Evaluation of the Galalpha1-3Gal epitope as a host modification factor eliciting natural humoral immunity to enveloped viruses

Paleo-immunology of human anti-carbohydrate antibodies preventing primate extinctions

Two human natural anti-carbohydrate antibodies appeared in critical evolutionary events that brought primates and hominins to brink of extinction. The first is the anti-Gal antibody, produced in Old-World monkeys (OWM), apes and humans. It binds the carbohydrate-antigen 'α-gal epitope' (Galα1-3Galβ1-4GlcNAc-R) on carbohydrate-chains (glycans) synthesized by non-primate mammals, lemurs and New-World monkeys (NWM). The second is anti-N-glycolylneuraminic-acid (anti-Neu5Gc) antibody binding Neu5Gc on glycans synthesized by OWM, apes and most non-primate mammals. Ancestral OWM and apes synthesized α-gal epitopes and were eliminated ~20-30 million-years-ago (mya). Only few accidentally mutated offspring lacking α-gal epitopes, produced anti-Gal and survived. Hominin-populations living ~3 mya synthesized Neu5Gc and were eliminated, but few mutated offspring that accidently lost their ability to synthesize Neu5Gc, produced natural anti-Neu5Gc antibody. These hominins survived and ultimately evolved into present-day humans. It is argued that these two near-extinction events were likely to be the result of epidemics caused by highly virulent and lethal enveloped viruses that killed parental-populations. These viruses presented α-gal epitopes or Neu5Gc synthesized in host-cells of the parental-populations. Mutated offspring survived the epidemics because they were protected from the lethal virus by the natural anti-Gal or anti-Neu5Gc antibodies they produced due to loss of immune-tolerance to α-gal epitopes or to Neu5Gc, respectively.

The α-Gal Syndrome and Potential Mechanisms

The α-Gal syndrome is a complex allergic disease characterized by the development of specific IgE antibodies against the carbohydrate galactose-α-1,3-galactose (α-Gal), an oligosaccharide present in cells and tissues of non-primate mammals. Individuals with IgE antibodies to α-Gal suffer from a delayed form of anaphylaxis following red meat consumption. There are several features that make the α-Gal syndrome such a unique allergic disease and distinguish it from other food allergies: (1) symptoms causing IgE antibodies are directed against a carbohydrate moiety, (2) the unusual delay between the consumption of the food and the onset of the symptoms, and (3) the fact that primary sensitization to α-Gal occurs via tick bites. This review takes a closer look at the immune response against α-Gal, in healthy and in α-Gal allergic individuals. Furthermore, the similarities and differences between immune response against α-Gal and against the other important glycan moieties associated with allergies, namely cross-reactive carbohydrate determinants (CCDs), are discussed. Then different mechanisms are discussed that could contribute to the delayed onset of symptoms after consumption of mammalian meat. Moreover, our current knowledge on the role of tick bites in the sensitization process is summarized. The tick saliva has been shown to contain proteins carrying α-Gal, but also bioactive molecules, such as prostaglandin E2, which is capable of stimulating an increased expression of anti-inflammatory cytokines while promoting a decrease in the production of proinflammatory mediators. Together these components might promote Th2-related immunity and trigger a class switch to IgE antibodies directed against the oligosaccharide α-Gal. The review also points to open research questions that remain to be answered and proposes future research directions, which will help to get a better understanding and lead to a better management of the disease.

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.

Tick Saliva and the Alpha-Gal Syndrome: Finding a Needle in a Haystack

Ticks and tick-borne diseases are significant public health concerns. Bioactive molecules in tick saliva facilitate prolonged blood-feeding and transmission of tick-borne pathogens to the vertebrate host. Alpha-gal syndrome (AGS), a newly reported food allergy, is believed to be induced by saliva proteins decorated with a sugar molecule, the oligosaccharide galactose-⍺-1,3-galactose (α-gal). This syndrome is characterized by an IgE antibody-directed hypersensitivity against α-gal. The α-gal antigen was discovered in the salivary glands and saliva of various tick species including, the Lone Star tick (Amblyomma americanum). The underlying immune mechanisms linking tick bites with α-gal-specific IgE production are poorly understood and are crucial to identify and establish novel treatments for this disease. This article reviews the current understanding of AGS and its involvement with tick species.

Increasing Efficacy of Enveloped Whole-Virus Vaccines by In situ Immune-Complexing with the Natural Anti-Gal Antibody

The appearance of variants of mutated virus in course of the Covid-19 pandemic raises concerns regarding the risk of possible formation of variants that can evade the protective immune response elicited by the single antigen S-protein gene-based vaccines. This risk may be avoided by inclusion of several antigens in vaccines, so that a variant that evades the immune response to the S-protein of SARS-CoV-2 virus will be destroyed by the protective immune response against other viral antigens. A simple way for preparing multi-antigenic enveloped-virus vaccines is using the inactivated whole-virus as vaccine. However, immunogenicity of such vaccines may be suboptimal because of poor uptake of the vaccine by antigen-presenting-cells (APC) due to electrostatic repulsion by the negative charges of sialic-acid on both the glycan-shield of the vaccinating virus and on the carbohydrate-chains (glycans) of APC. In addition, glycan-shield can mask many antigenic peptides. These effects of the glycan-shield can be reduced and immunogenicity of the vaccinating virus markedly increased by glycoengineering viral glycans for replacing sialic-acid units on glycans with α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R). Vaccination of humans with inactivated whole-virus presenting α-gal epitopes (virus_α-gal) results in formation of immune-complexes with the abundant natural anti-Gal antibody that binds to viral α-gal epitopes at the vaccination site. These immune-complexes are targeted to APC for rigorous uptake due to binding of the Fc portion of immunecomplexed anti-Gal to Fcγ receptors on APC. The APC further transport the large amounts of internalized vaccinating virus to regional lymph nodes, process and present the virus antigenic peptides for the activation of many clones of virus specific helper and cytotoxic T-cells. This elicits a protective cellular and humoral immune response against multiple viral antigens and an effective immunological memory. The immune response to virus_α-gal vaccine was studied in mice producing anti-Gal and immunized with inactivated influenza-virus_α-gal. These mice demonstrated 100-fold increase in titer of the antibodies produced, a marked increase in T-cell response, and a near complete protection against challenge with a lethal dose of live influenza-virus, in comparison to a similar vaccine lacking α-gal epitopes. This glycoengineering can be achieved in vitro by enzymatic reaction with neuraminidase removing sialic-acid and with recombinant α1,3galactosyltransferase (α1,3GT) synthesizing α-gal epitopes, by engineering host-cells to contain several copies of the α1,3GT gene (GGTA1), or by transduction of this gene in a replication-defective adenovirus vector into host-cells. Theoretically, these methods for increased immunogenicity may be applicable to all enveloped viruses with N-glycans on their envelope.

