In vivo targeting of vaccinating tumor cells to antigen-presenting cells by a gene therapy method with adenovirus containing the α1,3galactosyltransferase gene

Self-Tumor Antigens in Solid Tumors Turned into Vaccines by α-gal Micelle Immunotherapy

A major reason for the failure of the immune system to detect tumor antigens (TAs) is the insufficient uptake, processing, and presentation of TAs by antigen-presenting cells (APCs). The immunogenicity of TAs in the individual patient can be markedly increased by the in situ targeting of tumor cells for robust uptake by APCs, without the need to identify and characterize the TAs. This is feasible by the intra-tumoral injection of α-gal micelles comprised of glycolipids presenting the carbohydrate-antigen "α-gal epitope" (Galα1-3Galβ1-4GlcNAc-R). Humans produce a natural antibody called "anti-Gal" (constituting ~1% of immunoglobulins), which binds to α-gal epitopes. Tumor-injected α-gal micelles spontaneously insert into tumor cell membranes, so that multiple α-gal epitopes are presented on tumor cells. Anti-Gal binding to these epitopes activates the complement system, resulting in the killing of tumor cells, and the recruitment of multiple APCs (dendritic cells and macrophages) into treated tumors by the chemotactic complement cleavage peptides C5a and C3a. In this process of converting the treated tumor into a personalized TA vaccine, the recruited APC phagocytose anti-Gal opsonized tumor cells and cell membranes, process the internalized TAs and transport them to regional lymph-nodes. TA peptides presented on APCs activate TA-specific T cells to proliferate and destroy the metastatic tumor cells presenting the TAs. Studies in anti-Gal-producing mice demonstrated the induction of effective protection against distant metastases of the highly tumorigenic B16 melanoma following injection of natural and synthetic α-gal micelles into primary tumors. This treatment was further found to synergize with checkpoint inhibitor therapy by the anti-PD1 antibody. Phase-1 clinical trials indicated that α-gal micelle immunotherapy is safe and can induce the infiltration of CD4+ and CD8+ T cells into untreated distant metastases. It is suggested that, in addition to converting treated metastases into an autologous TA vaccine, this treatment should be considered as a neoadjuvant therapy, administering α-gal micelles into primary tumors immediately following their detection. Such an immunotherapy will convert tumors into a personalized anti-TA vaccine for the period prior to their resection.

Biosynthesis of α-Gal Epitopes (Galα1-3Galβ1-4GlcNAc-R) and Their Unique Potential in Future α-Gal Therapies

The α-gal epitope is a carbohydrate antigen which appeared early in mammalian evolution and is synthesized in large amounts by the glycosylation enzyme α1,3galactosyltransferase (α1,3GT) in non-primate mammals, lemurs, and New-World monkeys. Ancestral Old-World monkeys and apes synthesizing α-gal epitopes underwent complete extinction 20–30 million years ago, and their mutated progeny lacking α-gal epitopes survived. Humans, apes, and Old-World monkeys which evolved from the surviving progeny lack α-gal epitopes and produce the natural anti-Gal antibody which binds specifically to α-gal epitopes. Because of this reciprocal distribution of the α-gal epitope and anti-Gal in mammals, transplantation of organs from non-primate mammals (e.g., pig xenografts) into Old-World monkeys or humans results in hyperacute rejection following anti-Gal binding to α-gal epitopes on xenograft cells. The in vivo immunocomplexing between anti-Gal and α-gal epitopes on molecules, pathogens, cells, or nanoparticles may be harnessed for development of novel immunotherapies (referred to as “α-gal therapies”) in various clinical settings because such immune complexes induce several beneficial immune processes. These immune processes include localized activation of the complement system which can destroy pathogens and generate chemotactic peptides that recruit antigen-presenting cells (APCs) such as macrophages and dendritic cells, targeting of antigens presenting α-gal epitopes for extensive uptake by APCs, and activation of recruited macrophages into pro-reparative macrophages. Some of the suggested α-gal therapies associated with these immune processes are as follows: 1. Increasing efficacy of enveloped-virus vaccines by synthesizing α-gal epitopes on vaccinating inactivated viruses, thereby targeting them for extensive uptake by APCs. 2. Conversion of autologous tumors into antitumor vaccines by expression of α-gal epitopes on tumor cell membranes. 3. Accelerating healing of external and internal injuries by α-gal nanoparticles which decrease the healing time and diminish scar formation. 4. Increasing anti-Gal–mediated protection against zoonotic viruses presenting α-gal epitopes and against protozoa, such as Trypanosoma, Leishmania, and Plasmodium, by vaccination for elevating production of the anti-Gal antibody. The efficacy and safety of these therapies were demonstrated in transgenic mice and pigs lacking α-gal epitopes and producing anti-Gal, raising the possibility that these α-gal therapies may be considered for further evaluation in clinical trials.

