Synthesis of alpha-gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R) on human tumor cells by recombinant alpha1,3galactosyltransferase produced in Pichia pastoris

COVID-19 and Preparing Planetary Health for Future Ecological Crises: Hopes from Glycomics for Vaccine Innovation

A key lesson emerging from COVID-19 is that pandemic proofing planetary health against future ecological crises calls for systems science and preventive medicine innovations. With greater proximity of the human and animal natural habitats in the 21st century, it is also noteworthy that zoonotic infections such as COVID-19 that jump from animals to humans are increasingly plausible in the coming decades. In this context, glycomics technologies and the third alphabet of life, the sugar code, offer veritable prospects to move omics systems science from discovery to diverse applications of relevance to global public health and preventive medicine. In this expert review, we discuss the science of glycomics, its importance in vaccine development, and the recent progress toward discoveries on the sugar code that can help prevent future infectious outbreaks that are looming on the horizon in the 21st century. Glycomics offers veritable prospects to boost planetary health, not to mention the global scientific capacity for vaccine innovation against novel and existing infectious agents.

Amplifying immunogenicity of prospective Covid-19 vaccines by glycoengineering the coronavirus glycan-shield to present α-gal epitopes

The many carbohydrate chains on Covid-19 coronavirus SARS-CoV-2 and its S-protein form a glycan-shield that masks antigenic peptides and decreases uptake of inactivated virus or S-protein vaccines by APC. Studies on inactivated influenza virus and recombinant gp120 of HIV vaccines indicate that glycoengineering of glycan-shields to present α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R) enables harnessing of the natural anti-Gal antibody for amplifying vaccine efficacy, as evaluated in mice producing anti-Gal. The α-gal epitope is the ligand for the natural anti-Gal antibody which constitutes ~1% of immunoglobulins in humans. Upon administration of vaccines presenting α-gal epitopes, anti-Gal binds to these epitopes at the vaccination site and forms immune complexes with the vaccines. These immune complexes are targeted for extensive uptake by APC as a result of binding of the Fc portion of immunocomplexed anti-Gal to Fc receptors on APC. This anti-Gal mediated effective uptake of vaccines by APC results in 10-200-fold higher anti-viral immune response and in 8-fold higher survival rate following challenge with a lethal dose of live influenza virus, than same vaccines lacking α-gal epitopes. It is suggested that glycoengineering of carbohydrate chains on the glycan-shield of inactivated SARS-CoV-2 or on S-protein vaccines, for presenting α-gal epitopes, will have similar amplifying effects on vaccine efficacy. α-Gal epitope synthesis on coronavirus vaccines can be achieved with recombinant α1,3galactosyltransferase, replication of the virus in cells with high α1,3galactosyltransferase activity as a result of stable transfection of cells with several copies of the α1,3galactosyltransferase gene (GGTA1), or by transduction of host cells with replication defective adenovirus containing this gene. In addition, recombinant S-protein presenting multiple α-gal epitopes on the glycan-shield may be produced in glycoengineered yeast or bacteria expression systems containing the corresponding glycosyltransferases. Prospective Covid-19 vaccines presenting α-gal epitopes may provide better protection than vaccines lacking this epitope because of increased uptake by APC.

Host Synthesized Carbohydrate Antigens on Viral Glycoproteins as "Achilles' Heel" of Viruses Contributing to Anti-Viral Immune Protection

