethal challenge by the virus. This technology utilizes specific peptides which bind to CD4, CD8 or other proteins on the surface of T cells (T cell binding ligand (TCBL)), macrophage and dendritic cells (immune cell binding ligand (ICBL)) to promote the immunogenicity of an epitope, activate T cell and other protective responses, and direct the immune response to either a Th1 or a Th2 type of response. The J TCBL/ICBL is a peptide from beta-2-microglobulin which binds to the CD8 protein and promotes Th1 responses and the G TCBL/ICBL is a peptide from the beta chain of MHC II molecules that binds to the CD4 protein and promotes Th2 responses. Epitopes from the ICP27 (H1, H2), glycoprotein B (gB) and glycoprotein D (gD) proteins of HSV-1 were attached to either the J TCBL/ICBL or the G TCBL/ICBL. The JH1, JH2, JgB and JgD vaccines elicited DTH responses without antibody but conferred protection upon lethal challenge. Th1 related antibody was produced after challenge of the JgB and JgD immunized mice. Immunization with the GH1, GgB or GgD vaccines did not yield protection. The GgB and GgD produced Th2 related antibodies upon virus challenge. Initiation of the immune response by the JgD vaccine was dependent on functional CD4, CD8 expressing cells and interferon gamma and delivery of protection was dependent upon CD4 and interferon gamma. The L.E.A.P.S. HSV vaccines appear to elicit the appropriate immune responses for protection and further work is being performed to develop the JgD vaccine for human use.

THE L.E.A.P.S. APPROACH TO VACCINE DEVELOPMENT

The Ligand Epitope Antigen Presentation System (L.E.A.P.S.) approach to vaccine development utilizes immune peptides to promote the immunogenicity and influence the type of immune response generated towards epitopes in peptides which may be too small to elicit an immune response. The covalent attachment of these immune peptides to the antigenic peptide promotes the interaction of the epitope with T cells (T cell binding ligand (TCBL)) or antigen presenting cells (immune cell binding ligand (ICBL)) and ultimately promotes binding with the T cell receptor on CD4 or CD8 T cells. The, J, ICBL/TCBL peptide derived from the beta-2-microglobulin chain of MHC I molecules promotes Th1 type responses to the antigenic peptide while the, G, ICBL/TCBL peptide derived from the beta chain of MHC II molecules promotes Th2 types of responses. The efficacy of this approach has been demonstrated by characterization of the immune responses to L.E.A.P.S. vaccines and by elicitation of protection from infectious challenge with herpes simplex virus and other pathogens. The protection studies show that the L.E.A.P.S. approach allows customization of the immune response appropriate for inducing protection from disease. The theory, background, examples and studies of the mechanism of action of the L.E.A.P.S. vaccines will be discussed.

Rheumatoid arthritis vaccine therapies: perspectives and lessons from therapeutic ligand epitope antigen presentation system vaccines for models of rheumatoid arthritis

The current status of therapeutic vaccines for autoimmune diseases is reviewed with rheumatoid arthritis as the focus. Therapeutic vaccines for autoimmune diseases must regulate or subdue responses to common self-antigens. Ideally, such a vaccine would initiate an antigen-specific modulation of the T-cell immune response that drives the inflammatory disease. Appropriate animal models and types of T helper cells and signature cytokine responses that drive autoimmune disease are also discussed. Interpretation of these animal models must be done cautiously because the means of initiation, autoantigens, and even the signature cytokine and T helper cell (Th1 or Th17) responses that are involved in the disease may differ significantly from those in humans. We describe ligand epitope antigen presentation system vaccine modulation of T-cell autoimmune responses as a strategy for the design of therapeutic vaccines for rheumatoid arthritis, which may also be effective in other autoimmune conditions.

LEAPS therapeutic vaccines as antigen specific suppressors of inflammation in infectious and autoimmune diseases

The L.E.A.P.S.(™) (Ligand Epitope Antigen Presentation System) technology platform has been used to develop immunoprotective and immunomodulating small peptide vaccines for infectious and autoimmune diseases. Several products are currently in various stages of development, at the pre-clinical stage (in animal challenge efficacy studies). Vaccine peptides can elicit protection of animals from lethal viral (herpes simplex virus [HSV-1] and influenza A) infection or can block the progression of autoimmune diseases (e.g. rheumatoid arthritis as in the collagen induced arthritis (CIA] or experimental autoimmune myocarditis (EAM) models). L.E.A.P.S. technology is a novel T-cell immunization technology that enables the design and synthesis of non-recombinant, proprietary peptide immunogens. Combination of a small peptide that activates the immune system with another small peptide from a disease-related protein, thus a conjugate containing both an Immune Cell Binding Ligand (ICBL) and a disease specific epitope, which allows the L.E.A.P.S. vaccines to activate precursors to differentiate and become more mature cells that can initiate and direct appropriate T cell responses. As such, readily synthesized, defined immunogens can be prepared to different diseases and are likely to elicit protection or therapy as applicable in humans as they are in mice. L.E.A.P.S. vaccines have promise for the treatment of rheumatoid arthritis and other inflammatory diseases and for infections, such as influenza and HSV1. The protective responses are characterized as Th1 immune and immunomodulatory responses with increased IL-12p70 and IFN-γ (Th1 cytokines) but reduced inflammatory cytokines TNF-α, IL-1 and IL-17 (Th2 and Th17 cytokines) and concomitant changes in antibody subtypes. LEAPS immunogens have been used directly in vivo or as ex vivo activators of DC which are then administered to the host.

An epitope-specific DerG-PG70 LEAPS vaccine modulates T cell responses and suppresses arthritis progression in two related murine models of rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune joint disease maintained by aberrant immune responses involving CD4+ T helper (Th)1 and Th17 cells. In this study, we tested the therapeutic efficacy of Ligand Epitope Antigen Presentation System (LEAPS™) vaccines in two Th1 cell-driven mouse models of RA, cartilage proteoglycan (PG)-induced arthritis (PGIA) and PG G1-domain-induced arthritis (GIA). The immunodominant PG peptide PG70 was attached to a DerG or J immune cell binding peptide, and the DerG-PG70 and J-PG70 LEAPS vaccines were administered to the mice after the onset of PGIA or GIA symptoms. As indicated by significant decreases in visual and histopathological scores of arthritis, the DerG-PG70 vaccine inhibited disease progression in both PGIA and GIA, while the J-PG70 vaccine was ineffective. Splenic CD4+ cells from DerG-PG70-treated mice were diminished in Th1 and Th17 populations but enriched in Th2 and regulatory T (Treg) cells. In vitro spleen cell-secreted and serum cytokines from DerG-PG70-treated mice demonstrated a shift from a pro-inflammatory to an anti-inflammatory/regulatory profile. DerG-PG70 peptide tetramers preferentially bound to CD4+ T-cells of GIA spleen cells. We conclude that the DerG-PG70 vaccine (now designated CEL-4000) exerts its therapeutic effect by interacting with CD4+ cells, which results in an antigen-specific down-modulation of pathogenic T-cell responses in both the PGIA and GIA models of RA. Future studies will need to determine the potential of LEAPS vaccination to provide disease suppression in patients with RA.