Tumor-reactive Antibodies Research Articles

IMMU-25. B-CELL BASED THERAPY (BVAX) PRODUCES ANTIBODIES TO SUPPRESS GLIOBLASTOMA TUMOR MIGRATION AND INVASION

Abstract Glioblastoma (GBM) presents as a highly aggressive and malignant brain tumor with limited treatment options. Despite the availability of existing therapies, the invasive characteristics of GBM frequently result in tumor recurrence and poor prognosis. We previously developed a B-cell-based therapy (BVax) that has shown promising results in its ability to induce therapeutic responses in preclinical models of GBM. Our research revealed potency of BVax can be attributed to its robust antigen-presenting capability, cognate antigen specificity with T cells, and ability to generate tumor-reactive antibodies. The present study aims to characterize the unique antigenic reactivity of BVax-derived antibodies by evaluating their immunological effects and therapeutic potential in both murine models and GBM patient-specific samples. Leveraging CD45.1 and CD45.2 congenic mouse models, we first revealed that BVax preferentially migrated to glioma-bearing brains upon intravenous injection, resulting in a CD38+CD20-CD19+ plasmablast phenotype. To further characterize the reactivity of BVax-derived immunoglobulins (Ig), we utilized proteomic analysis and identified preferential targets of Gelsolin, Fibronectin, Versican, Fibrinogen, and collagen type IV alpha, commonly associated with cell motility and the extracellular matrix. Microdialysis data confirmed the increased presence of many of these BVax-derived Igs-recognized antigens in tumor regions compared to normal brain regions in GBM patients. Utilizing purified BVax-derived antibodies from patient specimen, in vitro cell motility assays demonstrated a significant prevention of the invasion and migration of cell lines from patient derived xenograft (PDX). In this study, we concluded that BVax elicits antitumor activity through targeted migration to tumor-bearing regions, differentiation into plasmablasts, and robust secretion of specific Igs that retain the ability to inhibit functionalities associated with cell invasion and migration. Here, we present the first in-depth study that characterizes GBM patients’ antibody reactivity, specifically a subset of inflammatory B cells (BVax) with therapeutic effects that offer an indication for a new direction of immunotherapies.

Investigation into aberrant B cell repertoire in myeloma on humoral immunity and patient survival.

8016 Background: B cells are critical to inhibiting tumor progression, as they generate tumor-reactive antibodies; promote anti-tumor killing capacity of NK cells and phagocytosis of macrophages/DCs; and enrich priming of T cells against the tumor. Multiple myeloma (MM) is a B-cell-derived malignancy, and its survival is partly driven by a deficiency in the immune response. Yet, the abnormalities of the B-cell-mediated humoral responses in MM are ill defined. Methods: We investigated B cell composition in bone marrow (BM) from patients with newly diagnosed MM (NDMM, N = 170), relapsed refractory MM (RRMM, N = 140) and healthy donors (HD, N = 21) by multi-color flow cytometry. Results: We observed that B1b cells was significantly reduced by 45% (p = 0.004) in NDMM patients compared to HD. B1b cells are important in generating long-lasting protective antibodies, particularly against vaccines, in a T cell independent fashion. Similarly, B2 cells, which can produce all antibody types, were significantly reduced in the periphery of NDMM and RRMM patients. Within the B2 cell population, germinal center (GC) matured B cells were significantly reduced in both BM and periphery of MM patients, as shown by significantly higher expression of Fas receptor. Because of deficiencies in the GC-maturation of these B cells, their ability to switch from IgM to IgG was also significantly decreased. On the other hand, the population of regulatory B cells (Bregs) were significantly elevated by 2.3-fold (p < 0.05) in the BM and periphery of NDMM and periphery of RRMM patients. However, the ability of Breg cells to produce suppressive cytokines, like IL-10, was significantly reduced (p = 0.03), indicating impaired suppressive functional capacity. We investigated whether this dysregulated B cell homeostasis impacts myeloma patient survival following treatment. We found that a higher proportion of Bregs and a lower percent of B1a in BM and periphery prior to treatment was associated with favorable progression-free survival (PFS) in both NDMM and RRMM patients. We hypothesized that reduction of B2 cells and their inability to have GC-based maturation could impair antibody generation against acute infections and tumor neoantigens. Therefore, we evaluated MM patients’ ability to produce antibodies against hepatitis B surface antigen-based vaccination. We observed that only 31% of MM patients (N = 32) respond to the vaccine compared to 90% of HD. Furthermore, MM patients’ antibody titers were significantly lower ( < 120 IU/L) compared to > 5000IU/L in HD. Conclusions: All together, these results show that in MM patients, vaccine-responsive populations of B cells are reduced, with fewer mature B cells with limited repertoires in GC to fight against acute infections, and with a high number of dysregulated regulatory B cells. These results indicate that compromised B cell functionality in MM patients could impact therapeutic outcome.

