CoVal fusions: a therapeutic vaccine platform using heat shock proteins to treat chronic viral infection and cancer.

We have developed an immunization platform which combines heat shock proteins (Hsp) with protein antigens, such as viral or cancer targets, into a single recombinant fusion protein. Pre-clinical data demonstrate the ability of Hsp fusion proteins to induce antigen-specific cytotoxic T lymphocytes, Type 1 cytokines and anti-tumour immunity. One Hsp fusion protein, HspE7, is now in clinical development for therapy of diseases caused by human papillomavirus (HPV). HPV infection is associated with development of proliferative lesions (papillomas or warts) as well as malignant lesions (anogenital dysplasia and cancer). HspE7 has been shown in efficacy trials to be active against genital warts and anal dysplasia, and a trial is underway in another HPV indication, recurrent respiratory papillomatosis. Having observed therapeutic activity for our lead product HspE7 in humans, we are currently developing Hsp fusion proteins as therapeutic vaccines for other chronic viral infections. Potential targets include hepatitis B, herpes simplex, hepatitis C, and human immunodeficiency virus.

Immunotherapy of a human papillomavirus (HPV) type 16 E7-expressing tumour by administration of fusion protein comprising Mycobacterium bovis bacille Calmette-Guérin (BCG) hsp65 and HPV16 E7.

Human papillomavirus type 16 (HPV16) infection has been linked to the development of cervical and anal dysplasia and cancer. One hallmark of persistent infection is the synthesis of the viral E7 protein in cervical epithelial cells. The expression of E7 in dysplastic and transformed cells and its recognition by the immune system as a foreign antigen make it an ideal target for immunotherapy. Utilizing the E7-expressing murine tumour cell line, TC-1, as a model of cervical carcinoma, an immunotherapy based on the administration of an adjuvant-free fusion protein comprising Mycobacterium bovis BCG heat shock protein (hsp)65 linked to HPV16 E7 (hspE7) has been developed. The data show that prophylactic immunization with hspE7 protects mice against challenge with TC-1 cells and that these tumour-free animals are also protected against re-challenge with TC-1 cells. In addition, therapeutic immunization with hspE7 induces regression of palpable tumours, confers protection against tumour re-challenge and is associated with long-term survival (> 253 days). In vitro analyses indicated that immunization with hspE7 leads to the induction of a Th1-like cell-mediated immune response based on the pattern of secreted cytokines and the presence of cytolytic activity following antigenic recall. In vivo studies using mice with targeted mutations in CD8 or MHC class II or depleted of CD8 or CD4 lymphocyte subsets demonstrate that tumour regression following therapeutic hspE7 immunization is CD8-dependent and CD4-independent. These studies extend previous observations on the induction of cytotoxic T lymphocytes by hsp fusion proteins and are consistent with the clinical application of hspE7 as an immunotherapy for human cervical and anal dysplasia and cancer.

Immunotherapy of a human papillomavirus type 16 E7-expressing tumor by administration of fusion protein comprised of Mycobacterium bovis BCG Hsp65 and HPV16 E7.

Human papillomavirus type 16 (HPV16) infection has been linked to the development of cervical and anal dysplasia and cancer. One hallmark of persistent infection is the synthesis of the viral E7 protein in cervical epithelial cells. The expression of E7 in dysplastic and transformed cells and its recognition by the immune system as a foreign antigen make it an ideal target for immunotherapy. Utilizing the E7-expressing murine tumor cell line, TC-1, as a model of cervical carcinoma, an immunotherapy based on the administration of an adjuvant-free fusion protein comprised of Mycobacterium bovis BCG Hsp65 linked to HPV16 E7 (HspE7) has been developed. Initial in vitro analyses indicate that immunization with HspE7 results in the induction of a type 1 immune response based on the pattern of secreted cytokines and the presence of cytolytic activity following antigenic recall. It has been previously shown that prophylactic immunization with HspE7 protected mice against challenge with TC-1 cells and that these tumor-free animals are also protected against rechallenge with TC-1 cells. The present report shows that a single therapeutic immunization with HspE7 induces regression of palpable tumors, confers protection against tumor rechallenge, and is associated with long-term survival (>253 days). In vivo studies using mice with targeted mutations in CD8 or MHC class II or depleted of CD8 or CD4 lymphocyte subsets demonstrate that tumor regression following therapeutic HspE7 immunization is CD8 dependent and CD4 independent. These studies extend previous observations on the induction of CTL by Hsp fusion proteins and are consistent with the clinical application of HspE7 as an immunotherapy for human cervical and anal dysplasia and cancer.