Synthetic Glycobiology: Parts, Systems, and Applications

Protein glycosylation, the attachment of sugars to amino acid side chains, can endow proteins with a wide variety of properties of great interest to the engineering biology community. However, natural glycosylation systems are limited in the diversity of glycoproteins they can synthesize, the scale at which they can be harnessed for biotechnology, and the homogeneity of glycoprotein structures they can produce. Here we provide an overview of the emerging field of synthetic glycobiology, the application of synthetic biology tools and design principles to better understand and engineer glycosylation. Specifically, we focus on how the biosynthetic and analytical tools of synthetic biology have been used to redesign glycosylation systems to obtain defined glycosylation structures on proteins for diverse applications in medicine, materials, and diagnostics. We review the key biological parts available to synthetic biologists interested in engineering glycoproteins to solve compelling problems in glycoscience, describe recent efforts to construct synthetic glycoprotein synthesis systems, and outline exemplary applications as well as new opportunities in this emerging space.

Covalent decoration of adenovirus vector capsids with the carbohydrate epitope αGal does not improve vector immunogenicity, but allows to study the in vivo fate of adenovirus immunocomplexes

Adenovirus-based vectors are promising tools for genetic vaccination. However, several obstacles have to be overcome prior to a routine clinical application of adenovirus-based vectors as efficacious vectored vaccines. The linear trisaccharide epitope αGal (alpha-Gal) with the carbohydrate sequence galactose-α-1,3-galactosyl-β-1,4-N-acetylglucosamine has been described as a potent adjuvant for recombinant or attenuated vaccines. Humans and α-1,3-galactosyltransferase knockout mice do not express this epitope. Upon exposure of α-1,3-galactosyltransferase-deficient organisms to αGal in the environment, large amounts of circulating anti-Gal antibodies are produced consistently. Immunocomplexes formed between recombinant αGal-decorated vaccines and anti-Gal antibodies exhibit superior immunogenicity. We studied the effects of the trisaccharide epitope on CD8 T cell responses that are directed specifically to vector-encoded transgenic antigens. For that, covalently αGal-decorated adenovirus vectors were delivered to anti-Gal α-1,3-galactosyltransferase knockout mice. We generated replication-defective, E1-deleted adenovirus type 5 vectors that were decorated with αGal at the hexon hypervariable regions 1 or 5, at fiber knob, or at penton base. Surprisingly, none of the adenovirus immunocomplexes being formed from αGal-decorated adenovirus vectors and anti-Gal immunoglobulins improved the frequencies of CD8 T cell responses against the transgenic antigen ovalbumin. Humoral immunity directed to the adenovirus vector was neither increased. However, our data indicated that decoration of Ad vectors with the αGal epitope is a powerful tool to analyze the fate of adenovirus immunocomplexes in vivo.

Epithelial ovarian cancer stem-like cells expressing α-gal epitopes increase the immunogenicity of tumor associated antigens

Background

As ovarian cancer stem cells (CSCs) are responsible for tumor initiation, invasion, metastasis, and chemo-resistance, new stratagems that selectively target ovarian CSCs are critically significant. Our previous work have demonstrated that ovarian cancer spheroid cells are tumorigenic and chemo-resistant, and have the properties of ovarian CSCs. Herein, we hypothesized that expressing α-gal epitopes on ovarian spheroid cells may help eliminate CSCs and improve the outcome of therapeutic intervention for ovarian cancer patients.

Methods

Lentivirus-mediated transfer of a pig α(1,3)galactosyltransferase [α1,3GT] enzyme gene into human ovarian cell line SKOV3 cells formed α-gal epitope-expressing cells (SKOV3-gal cells), and then these cells were maintained in a serum-free culture system to form SKOV3-gal spheroid cells. Efficacy of this cell vaccine was demonstrated in α1,3GT knockout mice (α1,3GT KO mice).