The glycans on enveloped viruses are synthesized by host-cell machinery. Some of these glycans on zoonotic viruses of mammalian reservoirs are recognized by human natural antibodies that may protect against such viruses. These antibodies are produced mostly against carbohydrate antigens on gastrointestinal bacteria and fortuitously, they bind to carbohydrate antigens synthesized in other mammals, neutralize and destroy viruses presenting these antigens. Two such antibodies are: anti-Gal binding to α-gal epitopes synthesized in non-primate mammals, lemurs, and New World monkeys, and anti-N-glycolyl neuraminic acid (anti-Neu5Gc) binding to N-glycolyl-neuraminic acid (Neu5Gc) synthesized in apes, Old World monkeys, and many non-primate mammals. Anti-Gal appeared in Old World primates following accidental inactivation of the α1,3galactosyltransferase gene 20–30 million years ago. Anti-Neu5Gc appeared in hominins following the inactivation of the cytidine-monophosphate-N-acetyl-neuraminic acid hydroxylase gene, which led to the loss of Neu5Gc <6 million-years-ago. It is suggested that an epidemic of a lethal virus eliminated ancestral Old World-primates synthesizing α-gal epitopes, whereas few mutated offspring lacking α-gal epitopes and producing anti-Gal survived because anti-Gal destroyed viruses presenting α-gal epitopes, following replication in parental populations. Similarly, anti-Neu5Gc protected few mutated hominins lacking Neu5Gc in lethal virus epidemics that eliminated parental hominins synthesizing Neu5Gc. Since α-gal epitopes are presented on many zoonotic viruses it is suggested that vaccines elevating anti-Gal titers may be of protective significance in areas endemic for such zoonotic viruses. This protection would be during the non-primate mammal to human virus transmission, but not in subsequent human to human transmission where the virus presents human glycans. In addition, production of viral vaccines presenting multiple α-gal epitopes increases their immunogenicity because of effective anti-Gal-mediated targeting of vaccines to antigen presenting cells for extensive uptake of the vaccine by these cells.

A practical approach to pancreatic cancer immunotherapy using resected tumor lysate vaccines processed to express α-gal epitopes

Objectives

Single-agent immunotherapy is ineffective against poorly immunogenic cancers, including pancreatic ductal adenocarcinoma (PDAC). The aims of this study were to demonstrate the feasibility of production of novel autologous tumor lysate vaccines from resected PDAC tumors, and verify vaccine safety and efficacy.

Methods

Fresh surgically resected tumors obtained from human patients were processed to enzymatically synthesize α-gal epitopes on the carbohydrate chains of membrane glycoproteins. Processed membranes were analyzed for the expression of α-gal epitopes and the binding of anti-Gal, and vaccine efficacy was assessed in vitro and in vivo.

Results

Effective synthesis of α-gal epitopes was demonstrated after processing of PDAC tumor lysates from 10 different patients, and tumor lysates readily bound an anti-Gal monoclonal antibody. α-gal(+) PDAC tumor lysate vaccines elicited strong antibody production against multiple tumor-associated antigens and activated multiple tumor-specific T cells. The lysate vaccines stimulated a robust immune response in animal models, resulting in tumor suppression and a significant improvement in survival without any adverse events.

Conclusions

Our data suggest that α-gal(+) PDAC tumor lysate vaccination may be a practical and effective new immunotherapeutic approach for treating pancreatic cancer.

[Experimental study on A549 cell death mediated by xenoantigen α-gal in human serum]

BACKGROUND AND OBJECTIVE

The absence of α-gal in humans is caused by the inactivity of α-1,3GT gene. However, humans have pre-existing and abundant anti-gal antibodies. Xenotransplantation procedures have indicated the high potential of introducing α-1,3GT gene to synthesize α-gal for cancer gene therapy by mimicking hyper-acute rejection. The aim of this study is to construct a lung cancer A549 cell line that expressed α-gal, and to observe the antitumor mechanisms mediated by human serum.

METHODS

A549 cells were transfected with pEGFP-N1-GT plasmids constructed in a previous study. A stable transgenic cell line, A549-GT, was then selected and cultivated. The biological characteristics of A549-GT cells, including morphology and proliferation, were examined. α-1,3GT mRNA expression was detected by RT-PCR. Direct immunofluorescence staining and flow cytometry (FCM) were used to analyze the synthesis of α-gal in A549-GT. The binding of human serum IgM and C3 with A549-GT were also detected.

RESULTS

α-1,3GT mRNA was expressed in A549-GT. Direct immunofluorescence staining and FCM indicated a high and stable α-gal expression rate in A549-GT. Compared with parental A549 cells, the biological characteristics of A549-GT were unaltered. α-Gal expression was not detected in the human fetal lung fibroblast cell line MRC-5 even though A549-GT and its culture medium were cultivated with the enzyme. Immunofluorescence staining and FCM also indicated abundant binding between A549-GT treated with human serum and IgM/C3.