Role of IL-12 and 4-1BB ligand in cytokine production by CD28+ and CD28- T cells.

The costimulatory receptor CD28 is important in the development of both Th1 and Th2 responses. To further assess the requirement for CD28 in the development of Th1 and Th2 responses, we analyzed the ability of T cells from wild-type or CD28- mice to secrete cytokines in MLRs with B lymphomas. We find that in the absence of added IL-12, B lymphomas expressing the alternate costimulatory ligand 4-1BBL can support the production of IL-2 and IL-4 but little detectable IFN-gamma by allogeneic CD28+ and CD28- T cells. IL-4 production by CD28+ or CD28- T cells responding to B7(low) B lymphomas was abrogated by blocking 4-1BB ligand-4-1BB interaction. When APC express high levels of B7 family molecules as well as 4-1BBL, soluble 4-1BB inhibits IL-4 production by CD28- but not by CD28+ cells. Addition of IL-12 to the CD28- MLRs results in increased production of IFN-gamma and decreased amounts of IL-2 and IL-4. Thus, both Th1 and Th2 responses can develop in the complete absence of a signal through the CD28 molecule. CD28+ and CD28- T cells differed, however, with respect to the effect of IL-12 on IL-4 production. IL-12 severely curtailed the amount of IL-4 produced in the CD28- T cell cultures but had a less profound effect on the level of IL-4 produced in the CD28+ cultures, suggesting that a strong signal through the CD28 molecule prevents down-regulation of IL-4 production by IL-12.

Enhanced immunogenicity of B cell lymphoma genetically engineered to express both B7-1 and interleukin-12.

The A20 murine B cell lymphoma was transfected with B7-1 and subsequently these variants and vector control variants were retrovirally infected to express murine interleukin-12 (mIL-12). In vitro data showed that the B7-1 variants enhanced secretion of IL-2 and IL-4 by allogeneic T cells in mixed lymphocyte tumor cultures. While IL-12 variants stimulated IFN-gamma, variants expressing both B7-1 and IL-12 stimulated IFN-gamma, IL-2, and IL-4 secretion. Tumorigenicity experiments showed that whereas B7-1 delayed tumor onset, only the mIL-12 variants with or without B7-1 were completely rejected in syngeneic hosts. In addition, tumor-free mice were protected against subsequent challenge with the parental unmodified cells and had enhanced cytotoxic T lymphocyte (CTL) lysis activity. Results from minimal disease mixing experiments demonstrated that only the A20/B7-1/mIL-12 variant was able to reject A20 unmodified cells inoculated at the same site, whereas prolonged survival was observed when the A20 parental cells were inoculated at different sites. Depletion studies and injections into nu-/nu- mice demonstrated that both CD4+ and CD8+ T cells may mediate immunity. These data suggest that vaccinations with tumor cells genetically modified to express both B7-1 and IL-12 may alter cytokine profiles and generate CTL activity and, thus, the mechanisms of enhanced antitumor immunity may be multifactorial.

Comparison of peptide and superantigen-induced anergy in a peptide-specific polyclonal human T cell line.

T cells recognizing tetanus toxin peptide 'p2' (sequence 830-844) raised in HLA DR6 individuals preferentially express V beta 2 in the TCR. A p2-specific T cell line (60% V beta 2+) was used to compare peptide and superantigen [toxic shock syndrome toxin-1 (TSST-1)]-induced clonal anergy. Many experiments consistently revealed that the degree of 'tolerance' or 'clonal anergy' induced by peptide was greater than with the superantigen TSST-1. These results are of interest in a number of contexts. First they suggest that using superantigens or anti-V beta to delete the majority population of T cells may not be sufficient to diminish an autoimmune response. Secondly, the results indicate that induction of anergy of a large proportion of peptide-specific T cells does not lead to a suppressive bystander effect on the remaining responsive T cells. These results emphasize the need to define the dominant autoantigenic epitopes in human autoimmune diseases, since peptide based therapy such as the use of peptide analogues to induce anergy or a change in cytokine profile, is possibly more effective in controlling undesired immune responses than the use of non-antigen, TCR-directed approaches such as superantigens.