Results

The antibody titers to α-gal epitopes measured by ELISA were significantly increased in α1,3GT KO mice after immunization with SKOV3-gal spheroid cells. Furthermore, compared with the non-immunized KO mice, the SKOV3 tumors grafted under renal capsules of KO mice immunized with SKOV3-gal spheroid cells grew slower and began to shrink on day 12. Western blot analysis also showed that immunized KO mice can produce effective antibody against certain tumor associated antigens (TAAs) derived from both SKOV3 cells and SKOV3 spheroid cells. The TAAs were further investigated by mass spectrometry and RNA interference (RNAi) technology. The results suggested that antibodies responding to protein c-erbB-2 may be raised in the sera of the mice after immunization with SKOV3-gal spheroid cells. Ultimately, vaccination with SKOV3-gal spheroid cells induced more CD3 + CD4 + T cells in the spleen of immunized mice than non-immunized KO mice.

Conclusions

The results suggest that vaccination using ovarian cancer stem-like cells engineered to express α-gal epitopes may be a novel strategy for treatment of ovarian cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1973-7) contains supplementary material, which is available to authorized users.

Anti-Gal: an abundant human natural antibody of multiple pathogeneses and clinical benefits

Anti-Gal is the most abundant natural antibody in humans, constituting ~ 1% of immunoglobulins. Anti-Gal is naturally produced also in apes and Old World monkeys. The ligand of anti-Gal is a carbohydrate antigen called the 'α-gal epitope' with the structure Galα1-3Galβ1-4GlcNAc-R. The α-gal epitope is present as a major carbohydrate antigen in non-primate mammals, prosimians and New World monkeys. Anti-Gal can contributes to several immunological pathogeneses. Anti-Gal IgE produced in some individuals causes allergies to meat and to the therapeutic monoclonal antibody cetuximab, all presenting α-gal epitopes. Aberrant expression of the α-gal epitope or of antigens mimicking it in humans may result in autoimmune processes, as in Graves' disease. α-Gal epitopes produced by Trypanosoma cruzi interact with anti-Gal and induce 'autoimmune like' inflammatory reactions in Chagas' disease. Anti-Gal IgM and IgG further mediate rejection of xenografts expressing α-gal epitopes. Because of its abundance, anti-Gal may be exploited for various clinical uses. It increases immunogenicity of microbial vaccines (e.g. influenza vaccine) presenting α-gal epitopes by targeting them for effective uptake by antigen-presenting cells. Tumour lesions are converted into vaccines against autologous tumour-associated antigens by intra-tumoral injection of α-gal glycolipids, which insert into tumour cell membranes. Anti-Gal binding to α-gal epitopes on tumour cells targets them for uptake by antigen-presenting cells. Accelerated wound healing is achieved by application of α-gal nanoparticles, which bind anti-Gal, activate complement, and recruit and activate macrophages that induce tissue regeneration. This therapy may be of further significance in regeneration of internally injured tissues such as ischaemic myocardium and injured nerves.

Conversion of tumors into autologous vaccines by intratumoral injection of α-Gal glycolipids that induce anti-Gal/α-Gal epitope interaction

Anti-Gal is the most abundant antibody in humans, constituting 1% of immunoglobulins. Anti-Gal binds specifically α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R). Immunogenicity of autologous tumor associated antigens (TAA) is greatly increased by manipulating tumor cells to express α-gal epitopes and bind anti-Gal. Glycolipids with αgal epitopes (α-gal glycolipids) injected into tumors insert into the tumor cell membrane. Anti-Gal binding to the multiple α-gal epitopes de novo presented on the tumor cells results in targeting of these cells to APC via the interaction between the Fc portion of the bound anti-Gal and Fcγ; receptors on APC. The APC process and present immunogenic TAA peptides and thus, effectively activate tumor specific CD4+ helper T cells and CD8+ cytotoxic T cells which destroy tumor cells in micrometastases. The induced immune response is potent enough to overcome immunosuppression by Treg cells. A phase I clinical trial indicated that α-gal glycolipid treatment has no adverse effects. In addition to achieving destruction of micrometastases in cancer patients with advance disease, α-gal glycolipid treatment may be effective as neo-adjuvant immunotherapy. Injection of α-gal glycolipids into primary tumors few weeks prior to resection can induce a protective immune response capable of destroying micrometastases expressing autologous TAA, long after primary tumor resection.

