Ascensión López-Díaz de Cerio

CD4+/CD25+ Regulatory Cells Inhibit Activation of Tumor-Primed CD4+ T Cells with IFN-γ-Dependent Antiangiogenic Activity, as well as Long-Lasting Tumor Immunity Elicited by Peptide Vaccination

CD25+ regulatory T (T reg) cells suppress the activation/proliferation of other CD4+ or CD8+ T cells in vitro. Also, down-regulation of CD25+ T reg cells enhance antitumor immune responses. In this study, we show that depletion of CD25+ T reg cells allows the host to induce both CD4+ and CD8+ antitumoral responses following tumor challenge. Simultaneous depletion of CD25+ and CD8+ cells, as well as adoptive transfer experiments, revealed that tumor-specific CD4+ T cells, which emerged in the absence of CD25+ T reg cells, were able to reject CT26 colon cancer cells, a MHC class II-negative tumor. The antitumoral effect mediated by CD4+ T cells was dependent on IFN-γ production, which exerted a potent antiangiogenic activity. The capacity of the host to mount this antitumor response is lost once the number of CD25+ T reg cells is restored over time. However, CD25+ T reg cell depletion before immunization with AH1 (a cytotoxic T cell determinant from CT26 tumor cells) permits the induction of a long-lasting antitumoral immune response, not observed if immunization is conducted in the presence of regulatory cells. A study of the effect of different levels of depletion of CD25+ T reg cells before immunization with the peptide AH1 alone, or in combination with a Th determinant, unraveled that Th cells play an important role in overcoming the suppressive effect of CD25+ T reg on the induction of long-lasting cellular immune responses.

Abnormal Priming of CD4+ T Cells by Dendritic Cells Expressing Hepatitis C Virus Core and E1 Proteins

ABSTRACT Patients infected with hepatitis C virus (HCV) have an impaired response against HCV antigens while keeping immune competence for other antigens. We hypothesized that expression of HCV proteins in infected dendritic cells (DC) might impair their antigen-presenting function, leading to a defective anti-HCV T-cell immunity. To test this hypothesis, DC from normal donors were transduced with an adenovirus coding for HCV core and E1 proteins and these cells (DC-CE1) were used to stimulate T lymphocytes. DC-CE1 were poor stimulators of allogeneic reactions and of autologous primary and secondary proliferative responses. Autologous T cells stimulated with DC-CE1 exhibited a pattern of incomplete activation characterized by enhanced CD25 expression but reduced interleukin 2 production. The same pattern of incomplete lymphocyte activation was observed in CD4+ T cells responding to HCV core in patients with chronic HCV infection. However, CD4+ response to HCV core was normal in patients who cleared HCV after alpha interferon therapy. Moreover, a normal CD4+ response to tetanus toxoid was found in both chronic HCV carriers and patients who had eliminated the infection. Our results suggest that expression of HCV structural antigens in infected DC disturbs their antigen-presenting function, leading to incomplete activation of anti-HCV-specific T cells and chronicity of infection. However, presentation of unrelated antigens by noninfected DC would allow normal T-cell immunity to other pathogens.

IL-10 suppressor activity and ex vivo Tr1 cell function are impaired in multiple sclerosis.

T regulatory cells type 1 (Tr1 cells) are excellent candidates for cell therapy in multiple sclerosis (MS). The aim of our study was to assess the functional state of Tr1 cells and IL‐10R signaling in patients with MS. Tr1 cells were induced in vitro by activation with anti‐CD46 antibodies in controls and patients with MS. Cells were phenotyped by cytometry and suppression assays, and the expression of cytokines and transcription factors was evaluated by real‐time PCR, ELISA, cytometry and Western blotting. We found that the activity of Tr1 cells and IL‐10R signaling is impaired in MS patients since Tr1 cells isolated from MS patients produced less IL‐10 than those obtained from controls. Indeed, the supernatants from Tr1 cells from controls did not suppress the proliferation of stimulated CD4+ cells from patients with MS. Furthermore, the IL‐10R signaling pathway was not fully active in CD4+ cells from MS patients and these cells had higher baseline levels of SOCS3 transcripts than controls. Indeed, after in vitro IL‐10 stimulation, the expression levels of the STAT1, STAT3 and IL‐10RA genes were higher in MS patients than in controls. Moreover, Stat‐3 phosphorylation was lower in controls than in patients after IL‐10 stimulation. These results indicate that IL‐10 regulatory function is impaired in patients with MS.