Abstract 602: Single cell evaluation of intratumoral B cells across solid tumor indications

Abstract The immune system is a critical component of the tumor microenvironment that has both tumor-promoting and tumor-eradicating activity based on the specific immune cell subtype and their activation status. T lymphocytes represent the largest lymphocyte population within the tumor, and numerous immunotherapies have been developed to specifically target this cellular subset. B cells are the next most abundant lymphocyte subset within the tumor microenvironment, and recent studies have identified crucial roles for intratumoral B cells in the production of tumor-reactive antibodies. Using human dissociated tumor cells (DTCs) samples, we have profiled intratumoral B cells to determine their frequency and subset breakdown across thirteen different solid tumor indications. Intratumoral B cells were prevalent in lung cancer and cancers of the gastrointestinal tract (esophageal, gastric, and colorectal), while they were rarer in cancers of the female reproductive tract (endometrial and ovarian). The transcriptional profile and B cell repertoire of the intratumoral B cell subsets were evaluated to provide a deeper understanding of the biology of these tumor-infiltrating lymphocyte subsets. Additionally, spatial transcriptomics were utilized to understand the spatiotemporal location of these subsets within the tumor microenvironment. These studies will provide critical insight for the development of the next generation of immunotherapies. Citation Format: Shawn P. Fahl, Kerri Colwell, Casey Smith, Cavin Ott, Alex Moore, Kayla Williams. Single cell evaluation of intratumoral B cells across solid tumor indications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 602.

Tumor-Reactive Antibodies Emerge from Nonbinding and Autoreactive Precursors.

Immune cell-generated autoantibodies coat tumor cells and support antitumor immune response.

Systematic Analysis of the Expression and Prognosis of Fcγ Receptors in Clear Cell Renal Cell Carcinoma.

BackgroundClear cell renal cell carcinoma (ccRCC) remains a common malignancy in the urinary system. Although dramatic progress was made in multimodal therapies, the improvement of its prognosis continues to be unsatisfactory. The antibody-binding crystallizable fragment (Fc) γ receptors (FcγRs) are expressed on the surface of leukocytes, to mediate antibody-induced cell-mediated anti-tumor responses when tumor-reactive antibodies are present. FcγRs have been studied extensively in immune cells, but rarely in cancer cells.MethodsONCOMINE, UALCAN, GEPIA, TIMER, TISIDB, Kaplan–Meier Plotter, SurvivalMeth, and STRING databases were utilized in this study.ResultsTranscriptional levels of FcγRs were upregulated in patients with ccRCC. There was a noticeable correlation between the over expressions of FCGR1A/B/C, FCGR2A, and clinical cancer stages/tumor grade in ccRCC patients. Besides, higher transcription levels of FcγRs were found to be associated with poor overall survival (OS) in ccRCC patients. Further, high DNA methylation levels of FcγRs were also observed in ccRCC patients, and higher DNA methylation levels of FcγRs were associated with shorter OS. Moreover, we also found that the expression of FcγRs was significantly correlated with immune infiltrates, namely, immune cells (NK, macrophages, Treg, cells) and immunoinhibitor (IL-10, TGFB1, and CTLA-4).ConclusionsOur study demonstrated that high DNA methylation levels of FcγRs lead to their low mRNA, protein levels, and poor prognosis in ccRCC patients, which may provide new insights into the choice of immunotherapy targets and prognostic biomarkers.