Current vaccine updates for lung cancer

Current treatments for lung cancer are far from optimal. Several immunotherapeutic strategies involving vaccines incorporating different tumor-associated antigens to induce immune responses against tumors are being tested in clinical trials internationally. Although small, benefits have indeed been observed from the early studies of these vaccines, and the future is looking brighter for lung cancer patients as a handful of these immunotherapies reach Phase III trials. In addition, optimizing the induced immune response by these vaccines has become a priority, and a number of techniques are being considered, including addition of adjuvants and combining vaccines, which affect synergy based on their mechanism of action. This review is an update on the current vaccines in production, the benefits observed from their most recent studies, and the upcoming plans for improvements in these immunotherapies.

In Situ Conversion of Melanoma Lesions into Autologous Vaccine by Intratumoral Injections of α-gal Glycolipids

Autologous melanoma associated antigens (MAA) on murine melanoma cells can elicit a protective anti-tumor immune response following a variety of vaccine strategies. Most require effective uptake by antigen presenting cells (APC). APC transport and process internalized MAA for activation of anti-tumor T cells. One potential problem with clinical melanoma vaccines against autologous tumors may be that often tumor cells do not express surface markers that label them for uptake by APC. Effective uptake of melanoma cells by APC might be achieved by exploiting the natural anti-Gal antibody which constitutes ~1% of immunoglobulins in humans. This approach has been developed in a syngeneic mouse model using mice capable of producing anti-Gal. Anti-Gal binds specifically to α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R). Injection of glycolipids carrying α-gal epitopes (α-gal glycolipids) into melanoma lesions results in glycolipid insertion into melanoma cell membranes, expression of α-gal epitopes on the tumor cells and binding of anti-Gal to these epitopes. Interaction between the Fc portions of bound anti-Gal and Fcγ receptors on APC induces effective uptake of tumor cells by APC. The resulting anti-MAA immune response can be potent enough to destroy distant micrometastases. A clinical trial is now open testing effects of intratumoral α-gal glycolipid injections in melanoma patients.

Mechanism for increased immunogenicity of vaccines that form in vivo immune complexes with the natural anti-Gal antibody

Anti-Gal constitutes approximately 1% of circulating IgG in humans and interacts specifically with alpha-gal epitopes. We reported previously that expression of alpha-gal epitopes on HIV gp120 and influenza virus vaccines increases immunogenicity by approximately 100-fold. We hypothesize that immunogenicity of any microbial vaccine can be markedly increased by linked alpha-gal epitopes due to in vivo formation of immune complexes with anti-Gal and the effective internalization of such immune complexes by APC, via Fc/FcgammaR interaction. The increased transport to lymph nodes and processing of anti-Gal complexed vaccines internalized by APC, results in effective activation of vaccine specific CD4(+) and CD8(+) T cells, and high cellular and humoral immune response. This universal mechanism for anti-Gal mediated increased immunogenicity is demonstrated in alpha1,3galactosyltransferase knockout mice with ovalbumin as a model vaccine.

Therapeutics targeting tumor immune escape: towards the development of new generation anticancer vaccines

Despite the evidence that immune effectors can play a significant role in controlling tumor growth under natural conditions or in response to therapeutic manipulation, it is clear that malignant cells evade immune surveillance in most cases. Considering that anticancer vaccination has reached a plateau of results and currently no vaccination regimen is indicated as a standard anticancer therapy, the dissection of the molecular events underlying tumor immune escape is the necessary condition to make anticancer vaccines a therapeutic weapon effective enough to be implemented in the routine clinical setting. Recent years have witnessed significant advances in our understanding of the molecular mechanisms underlying tumor immune escape. These mechanistic insights are fostering the development of rationally designed therapeutics aimed at reverting the immunosuppressive circuits that undermine an effective antitumor immune response. In this review, the best characterized mechanisms that allow cancer cells to evade immune surveillance are overviewed and the most debated controversies constellating this complex field are highlighted. In addition, the latest therapeutic strategies devised to overcome tumor immune escape are described, with special regard to those entering clinical phase investigation.

