Treatment of neuroblastoma with human natural antibodies

Harnessing Antibody Polyspecificity for Cancer Immunotherapy

Targeting the diverse glycan repertoire expressed on tumor cells is considered a viable therapeutic strategy to deal with tumor cell heterogeneity. Inherently polyspecific, natural, glycan-reactive antibodies are purported to be protective in thwarting infections and in cancer immunotherapy. Tumor-associated carbohydrate antigens (TACAs) are related to pathogen glycans, to which nascent or natural antibodies exist and IgM responses are elicited. To capture the polyspecific nature of anticarbohydrate responses, we have focused on the rational design of carbohydrate mimetic peptides (CMPs) cross-reactive with TACA reactive antibodies. In particular, we have focused on the development of CMPs that display reactivity to GD2 and Lewis Y (LeY) reactive monoclonal antibodies. They would serve as templates for pan-immunogens inducing biosimilar polyreactive antibodies. In the design, we relied on structural analyses of CMP's enhanced binding to the templates using molecular modeling. Glycan reactivity patterns of affinity CMP-purified human antibodies further refined specificity profiles in comparison with the immune response to the CMP in clinical trials. In this study, we further define the molecular characteristics for this mimicry by considering the polyspecificity of LeY and GD2 reactive antibodies binding to the lacto-ceramide core Galβ(1,4)Glcβ(1-1')Cer. Binding to this minimum building block can be capitalized on for cancer therapy and diagnostics and illustrates a new approach in designing cancer vaccines taking advantage of the latent polyspecificity of antibodies and the relevance of natural antibodies in antigen discovery and design.

IgM Natural Autoantibodies in Physiology and the Treatment of Disease

Antibodies are vital components of the adaptive immune system for the recognition and response to foreign antigens. However, some antibodies recognize self-antigens in healthy individuals. These autoreactive antibodies may modulate innate immune functions. IgM natural autoantibodies (IgM-NAAs) are a class of primarily polyreactive immunoglobulins encoded by germline V-gene segments which exhibit low affinity but broad specificity to both foreign and self-antigens. Historically, these autoantibodies were closely associated with autoimmune disease. Nevertheless, not all human autoantibodies are pathogenic and compelling evidence indicates that IgM-NAAs may exert a spectrum of effects from injurious to protective depending upon cellular and molecular context. In this chapter, we review the current state of knowledge regarding the potential physiological and therapeutic roles of IgM-NAAs in different disease conditions such as atherosclerosis, cancer, and autoimmune disease. We also describe the discovery of two reparative IgM-NAAs by our laboratory and delineate their proposed mechanisms of action in central nervous system (CNS) disease.

Detection of Naturally Occurring Human Antibodies Against Gangliosides by ELISA

Gangliosides are sialic acid-containing glycolipids that have been considered attractive targets for cancer immunotherapy, based on the qualitative and quantitative changes they suffer during malignant transformation and due to their importance for tumor biology. Natural antibodies against gangliosides have been detected not only in cancer patients but also in healthy donors. The presence of these antibodies can be used as diagnostic or prognostic factor. However, these responses are difficult to detect because anti-ganglioside antibodies are usually of IgM isotype and low affinity. Enzyme Linked Immunosorbent Assay (ELISA) is an immunoassay based on the specific binding of antibodies to antigens bound to a solid phase. These antigens can be glycolipids like gangliosides. An enzyme linked to the last reactant allows the detection of specific binding through the development of color after the addition of a suitable substrate. ELISA combines the specificity of antibodies with the sensitivity of enzyme reactions. The ELISA method described herein can be used to detect antibody responses against gangliosides not only related to cancer but also to autoimmune diseases and infections, both in healthy donors, and patients, untreated or receiving specific immunotherapy.

Immunoglubolin dynamics and cancer prevalence in Tasmanian devils (Sarcophilus harrisii)

Immunoglobulins such as IgG and IgM have been shown to induce anti-tumour cytotoxic activity. In the present study we therefore explore total serum IgG and IgM expression dynamics in 23 known-aged Tasmanian devils (Sarcophilus harrisii) of which 9 where affected by Devil Facial Tumour Disease (DFTD). DFTD is clonally transmissible cancer that has caused massive declines in devil numbers. Our analyses revealed that IgM and IgG expression levels as well as IgM/IgG ratios decreased with increasing devil age. Neither age, sex, IgM nor IgG expression levels affected devil DFTD status in our analyses. However, devils with increased IgM relative to IgG expression levels had significantly lower DFTD prevalence. Our results therefore suggest that IgM/IgG ratios may play an important role in determining devil susceptibility to DFTD. We consequently propose that our findings warrant further studies to elucidate the underpinning(s) of devil IgM/IgG ratios and DFTD status.