Altered Blood Levels of Anti-Gal Antibodies in Alzheimer's Disease: A New Clue to Pathogenesis?

Alzheimer's disease is a neurodegenerative disorder whose pathological mechanisms, despite recent advances, are not fully understood. However, the deposition of beta amyloid -peptide and neuroinflammation, which is probably aggravated by dysbiotic microbiota, seem to play a key role. Anti-Gal are the most abundant xenoreactive natural antibodies. They are supposed to stem from immunization against the gut microbiota and have been implicated in the pathogenesis of several diseases, including multiple sclerosis. These antibodies target the alpha-Gal epitope, expressed on the terminal sugar units of glycoprotein or glycolipid of all mammals except apes, Old World monkeys and humans. The alpha-Gal is constitutively expressed in several bacteria constituting the brain microbiota, and alpha-Gal-like epitopes have been detected in gray matter, amyloid plaque, neurofibrillary tangles and corpora amylacea of the human brain, suggesting a potential link between anti-Gal and Alzheimer's disease etiopathogenesis. For the first time, our study searched for possible alterations of anti-Gal immunoglobulin levels in Alzheimer's disease patients. IgG and IgM blood levels were significantly lower, and IgA significantly higher in patients than in healthy subjects. These results suggest that such immunoglobulins might be implicated in Alzheimer's disease pathogenesis and open new scenarios in the research for new biomarkers and therapeutic strategies.

The History of Carbohydrates in Type I Allergy

Although first described decades ago, the relevance of carbohydrate specific antibodies as mediators of type I allergy had not been recognized until recently. Previously, allergen specific IgE antibodies binding to carbohydrate epitopes were considered to demonstrate a clinically irrelevant cross-reactivity. However, this changed following the discovery of type I allergies specifically mediated by oligosaccharide structures. Especially the emerging understanding of red meat allergy characterized by IgE directed to the oligosaccharide alpha-gal showed that carbohydrate-mediated reactions can result in life threatening systemic anaphylaxis which in contrast to former assumptions proves a high clinical relevance of some carbohydrate allergens. Within the scope of this review article, we illustrate the historical development of carbohydrate-allergen-research, reaching from only diagnostically relevant crossreactive-carbohydrate-determinants to clinically important antigens mediating type I allergy. Focusing on clinical and immunological features of the alpha-gal syndrome, we highlight the discovery of oligosaccharides as potentially highly immunogenic antigens and mediators of type I allergy, report what is known about the route of sensitization and the immunological mechanisms involved in sensitization and elicitation phase of allergic responses as well as currently available diagnostic and therapeutic tools. Finally, we briefly report on carbohydrates being involved in type I allergies different from alpha-gal.

Live unattenuated vaccines for controlling viral diseases, including COVID-19

Live unattenuated vaccines (LUVs) have been neglected for decades, due to widespread prejudice against their safety, even though they have successfully controlled yellow fever and adenovirus infection in humans as well as rinderpest and infectious bursal disease in animals. This review elucidated that LUVs could be highly safe with selective use of neutralizing antivirus antibodies, natural antiglycan antibodies, nonantibody antivirals, and ectopic inoculation. Also, LUVs could be of high efficacy, high development speed, and high production efficiency, with the development of humanized monoclonal antibodies and other modern technologies. They could circumvent antibody-dependent enhancement and maternal-derived antibody interference. With these important advantages, LUVs could be more powerful than other vaccines for controlling some viral diseases, and they warrant urgent investigation with animal experiments and clinical trials for defeating the COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2.

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.

SARS-CoV-2 replicating in nonprimate mammalian cells probably have critical advantages for COVID-19 vaccines due to anti-Gal antibodies: A minireview and proposals

Glycoproteins of enveloped viruses replicating in nonprimate mammalian cells carry α‐1,3‐galactose (α‐Gal) glycans, and can bind to anti‐Gal antibodies which are abundant in humans. The antibodies have protected humans and their ancestors for millions of years, because they inhibit replication of many kinds of microbes carrying αGal glycans and aid complements and macrophages to destroy them. Therefore, severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) replicating in nonprimate mammalian cells (eg, PK‐15 cells) carry αGal glycans and could be employed as a live vaccine for corona virus 2019 (COVID‐19). The live vaccine safety could be further enhanced through intramuscular inoculation to bypass the fragile lungs, like the live unattenuated adenovirus vaccine safely used in US recruits for decades. Moreover, the immune complexes of SARS‐CoV‐2 and anti‐Gal antibodies could enhance the efficacy of COVID‐19 vaccines, live or inactivated, carrying α‐Gal glycans. Experiments are imperatively desired to examine these novel vaccine strategies which probably have the critical advantages for defeating the pandemic of COVID‐19 and preventing other viral infectious diseases.

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) replicating in nonprimate mammalian cells carries α‐1,3‐galactose (α‐Gal) glycans which can bind to anti‐Gal antibodies abundant in humans.

Anti‐Gal antibodies inhibit replication of various α‐Gal‐carrying pathogens and aid complements and macrophages to destroy them.

α‐Gal‐carrying SARS‐CoV‐2 could be used as a live vaccine for corona virus 2019 (COVID‐19).

The live vaccine safety could be enhanced through intramuscular inoculation to bypass the fragile lungs.

Live and inactivated COVID‐19 vaccines could be more effective if produced using PK‐15 rather than Vero cells.