Human Follicular Lymphoma Cells Contain Oligomannose Glycans in the Antigen-binding Site of the B-cell Receptor

Expression of surface immunoglobulin appears critical for the growth and survival of B-cell lymphomas. In follicular lymphoma, we found previously that the Ig variable (V) regions in the B-cell receptor express a strikingly high incidence of N-glycosylation sequons, NX(S/T). These potential glycosylation sites are introduced by somatic mutation and are lymphoma-specific, pointing to their involvement in tumor pathogenesis. Analysis of the V region sugars from lymphoma-derived IgG/IgM reveals that they are mostly oligomannose and, remarkably, are located in the antigen-binding site, possibly precluding conventional antigen binding. The Fc region contains complex glycans, confirming that the normal glycan processing pathway is intact. Binding studies indicate that the oligomannose glycans occupying the V regions are accessible to mannose-binding lectin. These findings suggest a potential contribution to lymphoma pathogenesis involving antigen-independent interaction of surface immunoglobulin of the B-cell receptor with mannose-binding molecules of innate immunity in the germinal center.

Immunization with a tumor-associated CTL epitope plus a tumor-related or unrelated Th1 helper peptide elicits protective CTL immunity

Immunization with cytotoxic T cell epitope SPSYVYHQF (AH1), derived from MuLV gp70 envelope protein expressed by CT26 tumor cells, does not protect BALB/c mice against challenge with CT26 tumor cells. By contrast, immunization with AH1 plus T helper peptides OVA(323–337) or SWM(106–118) eliciting Th1 and Th0 profiles, protected 83% and 33% of mice, respectively. Interestingly, immunization with AH1 plus both helper peptides reverted the efficacy to 33%. We identified the endogenous T helper peptide p(320–333) from gp70 which elicits a Th1 profile and is naturally processed. As for OVA(323–337), immunization with p(320–333) alone did not protect against tumor challenge. However, p(320–333) plus AH1 protected 89% of mice at day 10 after vaccination. Only 20% of mice vaccinated with AH1 + OVA(323–337) or AH1 + p(320–333) were protected when challenged 80 days after immunization. Treatment with OVA(323–337) or with p(320–333) around established tumors delayed tumor growth. Our results show that tumor‐related as well as tumor‐unrelated but strong Th1 peptides may be useful for inducing CTL responses in tumor immunotherapy.

CD28 Aptamers as Powerful Immune Response Modulators

CD28 is one of the main costimulatory receptors responsible for the proper activation of T lymphocytes. We have isolated two aptamers that bind to the CD28 receptor. As a monomer, one of them interfered with the binding of CD28 to its ligand (B7), precluding the costimulatory signal, whereas the other one was inactive. However, dimerization of any of the anti-CD28 aptamers was sufficient to provide an artificial costimulatory signal. No antibody has featured a dual function (i.e., the ability to work as agonist and antagonist) to date. Two different agonistic structures were engineered for each anti-CD28 aptamer. One showed remarkably improved costimulatory properties, surpassing the agonistic effect of an anti-CD28 antibody. Moreover, we showed in vivo that the CD28 agonistic aptamer is capable of enhancing the cellular immune response against a lymphoma idiotype and of prolonging survival of mice which receive the aptamer together with an idiotype vaccine. The CD28 aptamers described in this work could be used to modulate the immune response either blocking the interaction with B7 or enhancing vaccine-induced immune responses in cancer immunotherapy.

Targeting NK-cell checkpoints for cancer immunotherapy.

Natural Killer (NK) cells are cytotoxic lymphocytes specialized in early defense against virus-infected and transformed cells. NK-cell function is regulated by activating and inhibitory surface receptors recognizing their ligands on transformed cells. Modulation of NK numbers and/or function by a variety of agents such as cytokines and monoclonal antibodies may result in enhanced anti-tumor activity. Recombinant cytokines (i.e., IL-15 and IL-2), antibodies blocking inhibitory receptors (i.e., KIR, NKG2A and TIGIT) and agonists delivering signals via CD137, NKG2D and CD16 stand out as the most suitable opportunities. These agents can be used to potentiate NKcell- mediated antibody-dependent cellular cytotoxicity (ADCC) against antibody-coated tumor cells, offering potential for multiple combinatorial immunotherapy strategies against cancer.

