Generation of a monoclonal antibody against the glycosylphosphatidylinositol-linked protein Rae-1 using genetically engineered tumor cells

Monoclonal Antibodies Generation: Updates and Protocols on Hybridoma Technology

Since its inception in 1975, the hybridoma technology revolutionized science and medicine, facilitating discoveries in almost any field from the laboratory to the clinic. Many technological advancements have been developed since then, to create these "magical bullets." Phage and yeast display libraries expressing the variable heavy and light domains of antibodies, single B-cell cloning from immunized animals of different species including humans or in silico approaches, all have rendered a myriad of newly developed antibodies or improved design of existing ones. However, still the majority of these antibodies or their recombinant versions are from hybridoma origin, a preferred methodology that trespass species barriers, due to the preservation of the natural functions of immune cells in producing the humoral response: antigen specific immunoglobulins. Remarkably, this methodology can be reproduced in small laboratories without the need of sophisticate equipment. In this chapter, we will describe the most recent methods utilized by our Monoclonal Antibodies Core Facility at the University of Texas-M.D. Anderson Cancer Center. During the last 10 years, the methods, techniques, and expertise implemented in our core had generated more than 350 antibodies for various applications.

Lysine acetylation of NKG2D ligand Rae-1 stabilizes the protein and sensitizes tumor cells to NKG2D immune surveillance

Shedding, loss of expression, or internalization of natural killer group 2, member D (NKG2D) ligands from the tumor cell surface leads to immune evasion, which is associated with poor prognosis in patients with cancer. In many cancers, matrix metalloproteinases cause the proteolytic shedding of NKG2D ligands. However, it remained unclear how to protect NKG2D ligands from shedding. Here, we showed that the shedding of the mouse NKG2D ligand Rae-1 can be prevented by two critical acetyltransferases, GCN5 and PCAF, which acetylate the lysine residues of Rae-1 to avoid shedding both in vitro and in vivo. In contrast, mutations at lysines 80 and 87 of Rae-1 abrogated this acetylation and thereby desensitized tumor cells to NKG2D-dependent immune surveillance. Notably, the protein levels of GCN5 correlated with the expression levels of the human NKG2D ligand ULPB1 in a human tumor tissue microarray and, more importantly, with prolonged overall survival in many cancers. Our results suggest that the acetylation of Rae-1 protein at lysines 80 and 87 by GCN5 and PCAF protects Rae-1 from shedding so as to activate NKG2D-dependent immune surveillance. This discovery may shed light on new targets for NKG2D immunotherapy in cancer treatment.

Anticancer Immunotherapy by MFAP5 Blockade Inhibits Fibrosis and Enhances Chemosensitivity in Ovarian and Pancreatic Cancer

PURPOSE

Recent studies demonstrate the role of the tumor microenvironment in tumor progression. However, strategies used to overcome the malignant phenotypes of cancer cells modulated by the microenvironment have not been thoroughly explored. In this study, we evaluated the therapeutic efficacy of a newly developed mAb targeting microfibril-associated protein 5 (MFAP5), which is secreted predominately by cancer-associated fibroblast (CAF), in ovarian and pancreatic cancer models.Experimental Design: MAbs were developed using human MFAP5 recombinant protein as an antigen in mice, and antibodies from hybridoma clones were evaluated for their specificity to human and murine MFAP5. An Octet RED384 system was used to determine the kinetics of binding affinity and the specificity of the antibody clones, which were followed by epitope mapping and functional characterization by in vitro assays. The therapeutic efficacy of a lead anti-MFAP5 antibody clone 130A in tumor suppression was evaluated by ovarian tumor- and pancreatic tumor-bearing mouse models.

RESULTS

Three hybridoma clones, which produced antibodies with high affinity and specificity to MFAP5, were selected for functional studies. Antibody clone 130A, which recognizes a common epitope shared between human and murine MFAP5 protein, was further selected for in vivo studies. Results showed that clone 130A downregulated MFAP5-induced collagen production in CAFs, suppressed intratumoral microvessel leakiness, and enhanced paclitaxel bioavailability in both ovarian and pancreatic cancer mouse models.