Human Natural Antibodies to Mammalian Carbohydrate Antigens as Unsung Heroes Protecting against Past, Present, and Future Viral Infections

Human natural antibodies to mammalian carbohydrate antigens (MCA) bind to carbohydrate-antigens synthesized in other mammalian species and protect against zoonotic virus infections. Three such anti-MCA antibodies are: (1) anti-Gal, also produced in Old-World monkeys and apes, binds to α-gal epitopes synthesized in non-primate mammals, lemurs, and New-World monkeys; (2) anti-Neu5Gc binds to Neu5Gc (N-glycolyl-neuraminic acid) synthesized in apes, Old-World monkeys, and many non-primate mammals; and (3) anti-Forssman binds to Forssman-antigen synthesized in various mammals. Anti-viral protection by anti-MCA antibodies is feasible because carbohydrate chains of virus envelopes are synthesized by host glycosylation machinery and thus are similar to those of their mammalian hosts. Analysis of MCA glycosyltransferase genes suggests that anti-Gal appeared in ancestral Old-World primates following catastrophic selection processes in which parental populations synthesizing α-gal epitopes were eliminated in enveloped virus epidemics. However, few mutated offspring in which the α1,3galactosyltransferase gene was accidentally inactivated produced natural anti-Gal that destroyed viruses presenting α-gal epitopes, thereby preventing extinction of mutated offspring. Similarly, few mutated hominin offspring that ceased to synthesize Neu5Gc produced anti-Neu5Gc, which destroyed viruses presenting Neu5Gc synthesized in parental hominin populations. A present-day example for few humans having mutations that prevent synthesis of a common carbohydrate antigen (produced in >99.99% of humans) is blood-group Bombay individuals with mutations inactivating H-transferase; thus, they cannot synthesize blood-group O (H-antigen) but produce anti-H antibody. Anti-MCA antibodies prevented past extinctions mediated by enveloped virus epidemics, presently protect against zoonotic-viruses, and may protect in future epidemics. Travelers to regions with endemic zoonotic viruses may benefit from vaccinations elevating protective anti-MCA antibody titers.

Xenoantigen-Dependent Complement-Mediated Neutralization of Lymphocytic Choriomeningitis Virus Glycoprotein-Pseudotyped Vesicular Stomatitis Virus in Human Serum

Neutralization by antibodies and complement limits the effective dose and thus the therapeutic efficacy of oncolytic viruses after systemic application. We and others previously showed that pseudotyping of oncolytic rhabdoviruses such as maraba virus and vesicular stomatitis virus (VSV) with the lymphocytic choriomeningitis virus glycoprotein (LCMV-GP) results in only a weak induction of neutralizing antibodies. Moreover, LCMV-GP-pseudotyped VSV (VSV-GP) was significantly more stable in normal human serum (NHS) than VSV. Here, we demonstrate that depending on the cell line used for virus production, VSV-GP showed different complement sensitivities in nonimmune NHS. The NHS-mediated titer reduction of VSV-GP was dependent on activation of the classical complement pathway, mainly by natural IgM antibodies against xenoantigens such as galactose-α-(1,3)-galactose (α-Gal) or N-glycolylneuraminic acid (Neu5Gc) expressed on nonhuman production cell lines. VSV-GP produced on human cell lines was stable in NHS. However, VSV-GP generated in transduced human cells expressing α-Gal became sensitive to NHS. Furthermore, GP-specific antibodies induced complement-mediated neutralization of VSV-GP independently of the producer cell line, suggesting that complement regulatory proteins potentially acquired by the virus during the budding process are not sufficient to rescue the virus from antibody-dependent complement-mediated lysis. Thus, our study points to the importance of a careful selection of cell lines for viral vector production for clinical use.IMPORTANCE Systemic application aims to deliver oncolytic viruses to tumors as well as to metastatic lesions. However, we found that xenoantigens incorporated onto the viral surface from nonhuman production cell lines are recognized by natural antibodies in human serum and that the virus is thereby inactivated by complement lysis. Hence, to maximize the effective dose, careful selection of cell lines for virus production is crucial.

Role and Mechanism of Galactose-Alpha-1,3-Galactose in the Elicitation of Delayed Anaphylactic Reactions to Red Meat

Purpose of Review

The alpha-Gal (α-Gal) syndrome is characterized by the presence of IgE antibodies directed at the carbohydrate galactose-alpha-1,3-galactose (α-Gal). In this article, we review the presence of α-Gal in food and non-food sources; we discuss the evolutionary context of the antibody response to α-Gal and highlight immune responses to α-Gal and other carbohydrates.

Recent findings

IgE antibodies have been associated with delayed allergy to red meat. In addition to food, drugs, and other products of animal origin are increasingly perceived as a risk for patients sensitized to α-Gal. The link between tick bites and anti-α-Gal IgE-antibody production that has been established first by epidemiological studies has now been confirmed in mouse models.

Summary

The anti-α-Gal immune response is complex and characterized by a unique feature. IgM and IgG antibodies have been found to confer protection against pathogens whereas the IgE-response to α-Gal is detrimental and causes severe reactions upon exposure to mammalian meat and other products.