CONCLUSIONS

α-Gal expression in tumor cells by gene transduction can induce complement-dependent cytototic antitumor effects.

“Lost sugars” — reality of their biological and medical applications

The glycan chains attached to cell surfaces or to single proteins are highly dynamic structures with various functions. The glycan chains of mammals and of some microorganisms often terminate in sialic acids or α-1,3-galactose. Although these two sugars are completely distinct, there are several similarities in their biological and medical importance. First, one type of sialic acid, N-glycolylneuraminic acid, and the galactose bound by an α-1,3-linkage to LacNAc, that forms an α-gal epitope, were both eliminated in human evolution, resulting in the production of antibodies to these sugars. Both of these evolutionary events have consequences connected with the consumption of foods of mammalian origin, causing medical complications of varying severity. In terms of ageing, sialic acids prevent the clearance of glycoproteins and circulating blood cells, whereas cryptic α-gal epitopes on senescent red blood cells contribute to their removal from circulation. The efficiency of therapeutic proteins can be increased by sialylation. Another common feature is the connection with microorganisms since sialic acids and α-gal epitopes serve as receptors on host cells and can also be expressed on the surfaces of some microorganisms. Whereas, the sialylation of IgG antibodies may help to treat inflammation, the expression of the α-gal epitope on microbial antigens increases the immunogenicity of the corresponding vaccines. Finally, sialic acids and the α-gal epitope have applications in cancer immunotherapy. N-glycolylneuraminic acid is a powerful target for cancer immunotherapy, and the α-gal epitope increases the efficiency of cancer vaccines. The final section of this article contains a brief overview of the methods for oligosaccharide chain synthesis and the characteristics of sialyltransferases and α-1,3-galactosyltransferase.

The αGal HyperAcute(®) Technology: enhancing immunogenicity of antiviral vaccines by exploiting the natural αGal-mediated zoonotic blockade

The αGal HyperAcute(®) Technology exploits a robust zoonotic blockade to enhance potency of antiviral vaccines. Naturally acquired immunity against the common αGal epitope [galactose-alpha(1,3)-galactose-beta(1,4)N-acetylglucosamine-R (Gal-α(1,3)-Gal-β(1,4)-GlcNAc-R)] is facilitated by the loss of a key enzyme in the epitope's biosynthetic pathway. As human cells are devoid of this epitope, chronic stimulus from gut flora leads to high levels of circulating anti-αGal antibodies and the development of a robust immune pathway. As the αGal epitope is immediately recognized as foreign, the naturally acquired αGal immune pathway in humans serves as a strong barrier to zoonotic infection. The αGal HyperAcute(®) Technology takes advantage of this natural process to facilitate the rapid presentation of modified antigens to antigen-presenting cells, leading to a strong immune response. The evolutionary immunity to αGal ensures that the presence of αGal epitopes on antigens will lead to a robust immune response involving cross-activation of T(H)1 immunity, characterized by cytokine secretion and increased phagocytic activity, and T(H)2 immunity characterized by high antibody titres. αGal epitopes can be applied to antiviral vaccines by biological, enzymatic or chemical means. Several detection methods that directly and indirectly verify αGal addition are discussed. Enhanced immunogenicity (humoral and cellular) of αGal-modified vaccines is shown for several antiviral vaccine candidates. αGal modification of antiviral vaccine components leads to enhanced immunogenicity. The existing body of literature describing the utility of αGal epitopes as a safe and robust immunostimulatory and -modulatory agent in humans supports the basis for applying the αGal HyperAcute(®) Technology to the improvement of antiviral vaccines, both new and currently approved.

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.