Role of 4-1BB ligand in costimulation of T lymphocyte growth and its upregulation on M12 B lymphomas by cAMP.

K46J B lymphomas express a T cell costimulatory activity that is not inhibited by CTLA-4Ig, anti-B7-1, anti-B7-2, anti-intercellular adhesion molecule 1 or antibodies to heat stable antigen. In this paper we report that this costimulatory activity is mediated at least in part by 4-1BB ligand, a member of the tumor necrosis factor (TNF) gene family that binds to 4-1BB, a T cell activation antigen with homology to the TNF/nerve growth factor receptor family. A fusion protein between 4-1BB and alkaline phosphatase (4-1BB-AP) blocks T cell activation by K46J lymphomas in both an antigen-specific system and with polyclonally (anti-CD3) activated T cells. 4-1BB-AP also blocks antigen presentation by normal spleen cells. When the antigen-presenting cells express B7 molecules as well as 4-1BB ligand, we find that B7 molecules and 4-1BB-AP both contribute to T cell activation. These data suggest that 4-1BB ligand plays an important role in costimulation of IL-2 production and proliferation by T cells. The B lymphoma M12 expresses low levels of 4-1BB-L but can be induced to express higher levels by treatment of the B cells with cAMP, which also induces B7-1 and B7-2 in these cells. Thus cAMP appears to coordinately induce several costimulatory molecules on B cells.

Soluble TNF receptor production by activated T lymphocytes: differential effects of acute and chronic exposure to TNF.

Soluble tumour necrosis factor receptors (sTNF-R) are up-regulated at sites of chronic inflammation such as rheumatoid synovial joints. The p75 sTNF-R is the more abundant, suggesting an important role for this TNF inhibitor in regulating TNF bioactivity in vivo. As the precise cellular source of these soluble receptors is not known, we investigated the production and regulation of sTNF-R by T lymphocytes, an abundant cell type in inflammatory infiltrates, which upon activation express high levels of p75 surface receptors. Using panels of T-cell lines and clones expressing high levels of p75 TNF-R, we found that p75 sTNF-R production upon stimulation is a feature common to all subsets of T cells, including cells of the CD4-CD8- double negative phenotype expressing either alpha beta or gamma delta T-cell receptors (TCR). In contrast, levels of p55 sTNF-R were only detected when T cells were stimulated at higher densities and by potent mitogens such as phorbol 12-myristate 13-acetate (PMA). Detailed kinetic analyses revealed that the production of p75 sTNF-R was biphasic, the first phase was activation dependent, occurring in the absence of detectable TNF, while the second phase of p75 sTNF-R production was regulated by cytokines such as TNF. Unlike short-term exposure to TNF which enhances sTNF-R production in vitro and in vivo, prolonged exposure of T lymphocytes to TNF suppressed p75 sTNF-R (but not p55 sTNF-R) production in a dose- and time-dependent fashion. These results suggest that in patients with chronic inflammatory disease, which are exposed to augmented levels of bioactive TNF for prolonged periods, the production of p75 sTNF-R may be impaired.

Chronic exposure to tumor necrosis factor (TNF) in vitro impairs the activation of T cells through the T cell receptor/CD3 complex; reversal in vivo by anti-TNF antibodies in patients with rheumatoid arthritis.

Experiments were designed to test the hypothesis that chronic exposure to tumor necrosis factor alpha (TNF) alters the function of activated T lymphocytes. Pretreatment of tetanus toxoid-specific T cell clones with TNF for up to 16 d impaired rechallenge proliferative responses to antigen in a dose- and time-dependent fashion. IL-2 and PHA responses were preserved. Prolonged treatment with TNF impaired production of IL-2, IL-10, IFN gamma, TNF, and lymphotoxin (LT) following stimulation with immobilized OKT3, and resulted in suboptimal expression of the IL-2R alpha chain (Tac) but not CD3, CD4, or HLA-DR antigens, when compared to untreated control cells. By contrast, pretreatment of T cells for prolonged periods in vitro with neutralizing anti-TNF monoclonal antibodies (mAb) enhanced proliferative responses, increased lymphokine production, and upregulated Tac expression following stimulation with OKT3. To determine whether TNF exerts immunosuppressive effects on T cells in vivo, we studied cell-mediated immunity in patients with active rheumatoid arthritis (RA), before and after treatment with a chimeric anti-TNF mAb. Treatment with anti-TNF restored the diminished proliferative responses of PBMC to mitogens and recall antigens towards normal in all patients tested. These data demonstrate that persistent expression of TNF in vitro and in vivo impairs cell-mediated immune responses.

