Laura Vitale

Induction of Antigen-Specific Immunity with a Vaccine Targeting NY-ESO-1 to the Dendritic Cell Receptor DEC-205

Dendritic cell targeting safely leads to integrated humoral and cellular immunity when combined with TLR agonists in cancer patients. Start Spreading the News Dendritic cells are the matchmakers of the immune system: They introduce T cells to antigen, providing the right context for the T cell to react. However, tumor alters the nearby microenvironment in such a way as to block immune activation. Dhodapkar et al. attempt to overcome this inhibition by targeting a tumor antigen directly to dendritic cells. The authors tested a vaccine that consisted of a human antibody targeted to the dendritic cell receptor DEC-205 fused with the tumor antigen NY-ESO-1 in a cohort of patients with tumors refractory to other therapies. They also added Toll-like receptor ligands as adjuvants in a dose-escalating study. They found that treatment induced both humoral and cellular immunity in these patients, with no dose-limiting toxicities. What’s more, a subset of patients had either stable disease or disease regression, particularly those who had received immune checkpoint inhibitors. If these data can be reproduced in larger trials, this study suggests that targeting antigen to dendritic cells could be an additional avenue to boost the immune response to cancer. Immune-based therapies for cancer are generating substantial interest because of the success of immune checkpoint inhibitors. This study aimed to enhance anticancer immunity by exploiting the capacity of dendritic cells (DCs) to initiate T cell immunity by efficient uptake and presentation of endocytosed material. Delivery of tumor-associated antigens to DCs using receptor-specific monoclonal antibodies (mAbs) in the presence of DC-activating agents elicits robust antigen-specific immune responses in preclinical models. DEC-205 (CD205), a molecule expressed on DCs, has been extensively studied for its role in antigen processing and presentation. CDX-1401 is a vaccine composed of a human mAb specific for DEC-205 fused to the full-length tumor antigen NY-ESO-1. This phase 1 trial assessed the safety, immunogenicity, and clinical activity of escalating doses of CDX-1401 with the Toll-like receptor (TLR) agonists resiquimod (TLR7/8) and Hiltonol (poly-ICLC, TLR3) in 45 patients with advanced malignancies refractory to available therapies. Treatment induced humoral and cellular immunity to NY-ESO-1 in patients with confirmed NY-ESO-1–expressing tumors across various dose levels and adjuvant combinations. No dose-limiting or grade 3 toxicities were reported. Thirteen patients experienced stabilization of disease, with a median duration of 6.7 months (range, 2.4+ to 13.4 months). Two patients had tumor regression (~20% shrinkage in target lesions). Six of eight patients who received immune-checkpoint inhibitors within 3 months after CDX-1401 administration had objective tumor regression. This first-in-human study of a protein vaccine targeting DCs demonstrates its feasibility, safety, and biological activity and provides rationale for combination immunotherapy strategies including immune checkpoint blockade.

Mannose Receptor Targeting of Tumor Antigen pmel17 to Human Dendritic Cells Directs Anti-Melanoma T Cell Responses via Multiple HLA Molecules

Targeting recycling endocytic receptors with specific Abs provides a means for introducing a variety of tumor-associated Ags into human dendritic cells (DCs), culminating in their efficient presentation to T cells. We have generated a human mAb (B11) against the mannose receptor that is rapidly internalized by DCs through receptor-mediated endocytosis. By genetically linking the melanoma Ag, pmel17, to Ab B11, we obtained the fully human fusion protein, B11-pmel17. Treatment of DCs with B11-pmel17 resulted in the presentation of pmel17 in the context of HLA class I and class II molecules. Thus, potent pmel17-specific T cells were cytotoxic toward gp100+ HLA-matched melanoma targets, but not HLA-mismatched melanoma or gp100− nonmelanoma tumor lines. Importantly, competitive inhibition of lysis of an otherwise susceptible melanoma cell line by cold targets pulsed with known gp100 CD8 T cell epitopes as well as a dose-dependent proliferative response to Th epitopes demonstrates that DCs can process targeted Ag for activation of cytotoxic as well as helper arms of the immune response. Thus, the specific targeting of soluble exogenous tumor Ag to the DC mannose receptor directly contributes to the generation of multiple HLA-restricted Ag-specific T cell responses.