Increased immunogenicity of HIV-1 p24 and gp120 following immunization with gp120/p24 fusion protein vaccine expressing alpha-gal epitopes

Developing an effective HIV-1 vaccine will require strategies to enhance antigen presentation to the immune system. In a previous study we demonstrated a marked increase in immunogenicity of the highly glycosylated HIV-1 gp120 protein following enzymatic addition of alpha-gal epitopes to the carbohydrate chains. In the present study we determined whether gp120(alphagal) can also serve as an effective platform for targeting other HIV-1 proteins to APC and thus increase immunogenicity of both proteins. For this purpose we produced a recombinant fusion protein between gp120 and the HIV-1 matrix p24 protein (gp120/p24). Multiple alpha-gal epitopes were synthesized enzymatically on the gp120 portion of the fusion protein to generate a gp120(alphagal)/p24 vaccine. Immune responses to gp120(alphagal)/p24 compared to gp120/p24 vaccine lacking alpha-gal epitopes were evaluated in alpha1,3galactosyltransferase knockout (KO) mice. These mice lack alpha-gal epitopes and, therefore, are capable of producing the anti-Gal antibody. T cell responses to p24, as assessed by ELISPOT and by CD8+ T cells intracellular staining assays for IFNgamma, was on average 12- and 10-fold higher, respectively, in gp120(alphagal)/p24 immunized mice than in mice immunized with gp120/p24. In addition, cellular and humoral immune responses against gp120 were higher by 10-30-fold in mice immunized with gp120(alphagal)/p24 than in gp120/p24 immunized mice. Our data suggest that the alpha-gal epitopes on the gp120 portion of the fusion protein can significantly augment the immunogenicity of gp120, as well as that of the fused viral protein which lacks alpha-gal epitopes. This strategy of anti-Gal mediated targeting to APC may be used for production of effective HIV-1 vaccines comprised of various viral proteins fused to gp120.

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.

Glycoengineering of alphaGal xenoantigen on recombinant peptide bearing the J28 pancreatic oncofetal glycotope

In human pancreatic adenocarcinoma, alterations of glycosylation processes leads to the expression of tumor-associated carbohydrate antigens, representing potential targets for cancer immunotherapy. Among these pancreatic tumor-associated carbohydrate antigens, the J28 glycotope located within the O-glycosylated mucin-like C-terminal domain of the fetoacinar pancreatic protein (FAPP) and expressed at the surface of human tumoral tissues, can be a good target for anticancer therapeutic vaccines. However, the oncodevelopmental self character of the J28 glycotope associated with the low immunogenicity of tumor-associated carbohydrate antigens may be a major obstacle to effective anti-tumor vaccine therapy. In this study, we have investigated a method to increase the immunogenicity of the recombinant pancreatic oncofetal J28 glycotope by glycoengineering Galalpha1,3Galss1,4GlcNAc-R (alphaGal epitope) which may be recognized by natural anti-alphaGal antibody present in humans. For this purpose, we have developed a stable Chinese hamster ovary cell clone expressing the alphaGal epitope by transfecting the cDNA encoding the alpha1,3galactosyltransferase. These cells have been previously equipped to produce the recombinant O-glycosylated C-terminal domain of FAPP carrying the J28 glycotope. As a consequence, the C-terminal domain of FAPP produced by these cells carries the alphaGal epitope on oligosaccharide structures associated with the J28 glycotope. Furthermore, we show that this recombinant "alpha1,3galactosyl and J28 glycotope" may not only be targeted by human natural anti-alphaGal antibodies but also by the mAbJ28, suggesting that the J28 glycotope remains accessible to the immune system as vaccinating agent. This approach may be used for many identified tumor-associated carbohydrate antigens which can be glycoengineered to carry a alphaGal epitope to increase their immunogenicity and to develop therapeutic vaccines.

Profiling terminal N-acetyllactosamines of glycans on mammalian cells by an immuno-enzymatic assay