Characterization of an immunologically conserved epitope from hepatitis C virus E2 glycoprotein recognized by HLA-A2 restricted cytotoxic T lymphocytes

BACKGROUND/AIMS Identification of epitopes recognized by cytotoxic T lymphocytes (CTL) in hepatitis C virus (HCV) proteins is of importance because they can be used for vaccination, treatment of infection or monitoring of immune responses. Our purpose was to characterize new CTL epitopes in HCV structural proteins. METHODS Peptides were synthesized and tested in HLA-A2 binding assays. Binder peptides were used to stimulate peripheral blood mononuclear cells from HCV+ patients and controls, and activity measured in chromium release and ELISPOT assays. RESULTS Twenty binder peptides were found, and stimulation of HCV+ patient cells with nine peptides showing high binding ability led to the growth of CD8+ CTL recognizing peptide E2(614-622) in association with HLA-A2. Peptide E2(614-622) was recognized by 30% of HLA-A2+ patients with chronic HCV infection, but no responses were observed in control groups. Five peptides derived from region E2(614-622) from 26 different viral isolates bound to HLA-A2 molecules, and all of them but one, containing Phe at position 622, were recognized by E2(614-622) specific CTL. CONCLUSIONS These results show that peptide E2(614-622) belongs to a highly conserved region of HCV E2, and might be a good candidate to induce anti-HCV CTL responses in HLA-A2+ subjects.

Clinical Safety and Immunogenicity of Tumor-Targeted, Plant-Made Id-KLH Conjugate Vaccines for Follicular Lymphoma

We report the first evaluation of plant-made conjugate vaccines for targeted treatment of B-cell follicular lymphoma (FL) in a Phase I safety and immunogenicity clinical study. Each recombinant personalized immunogen consisted of a tumor-derived, plant-produced idiotypic antibody (Ab) hybrid comprising the hypervariable regions of the tumor-associated light and heavy Ab chains, genetically grafted onto a common human IgG1 scaffold. Each immunogen was produced in Nicotiana benthamiana plants using twin magnICON vectors expressing the light and heavy chains of the idiotypic Ab. Each purified Ab was chemically linked to the carrier protein keyhole limpet hemocyanin (KLH) to form a conjugate vaccine. The vaccines were administered to FL patients over a series of ≥6 subcutaneous injections in conjunction with the adjuvant Leukine (GM-CSF). The 27 patients enrolled in the study had previously received non-anti-CD20 cytoreductive therapy followed by ≥4 months of immune recovery prior to first vaccination. Of 11 patients who became evaluable at study conclusion, 82% (9/11) displayed a vaccine-induced, idiotype-specific cellular and/or humoral immune response. No patients showed serious adverse events (SAE) related to vaccination. The fully scalable plant-based manufacturing process yields safe and immunogenic personalized FL vaccines that can be produced within weeks of obtaining patient biopsies.

Prolonged idiotypic vaccination against follicular lymphoma.

During the last 2 decades, idiotypic vaccination has provided proof of principle of biological efficacy, clinical efficacy and clinical benefit in small follicular lymphoma trials. However, with the exception of anecdotal reports, most patients have received no more than 10 doses of their customised idiotype (Id) vaccine. Therefore, it is not known whether prolonged usage of idiotypic vaccination is safe. Since 2002, 18 previously treated patients with follicular lymphoma have received extended idiotypic vaccination at our institution outside clinical trials. Vaccination was provided as a compassionate alternative to no further treatment, and was meant to be stopped only upon complete consumption of the available patient- and tumor-specific vaccine [Id-keyhole limpet hemocyanin + granulocyte-macrophage colony-stimulating factor (Id-KLH + GM-CSF)], or in case of disease relapse or any serious non-local toxicity. So far, 18 patients have received an average of 18 doses of Id vaccine (median: 17; mean: 18; range: 10–31). Eleven patients are still actively receiving idiotypic vaccination: some of them are now over more than 6 years. Toxicity has been systematically negligible and mostly local. No patient has abandoned the vaccination program because of toxicity. Prolonged idiotypic vaccination with the soluble protein Id-KLH + GM-CSF formulation is safe and well tolerated.