Why Do We Produce Anti-Gal

The natural anti-Gal antibody is one of the multiple natural anti-carbohydrate antibodies produced in humans against a wide range of carbohydrate antigens on GI bacteria. The antibody is unique to humans, apes, and Old World monkeys, and it binds specifically to a mammalian carbohydrate antigen called the α-gal epitope that is synthesized in nonprimate mammals, lemurs (prosimians) and New World monkeys by the glycosylation enzyme α1,3GT. The α1,3GT gene (GGTA1) appeared in mammals >100 million years ago, prior to the split between marsupial and placental mammals. This gene has been conserved in its active form, in all mammals, except for Old World monkeys, apes, and humans. Inactivation of the α1,3GT gene in ancestral Old World primates occurred 20–30 million years ago and could have been associated with epidemics of enveloped viruses in the Eurasia-Africa continent. It is suggested that prior to such epidemics, few ancestral Old World primates acquired deletion point mutations that inactivated the α1,3GT gene and eliminated α-gal epitopes. This resulted in loss of immune tolerance to the α-gal epitope and thus, in production of the anti-Gal antibody against antigens on bacteria colonizing the GI tract. This accidental inactivation of the α1,3GT gene in very small populations is analogous to the highly rare blood type “Bombay” individuals who do not synthesize blood group H (O antigen) because of inactivation of the α1,2-fucosyltransferase gene. The loss of immune tolerance to blood group H antigen has resulted in production of natural anti-blood group H antibodies in the blood group Bombay individuals. It is suggested that anti-Gal protected against infections by enveloped viruses presenting α-gal epitopes, which were lethal to the parental primate populations that conserved active α1,3GT and thus, synthesized α-gal epitopes. Alternative causes for the elimination of Old World primates synthesizing α-gal epitopes could be bacteria or protozoa parasites presenting α-gal or α-gal-like epitopes, and bacterial toxins, or detrimental viruses that used α-gal epitopes in these primates as “docking receptors.” Ultimately, any of these proposed selective processes could result in extinction of Old World primates synthesizing α-gal epitopes on their cells. These ancestral primates were replaced by offspring populations lacking α-gal epitopes and producing the anti-Gal antibody, which continues to be produced by Old World monkeys, apes, and humans. New World monkeys and lemurs were protected from pathogens of the Old World by oceanic barriers, thus they continue to synthesize α-gal epitopes and lack the ability to produce the anti-Gal antibody. This scenario of few individuals in a large population having a mutation(s) that inactivates a glycosyltransferase gene thus, resulting in production of evolutionary advantageous natural antibodies against the eliminated carbohydrate antigen, may reflect one of the mechanisms inducing changes in the carbohydrate profile of various mammalian populations.

Virus-like Particle Display of the α-Gal Carbohydrate for Vaccination against Leishmania Infection

Secreted and surface-displayed carbohydrates are essential for virulence and viability of many parasites, including for immune system evasion. We have identified the α-Gal trisaccharide epitope on the surface of the protozoan parasites Leishmania infantum and Leishmania amazonensis, the etiological agents of visceral and cutaneous leishmaniasis, respectively, with the latter bearing larger amounts of α-Gal than the former. A polyvalent α-Gal conjugate on the immunogenic Qβ virus-like particle was tested as a vaccine against Leishmania infection in a C57BL/6 α-galactosyltransferase knockout mouse model, which mimics human hosts in producing high titers of anti-α-Gal antibodies. As expected, α-Gal-T knockout mice infected with promastigotes of both Leishmania species showed significantly lower parasite load in the liver and slightly decreased levels in the spleen, compared with wild-type mice. Vaccination with Qβ-α-Gal nanoparticles protected the knockout mice against Leishmania challenge, eliminating the infection and proliferation of parasites in the liver and spleen as probed by qPCR. The α-Gal epitope may therefore be considered as a vaccine candidate to block human cutaneous and visceral leishmaniasis.

Evidence against a role for jaagsiekte sheep retrovirus in human lung cancer

BACKGROUND

Jaagsiekte sheep retrovirus (JSRV) causes a contagious lung cancer in sheep and goats that can be transmitted by aerosols produced by infected animals. Virus entry into cells is initiated by binding of the viral envelope (Env) protein to a specific cell-surface receptor, Hyal2. Unlike almost all other retroviruses, the JSRV Env protein is also a potent oncoprotein and is responsible for lung cancer in animals. Of concern, Hyal2 is a functional receptor for JSRV in humans.

RESULTS

We show here that JSRV is fully capable of infecting human cells, as measured by its reverse transcription and persistence in the DNA of cultured human cells. Several studies have indicated a role for JSRV in human lung cancer while other studies dispute these results. To further investigate the role of JSRV in human lung cancer, we used highly-specific mouse monoclonal antibodies and a rabbit polyclonal antiserum against JSRV Env to test for JSRV expression in human lung cancer. JSRV Env expression was undetectable in lung cancers from 128 human subjects, including 73 cases of bronchioalveolar carcinoma (BAC; currently reclassified as lung invasive adenocarcinoma with a predominant lepidic component), a lung cancer with histology similar to that found in JSRV-infected sheep. The BAC samples included 8 JSRV DNA-positive samples from subjects residing in Sardinia, Italy, where sheep farming is prevalent and JSRV is present. We also tested for neutralizing antibodies in sera from 138 Peruvians living in an area where sheep farming is prevalent and JSRV is present, 24 of whom were directly exposed to sheep, and found none.

CONCLUSIONS

We conclude that while JSRV can infect human cells, JSRV plays little if any role in human lung cancer.

Natural anti-carbohydrate antibodies contributing to evolutionary survival of primates in viral epidemics?

Humans produce multiple natural antibodies against carbohydrate antigens on gastrointestinal bacteria. Two such antibodies appeared in primates in recent geological times. Anti-Gal, abundant in humans, apes and Old-World monkeys, appeared 20-30 million years ago (mya) following inactivation of the α1,3GT gene (GGTA1). This gene encodes in other mammals the enzyme α1,3galactosyltransferase (α1,3GT) that synthesizes α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R) which bind anti-Gal. Anti-Neu5Gc, found only in humans, appeared in hominins <6 mya, following elimination of N-glycolylneuraminic-acid (Neu5Gc) because of inactivation of CMAH, the gene encoding hydroxylase that converts N-acetylneuraminic-acid (Neu5Ac) into Neu5Gc. These antibodies, were initially produced in few individuals that acquired random mutations inactivating the corresponding genes and eliminating α-gal epitopes or Neu5Gc, which became nonself antigens. It is suggested that these evolutionary selection events were induced by epidemics of enveloped viruses, lethal to ancestral Old World primates or hominins. Such viruses presented α-gal epitopes or Neu5Gc, synthesized in primates that conserved active GGTA1 or CMAH, respectively, and were lethal to their hosts. The natural anti-Gal or anti-Neu5Gc antibodies, produced in offspring lacking the corresponding carbohydrate antigens, neutralized and destroyed viruses presenting α-gal epitopes or Neu5Gc. These antibodies further induced rapid, effective immune responses against virus antigens, thus preventing infections from reaching lethal stages. These epidemics ultimately resulted in extinction of primate populations synthesizing these carbohydrate antigens and their replacement with offspring populations lacking the antigens and producing protective antibodies against them. Similar events could mediate the elimination of various carbohydrate antigens, thus preventing the complete extinction of other vertebrate species.