Profiling of carbohydrate structures on cell membranes has been difficult to perform because of the complexity and the variations of such structures on cell surface glycans. This study presents a novel method for rapid profiling of cell surface glycans for terminal N-acetyllactosamines (Galbeta1-(3)4GlcNAc-R) that are uncapped, capped with sialic acid as SA-Galbeta1-(3)4GlcNAc-R, or with alpha1,3galactosyls as the alpha-gal epitope- Galalpha1-3Galbeta1-(3)4GlcNAc-R. This method includes two enzymatic reactions: (1) Terminal sialic acid is removed by neuraminidase, and (2) alpha-gal epitopes are synthesized on the exposed N-acetyllactosamines by alpha1,3galactosyltransferase. Existing and de novo synthesized alpha-gal epitopes on cells are quantified by a modification of radioimmunoassay designated as "ELISA inhibition assay," which measures binding of the monoclonal anti-Gal antibody M86 to alpha-gal epitopes. This binding is proportional to the number of cell surface alpha-gal epitopes. The amount of free M86 antibody molecules remaining in the solution is determined by ELISA using synthetic alpha-gal epitopes linked to albumin as solid phase antigen. The number of alpha-gal epitopes on cells is estimated by comparing binding curves of M86 incubated with the assayed cells, at various concentrations of the cells, with the binding of M86 to rabbit red cells expressing 2 x 10(6) alpha-gal epitopes/cell. We could demonstrate large variations in the number of sialic acid capped N-acetyllactosamines, alpha-gal epitopes and uncapped N-acetyllactosamines on different mammalian red blood cells, and on nucleated cells originating from a given tissue in various species. This method may be useful for rapid identification of changes in glycosylation patterns in cells subjected to various treatments, or in various states of differentiation.

Increased immunogenicity of human immunodeficiency virus gp120 engineered to express Galalpha1-3Galbeta1-4GlcNAc-R epitopes

The glycan shield comprised of multiple carbohydrate chains on the human immunodeficiency virus (HIV) envelope glycoprotein gp120 helps the virus to evade neutralizing antibodies. The present study describes a novel method for increasing immunogenicity of gp120 vaccine by enzymatic replacement of sialic acid on these carbohydrate chains with Galalpha1-3Galbeta1-4GlcNAc-R (alpha-gal) epitopes. These epitopes are ligands for the natural anti-Gal antibody constituting approximately 1% of immunoglobulin G in humans. We hypothesize that vaccination with gp120 expressing alpha-gal epitopes (gp120(alphagal)) results in in vivo formation of immune complexes with anti-Gal, which targets vaccines for effective uptake by antigen-presenting cells (APC), due to interaction between the Fc portion of the antibody and Fcgamma receptors on APC. This in turn results in effective transport of the vaccine to lymph nodes and effective processing and presentation of gp120 immunogenic peptides by APC for eliciting a strong anti-gp120 immune response. This hypothesis was tested in alpha-1,3-galactosyltransferase knockout mice, which produce anti-Gal. Mice immunized with gp120(alphagal) produced anti-gp120 antibodies in titers that were >100-fold higher than those measured in mice immunized with comparable amounts of gp120 and effectively neutralized HIV. T-cell response, measured by ELISPOT, was much higher in mice immunized with gp120(alphagal) than in mice immunized with gp120. It is suggested that gp120(alphagal) can serve as a platform for anti-Gal-mediated targeting of additional vaccinating HIV proteins fused to gp120(alphagal), thereby creating effective prophylactic vaccines.

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.

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

Poor uptake by antigen-presenting cells (APC) is a major reason for low immunogenicity of autologous tumor vaccines. This immunogenicity may be increased by exploiting the natural anti-Gal antibody that is present in humans as approximately 1% of circulating IgG. Anti-Gal binds to alpha-gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R) on vaccinating tumor cells and opsonizes them for effective uptake by APC. This epitope is synthesized in human tumor cells by transduction with AdalphaGT- a replication deficient adenovirus containing the alpha1,3galactosyltransferase (alpha1,3GT) gene. Protection against tumors by immunization with AdalphaGT-transduced tumor cells was studied in alpha1,3GT knockout (KO) mice, challenged with the highly tumorigenic BL6 melanoma cells. These mice lack alpha-gal epitopes and can produce anti-Gal. Immunization of KO mice with AdalphaGT-transduced BL6 cells protects many of the mice against challenge with live BL6 cells lacking alpha-gal epitopes. Immunization with AdalphaGT transduced autologous tumor cells may serve as adjuvant immunotherapy delivered after completion of standard therapy. This method may complement another gene therapy method in which GM-CSF-secreting vaccinating tumor cells recruit APC to vaccination sites. Anti-Gal-opsonized vaccinating tumor cells will be effectively internalized by GM-CSF recruited APC and transported to draining lymph nodes for processing and presentation of tumor antigens. Alternatively, injection of AdalphaGT directly into solid tumor masses of cancer patients may result in anti-Gal-mediated destruction of the transduced tumor cells in a manner similar to xenograft rejection. The subsequent uptake of anti-Gal-opsonized tumor membranes by APC results in their effective transportation to lymph nodes where processed tumor antigens may elicit a protective antitumor immune response.