The Galalpha1,3Galbeta1,4GlcNAc-R (alpha-Gal) epitope: a carbohydrate of unique evolution and clinical relevance

In 1985, we reported that a naturally occurring human antibody (anti-Gal), produced as the most abundant antibody (1% of immunoglobulins) throughout the life of all individuals, recognizes a carbohydrate epitope Galalpha1-3Galbeta1-4GlcNAc-R (the alpha-gal epitope). Since that time, an extensive literature has developed on discoveries related to the alpha-gal epitope and the anti-Gal antibody, including the barrier they form in xenotransplantation and their reciprocity in mammalian evolution. This review covers these topics and new avenues of clinical importance related to this unique antigen/antibody system (alpha-gal epitope/anti-Gal) in improving the efficacy of viral vaccines and in immunotherapy against cancer.

Immunogenicity of influenza virus vaccine is increased by anti-gal-mediated targeting to antigen-presenting cells

This study describes a method for increasing the immunogenicity of influenza virus vaccines by exploiting the natural anti-Gal antibody to effectively target vaccines to antigen-presenting cells (APC). This method is based on enzymatic engineering of carbohydrate chains on virus envelope hemagglutinin to carry the alpha-Gal epitope (Gal alpha 1-3Gal beta 1-4GlcNAc-R). This epitope interacts with anti-Gal, the most abundant antibody in humans (1% of immunoglobulins). Influenza virus vaccine expressing alpha-Gal epitopes is opsonized in situ by anti-Gal immunoglobulin G. The Fc portion of opsonizing anti-Gal interacts with Fc gamma receptors on APC and induces effective uptake of the vaccine virus by APC. APC internalizes the opsonized virus to transport it to draining lymph nodes for stimulation of influenza virus-specific T cells, thereby eliciting a protective immune response. The efficacy of such an influenza vaccine was demonstrated in alpha 1,3galactosyltransferase (alpha 1,3GT) knockout mice, which produce anti-Gal, using the influenza virus strain A/Puerto Rico/8/34-H1N1 (PR8). Synthesis of alpha-Gal epitopes on carbohydrate chains of PR8 virus (PR8(alpha gal)) was catalyzed by recombinant alpha1,3GT, the glycosylation enzyme that synthesizes alpha-Gal epitopes in cells of nonprimate mammals. Mice immunized with PR8(alpha gal) displayed much higher numbers of PR8-specific CD8(+) and CD4(+) T cells (determined by intracellular cytokine staining and enzyme-linked immunospot assay) and produced anti-PR8 antibodies with much higher titers than mice immunized with PR8 lacking alpha-Gal epitopes. Mice immunized with PR8(alpha gal) also displayed a much higher level of protection than PR8 immunized mice after being challenged with lethal doses of live PR8 virus. We suggest that a similar method for increasing immunogenicity may be applicable to avian influenza vaccines.

Intratumoral injection of alpha-gal glycolipids induces xenograft-like destruction and conversion of lesions into endogenous vaccines

This study describes a novel cancer immunotherapy treatment that exploits the natural anti-Gal Ab to destroy tumor lesions and convert them into an endogenous vaccine targeted to APC via FcgammaR. Anti-Gal constitutes 1% of immunoglobulins in humans and interacts specifically with alpha-gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R). The binding of anti-Gal to alpha-gal epitopes on pig cells mediates xenograft rejection. The proposed method uses glycolipid micelles with multiple alpha-gal epitopes (alpha-gal glycolipids). These glycolipids are extracted from rabbit red cell membranes and are comprised of ceramides with carbohydrate chains containing 5-25 carbohydrates, all capped with alpha-gal epitopes. Efficacy of this treatment was demonstrated in alpha1,3-galactosyltransferase knockout mice producing anti-Gal and bearing B16 melanoma or B16/OVA producing OVA as a surrogate tumor Ag. These mice are unique among nonprimate mammals in that, similar to humans, they lack alpha-gal epitopes and can produce the anti-Gal Ab. Intratumoral injection of alpha-gal glycolipids results in local inflammation mediated by anti-Gal binding to the multiple alpha-gal epitopes and activation of complement. These glycolipids spontaneously insert into tumor cell membranes. The binding of anti-Gal to alpha-gal expressing tumor cells induces the destruction of treated lesions as in anti-Gal-mediated xenograft rejection. Anti-Gal further opsonizes tumor cells within the lesion and, thus, targets them for effective uptake by APC that transport the tumor Ags to draining lymph nodes. APC further cross-present immunogenic tumor Ag peptides and elicit a systemic anti-tumor immune response. Similar intratumoral injection of alpha-gal glycolipids in humans is likely to induce the destruction of treated lesions and elicit a protective immune response against micrometastases.