Phase I study utilizing a novel antigen-presenting cell-targeted vaccine with Toll-like receptor stimulation to induce immunity to self antigens in cancer patients

Purpose: The use of tumor-derived proteins as cancer vaccines is complicated by tolerance to these self-antigens. Tolerance may be broken by immunization with activated, autologous, ex vivo generated and antigen-loaded, antigen-presenting cells (APC); however, targeting tumor antigen directly to APC in vivo would be a less complicated strategy. We wished to test whether targeted delivery of an otherwise poorly immunogenic, soluble antigen to APC through their mannose receptors (MR) would induce clinically relevant immunity. Experimental Design: Two phase I studies were conducted with CDX-1307, a vaccine composed of human chorionic gonadotropin beta-chain (hCG-β) fused to an MR-specific monoclonal antibody, administered either locally (intradermally) or systemically (intravenously) in patients with advanced epithelial malignancies. An initial dose escalation of single-agent CDX-1307 was followed by additional cohorts of CDX-1307 combined with granulocyte-macrophage colony-stimulating factor (GM-CSF) and the Toll-like receptor (TLR) 3 agonist polyinosinic-polycytidylic acid (poly-ICLC) and TLR7/8 agonist resiquimod to activate the APC. Results: CDX-1307 induced consistent humoral and T-cell responses to hCG-β when coadministered with TLR agonists. Greater immune responses and clinical benefit, including the longest duration of stable disease, were observed with immunization combined with local TLR agonists. Immune responses were induced equally efficiently in patients with elevated and nonelevated levels of serum hCG-β. Antibodies within the serum of vaccinated participants had tumor suppressive function in vitro. Toxicity consisted chiefly of mild injection site reactions. Conclusions: APC targeting and activation induce adaptive immunity against poorly immunogenic self-antigens which has implications for enhancing the efficacy of cancer immunotherapy. Clin Cancer Res; 17(14); 4844–53. ©2011 AACR.

Antibody-Targeted NY-ESO-1 to Mannose Receptor or DEC-205 In Vitro Elicits Dual Human CD8+ and CD4+ T Cell Responses with Broad Antigen Specificity

Immunization of cancer patients with vaccines containing full-length tumor Ags aims to elicit specific Abs and both CD4+ and CD8+ T cells. Vaccination with protein Ags, however, often elicits only CD4+ T cell responses without inducing Ag-specific CD8+ T cells, as exogenous protein is primarily presented to CD4+ T cells. Recent data revealed that Ab-mediated targeting of protein Ags to cell surface receptors on dendritic cells could enhance the induction of both CD4+ and CD8+ T cells. We investigated in this study if these observations were applicable to NY-ESO-1, a cancer-testis Ag widely used in clinical cancer vaccine trials. We generated two novel targeting proteins consisting of the full-length NY-ESO-1 fused to the C terminus of two human mAbs against the human mannose receptor and DEC-205, both internalizing molecules expressed on APC. These targeting proteins were evaluated for their ability to activate NY-ESO-1–specific human CD4+ and CD8+ T cells in vitro. Both targeted NY-ESO-1 proteins rapidly bound to their respective targets on APC. Whereas nontargeted and Ab-targeted NY-ESO-1 proteins similarly activated CD4+ T cells, cross-presentation to CD8+ T cells was only efficiently induced by targeted NY-ESO-1. In addition, both mannose receptor and DEC-205 targeting elicited specific CD4+ and CD8+ T cells from PBLs of cancer patients. Receptor-specific delivery of NY-ESO-1 to APC appears to be a promising vaccination strategy to efficiently generate integrated and broad Ag-specific immune responses against NY-ESO-1 in cancer patients.