Acceleration of wound healing by α-gal nanoparticles interacting with the natural anti-Gal antibody

Application of α-gal nanoparticles to wounds and burns induces accelerated healing by harnessing the natural anti-Gal antibody which constitutes ~1% of human immunoglobulins. α-gal nanoparticles present multiple α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R), the carbohydrate ligand of anti-Gal. Studied α-gal nanoparticles were comprised of glycolipids with α-gal epitopes, phospholipids, and cholesterol. Binding of anti-Gal to α-gal nanoparticles in wounds activates the complement cascade, resulting in formation of chemotactic complement cleavage peptides that induce rapid recruitment of many macrophages. The Fc/Fcγ receptors interaction between anti-Gal coating α-gal nanoparticles and the recruited macrophages activates macrophages to produce cytokines/growth factors that promote wound healing and recruit stem cells. Studies of wound healing by α-gal nanoparticles were feasible in α1,3galactosyltransferase knockout mice and pigs. In contrast to other nonprimate mammals, these mice and pigs lack the α-gal epitope, and thus they are not immunotolerant to it and produce anti-Gal. Treatment of skin wounds and burns with α-gal nanoparticles resulted in 40-60% decrease in healing time in comparison with control wounds treated with saline. This accelerated healing is associated with increased recruitment of macrophages and extensive angiogenesis in wounds, faster regrowth of epidermis, and regeneration of the dermis. The accelerated healing further decreases and may completely eliminate fibrosis and scar formation in wounds. Since healing of internal injuries is mediated by mechanisms similar to those in external wound healing, it is suggested that α-gal nanoparticles treatment may also improve regeneration and restoration of biological function following internal injuries such as surgical incisions, myocardial ischemia following infarction, and nerve injuries.

Significance of the evolutionary α1,3-galactosyltransferase (GGTA1) gene inactivation in preventing extinction of apes and old world monkeys

The α1,3-galactosyltransferase (α1,3GT or GGTA1) gene displays unique evolutionary characteristics. This gene appeared early in mammalian evolution and is absent in other vertebrates. The α1,3GT gene is active in marsupials, nonprimate placental mammals, lemurs (prosimians) and New World monkeys, encoding the α1,3GT enzyme that synthesizes a carbohydrate antigen called "α-gal epitope." The α-gal epitope is present in large numbers on cell membrane glycolipids and glycoproteins. The α1,3GT gene was inactivated in ancestral Old World monkeys and apes by frameshift single-base deletions forming premature stop codons. Because of this gene inactivation, humans, apes, and Old World monkeys lack α-gal epitopes and naturally produce an antibody called the "anti-Gal antibody" which binds specifically to α-gal epitopes and which is the most abundant antibody in humans. The evolutionary event that resulted in the inactivation of the α1,3GT gene in ancestral Old World primates could have been mediated by a pathogen endemic to Eurasia-Africa landmass that exerted pressure for selection of primate populations lacking the α-gal epitope. Once the α-gal epitope was eliminated, primates could produce the anti-Gal antibody, possibly as means of defense against pathogens expressing this epitope. This assumption is supported by the fossil record demonstrating an almost complete extinction of apes in the late Miocene and failure of Old World monkeys to radiate into multiple species before that period. A present outcome of this evolutionary event is the anti-Gal-mediated rejection of mammalian xenografts expressing α-gal epitopes in humans, apes, and Old World monkeys.

Re-engineering vesicular stomatitis virus to abrogate neurotoxicity, circumvent humoral immunity, and enhance oncolytic potency

As cancer treatment tools, oncolytic viruses (OV) have yet to realize what some see as their ultimate clinical potential. In this study, we have engineered a chimeric vesicular stomatitis virus (VSV) that is devoid of its natural neurotoxicity while retaining potent oncolytic activity. The envelope glycoprotein (G) of VSV was replaced with a variant glycoprotein of the lymphocytic choriomeningitis virus (LCMV-GP), creating a replicating therapeutic, rVSV(GP), that is benign in normal brain but can effectively eliminate brain cancer in multiple preclinical tumor models in vivo. Furthermore, it can be safely administered systemically to mice and displays greater potency against a spectrum of human cancer cell lines than current OV candidates. Remarkably, rVSV(GP) escapes humoral immunity, thus, for the first time, allowing repeated systemic OV application without loss of therapeutic efficacy. Taken together, rVSV(GP) offers a considerably improved OV platform that lacks several of the major drawbacks that have limited the clinical potential of this technology to date.

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.

α1,3Galactosyltransferase knockout pigs produce the natural anti-Gal antibody and simulate the evolutionary appearance of this antibody in primates

BACKGROUND

Anti-Gal is the most abundant natural antibody in humans and Old World primates (apes and Old World monkeys). Its ligand, the α-gal epitope (Galα1-3Galβ1-4GlcNAc-R), is abundant in nonprimate mammals, prosimians and New World monkeys whereas it is absent in humans and Old World primates as a result of inactivation of the α1,3galactosyltransferase (α1,3GT) gene in ancestral Old World primates, as recent as 20-28 million years ago. Since anti-Gal has been a "forbidden" autoantibody for >140 million years of evolution in mammals producing α-gal epitopes it was of interest to determine whether ancestral Old World primates could produce anti-Gal once α-gal epitopes were eliminated, i.e. did they carry anti-Gal encoding immunoglobulin genes, or did evolutionary selection eliminate these genes that may be detrimental in mammals synthesizing α-gal epitopes. This question was studied by evaluating anti-Gal prodution in α1,3GT knockout (GT-KO) pigs recently generated from wild-type pigs in which the α-gal epitope is a major self-antigen.

METHODS

Anti-Gal antibody activity in pig sera was assessed by ELISA, flow cytometry and complement mediated cytolysis and compared to that in human sera.