Tumor-reactive antibodies evolve from non-binding and autoreactive precursors

The tumor microenvironment hosts antibody-secreting cells (ASCs) associated with a favorable prognosis in several types of cancer. Patient-derived antibodies have diagnostic and therapeutic potential; yet, it remains unclear how antibodies gain autoreactivity and target tumors. Here, we found that somatic hypermutations (SHMs) promote antibody antitumor reactivity against surface autoantigens in high-grade serous ovarian carcinoma (HGSOC). Patient-derived tumor cells were frequently coated with IgGs. Intratumoral ASCs in HGSOC were both mutated and clonally expanded and produced tumor-reactive antibodies that targeted MMP14, which is abundantly expressed on the tumor cell surface. The reversion of monoclonal antibodies to their germline configuration revealed two types of classes: one dependent on SHMs for tumor binding and a second with germline-encoded autoreactivity. Thus, tumor-reactive autoantibodies are either naturally occurring or evolve through an antigen-driven selection process. These findings highlight the origin and potential applicability of autoantibodies directed at surface antigens for tumor targeting in cancer patients.

Innate stimulation of B cells ex vivo enhances antibody secretion and identifies tumour-reactive antibodies from cancer patients.

Human B cells and their expressed antibodies are crucial in conferring immune protection. Identifying pathogen-specific antibodies following infection is possible due to enhanced humoral immunity against well-described molecules on the pathogen surface. However, screening for cancer-reactive antibodies remains challenging since target antigens are often not identified a priori and the frequency of circulating B cells recognizing cancer cells is likely very low. We investigated whether combined ex vivo culture of human B cells with three innate stimuli, interleukin-17 (IL-17), B-cell activation factor (BAFF), and the toll-like receptor 9 (TLR-9) agonist DNA motif CpG ODN 2006 (CpG), each known to activate B cells through different signalling pathways, promote cell activation, proliferation, and antibody production. Combined IL-17+BAFF+CpG prolonged B-cell survival and increased proliferation compared with single stimuli. IL-17+BAFF+CpG triggered higher IgG secretion, likely by activating differentiated, memory and class-switched CD19+CD20+CD27+IgD- B cells. Regardless of anti-FOLR antibody seropositive status, IL-17+BAFF+CpG combined with a monovalent tumour-associated antigen (folate receptor alpha [FOLR]) led to secreted antibodies recognizing the antigen and the antigen-expressing IGROV1 cancer cells. In a seropositive individual, FOLR stimulation favoured class-switched memory B-cell precursors (CD27-CD38-IgD-), class-switched memory B cells and anti-FOLR antibody production, while IL-17+BAFF+CpG combined with FOLR, promoted class-switched memory B-cell precursors and antibody-secreting (CD138+IgD-) plasma cells. Furthermore, IL-17+BAFF+CpG stimulation of peripheral blood B cells from patients with melanoma revealed tumour cell-reactive antibodies in culture supernatants. These findings suggest that innate signals stimulate B-cell survival and antibody production and may help identify low-frequency antigen-reactive humoral responses.

PC-5 En masse discovery of human anti-cancer antibodies

Generation of specific antibodies for cancer therapy is a major endeavor. As a radical departure from conventional approach, we hereby describe rapid and potentially en masse identification of cancer-specific antibodies directly from human cancer tissues. A computational framework was developed and successfully tested for antibody discovery by mining TCGA RNA-seq data from 1945 cases of solid tumor samples. Surprisingly, synthetic antibodies based on high-abundance CDR3 sequences from lung adenocarcinoma (LUAD) patients bound all lung cancer samples tested and cross-reactive to other cancer types but rarely to normal tissues. Targeted DNA sequencing of the B cell receptor from 5 lung tumortissues also allowed us to identify variable region sequences with somaticmutations. Antibodies based on predominant variable region sequences showed specific binding to autologous lung cancer samples. Our platform dramatically reduces barrier in developing human anti-cancer antibodies and paved the way for cancer treatment using patient-derived tumor-reactive monoclonal antibodies.