Differential Effect of Cytokine Treatment on Fcα Receptor I- and Fcγ Receptor I-Mediated Tumor Cytotoxicity by Monocyte-Derived Macrophages

Macrophages represent an important effector cell for Ab-mediated tumor therapy. Previous studies have documented that cytokines can influence Fc receptor (FcR) expression and function. In this study we examined the tumoricidal activities of the type I receptors for IgG (FcγRI) and the IgA FcR (FcαRI) on monocyte-derived macrophages (MDM) cultured in the presence of IFN-γ, M-CSF, or GM-CSF. Bispecific Abs were used to target a Her2/neu breast carcinoma cell line, SKBR-3, to FcαRI or FcγRI on MDM. Although FcαRI and FcγRI share a common signaling pathway contingent on association with the γ-chain (FcRγ subunit), a marked difference in their efficiency in mediating tumoricidal functions was seen in response to specific cytokines. M-CSF- and GM-CSF-treated MDM mediated efficient phagocytosis of SKBR-3 cells by FcαRI and FcγRI; however, IFN-γ-treated MDM phagocytosed tumor cells only with the FcγRI-directed bispecific Abs. Similarly, IFN-γ-cultured MDM lysed tumor cells more efficiently via FcγRI then by FcαRI as measured in Ab-dependent cellular cytotoxicity assays. Conversely, GM-CSF-treated MDM mediated more efficient lysis of tumor cells via FcαRI than FcγRI, while M-CSF-cultured MDM were relatively less efficient in mediating Ab-dependent cellular cytotoxicity through either receptor. With the exception of IFN-γ-mediated enhancement of FcγRI expression and FcγRI γ-chain complexes, the regulation of FcγRI- or FcαRI-mediated activity occurred without significant change in either receptor expression or total complexes with γ subunit. These data suggest that the efficiency of Ab-mediated tumor therapy, which depends on FcR effector cell functions, may be modified by the use of specific cytokines.

Targeting Weak Antigens to CD64 Elicits Potent Humoral Responses in Human CD64 Transgenic Mice

Previous studies have documented that targeting foreign Ags to IgG FcγR leads to enhanced Ag-specific responses in vitro and in vivo. However, the ability to overcome immunologic nonresponsiveness by targeting poorly immunogenic Ags to FcγR has not been investigated. To address this question in a simple model, we immunized transgenic mice expressing human CD64 (FcγRI) and their nontransgenic littermates with Fab′ derived from the murine anti-human CD64 mAb m22. The m22 Fab′ served as both the targeting molecule and the Ag. We found that only CD64-expressing mice developed anti-Id titers to m22. Furthermore, chemically linked multimers of m22 Fab′, which mediated efficient internalization of the human CD64, were significantly more potent than monomeric m22 F(ab′)2 at inducing anti-Id responses. In all cases, the humoral responses were specific for m22 Id and did not react with other murine IgG1 Fab′ fragments. Chemical addition of a second murine Fab′ (520C9 anti-human HER2/neu) to m22 Fab′ multimers demonstrated that IgG1 and IgG2a anti-Id titers could be generated to 520C9 only in the CD64-expressing mice. These results show that targeting to CD64 can overcome immunological nonresponsiveness to a weak immunogen. Therefore, targeting to CD64 may be an effective method to enhance the activity of nonimmunogenic tumor vaccines.

Receptor Modulation by FcγRI-Specific Fusion Proteins Is Dependent on Receptor Number and Modified by IgG

The high-affinity IgG receptor, FcγRI (CD64), is constitutively expressed exclusively on professional APCs. Human FcγRI binds monomeric IgG with high affinity and is, therefore, saturated in vivo. The binding of IgG to FcγRI causes receptor recycling, while Abs that cross-link FcγRI cause rapid down-modulation of surface FcγRI. Because studies performed in the absence of ligand may not be representative of FcγRI modulation in vivo, we investigated the ability of FcγRI-cross-linking Abs and non-cross-linking derivatives to modulate FcγRI in the presence and absence of ligand. In the absence of ligand mAb H22 and wH22xeGFP, an enhanced green fluorescent protein (eGFP)-labeled fusion protein of H22, cross-linked and rapidly down-modulated surface FcγRI on the human myeloid cell line, U937, and its high FcγRI-expressing subclone, 10.6. This effect was dependent on the concentration of fusion protein and the level of FcγRI expression and correlated with internalization of both wH22xeGFP and FcγRI, itself, as assessed by confocal microscopy. A single-chain Fv version, sFv22xeGFP, which does not cross-link FcγRI, was unable to modulate FcγRI in the absence of IgG. However, if ligand was present, treatment with either monovalent or cross-linking fusion protein led to intracellular receptor accumulation. These findings suggest at least two alternate mechanisms of internalization that are influenced by ligand and demonstrate the physiologic potential of FcγRI to transport a large antigenic load into APCs for processing. These studies may lead to the development of better FcγRI-targeted vaccines, as well as therapies to down-modulate FcR involved in autoimmune diseases.