Relationship between ?Gal epitope expression and decrease of tumorigenicity in pancreatic adenocarcinoma model

The alphaGal epitope is a carbohydrate structure, Galalpha1,3Galbeta1,4GlcNAc-R, synthesized on glycoconjugates in many mammals by alpha1,3galactosyltransferase. Humans do not express this epitope and present in serum large amounts of naturally occuring antibodies, which recognize the alphaGal epitopes and participate in the hyperacute rejection of xenograft. Studies indicated that the fundamental mechanism of hyperacute rejection involving the alphaGal epitope expression can be used in cancer therapy. We have previously suggested that the alphaGal epitope expression by human pancreatic tumoral cells could decrease the tumorigenic behavior of these cells. To determine whether the expression of the alphaGal epitope can modify the tumorigenicity of pancreatic cancer cells, we used a Syrian golden hamster pancreatic adenocarcinoma experimental model. The expression of alphaGal epitopes in the Syrian golden hamster pancreatic cancer cell line HaP-T1 was obtained by selecting stable cell clones transfected with murine alpha1,3galactosyltransferase gene. The alphaGal epitope expression resulted in a delay in the tumoral development of HaP-T1 cells in vivo after allograft transplantation of Syrian golden hamsters (2.5-fold, P < 0.05) and of nude mice. This result is associated with an 100% increase in survival time of nude mice bearing tumors expressing the alphaGal epitope. Our results confirm that the cell surface expression of alphaGal epitope decreases the tumorigenic behavior of pancreatic cancer cells. This novel property may be useful for the development of cancer gene immunotherapy strategy.

Expression of alpha-gal epitopes on ovarian carcinoma membranes to be used as a novel autologous tumor vaccine

OBJECTIVE

Poor presentation of tumor-associated antigens (TAA) to the immune system remains a major obstacle to effective anti-tumor vaccine therapy. The aim of this study is to demonstrate the feasibility of producing a novel autologous tumor vaccine from ovarian carcinoma that is expected to have increased immunogenicity. The strategy is based on the ability of the anti-Gal IgG antibody (a natural antibody comprising 1% of IgG in humans) to target tumor membranes expressing alpha-gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R) to antigen-presenting cells (APC).

STUDY DESIGN

Freshly obtained ovarian carcinoma tumors are homogenized, washed, and incubated with a mixture of neuraminidase, recombinant alpha1,3 galactosyltransferase (ralpha1,3GT) and uridine diphosphate galactose (UDP-Gal) to synthesize alpha-gal epitopes on carbohydrate chains of glycoproteins of these membranes. Subsequently, the processed membranes are analyzed for expression of alpha-gal epitopes and for the binding of anti-Gal.

RESULTS

Incubation of 3 g of ovarian carcinoma membranes, from five different patients, at 100 mg/ml, mixed together with ralpha1,3GT (50 microg/ml), neuraminidase (1 mU/ml), and UDP-Gal (2 mM), resulted in the effective synthesis of alpha-gal epitopes to the extent of approximately 2 x 10(11) epitopes/mg of tumor membranes. As a result of this de novo expression of alpha-gal epitopes, the tumor membranes readily bound purified anti-Gal antibody, as well as anti-Gal in autologous serum.

CONCLUSIONS

The method described in this study is very effective in the synthesis of many alpha-gal epitopes on tumor membranes obtained from ovarian carcinoma. These novel epitopes readily bind the naturally occurring anti-Gal antibody. This technique of opsonization of alpha-gal-modified autologous tumor membranes carrying TAA is expected to increase effective uptake of the vaccine by APC, which is key to successful anti-tumor vaccination.