Abstract 3966: Mining the cancer immuno-responsome: The identification of functional antitumor antibodies from patients receiving checkpoint inhibitors

Abstract Background: The role of B cells and antibodies in anticancer immune responses may correlate with improved prognosis in several types of cancer. Indeed, tumor-reactive antibodies are detected in the blood of cancer patients, tumor-infiltrating B cells have been shown to produce tumor-reactive antibodies, and tumor-reactive antibodies can cause tumor regression in several mouse models. Taken together, these observations support further identification, isolation and characterization of antitumor antibodies from patients demonstrating effective anticancer responses and defining the cognate targets and mechanisms whereby they contribute to tumor control. Methods: We identified cohorts of patients with nonprogressing metastatic cancer who had received checkpoint immunotherapy and isolated their circulating plasmablasts. Antibody heavy and light chain paired sequences were obtained from individual cells using Atreca's Immune Repertoire Capture (IRCTM) technology. The expressed antibodies were then analyzed for their ability to bind to tumor cells as well as tumor tissue and their ability to mediate antitumor activity was explored in syngeneic mouse tumor models. Results: Elevated plasmablast levels were observed in individuals with nonprogressing metastatic cancer, and analysis of plasmablast antibody sequences revealed clonal families of B cells that persisted over time with hallmarks of affinity maturation and class switching. We also identified antibody sequences with features common to more than one patient, consistent with convergent antibody selection. In particular, one antibody (AB-213) isolated from a NSCLC patient was found to demonstrate binding to unrelated human tumors as well as the mouse EMT6 tumor. When AB-213 was expressed with a mouse IgG2a constant region the chimeric antibody showed efficacy in vivo by reducing tumor volume and increasing survival in Balb/c mice harboring the syngeneic EMT6 model. Antitumor activity of the chimeric antibody was observed to be dose-dependent when administered as monotherapy or in combination with checkpoint inhibitors. We feel, based on these data, AB-213 could become a very important clinical therapeutic. Citation Format: Gilson Baia, Amy Manning-Bog, Alexander Scholz, Jeff DeFalco, Michael Harbell, Danhui Zhang, Felix Chu, Beatriz Millare, May Sumi, Patricia Zuno, Judevin Lugar Sapugay, Dongkyoon Kim, Yvonne Leung, Shuwei Jiang, Xiaobin Tang, Kevin Williamson, Xiaomu Chen, Sean Carroll, Christine Dowd, Ish Dhawan, Jonathan Benjamin, Gregg Espiritu Santo, Nicole Haaser, Ngan Nguyen, Eldar Giladi, David Minor, Yann Chong Tan, Jeremy B. Sokolove, Lawrence Steinman, Tito Serafini, Guy Cavet, Norman M. Greenberg, Jacob Glanville, Wayne Volkmuth, Daniel E. Emerling, William H. Robinson. Mining the cancer immuno-responsome: The identification of functional antitumor antibodies from patients receiving checkpoint inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3966.

Pro- and anti-tumour effects of B cells and antibodies in cancer: a comparison of clinical studies and preclinical models.

The primary immune role of B cells is to produce antibodies, but they can also influence T cell function via antigen presentation and, in some contexts, immune regulation. Whether their roles in tumour immunity are similar to those in other chronic immune responses such as autoimmunity and chronic infection, where both pro- and anti-inflammatory roles have been described, remains controversial. Many studies have aimed to define the role of B cells in antitumor immune responses, but despite this considerable body of work, it is not yet possible to predict how they will affect immunity to any given tumour. In many human cancers, the presence of tumour-infiltrating B cells and tumour-reactive antibodies correlates with extended patient survival, and this clinical observation is supported by data from some animal models. On the other hand, T cell responses can be adversely affected by B cell production of immunoregulatory cytokines, a phenomenon that has been demonstrated in humans and in animal models. The isotype and concentration of tumour-reactive antibodies may also influence tumour progression. Recruitment of B cells into tumours may directly reflect the subtype and strength of the anti-tumour T cell response. As the response becomes chronic, B cells may attenuate T cell responses in an attempt to decrease host damage, similar to their described role in chronic infection and autoimmunity. Understanding how B cell responses in cancer are related to the effectiveness of the overall anti-tumour response is likely to aid in the development of new therapeutic interventions against cancer.