Xenovaccinotherapy for colorectal cancer

The objectives of this phase I-II trial were to assess the toxicity, immunological and clinical responses induced in 37 patients with stage IV colorectal cancer by the subcutaneous administration of a xenogenic polyantigenic vaccine (XPV) prepared from disrupted murine melanoma (B16) and carcinoma (LLC) cells. An inducing course of vaccinotherapy consisted of 10 immunizations (5 at weekly and 5 at fortnight intervals). Twenty-four hours later each of first 5 vaccinations the patient was subcutaneously given a low dose of the recombinant interleukin-2 (IL-2). A consolidating course of vaccinotherapy consisted of monthly vaccinations. No grade III or IV toxicities, but also laboratory and clinical signs of developing systemic autoimmune disorders were noted in any XPV-treated patient. A significant increase in cell-mediated immunoreactivity to both LLC and B16 antigens (Ags) occurred in the patients after inducing vaccinations, as determined by delayed-type hypersensitivity (DTH) skin reactions, as well as by blood lymphocyte proliferation responses. Vaccinations also led to increased cell-mediated reactivity to murine non-tumor, spleen cell (SC)-associated Ags. This reactivity, however, was not as significant as that to tumor-associated antigens (TAAs). XPV was also found to capable of generating IgG antibody-mediated responses. With immunotherapy concentrations of both interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) detectably elevated in patients' sera, suggesting intensification of T helper 1-/T helper 2-mediated responses in the XPV-treated patients. The average survival of the XPV-treated patients was noticeably superior than was that of the clinically comparable control patients (17 vs 7 months). Collectively the results suggest that xenogenic TAAs are safe to use, able to induce measurable cellular and humoral immune responses, and may be clinically effective in certain colorectal cancer patients.

Complement insufficiency limits efficacy in a xenograft model of hyperacute rejection for cancer therapy

Hyperacute rejection (HAR) is a rapid immunological response to an organ xenotransplant caused by recognition of endothelial galactose(alpha1,3)galactose (alphaGal) epitopes and complement-mediated cell lysis by host anti-alphaGal antibody ('natural antibody'). The alphaGal epitope is synthesised by a galactosyl transferase ((alpha1,3)GT) which humans lack. Because human cells transduced with (alpha1,3)GT are sensitised to natural antibody/complement-mediated lysis in human serum, delivery of (alpha1,3)GT to tumour vasculature in patients is a potential therapeutic strategy, by mimicking the pathophysiology of organ rejection. We therefore sought to develop an animal model of HAR for cancer therapy. Nude/(alpha1,3)GT knock-out mice allowed the growth of human tumour xenografts and the use of ecotropic retrovirus producer cells to generate expression of alphaGal on tumour vasculature. Lysis of alphaGal-positive murine endothelial cells with rabbit complement in conjunction with murine anti-alphaGal antibody in vitro was used to define the conditions necessary for HAR. However, tumour growth retardation and destruction of alphaGal-positive tumour endothelium were minimal after their administration, despite sera retaining post hoc cytolytic activity with fresh complement. The major limitation of this experimental system, of relevance to other therapeutic approaches, results from the use of a xenograft, in which additional xenoreactivities lead to complement insufficiency. Development of a tractable preclinical model in which to evaluate HAR for cancer therapy requires a syngeneic experimental system.

Ablation of undifferentiated human embryonic stem cells: exploiting innate immunity against the Gal alpha1-3Galbeta1-4GlcNAc-R (alpha-Gal) epitope