RESULTS

The study demonstrates abundant production of the natural anti-Gal antibody in GT-KO pigs at titers even higher than in humans. The fine specificity of GT-KO pig anti-Gal is identical to that of human anti-Gal.

CONCLUSIONS

Pigs and probably other mammals producing α-gal epitopes carry immunoglobulin genes encoding anti-Gal as an autoantibody. Once the α-gal epitope is eliminated in GT-KO pigs, they produce anti-Gal. These findings strongly suggest that similar to GT-KO pigs, inactivation of the α1,3GT gene in ancestral Old World primates enabled the immediate production of anti-Gal, possibly as a protective antibody against detrimental microbial agents carrying α-gal epitopes.

Possible role of a cell surface carbohydrate in evolution of resistance to viral infections in old world primates

Due to inactivation of the α1,3-galactosyltransferase gene (GGTA1, or the α1,3GT gene) approximately 28 million years ago, the carbohydrate αGal (Galα1,3Galβ1,4GlcNAc) is not expressed on the cells of Old World monkeys and apes (including humans) but is expressed in all other mammals. The proposed selective advantage of this mutation for these primates is the ability to produce anti-Gal antibodies, which may be an effective immune component in neutralizing αGal-expressing pathogens. However, loss of α1,3GT expression may have been advantageous by providing natural resistance against viral pathogens that exploited the α1,3GT pathway or cell surface αGal for infection. Infections of paired cell lines with differential expression of α1,3GT showed that Sindbis viruses (SINV) preferentially replicate in α1,3GT-positive cells, whereas herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) preferentially grow in cells lacking α1,3GT. Viral growth and spread correlated with the ability of the different viruses to successfully initiate infection in the presence or absence of α1,3GT expression. GT knockout (KO) suckling mice infected with SINV strains (AR339 and S.A.AR86) experienced significant delay in onset of disease symptoms and mortality compared to wild-type (WT) B6 suckling mice. In contrast, HSV-2-infected GT KO mice had higher viral titers in spleen and liver and exhibited significantly more focal hepatic necrosis than WT B6 mice. This study demonstrates that α1,3GT activity plays a role in the course of infections for certain viruses. Furthermore, this study has implications for the evolution of resistance to viral infections in primates.

Point mutations in the paramyxovirus F protein that enhance fusion activity shift the mechanism of complement-mediated virus neutralization

Parainfluenza virus 5 (PIV5) activates and is neutralized by the alternative pathway (AP) in normal human serum (NHS) but not by heat-inactivated (HI) serum. We have tested the relationship between the fusion activity within the PIV5 F protein, the activation of complement pathways, and subsequent complement-mediated virus neutralization. Recombinant PIV5 viruses with enhanced fusion activity were generated by introducing point mutations in the F fusogenic peptide (G3A) or at a distal site near the F transmembrane domain (S443P). In contrast to wild-type (WT) PIV5, the mutant G3A and S443P viruses were neutralized by both NHS and HI serum. Unlike WT PIV5, hyperfusogenic G3A and S443P viruses were potent C4 activators, C4 was deposited on NHS-treated mutant virions, and the mutants were neutralized by factor B-depleted serum but not by C4-depleted serum. Antibodies purified from HI human serum were sufficient to neutralize both G3A and S443P viruses in vitro but were ineffective against WT PIV5. Electron microscopy data showed greater deposition of purified human antibodies on G3A and S443P virions than on WT PIV5 particles. These data indicate that single amino acid changes that enhance the fusion activity of the PIV5 F protein shift the mechanism of complement activation in the context of viral particles or on the surface of virus-infected cells, due to enhanced binding of antibodies. We present general models for the relationship between enhanced fusion activity in the paramyxovirus F protein and increased susceptibility to antibody-mediated neutralization.

Discovery of the natural anti-Gal antibody and its past and future relevance to medicine

This is a personal account of the discovery of the natural anti-Gal antibody, the most abundant natural antibody in humans, the reciprocal distribution of this antibody and its ligand the α-gal epitope in mammals and the immunological barrier this antibody has formed in porcine to human xenotransplantation. This barrier has been overcome in the recent decade with the generation of α1,3-galactosyltransferase gene-knockout pigs. However, anti-Gal continues to be relevant in medicine as it can be harnessed for various therapeutic effects. Anti-Gal converts tumor lesions injected with α-gal glycolipids into vaccines that elicit a protective anti-tumor immune response by in situ targeting of tumor cells for uptake by antigen-presenting cells. This antibody further accelerates wound and burn healing by interaction with α-gal nanoparticles applied to injured areas and induction of rapid recruitment and activation of macrophages. Anti-Gal/α-gal nanoparticle immune complexes may further induce rapid recruitment and activation of macrophages in ischemic myocardium and injured nerves, thereby inducing tissue regeneration and prevention of fibrosis.

Distribution of the Galβ1-4Gal epitope among birds: species-specific loss of the glycan structure in chicken and its relatives

The Galβ1-4Gal epitope is rarely found in mammals, and the natural antibody against Galβ1-4Gal is rich in human. In contrast, we have previously demonstrated the presence of Galβ1-4Gal in pigeon and ostrich, and the absence of this epitope in chicken. Here, to further investigate the expression of this glycan among birds, egg white glycoproteins and egg yolk IgG from nine species of birds, namely, chicken, duck, emu, guineafowl, ostrich, peafowl, pigeon, quail, and turkey, were analyzed by western blot using an anti-(Galβ1-4Gal) antibody. The results indicated that some egg white glycoproteins from emu, ostrich, and quail, and heavy chains of IgG from all of the birds, except chicken and quail, were stained with the antibody. The presence of Galβ1-4Gal on N-glycans of IgGs from guineafowl, peafowl, and turkey were confirmed by mass spectrometry (MS), MS/MS, and MS(n) analyses. In quail, the presence of Galβ1-4Gal was confirmed by detecting the activities of UDP-galactose: β-galactoside β1,4-galactosyltransferase (β4GalT(Gal)) in various tissues, and by detecting Galβ1-4Gal by western blotting. In contrast, bamboo partridge, which is a close relative of chicken, did not show any detectable activities of β4GalT(Gal) or Galβ1-4Gal on glycoproteins. Because quail, peafowl, turkey, chicken, and bamboo partridge belong to the same family, i.e., Phasianidae, expression of Galβ1-4Gal was most likely differentiated within this family. Considering that Galβ1-4Gal is also expressed in ostrich, emu, and pigeon, which are phylogenetically distant relatives within modern birds, Galβ1-4Gal expression appears to be widely distributed among birds, but might have been abolished in the ancestors of chicken and bamboo partridge.