Abstract 5019: Characterization of sentinel node-derived antibodies from breast cancer patients

Abstract Lymph nodes are one of the important sites in the body where immune responses to antigens are initiated. The tumor-draining lymph node or sentinel node is the first site where cancer cells and cancer-related antigens are most likely to spread. In response to antigen exposure and immune activation, the lymph node B cells undergo clonal expansion and somatic hypermutation, leading to the affinity-matured populations of effector B cells secreting antibodies that bind to the tumor. The cancer-draining node is therefore an ideal source of B cells that produce anticancer antibodies. In the present investigation, we have characterized the antibodies derived from immortalization of sentinel node B cells from 29 breast cancer patients. The antibodies were screened for their isotypes and for binding to breast cancers classified as luminal A, luminal B, HER2, and basal/normal subtypes, based on the expressions of estrogen, progesterone and HER2 receptors. The isotype analysis showed a higher percentages of antibodies belong to IgG (48%) and IgM (34%) isotypes along with a smaller share of IgA (18%). The cell-binding studies were conducted using ELISA, immunofluorescence microscopy, and flow cytometry techniques. Of the studied antibodies, about 28% showed binding to the tumor cells. The comparative studies of antibody-binding to breast tumor cells and non-cancer breast cells identified several antibodies showing differential binding profile. The binding analyses also demonstrated that all of the tumor-binding antibodies belonged to IgM isotype. It is evident from the results that the tumor-reactive antibodies are generated in the sentinel nodes of breast cancer patients; however, the absence of class-switched anti-tumor antibodies in the repertoire raises a possibility of tumor-induced node suppression leading to an inefficient humoral immune response towards tumor antigens. The results are important in assessing the tumor immune response/lymph node suppression, and the possible role of the autoantibodies in diagnosis and therapy of breast cancer. Citation Format: Girja S. Shukla, Stephanie C. Pero, Yu-Jing Sun, Chelsea L. Carman, David N. Krag. Characterization of sentinel node-derived antibodies from breast cancer patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5019. doi:10.1158/1538-7445.AM2015-5019

Abstract LB-217: PD-1 suppresses antibody responses to Tn+ tumors

Abstract Cancer cells often have aberrant glycosylation of surface molecules leading to glycan antigens that are not typically found on normal cells. These antigens are referred to as tumor associated carbohydrate antigens (TACAs) and are a promising target for anti-cancer vaccines. One such TACA is the Thomsen-nouvelle (Tn) antigen, which is expressed by up to 90% of adenocarcinomas. The mechanisms regulating the B cell response to Tn and other TACAs are not well understood. This knowledge is essential for the development of vaccines to elicit protective immune responses to tumors bearing TACAs. PD-1 (programmed cell death 1) is a member of the B7:CD28 superfamily of receptors found on antigen-activated B and T cells. It negatively regulates antigen receptor signaling and thereby limits adaptive immune responses, including the anti-tumor T cell response. However, virtually nothing is known about the role of PD-1 in regulating B cell responses to tumors. In this study, we tested the hypothesis that PD-1 suppresses B cell production of Tn-specific antibodies and thereby suppresses protective humoral immunity against Tn+ tumors. Our results show that PD-1−/− mice immunized with a Tn-bearing mucin (desialyated bovine submaxillary mucin) have increased Tn+ tumor-reactive IgM and IgG antibodies, relative to wild type mice. PD-1−/− mice immunized with the Tn+ mucin had significantly increased survival relative to wild type mice following challenge with a Tn+ bearing mammary tumor (TA3-Ha). Survival in PD-1−/− mice was dependent on the presence of B cells. Therefore, our results show that PD-1 plays a critical role in suppressing the protective anti-tumor B cell response elicited by Tn-bearing antigen immunization. This work was supported by NIH/NCI F31 CA183567-01 fellowship to M.A.L. and an American Cancer Society Research Scholar Grant (RSG-12-170-01-LIB) to K.M.H. Citation Format: Marcela A. Leyva, Karen M. Haas. PD-1 suppresses antibody responses to Tn+ tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-217. doi:10.1158/1538-7445.AM2015-LB-217