CONCLUSIONS

These data suggest that MFAP5 blockade using an immunologic approach inhibits fibrosis, induces tumor vessel normalization, and enhances chemosensitivity in ovarian and pancreatic cancer, and can be used as a novel therapeutic agent.

Asian Elephant T Cell Responses to Elephant Endotheliotropic Herpesvirus

Elephant endotheliotropic herpesvirus (EEHV) can cause lethal hemorrhagic disease in juvenile Asian elephants, an endangered species. One hypothesis to explain this vulnerability of some juvenile elephants is that they fail to mount an effective T cell response to the virus. To our knowledge, there have been no studies of Asian elephant T cell responses to EEHV. To address this deficiency, we validated the gamma interferon (IFN-γ) enzyme-linked immunospot assay for tracking antigen-directed T cell activity by monitoring rabies-specific responses in vaccinated elephants. In addition, we generated monoclonal antibodies to Asian elephant CD4 and CD8 to facilitate phenotypic T cell profiling. Using these tools, we screened healthy elephants with a history of EEHV infection for reactivity against nine EEHV proteins whose counterparts in other herpesviruses are known to induce T cell responses in their natural hosts. We identified glycoprotein B (gB) and the putative regulatory protein E40 as the most immunogenic T cell targets (IFN-γ responses in five of seven elephants), followed by the major capsid protein (IFN-γ responses in three of seven elephants). We also observed that IFN-γ responses were largely from CD4⁺ T cells. We detected no activity against the predicted major immediate early (E44) and large tegument (E34) proteins, both immunodominant T cell targets in humans latently infected with cytomegalovirus. These studies identified EEHV-specific T cells in Asian elephants for the first time, lending insight into the T cell priming that might be required to protect against EEHV disease, and will guide the design of effective vaccine strategies.

IMPORTANCE Endangered Asian elephants are facing many threats, including lethal hemorrhagic disease from elephant endotheliotropic herpesvirus (EEHV). EEHV usually establishes chronic, benign infections in mature Asian elephants but can be lethal to juvenile elephants in captivity and the wild. It is the leading cause of death in captive Asian elephants in North America and Europe. Despite the availability of sensitive tests and protocols for treating EEHV-associated illness, these measures are not always effective. The best line of defense would be a preventative vaccine. We interrogated normal healthy elephants previously infected with EEHV for T cell responses to nine EEHV proteins predicted to induce cellular immune responses. Three proteins elicited IFN-γ responses, suggesting their potential usefulness as vaccine candidates. Our work is the first to describe T cell responses to a member of the proposed fourth subfamily of mammalian herpesviruses, the Deltaherpesvirinae, within a host species in the clade Afrotheria. An EEHV vaccine would greatly contribute to the health care of Asian and African elephants that are also susceptible to this disease.

Induction of NKG2D Ligands on Solid Tumors Requires Tumor-Specific CD8+ T Cells and Histone Acetyltransferases

NKG2D-mediated immune surveillance is crucial for inhibiting tumor growth and metastases. Malignant tumor cells often downregulate NKG2D ligands to escape from immune surveillance. High-profile studies have shown that restoring NKG2D ligand expression via genetic engineering inhibits tumor formation and progression. However, no effective in vivo approaches are available to restore these ligands across different types of solid tumors because the classic stress signal-dependent induction of this ligand in vitro is transient and has rarely been duplicated in solid tumors in vivo We found that coadministration of an immune stimulatory signal (IL12) and chemotherapy (doxorubicin) restored the NKG2D ligand Rae-1 in multiple tumor types, including a human tumor model. The restored expression of NKG2D ligands was associated with tumor cell death and delay of tumor progression in vivo Induction of tumor-specific NKG2D ligands required the engagement of CD8⁺ T cells and was regulated by the histone acetyltransferases GCN5 and PCAF. The tumor-specific restoration of NKG2D ligands in a variety of tumor models, including a human tumor model, resulted in NKG2D-dependent tumor regression and extended survival time. The elucidation of a CD8⁺ T cell-dependent mechanism suggests that activated NKG2D⁺CD8⁺ T-cell therapy alone may be able to restore the NKG2D ligand in tumors. Cancer Immunol Res; 5(4); 300-11. ©2017 AACR.