Incorporation of host complement regulatory proteins into Newcastle disease virus enhances complement evasion

Newcastle disease virus (NDV), an avian paramyxovirus, is inherently tumor selective and is currently being considered as a clinical oncolytic virus and vaccine vector. In this study, we analyzed the effect of complement on the neutralization of NDV purified from embryonated chicken eggs, a common source for virus production. Fresh normal human serum (NHS) neutralized NDV by multiple pathways of complement activation, independent of neutralizing antibodies. Neutralization was associated with C3 deposition and the activation of C2, C3, C4, and C5 components. Interestingly, NDV grown in mammalian cell lines was resistant to complement neutralization by NHS. To confirm whether the incorporation of regulators of complement activity (RCA) into the viral envelope afforded complement resistance, we grew NDV in CHO cells stably transfected with CD46 or HeLa cells, which strongly express CD46 and CD55. NDV grown in RCA-expressing cells was resistant to complement by incorporating CD46 and CD55 on virions. Mammalian CD46 and CD55 molecules on virions exhibited homologous restriction, since chicken sera devoid of neutralizing antibodies to NDV were able to effectively neutralize these virions. The incorporation of chicken RCA into NDV produced in embryonated eggs similarly provided species specificity toward chicken sera.

Gal/non-Gal antigens in pig tissues and human non-Gal antibodies in the GalT-KO era

Our knowledge regarding Gal and non-Gal antigens in GalT-KO pig tissues can be summarized as α3Galactosyl-tranferase gene knock out eliminates the Galα3Galβ4GlcNAc-R antigen expression in pig tissues as well as anti-Gal antibody binding. Other Galα-terminating saccharides (e.g. iGb3 glycolipids and Galα2 determinants) may be present but have not been documented. α3Galactosyl-tranferase gene knock out slightly changes the carbohydrate antigen expression but no "new" antigens recognized by the human immune system have been found. Non-Gal antigens are both of protein and carbohydrate nature but their exact chemical structures are poorly defined. Regarding human non-Gal antibodies our knowledge is as Non-Gal antibodies exist naturally and increase in humans/non-human primate (NHP) receiving WT or GalT-KO pig grafts. Non-Gal antibodies with new antigen epitope recognition can be induced in humans/NHP after challenge by WT or GalT-KO pig grafts. Non-Gal antibodies react with both carbohydrates and proteins. Part of the protein reactivity is directed to glycoprotein carbohydrates chains. Non-Gal antibodies reacting with neuraminic acid terminated saccharides (both N-Acetyl and N-Glycoloyl variants) are present in humans/NHP. Anti-neuraminic acid antibodies are increased, as well as induced, after grafting pig organs into humans/NHP. Non-Gal antibodies does not cause hyperacute xenorejection but can be cytotoxic and cause xenoorgan damage. If humans sensitized to HLA antigens are at a higher risk of rejecting pig xenograft compared with non-sensitized individuals is not fully clarified. Clinical trials are needed to evaluate the relevance of non-Gal antigens/antibodies and for the xenofield to advance.

Changes in antigen-specific IgG1 Fc N-glycosylation upon influenza and tetanus vaccination

Antibody effector functions have been shown to be influenced by the structure of the Fc N-glycans. Here we studied the changes in plasma or serum IgG Fc N-glycosylation upon vaccination of 10 Caucasian adults and 10 African children. Serum/plasma IgG was purified by affinity chromatography prior to and at two time points after vaccination. Fc N-glycosylation profiles of individual IgG subclasses were determined for both total IgG and affinity-purified anti-vaccine IgG using a recently developed fast nanoliquid chromatography-electrospray ionization MS (LC-ESI-MS) method. While vaccination had no effect on the glycosylation of total IgG, anti-vaccine IgG showed increased levels of galactosylation and sialylation upon active immunization. Interestingly, the number of sialic acids per galactose increased during the vaccination time course, suggesting a distinct regulation of galactosylation and sialylation. In addition we observed a decrease in the level of IgG1 bisecting N-acetylglucosamine whereas no significant changes were observed for the level of fucosylation. Our data indicate that dependent on the vaccination time point the infectious agent will encounter IgGs with different glycosylation profiles, which are expected to influence the antibody effector functions relevant in immunity.

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.

Ig knock-in mice producing anti-carbohydrate antibodies: breakthrough of B cells producing low affinity anti-self antibodies

Natural Abs specific for the carbohydrate Ag Galalpha1-3Galbeta1-4GlcNAc-R (alphaGal) play an important role in providing protective host immunity to various pathogens; yet little is known about how production of these or other anti-carbohydrate natural Abs is regulated. In this study, we describe the generation of Ig knock-in mice carrying functionally rearranged H chain and L chain variable region genes isolated from a B cell hybridoma producing alphaGal-specific IgM Ab that make it possible to examine the development of B cells producing anti-carbohydrate natural Abs in the presence or absence of alphaGal as a self-Ag. Knock-in mice on a alphaGal-deficient background spontaneously developed alphaGal-specific IgM Abs of a sufficiently high titer to mediate rejection of alphaGal expressing cardiac transplants. In the spleen of these mice, B cells expressing alphaGal-specific IgM are located in the marginal zone. In knock-in mice that express alphaGal, B cells expressing the knocked in BCR undergo negative selection via receptor editing. Interestingly, production of low affinity alphaGal-specific Ab was observed in mice that express alphaGal that carry two copies of the knocked in H chain. We suggest that in these mice, receptor editing functioned to lower the affinity for self-Ag below a threshold that would result in overt pathology, while allowing development of low affinity anti-self Abs.