PM-17 * INTRACEREBRAL IFN- DOES NOT ENHANCE THE RESPONSE TO VACCINE IMMUNOTHERAPY FOR CANINE GLIOMA

Due to the complexity of human tumor environment and host immune interactions, the majority of successful brain cancer therapies in rodent models fail to show the same efficacy when translated to human patients. Pet dogs with spontaneous glioma recapitulate important features of human disease and we have used this more representative model to assess the response to vaccine immunotherapy with and without interferon gamma (IFN-γ) gene therapy after surgery. Dogs with newly diagnosed glioma underwent surgical tumor debulking and were randomized to receive 1) autologous tumor lysate vaccines with CpG ODN as an adjuvant (n = 12) or 2) Ad-mediated interferon gamma (IFN-γ) gene therapy injected around the resection cavity followed by vaccine immunotherapy (n = 12). A grade IV IFN-γ dose-related toxicity (severe encephalitis and lymphocytic perivascular cuffing) resulted in death of one dog. No further adverse events were seen at a lower IFN-γ dose supporting the safety of the treatment. This immunotherapy activated a humoral response with specific tumor-reactive IgG antibodies detected after vaccination in all dogs. Addition of IFN-γ gene therapy did not affect the median overall survival time of 204 days versus 211 days with vaccine alone. As expected, there were significant differences (P = 0.036) in survival between dogs with low-grade (369 days) versus high-grade (204 days) tumors. During postmortem analysis, no dog with a low-grade tumor had recurrence, whereas all dogs with grade III/IV tumors died from progression. We hoped that forced IFN-γ expression would sensitize residual tumor cells to CTL recognition and recruit NK cells to kill MHC Ilow/- cells, thereby enhancing the effects of vaccine immunotherapy. Our data failed to support this theory, however the lack of difference could be due to the small number of dogs in each group (type II error) or to insufficient in situ expression of IFN-γ to elicit the desired effect.

Vaccination for invasive canine meningioma induces in situ production of antibodies capable of antibody-dependent cell-mediated cytotoxicity.

Malignant and atypical meningiomas are resistant to standard therapies and associated with poor prognosis. Despite progress in the treatment of other tumors with therapeutic vaccines, this approach has not been tested preclinically or clinically in these tumors. Spontaneous canine meningioma is a clinically meaningful but underutilized model for preclinical testing of novel strategies for aggressive human meningioma. We treated 11 meningioma-bearing dogs with surgery and vaccine immunotherapy consisting of autologous tumor cell lysate combined with toll-like receptor ligands. Therapy was well tolerated, and only one dog had tumor growth that required intervention, with a mean follow up of 585 days. IFN-γ-elaborating T cells were detected in the peripheral blood of 2 cases, but vaccine-induced tumor-reactive antibody responses developed in all dogs. Antibody responses were polyclonal, recognizing both intracellular and cell surface antigens, and HSP60 was identified as one common antigen. Tumor-reactive antibodies bound allogeneic canine and human meningiomas, showing common antigens across breed and species. Histologic analysis revealed robust infiltration of antibody-secreting plasma cells into the brain around the tumor in posttreatment compared with pretreatment samples. Tumor-reactive antibodies were capable of inducing antibody-dependent cell-mediated cytotoxicity to autologous and allogeneic tumor cells. These data show the feasibility and immunologic efficacy of vaccine immunotherapy for a large animal model of human meningioma and warrant further development toward human trials.

Abstract B32: Preclinical testing of three immune adjuvants in vaccination therapy for invasive canine meningioma.

Abstract Malignant and atypical meningiomas are resistant to standard therapies, but therapeutic vaccines have not been tested preclinically or clinically. Pet dogs with naturally occurring meningioma are an underutilized model for aggressive human meningioma and an outstanding opportunity for assessing experimental therapeutic approaches. We treated 11 meningioma-bearing dogs with surgery and vaccine immunotherapy consisting of autologous tumor cell lysate combined with CpG or imiquimod. Interferon gamma-elaborating T cells were detected in the peripheral blood of two of cases, but vaccine-induced tumor-reactive antibody responses were found in the sera of all dogs. Systemic antibody responses were polyclonal, recognizing intracellular and cell surface antigens, and heat shock protein 60 was identified as one common antigen. Tumor-reactive antibodies bound allogeneic canine and human meningiomas, demonstrating common antigens across breed and species. Histological analysis revealed robust infiltration of antibody-secreting plasma cells into the brain around the tumor in treated compared to pre-treatment samples. Tumor-reactive antibodies were capable of inducing antibody dependent cell-mediated cytotoxicity to autologous and allogeneic tumor cells. Moreover, median survival for lysate/CpG and lysate/imiquimod vaccination was 646 days versus 222 days in historic surgery controls (p<0.05). Compared to CpG, a novel imidazoquinoline with TLR7/8 and inflammasome activity, compound 528, was equally potent at activating canine PBMCs. A prospective randomized two-arm trial was recently launched, using lysate—compound 528 vaccines, versus surgery controls. Mean follow-up is 139 days at the time of writing, and recruitment is ongoing. These data demonstrate the feasibility and immunologic efficacy of vaccine immunotherapy for treating a large animal model of human meningioma and warrant further development towards human trials. Citation Format: Brian M. Andersen, G Elizabeth Pluhar, Charles E. Seiler, Zhengming Xiong, Michelle R. Goulart, Matthew Gerry O'Sullivan, Matthew A. Hunt, Charles E. Schiaffo, David M. Ferguson, John R. Ohlfest. Preclinical testing of three immune adjuvants in vaccination therapy for invasive canine meningioma. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr B32.