A novel human CD32 mAb blocks experimental immune haemolytic anaemia in FcγRIIA transgenic mice

A fully human IgG1 kappa antibody (MDE‐8) was generated, which recognised Fc‐gamma receptor IIa (FcγRIIa) molecules on CD32 transfectants, peripheral blood monocytes, polymorphonuclear cells and platelets. This antibody blocked FcγRIIa ligand‐binding via its F(ab′)2 fragment. Overnight incubation of monocytes with F(ab′)2 fragments of MDE‐8 leads to a c. 60% decrease in cell surface expression of FcγRIIa. MDE‐8 whole antibody induced a concomitant c. 30% decrease of FcγRI on THP‐1 cells and monocytes. In humans FcγRIIa plays an important role in the clearance of antibody‐coated red blood cells in vivo. As an equivalent of FcγRIIa does not exist in mice, the in vivo effect of MDE‐8 was studied in an FcγRIIa transgenic mouse model. In these mice, antibody‐induced anaemia could readily be blocked by MDE‐8. These data document a new human antibody that effectively blocks FcγRIIa, induces modulation of both FcγRIIa and FcγRI from phagocytic cells, and ameliorates antibody‐induced anaemia in vivo.

Direct targeting of genetically modified tumour cells to FcγRI triggers potent tumour cytotoxicity

Expression of the type I receptor for Fc domain of immunoglobulin (Ig)G (FcγRI or CD64) is restricted to myeloid effector cells, such as monocytes, macrophages and a subset of dendritic cells. Previous work has indicated a role for FcγRI in antibody‐dependent phagocytosis and lysis of tumour cells. We hypothesised that tagging of tumour cells with an anti‐FcγRI single chain Fv (sFv) may facilitate targeting to this receptor on effector cells, thereby initiating tumour cytotoxicity. A vector encoding the sFv for an FcγRI‐specific antibody (H22), linked to the transmembrane domain of platelet‐derived growth factor was constructed. Transfected tumour cells expressed high surface levels of functional H22‐sFv, which greatly enhanced susceptibility for phagocytosis and lysis by monocytes and macrophages. The expression of H22‐sFv evoked the ability of tumour cells to directly activate monocytes, as evidenced by phosphorylation of mitogen‐activated protein kinase and secretion of the inflammatory cytokines interleukin (IL)‐1β, tumour necrosis factor‐α and IL‐6. Moreover, growth of tumour cells in mice expressing H22‐sFv was profoundly delayed (or absent) in transgenic mice expressing human FcγRI. These results demonstrated that tumour cells can be readily modified to activate cell effector mechanisms, a strategy that may be useful for in vivo targeting in patients.

Development of T-cell lines expressing functional HIV-1 envelope glycoproteins for evaluation of immune responses in HIV-infected individuals.

The human T-lymphoid cell line, CEM, was transfected with gp 160 cDNA of human immunodeficiency virus type 1 (HIV-1)pm213. Three clones expressing the envelope glycoproteins (env), designated CEM-213env1, -env4, and -env7, were isolated. These clones expressed high levels of surface gp41 and gp120, as demonstrated by flow cytometry with anti-HIV env monoclonal antibodies. Processing and function of env was shown by induction of syncytia with CD4-expressing HeLa cells and by immunoblot analysis. The env expression resulted in specific down-regulation of surface CD4 levels, supporting the role of HIV env in CD4 modulation. Furthermore, serum samples from nine of nine HIV-1-infected individuals bound specifically to the env-expressing transfectants, substantiating the presence of conserved antigenic determinants. These sera also mediated antibody-dependent cellular cytotoxicity (ADCC) of the env-expressing cell lines. The env-expressing cell lines provide a relevant, safe, and practical model for qualitative and quantitative analysis of humoral and cellular immune responses and their role in HIV-1 pathogenesis and therapy.