NCR1 Expression Identifies Canine Natural Killer Cell Subsets with Phenotypic Similarity to Human Natural Killer Cells

Canines spontaneously develop many cancers similar to humans - including osteosarcoma, leukemia, and lymphoma - offering the opportunity to study immune therapies in a genetically heterogeneous and immunocompetent environment. However, a lack of antibodies recognizing canine NK cell markers has resulted in suboptimal characterization and unknown purity of NK cell products, hindering the development of canine models of NK cell adoptive immunotherapy. To this end, we generated a novel antibody to canine NCR1 (NKp46), the putative species-wide marker of NK cells, enabling purification of NK cells for further characterization. We demonstrate that CD3^-/NKp46⁺ cells in healthy and osteosarcoma-bearing canines have phenotypic similarity to human CD3^-/NKp46⁺ NK cells, expressing mRNA for CD16 and the natural cytotoxicity receptors NKp30, NKp44, and NKp80. Functionally, we demonstrate with the calcein release assay that canine CD3^-/NKp46⁺ cells kill canine tumor cell lines without prior sensitization and secrete IFN-γ, TNF-α, IL-8, IL-10, and granulocyte-macrophage colony-stimulating factor as measured by Luminex. Similar to human NK cells, CD3^-/NKp46⁺ cells expand rapidly on feeder cells expressing 4-1BBL and membrane-bound IL-21 (median = 20,283-fold in 21 days). Furthermore, we identify a minor Null population (CD3^-/CD21^-/CD14^-/NKp46^-) with reduced cytotoxicity against osteosarcoma cells, but similar cytokine secretion as CD3^-/NKp46⁺ cells. Null cells in canines and humans have reduced expression of NKG2D, NKp44, and CD16 compared to NKp46⁺ NK cells and can be induced to express NKp46 with further expansion on feeder cells. In conclusion, we have identified and characterized canine NK cells, including an NKp46^- subset of canine and human NK cells, using a novel anti-canine NKp46 antibody, and report robust ex vivo expansion of canine NK cells sufficient for adoptive immunotherapy.

FGL2 as a Multimodality Regulator of Tumor-Mediated Immune Suppression and Therapeutic Target in Gliomas

BACKGROUND

Fibrinogen-like protein 2 (FGL2) may promote glioblastoma multiforme (GBM) cancer development by inducing multiple immune-suppression mechanisms.

METHODS

The biological significance of FGL2 expression was assessed using the The Cancer Genome Atlast (TCGA) glioma database and tumor lysates analysis. The therapeutic effects of an anti-Fgl2 antibody and the role of immune suppression regulation by Fgl2 were determined in immune-competent, NOD-scid IL2Rgammanull (NSG), and FcɣRIIB-/- mice (n = 3-18 per group). Data were analyzed with two-way analysis of variance, log-rank survival analysis, and Pearson correlation. All statistical tests were two-sided.

RESULTS

In low-grade gliomas, 72.5% of patients maintained two copies of the FGL2 gene, whereas 83.8% of GBM patients had gene amplification or copy gain. Patients with high levels of FGL2 mRNA in glioma tissues had a lower overall survival (P = .009). Protein levels of FGL2 in GBM lysates were higher relative to low-grade glioma lysates (11.48±5.75ng/mg vs 3.96±1.01ng/mg, P = .003). In GL261 mice treated with an anti-FGL2 antibody, median survival was 27 days compared with only 17 days for mice treated with an isotype control antibody (P = .01). The anti-FGL2 antibody treatment reduced CD39(+) Tregs, M2 macrophages, programmed cell death protein 1 (PD-1), and myeloid-derived suppressor cells (MDSCs). FGL2-induced increases in M2, CD39, and PD-1 were ablated in FcɣRIIB-/- mice.

CONCLUSIONS

FGL2 augments glioma immunosuppression by increasing the expression levels of PD-1 and CD39, expanding the frequency of tumor-supportive M2 macrophages via the FcγRIIB pathway, and enhancing the number of MDSCs and CD39(+) regulatory T cells. Collectively, these results show that FGL2 functions as a key immune-suppressive modulator and has potential as an immunotherapeutic target for treating GBM.