Although undifferentiated human embryonic stem cells (hESCs) are tumorigenic, this capacity is lost after differentiation, and hESCs are being widely investigated for applications in regenerative medicine. To engineer protection against the unintentional transplantation of undifferentiated cells, we generated hESCs carrying a construct in which the alpha1,3-galactosyltransferase (GalT) open reading frame was transcribed from the hTERT promoter (pmGT). Because the endogenous GalT gene is inactive, GalT expression was limited to undifferentiated cells. A second chimeric construct (pmfGT) differed by replacement of the GalT leader sequence for that of the fucosyltransferase gene. Two subclones containing stable integrations of pmGT and pmfGT (M2 and F11, respectively) were assessed for their response to human serum containing antibodies to the Galalpha1-3Galbeta1-4GlcNAc-R (alpha-gal) epitope. The low-variegation line, M2, and to a lesser extent the more variegated line F11, were sensitive to human serum when exposed in the undifferentiated state. However, M2 cells were largely insensitive after differentiation and retained both a normal karyotype and the ability to differentiate into derivatives of the three germ layers in severe combined immunodeficient mice. These data exemplify a method of protection against residual, undifferentiated hESCs prior to engraftment and may provide ongoing immune surveillance after engraftment against dedifferentiation or against de novo tumorigenesis involving hTERT reactivation. Untransfected H9 cells were not sensitive to the human serum used in this study. Hence, in our system, interactions of hESCs with other circulating antibodies, such as anti-Neu5Gc, were not observed.

The alpha-gal epitope and the anti-Gal antibody in xenotransplantation and in cancer immunotherapy

The alpha-gal epitope (Galalpha1-3Galbeta1-(3)4GlcNAc-R) is abundantly synthesized on glycolipids and glycoproteins of non-primate mammals and New World monkeys by the glycosylation enzyme alpha1,3galactosyltransferase (alpha1,3GT). In humans, apes and Old World monkeys, this epitope is absent because the alpha1,3GT gene was inactivated in ancestral Old World primates. Instead, humans, apes and Old World monkeys produce the anti-Gal antibody, which specifically interacts with alpha-gal epitopes and which constitutes approximately 1% of circulating immunoglobulins. Anti-Gal has functioned as an immunological barrier, preventing the transplantation of pig organs into humans, because anti-Gal binds to the alpha-gal epitopes expressed on pig cells. The recent generation of alpha1,3GT knockout pigs that lack alpha-gal epitopes has resulted in the elimination of this immunological barrier. Anti-Gal can be exploited for clinical use in cancer immunotherapy by targeting autologous tumour vaccines to APC, thereby increasing their immunogenicity. Autologous intact tumour cells from haematological malignancies, or autologous tumour cell membranes from solid tumours are processed to express alpha-gal epitopes by incubation with neuraminidase, recombinant alpha1,3GT and with uridine diphosphate galactose. Subsequent immunization with such autologous tumour vaccines results in in vivo opsonization by anti-Gal IgG binding to these alpha-gal epitopes. The interaction of the Fc portion of the vaccine-bound anti-Gal with Fcgamma receptors of APC induces effective uptake of the vaccinating tumour cell membranes by the APC, followed by effective transport of the vaccinating tumour membranes to the regional lymph nodes, and processing and presentation of the tumour-associated antigen (TAA) peptides. Activation of tumour-specific T cells within the lymph nodes by autologous TAA peptides may elicit an immune response that in some patients will be potent enough to eradicate the residual tumour cells that remain after completion of standard therapy. A similar expression of alpha-gal epitopes can be achieved by transduction of tumour cells with an adenovirus vector (or other vectors) containing the alpha1,3GT gene, thus enabling anti-Gal-mediated targeting of the vaccinating transduced cells to APC. Intratumoral delivery of the alpha1,3GT gene by various vectors results in the expression of alpha-gal epitopes. Such expression of the xenograft carbohydrate phenotype is likely to induce anti-Gal-mediated destruction of the tumour lesion, similar to rejection of xenografts by this antibody. Opsonization of the destroyed tumour cell membranes by anti-Gal IgG further targets them to APC, thus converting the tumour lesion, treated by the alpha1,3GT gene, into an in situ autologous tumour vaccine.

Glycans in cancer and inflammation--potential for therapeutics and diagnostics

Changes in glycosylation are often a hallmark of disease states. For example, cancer cells frequently display glycans at different levels or with fundamentally different structures than those observed on normal cells. This phenomenon was first described in the early 1970s, but the molecular details underlying such transformations were poorly understood. In the past decade advances in genomics, proteomics and mass spectrometry have enabled the association of specific glycan structures with disease states. In some cases, the functional significance of disease-associated changes in glycosylation has been revealed. This review highlights changes in glycosylation associated with cancer and chronic inflammation and new therapeutic and diagnostic strategies that are based on the underlying glycobiology.