T cells involved in human autoimmune disease are resistant to tolerance induction.

Deletion of potentially self-reactive T-cell clones during intrathymic development provides an important mechanism of preventing autoreactivity. However, some potentially damaging cells may escape this process. Recent evidence suggests that these cells may be rendered 'anergic', that is, nonresponsive to Ag, in the absence of cell death. Such a mechanism may be particularly important in maintaining tolerance to organ-specific self Ag that are not expressed in the thymus. If so, the emergence of T cells resistant to anergy induction might be expected to result in autoimmune disease. It has previously been shown that anergy can be induced in human T cells in vitro by exposure to specific target peptide or bacterial enterotoxins in the absence of Ag-presenting cells. We have recently defined the antigenic specificity of multiple T-cell clones present at the site of a human organ-specific autoimmune disease, Graves' thyroiditis (Graves disease). In the current work, thyroid-derived T cells recognizing residues 535-551 of the thyroid tissue-specific enzyme, TPO3 have been used to examine whether cells actively involved in the autoimmune process are resistant to anergy induction, as defined by anergy induction with in vitro systems. Two systems were used. First, supraimmunogenic concentrations of peptide 535-551 (up to 1 mg/ml) failed to significantly anergize these T cells in the absence of APC. In addition, the bacterial enterotoxin SED that could stimulate these T cells in the presence of APC, failed to induce anergy when APC were not present. T cells from the peripheral blood of the same individual, in contrast, were anergizable with bacterial enterotoxins, using the same protocol. These results suggest that thyroid-infiltrating autoantigen-reactive T cells are refractory to induction of anergy, and the possibility is raised that this deficiency may be of importance in the development of autoimmunity.

Identification of a T cell subset using a rabbit antibody raised against a T suppressor molecule.

Rabbit antiserum to a unique component of an Ag-binding Ts-factor was generated by repeated immunization with purified 30-kDa protein isolated from Fd11 Ts factor (11). This antiserum (anti-p30) was shown to recognize cell surface determinants expressed on the Ts hybridomas Fd11 and A10 but not the fusion partner BW5147. Furthermore, this antiserum was shown to bind to approximately 4% of thymocytes and 10% of nylon wool-purified splenic T cells from all strains of mice tested. Sorting nylon wool-purified T cells from DBA/2 mice for the CD4+ and CD8+ subsets revealed both populations contained cells that bound anti-p30. In addition, when CD4-8- thymocytes were examined for anti-p30 labeling, it was found that about 30% of this enriched population also expressed p30 molecules. In a functional study, anti-p30 was able to neutralize the suppressive effects of Fd11 on a specific assay for in vitro antibody synthesis against ferredoxin.

Isolation of an antigen-specific T suppressor factor that suppresses the in vivo response of DBA/2 mice to ferredoxin.

A T cell hybridoma (Fd11) has been produced from B10.D2 mice that secretes a putative antigen-specific T suppressor factor (TsF). The TsF is isolable from culture supernatants of Fd11 by affinity purification over columns containing either a monoclonal antibody (B16G) shown previously to be capable of binding murine TsF or ferredoxin (Fd), the nominal antigen to which the Fd11 TsF binds. Specificity of the Fd11 TsF for Fd was established by comparing it to another TsF isolated by us (A10 TsF) in a sandwich ELISA, and by demonstrating the specific reactivity to Fd of the hybridoma in calcium flux studies. The Fd11 affinity-purified TsF was shown to contain two major unique components with m.w. in the region of 80,000 and 35,000 when run on reducing polyacrylamide gels in the presence of sodium dodecyl sulphate. Specific immunosuppressive properties of Fd11 were demonstrated when Fd11 TsF (10 micrograms) was injected i.v. into Fd-primed syngeneic mice at the time of antigen boost. Fd11 TsF specifically and significantly diminished the secondary antibody response to Fd in DBA/2 mice.