Expression of eukaryotic glycosyltransferases in the yeast Pichia pastoris

The methylotrophic yeast Pichia pastoris is often used as an organism for the heterologous expression of proteins and has been used already for production of a number of glycosyltransferases involved in the biosynthesis of N- and O-linked oligosaccharides. In our recent studies, we have examined the expression in P. pastoris of Arabidopsis thaliana and Drosophila melanogaster core alpha1,3-fucosyltransferases (EC 2.4.1.214), A. thaliana beta1,2-xylosyltransferase (EC 2.4.2.38), bovine beta1,4-galactosyltransferase I (EC 2.4.1.38), D. melanogaster peptide O-xylosyltransferase (EC 2.4.2.26), D. melanogaster and Caenorhabditis elegans beta1,4-galactosyltransferase VII (SQV-3; EC 2.4.1.133) and tomato Lewis-type alpha1,4-fucosyltransferase (EC 2.4.1.65). Temperature, cell density and medium formulation have varying effects on the amount of activity resulting from expression under the control of either the constitutive glyceraldehyde-3-phosphate dehydrogenase (GAP) or inducible alcohol oxidase (AOX1) promoters. In the case of the A. thaliana xylosyltransferase these effects were most pronounced, since constitutive expression at 16 degrees C resulted in 30-times more activity than inducible expression at 30 degrees C. Also, the exact nature of the constructs had an effect; whereas soluble forms of the A. thaliana xylosyltransferase and fucosyltransferase were active with N-terminal pentahistidine tags (in the former case facilitating purification of the recombinant protein to homogeneity), a C-terminally tagged form of the A. thaliana fucosyltransferase was inactive. In the case of D. melanogaster beta1,4-galactosyltransferase VII, expression with a yeast secretion signal yielded no detectable activity; however, when a full-length form of the enzyme was introduced into P. pastoris, an active secreted form of the protein was produced.

High-level expression and characterization of a secreted recombinant cation-dependent mannose 6-phosphate receptor in Pichia pastoris

Mannose 6-phosphate receptors (MPRs) form essential components of the lysosomal enzyme targeting system by binding newly synthesized acid hydrolases with high (nM) affinity. We report the use of Pichia pastoris as a host to efficiently express the extracytoplasmic ligand-binding domain of the cation-dependent mannose 6-phosphate receptor. A truncated and glycosylation-deficient form of the receptor AF-Asn(81)/Stop(155) was secreted into the culture medium, yielding approximately 28mg/L after purification, which is an improvement of 10-100-fold compared to expression in baculovirus-infected insect cells and mammalian cells, respectively. Enzymatic deglycosylation indicated high-mannose sugars at the single potential glycosylation site of Asn 81. The extent and heterogeneity of N-glycans were revealed by applying matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). In the case of AF-Asn(81)/Stop(155), the majority (75%) of the oligosaccharides contained chain lengths of Man(8-10)GlcNAc(2) while Man(11-12)GlcNAc(2) comprised the remaining (25%) N-linked sugars. A comparative MALDI-TOF spectra of Asn(81)/Stop(155) purified from insect cells indicated that Man(2-3)GlcNAc(2) and GlcNAcMan(2-3)GlcNAc(2) share the oligosaccharide pool. The receptor isolated from yeast was functional with respect to ligand binding and acid-dependent dissociation properties, as determined by pentamannosyl phosphate-agarose affinity chromatography. In addition, the protein was biochemically and functionally similar to Asn(81)/Stop(155) expressed in insect cells concerning its oligomeric state and binding affinity to the lysosomal enzyme, beta-glucuronidase (K(d)=1.4nM). These results demonstrate that P. pastoris is a convenient system for the production of large quantities of functional recombinant MPRs suitable for structure-function studies.

Emerging strategies in tumor vaccines

Reports of novel developments in tumor vaccines that have appeared in the year ending May 1, 2002 are reviewed here. Antigenic moieties were revealed for tumors previously considered nonimmunogenic. The use of peptides spanning mutations detected exclusively in tumor tissue avoids the common concern for autoimmune responses. Carbohydrate biology is revealing novel antigenic moieties. The search for helper epitopes from tumor antigens has come into full swing. Humoral immunity is regaining terrain, particularly through the development of antiidiotypic antibodies. Major steps forward have been made in optimizing modes and routes of antigen delivery and in the use of immune adjuvants. In the clinic, phase I/II trials support the notion that tumor vaccines are safe. Because these trials are conducted in patients in whom tumor remission is not a realistic endpoint, patient responses were established by immune monitoring strategies to detect subtle changes in antitumor reactivity. Both clinical and laboratory data stress the vast potential of tumor vaccines for the treatment of cancer.