Cytotoxic activity against human neuroblastoma and melanoma cells mediated by IgM antibodies derived from peripheral blood of healthy donors

A small percentage of healthy donors identified in the Western population carry antibodies in their peripheral blood which convey cytotoxic activity against certain human melanoma and neuroblastoma cell lines. We measured the cytotoxic activity of sera and plasmas from healthy donors on the human neuroblastoma cell line Kelly and various melanoma cell lines. Antibodies of IgM isotype, presumably belonging to the class of naturally occurring antibodies, exerted cytotoxic activity in a complement-dependent fashion. Apart from complement-dependent tumor cell lysis, we observed C3 opsonization in all tumor cell lines upon treatment with cytotoxic plasmas. Cell lines tested primarily expressed membrane complement regulatory proteins (mCRP) CD46, CD55 and CD59 to various extents. Blocking of mCRPs by monoclonal antibodies enhanced cell lysis and opsonization, though some melanoma cells remained resistant to complement attack. Epitopes recognized by cytotoxic antibodies were represented by gangliosides such as GD2 and GD3, as evidenced by cellular sialidase pretreatment and enhanced expression of distinct gangliosides. It remains to be clarified why only a small fraction of healthy persons carry these antitumor cytotoxic antibodies.

A novel IgM-H-ficolin complement pathway to attack allogenic cancer cells in vitro

The pentameric serum IgMs are critical to immune defense and surveillance through cytotoxicity against microbes and nascent cancer cells. Ficolins, a group of oligomeric lectins with an overall structure similar to C1q and mannose-binding lectin (MBL) participate in microbe infection and apoptotic cell clearance by activating the complement lectin pathway or a primitive opsonophagocytosis. It remains unknown whether serum IgMs interplay with ficolins in cancer immunosurveillance. Here we report a natural cancer killing of different types of cancer cells by sera from a healthy human population mediated by a novel IgM-H-ficolin complement activation pathway. We demonstrate for the first time that H-ficolin bound to a subset of IgMs in positive human sera and IgM-H-ficolin deposited on cancer cells to activate complement attack in cancer cells. Our data suggest that the IgM-H-ficolin -mediated complement activation pathway may be another defensive strategy for human cancer immunosurveillance.

Human antibodies reactive to NeuGcGM3 ganglioside have cytotoxic antitumor properties

N-glycolylated gangliosides are not naturally expressed in healthy human tissues but are overexpressed in several tumors. We demonstrate the existence of antibodies that bind (N-glycolylneuraminyl)-lactosylceramide (NeuGcGM3) and are detectable in the sera of 65 from the 100 donors (65%) tested by ELISA. From those 65 NeuGcGM3 antibody-positive donors, 35 had antibodies that were able to recognize and kill NeuGcGM3-expressing tumor cells by a complement-mediated mechanism. After complement inactivation, 11 of the 35 positive sera showed a direct cytotoxic effect on the tumor cells. This complement-independent cytotoxicity was dependent on the presence of antigen on the membrane and resembles an oncotic necrosis cell death. Both the levels of anti-NeuGcGM3 antibodies in the sera as well as the percentage of healthy donors with this immunity decreased with the age of the donor. In contrast to age and gender-matched healthy donors, we could only detect low reactivity against NeuGcGM3 in the sera of six out of 53 non-small cell lung cancer patients. These results suggest the existence of antibodies against NeuGcGM3 with antitumor immune surveillance functions, reinforcing the importance of N-glycolylated gangliosides as antitumor targets.

Naturally occurring antibodies directed against carbohydrate tumor antigens

Healthy persons carry within their pool of circulating antibodies immunoglobulins preferentially of IgM isotype, which are directed against a variety of tumor-associated antigens. In closer scrutiny of their nature, some of these antibodies could be defined as naturally occurring antibodies due to the germline configuration of the variable immunoglobulin region. The majority of these immunoglobulins recognize carbohydrate antigens which can be classified as oncofetal antigens. Many of these IgM antibodies present in the peripheral blood circulation can bind to tumor cells and of these a minor portion are also able to destroy tumor cells by several mechanisms, as for instance complement-mediated cytolysis or apoptosis. It was postulated that anti-carbohydrate antibodies are part of an anti-tumor immune response, while their presence in the peripheral blood of healthy donors is still waiting for a plausible explanation. It may be that recognition of defined epitopes, including carbohydrate sequences, by naturally occurring antibodies constitutes the humoral arm of an anti-tumor immune response as part of the often postulated tumor surveillance. The cytotoxic capacity of these antibodies inspired several research groups and pharmaceutical companies to design novel strategies of immunoglobulin-based anti-tumor immunotherapy.

Immunoglobulin M as a vaccine adjuvant

Vaccines are effective in preventing disease by stimulating the immune system and sustaining an immune response towards eradication of pathogens and diseased cells. However, designing successful vaccines is not always straightforward. For a vaccine to be successful, antigen-presenting cells (APC) need to be stimulated, primarily by adjuvants, towards a sustained immune response through integration of the innate and adaptive (humoral and cellular) immune systems. Furthermore, there is an immediate need for safe and effective adjuvants. There has been significant progress in understanding the mechanisms on how vaccines work and the role of adjuvants, dendritic cells, and the toll-like receptor (TLR) pathway. Currently, different adjuvants are actively explored but the potential of the immunoglobulin M (IgM) as a vaccine adjuvant has been overlooked. This article hypothesizes how the IgM molecule could function as a vaccine adjuvant by acting as a "soluble" toll-like receptor (TLR) through the formation of an immune complex with antigen (Ag) and other components of the innate immune system. The complex should lead to sustained humoral and/or cell-mediated immune responses. Hypothetically, it is also possible that the Ag-IgM complex recruits other components of complement or other factors that can activate other members of the adaptive immune system. As it is now possible to produce commercial-scale quantities of monoclonal human IgM antibodies, understanding the role of the IgM in linking the innate and adaptive immune systems may lead to practical therapeutic applications.