Identification of Immunoreactive Tumour Antigens Using Free and Exosome-Associated Humoral Responses

Altered tumour antigens can initiate cellular and humoral immune responses; however, they often fail to eliminate tumours. In humans, the presence of cancer is generally associated with the suppression of T cell activation and effector responses, characterized as a Th1 to Th2 biased response. This Th2 response leads to the production of tumour-reactive antibodies. Further, neoplastic lesions and biological fluids of cancer patients contain an abundance of tumour-derived exosomes (TDE) expressing tumour antigens. Expression of tumour antigens on TDE may represent an antibody target and serve to block antibody binding to the tumour, implicating a role for these nanovesicles in tumour survival. In this study, ovarian tumour cell proteins were separated by two-dimensional electrophoresis (2-DE) and patient-derived antibodies were used to analyse immunoreactivity. Common immunoreactive proteins among ovarian cancer patients were identified by mass spectrometry and six proteins were selected based on recognitio...

Ganglioside GD2-specific trifunctional surrogate antibody Surek demonstrates therapeutic activity in a mouse melanoma model

BackgroundTrifunctional bispecific antibodies (trAb) are a special class of bispecific molecules recruiting and activating T cells and accessory immune cells simultaneously at the targeted tumor. The new trAb Ektomab that targets the melanoma-associated ganglioside antigen GD2 and the signaling molecule human CD3 (hCD3) on T cells demonstrated potent T-cell activation and tumor cell destruction in vitro. However, the relatively low affinity for the GD2 antigen raised the question of its therapeutic capability. To further evaluate its efficacy in vivo it was necessary to establish a mouse model.MethodsWe generated the surrogate trAb Surek, which possesses the identical anti-GD2 binding arm as Ektomab, but targets mouse CD3 (mCD3) instead of hCD3, and evaluated its chemical and functional quality as a therapeutic antibody homologue. The therapeutic and immunizing potential of Surek was investigated using B78-D14, a B16 melanoma transfected with GD2 and GD3 synthases and showing strong GD2 surface expression. The induction of tumor-associated and autoreactive antibodies was evaluated.ResultsDespite its low affinity of approximately 107 M-1 for GD2, Surek exerted efficient tumor cell destruction in vitro at an EC50 of 70ng/ml [0.47nM]. Furthermore, Surek showed strong therapeutic efficacy in a dose-dependent manner and is superior to the parental GD2 mono-specific antibody, while the use of a control trAb with irrelevant target specificity had no effect. The therapeutic activity of Surek was strictly dependent on CD4+ and CD8+ T cells, and cured mice developed a long-term memory response against a second challenge even with GD2-negative B16 melanoma cells. Moreover, tumor protection was associated with humoral immune responses dominated by IgG2a and IgG3 tumor-reactive antibodies indicating a Th1-biased immune response. Autoreactive antibodies against the GD2 target antigen were not induced.ConclusionOur data suggest that Surek revealed strong tumor elimination and anti-tumor immunization capabilities. The results warrant further clinical development of the human therapeutic equivalent antibody Ektomab.

Current and Potential Uses of Immunocytokines as Cancer Immunotherapy

Immunocytokines (ICs) are a class of molecules created by linking tumor-reactive monoclonal antibodies to cytokines that are able to activate immune cells. Tumor selective localization is provided by the ability of the mAb component to bind to molecules found on the tumor cell surface or molecules found selectively in the tumor microenvronment. In this way the cytokine component of the immunocytokine is selectively localized to sites of tumor and can activate immune cells with appropriate receptors for the cytokine. Immunocytokines have been made and tested by us, and others, using a variety of tumor-reactive mAbs linked to distinct cytokines. To date, the majority of clinical progress has been made with ICs that have linked human interleukin-2 (IL2) to a select number of tumor reactive mAbs that had already been in prior clinical testing as non-modified mAbs (Figure 1). Here we briefly review the background for the creation of ICs, summarize current clinical progress, emphasize mechanisms of action for ICs that are distinct from those of their constituent components, and present some directions for future development and testing.

