Venky Ramakrishna

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.

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.

A Novel Human Cancer Vaccine Elicits Cellular Responses to the Tumor-Associated Antigen, Human Chorionic Gonadotropin β

Purpose: The oncofetal antigen, human chorionic gonadotropin β subunit (hCGβ), is expressed by a number of carcinomas and is a prognostic indicator in renal, colorectal, bladder, and pancreatic cancers. We describe the development of a novel antibody-based dendritic cell (DC)-targeted cancer vaccine capable of eliciting cellular immune responses directed against hCGβ. Experimental Design: The tumor-associated antigen hCGβ was coupled genetically to a human anti-DC antibody (B11). The resulting fusion protein (B11-hCGβ) was evaluated for its ability to promote tumor antigen-specific cellular immune responses in a human in vitro model. Monocyte-derived human DCs from normal donors were exposed to purified B11-hCGβ, activated with CD40 ligand, mixed with autologous lymphocytes, and tested for their ability to promote hCGβ-specific proliferative and cytotoxic T-lymphocyte responses. Results: B11-hCGβ was found to be a soluble, well-defined, and readily purified product that specifically recognized the human mannose receptor via the B11 antibody portion of the fusion protein. B11-hCGβ functionally promoted the uptake and processing of tumor antigen by DCs, which led to the generation of tumor-specific HLA class I and class II-restricted T-cell responses, including CTLs capable of killing human cancer cell lines expressing hCGβ. Conclusions: Although other hCG vaccines have been shown to be capable of eliciting antibody responses to hCGβ, this is the first time that cellular immune responses to hCGβ have been induced by a vaccine in a human system. This DC-targeted hCGβ vaccine holds promise for the management of a number of cancers and merits additional clinical development.

Toll-like receptor activation enhances cell-mediated immunity induced by an antibody vaccine targeting human dendritic cells

Previously, we have successfully targeted the mannose receptor (MR) expressed on monocyte-derived dendritic cells (DCs) using a fully human MR-specific antibody, B11, as a vehicle to deliver whole protein tumor antigens such as the human chorionic gonadotropin hormone (hCGβ). Since MRs play a role in bridging innate immunity with adaptive immunity we have explored several toll-like receptor (TLR)-specific ligands that may synergize with MR targeting and be applicable as adjuvants in the clinic. We demonstrate that antigen-specific helper and cytolytic T cells from both healthy donors and cancer patients were effectively primed with B11-hCGβ-treated autologous DCs when a combination of one or several TLR ligands is used. Specifically, concomitant signaling of DCs via TLR3 with dsRNA (poly I:C) and DC TLR 7/8 with Resiquimod (R-848), respectively, elicited efficient antigen presentation-mediated by MR-targeting. We demonstrate that MR and TLRs contribute towards maturation and activation of DCs by a mechanism that may be driven by a combination of adjuvant and antibody vaccines that specifically deliver antigenic targets to DCs.

Assessing vaccine potency using TCRmimic antibodies

Dendritic cells (DCs) are highly specialized antigen-presenting cells of the immune system that are efficient at presenting peptide-antigen for the activation of T cells and are often the cell type of choice for vaccine targeting by virtue of high expression levels of MHC and costimulatory molecules. Since the level of peptide-MHC complex significantly influences stimulation of T cells, a proof-of-concept potency assay was developed to directly examine the presentation and density of MHC class I peptides derived from the processing of a model tumor antigen, (hCGbeta), on the surface of DCs. In this study we first generated antibodies (TCR mimics or TCRm) to two peptide-HLA-A*0201 epitopes derived from hCGbeta designated as TMT (40-48) and GVL (47-55). Characterization of each TCRm by ELISA and flow cytometric analysis, demonstrated specific binding to soluble recombinant HLA-A2 protein and HLA-A2.1+ T2 cells loaded with relevant peptide. TCRm reactive against the TMT and GVL epitopes blocked granzyme-B production by peptide-specific cytotoxic T lymphocytes (CTL) lines further supporting their recognition specificity. For the assessment of antigen presentation function, human immature monocyte-derived DCs (iDCs) were treated with the mannose receptor targeting vaccine, B11-hCGbeta and matured with Poly I:C. The TMT and GVL epitope reactive CTL lines responded to vaccine-treated but not vehicle-treated mature DCs (mDCs) with TMT and GVL TCRm specifically blocking IFN-gamma production. The TCRm were then used to directly confirm specific peptide-MHC complexes on mDCs. TCRm staining of vaccine-treated mDCs showed detection of the TMT and GVL peptide-HLA-A2 complexes. These findings demonstrate that TCRms may be important tools for determining the potency of DC-based vaccines.

Immune correlates of Varlilumab treated cancer patients are consistent with CD27 costimulatory activity

Meeting abstracts Varlilumab is a human IgG1 agonist anti-CD27 antibody designed to activate T cells through CD27 costimulation. Preclinical studies have shown that Varlilumab efficiently activates human T cells when combined with T cell receptor stimulation, enhances antigen specific CD8 T cell

Abstract 3664: CDX-1402, a dendritic cell targeted fusion protein designed to elicit immunity to mesothelin and HER2 expressing tumors

The use of mAbs to target antigens to the endocytic receptor DEC-205 on dendritic cells (DC) is an effective means to elicit helper and cytolytic T cell responses in the presence of appropriate adjuvants to activate DC. We have translated this concept to clinical studies using a fully human DEC-205-specific mAb genetically altered to include the entire NY-ESO-1 cancer antigen (CDX1401), which when combined with TLR agonists results in effective stimulation of both cellular and humoral NY-ESO-1-specific responses in cancer patients (Dhodapkar MV et al., Sci. Transl. Med. 6:232-251, 2014). Pre-treatment of patients with the DC mobilizing agent, Flt3L (CDX-301), was subsequently shown to significantly augment both humoral and cellular responses to CDX-1401 (Bhardwaj N et al. ASCO 2016).