Elimination of anti-Gal B cells by alpha-Gal ricin1

BACKGROUND

A major barrier in pig to human organ transplantation is the binding of human anti-Gal to alpha-gal epitopes (Gal alpha 1-3Gal beta 1-4GlcNAc-R) on pig cells, resulting in hyperacute and acute vascular rejection of pig xenografts. Moreover, the immune system in xenograft recipients is activated by these epitopes to produce high affinity anti-Gal, which is also detrimental to xenografts. Production of anti-Gal can be prevented by specific elimination of anti-Gal B cells. This was achieved with the toxin ricin A, coupled to human alpha1-acid glycoprotein modified to carry alpha-gal epitopes. This complex, designated alpha-gal ricin, is targeted in vivo to anti-Gal B cells by interaction with the immunoglobulin molecules (i.e., B cell receptors) on these cells.

METHODS

Carbohydrate chains on alpha 1-acid glycoprotein were converted to carry alpha-gal epitopes by enzymatic treatment with recombinant alpha 1,3 galactosyltransferase (alpha 1,3GT). This molecule and ricin A were biotinylated and coupled by avidin to generate alpha-gal ricin. The efficacy of alpha-gal ricin in eliminating anti-Gal B cells was studied in the experimental model of alpha 1,3GT knockout (KO) mice. These mice produce large amounts of anti-Gal immunoglobulin G when immunized with pig kidney membranes, as measured by ELISA with alpha-gal epitopes linked to bovine serum albumin (BSA). In the absence of anti-Gal B cells, these mice lack the ability to produce anti-Gal.

RESULTS

Repeated administration of alpha-gal ricin into alpha1,3GT KO mice resulted in elimination of anti-Gal B cells, thereby preventing production of anti-Gal immunoglobulin G after immunization with pig kidney membranes. This prevention of anti-Gal production occurred with doses of alpha-gal ricin that were not toxic to the mice and did not affect production of antibodies with other specificities.

CONCLUSIONS

Administration of alpha-gal ricin results in specific elimination of anti-Gal B cells in alpha 1,3GT KO mice. The elimination of these B cells may prove to be helpful in attempts to achieve immune tolerance to alpha-gal epitopes in primates.

Expression of alpha-gal epitopes on HeLa cells transduced with adenovirus containing alpha1,3galactosyltransferase cDNA

Alpha1,3galactosyltransferase (alpha1,3GT) synthesizes alpha-gal epitopes (Gal(alpha)1-3Galbeta1-4GlcNAc-R) on glycoconjugates in nonprimate mammals but not in humans. Transduction of alpha1,3GT gene into human HeLa cells by an adenovirus vector allowed for accurate kinetics studies on the appearance of alpha1,3GT and of its product, the alpha-gal epitope, in the transduced cells. Mouse alpha1,3GT cDNA was inserted into a replication-defective adenovirus vector. This viral vector, designated Ad(alpha)GT, could be propagated in human 293 cells that have the viral E1 complementing gene. Transduction of HeLa cells resulted in immediate penetration of approximately 20 Ad(alpha)GT copies into each cell and the appearance of alpha1,3GT mRNA after 4h. Catalytic activity of alpha1,3GT was first detected in the cells after 6 h. The initial appearance of alpha-gal epitopes (approximately 6 x 10(4)/cell) on cell surface glycoconjugates was detected 10 h posttransduction, whereas 24 h posttransduction each cell expressed 2 x 10(6) epitopes. The activity of alpha1,3GT in cells transduced with approximately two copies of Ad(alpha)GT was eightfold lower than that in cells transduced with approximately 20 Ad(alpha)GT copies; however, the number of alpha-gal epitopes/cell remained closely similar. This implies that increased alpha1,3GT activity above a certain saturation level does not result in a corresponding increase in the carbohydrate product, possibly because of competing glycosyltransferases.