Abstract 4840: Blockade of IL-10 production in effector B cells significantly increases their therapeutic efficacy in cancer adoptive immunotherapy

Abstract We have previously reported the antitumor reactivity of adoptively transferred effector B cells and the mechanisms by which they mediate tumor regression in a spontaneous metastasis model. 4T1 breast cancer cells were inoculated into syngeneic Balb/c mice to prime tumor-draining lymph node (TDLN). TDLNs were subsequently harvested and B cells activated ex vivo. When adoptively transferred into mice inoculated with 4T1 tumor in the mammary fat pad, these activated B cells alone mediated the inhibition of spontaneous metastases to the lung. In this study, we used IL-10−/− Balb/c mice to generate IL-10−/− TDLN, and evaluated the antitumor immunity of IL-10−/− TDLN B cells. Adoptively transferred IL-10−/− TDLN B cells mediated significantly more effective antitumor immunity than equal numbers of WT TDLN B cells (p<0.05). Activated IL-10−/− effector 4T1 TDLN B cells were capable of killing 4T1 tumor cells in a tumor antigen specific manner in in vitro cytotoxicity assays independent of antibody and complement. Adoptive transfer of IL-10−/− TDLN B cells resulted in the induction of host T and B cell antitumor immunity significantly more than adoptive transfer of WT TDLN B cells (p<0.05). This was evident by significantly modulated cytokine production (e.g. up-regulated IFN-gamma and IL-2 production by host T cells, but down-regulated IL-10 production by host B cells). In addition, adoptively transferred IL-10−/− TDLN B cells increased the production of IgG which bound to 4T1 tumor cells. Furthermore, IL-10−/− TDLN B cell infusion significantly increased tumor cell lysis (CTL) activity mediated by host B cells as well as T cells in an immunologically specific fashion. The molecular and cellular pathways involved in the direct killing of 4T1 tumor cells by IL-10−/- 4T1 TDLN effector B cells and by host B cells subjected to IL-10−/- 4T1 TDLN effector B cell adoptive transfer is under active investigation in our lab. While the role played by B cells in the host immune response to cancer is complex and controversial, our results indicate that removal of IL-10-producing B cell subsets may represent an effective strategy to augment the therapeutic efficacy of TDLN B cells used in adoptive immunotherapy. Mechanistically, adoptive transfer of B cells depleted of IL-10-producing subsets destroys tumor cells directly and confers greater host cellular and humoral antitumor immunity by shifting cytokine production to a Type 1 profile and by producing tumor-reactive antibodies respectively. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4840. doi:1538-7445.AM2012-4840

Monitoring the Systemic Human Memory B Cell Compartment of Melanoma Patients for Anti-Tumor IgG Antibodies

Melanoma, a potentially lethal skin cancer, is widely thought to be immunogenic in nature. While there has been much focus on T cell-mediated immune responses, limited knowledge exists on the role of mature B cells. We describe an approach, including a cell-based ELISA, to evaluate mature IgG antibody responses to melanoma from human peripheral blood B cells. We observed a significant increase in antibody responses from melanoma patients (n = 10) to primary and metastatic melanoma cells compared to healthy volunteers (n = 10) (P<0.0001). Interestingly, we detected a significant reduction in antibody responses to melanoma with advancing disease stage in our patient cohort (n = 21) (P<0.0001). Overall, 28% of melanoma patient-derived B cell cultures (n = 1,800) compared to 2% of cultures from healthy controls (n = 600) produced antibodies that recognized melanoma cells. Lastly, a patient-derived melanoma-specific monoclonal antibody was selected for further study. This antibody effectively killed melanoma cells in vitro via antibody-mediated cellular cytotoxicity. These data demonstrate the presence of a mature systemic B cell response in melanoma patients, which is reduced with disease progression, adding to previous reports of tumor-reactive antibodies in patient sera, and suggesting the merit of future work to elucidate the clinical relevance of activating humoral immune responses to cancer.