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.

Natural antibody--complement dependent neutralization of bovine herpesvirus 4 by human serum

In contrast to most gammaherpesviruses, Bovine herpesvirus 4 (BoHV-4) has a broad range of host species both in vitro and in vivo. Several in vitro studies demonstrated that some human cell lines are sensitive or even permissive to BoHV-4. These observations led to the hypothesis that cross-species transmission of BoHV-4 could lead to human infections. In the present study, we investigate the sensitivity of BoHV-4 to neutralization by naïve human sera in order to determine if humans exhibit innate anti-viral activities against this virus. Our results demonstrate that human sera from naïve individuals, in contrast to the sera of naïve subjects from various animal species, neutralize BoHV-4 efficiently. A series of complementary experiments were performed to unravel the mechanism(s) of this neutralization. The data obtained in this study demonstrates that human serum neutralizes BoHV-4 in a complement dependent manner activated by natural antibodies raised against the Galalpha1-3Galbeta1-4GlcNAc-R epitope expressed by bovine cells.

Isolation of the feline alpha1,3-galactosyltransferase gene, expression in transfected human cells and its phylogenetic analysis

The enzyme alpha 1,3-galactosyltransferase (alpha1,3-GT), which catalyzes synthesis of terminal alpha-galactosyl epitopes (Gal alpha1,3Gal beta1-4GlcNAc-R), is produced in non-primate mammals, prosimians and new-world monkeys, but not in old-world monkeys, apes and humans. We cloned and sequenced a cDNA that contains the coding sequence of the feline alpha1,3-GT gene. Flow cytometric analysis demonstrated that the alpha-galactosyl epitope was expressed on the surface of a human cell line transduced with an expression vector containing this cDNA, and this alpha-galactosyl epitope expression subsided by alpha-galactosidase treatment. The open reading frame of the feline alpha1,3-GT cDNA is 1,113 base pairs in length and encodes 371 amino acids. The nucleotide sequence and its deduced amino acid sequence of the feline alpha1,3-GT gene are 88-90% and 85-87%, respectively, similar to the reported sequences of the bovine, porcine, marmoset and cebus monkey alpha1,3-GT genes, while they are 88% and 82-83%, respectively, similar to those of the orangutan and human alpha1,3-GT pseudogenes, and 81% and 77%, respectively, similar to the murine alpha1,3-GT gene. Thus, the alpha1,3-GT genes and pseudogenes of mammals are highly similar. Ratios of non-synonymous nucleotide changes among the primate pseudogenes as well as the primate genes are still higher than the ratios of non-primates, suggesting that the primate alpha1,3-GT genes tend to be divergent.

Herpes simplex virus type 1 and 2 glycoprotein C prevents complement-mediated neutralization induced by natural immunoglobulin M antibody

Glycoprotein C (gC) of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) binds complement component C3b and protects virus from complement-mediated neutralization. Differences in complement interacting domains exist between gC of HSV-1 (gC1) and HSV-2 (gC2), since the amino terminus of gC1 blocks complement C5 from binding to C3b, while gC2 fails to interfere with this activity. We previously reported that neutralization of HSV-1 gC-null virus by HSV antibody-negative human serum requires activation of C5 but not of downstream components of the classical complement pathway. In this report, we evaluated whether activation of C5 is sufficient to neutralize HSV-2 gC-null virus, or whether formation of the membrane attack complex by C6 to C9 is required for neutralization. We found that activation of the classical complement pathway up to C5 was sufficient to neutralize HSV-2 gC-null virus by HSV antibody-negative human serum. We evaluated the mechanisms by which complement activation occurred in seronegative human serum. Interestingly, natural immunoglobulin M antibodies bound to virus, which triggered activation of C1q and the classical complement pathway. HSV antibody-negative sera obtained from four individuals differed over an approximately 10-fold range in their potency for complement-mediated virus neutralization. These findings indicate that humans differ in the ability of their innate immune systems to neutralize HSV-1 or HSV-2 gC-null virus and that a critical function of gC1 and gC2 is to prevent C5 activation.

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.

The influence of natural antibody specificity on antigen immunogenicity

The natural antibody repertoire in humans, apes and Old World primates is distinct from the repertoire of all other placental mammals, and encodes antibodies specific for the carbohydrate epitope Galalpha1-3Galbeta1-4GlcNAc-R (alphaGal). Here, we examined whether conjugating antigens to the alphaGal epitope can augment their immunogenicity in alpha(1,3)galactosyltransferase knockout mice (GT0 mice) which, like humans, produce alphaGal-specific antibodies. Immunization of GT0 mice with BSA conjugated to alphaGal (alphaGal-BSA) led to significant production of anti-BSA IgG antibodies without the need for adjuvant. This response was dependent on the presence of alphaGal-reactive antibodies. Immunization of wild-type mice with alphaGal-BSA failed to induce an anti-BSA response. The presence of alphaGal-reactive antibodies also led to an increase in the T cell response to BSA following immunization with alphaGal-BSA when compared with mice that received BSA alone, resulting in an increased frequency of IFN-gamma- and IL-4-producing BSA-specific T cells. In addition, the ability to produce alphaGal-reactive antibodies enhanced the cytotoxic T lymphocyte anti-viral antigen response following vaccination with murine leukemia virus transformed cell lines that express alphaGal on their cell surface. Natural antibodies that bind alphaGal therefore play a key role in increasing the efficiency of priming to antigens decorated with alphaGal epitopes.

Generation of serum-stabilized retroviruses: Reduction of α1,3gal-epitope synthesis in a murine NIH3T3-derived packaging cell line by expression of chimeric glycosyltransferases

Retroviral vectors released from mouse-derived packaging cell lines are inactivated in human sera by naturally occurring antibodies due to the recognition of Galalpha1,3Galbeta1,4GlcNAc (alphagal-epitope) decorated surface proteins. In this study, an extensive analysis of the glycosylation potential of NIH3T3-derived PA317 packaging cells using combined MALDI/TOF-MS and HPAE-PAD reveals that 34% of the N-glycan moiety represents alphagal-epitope containing structures. Stable expression of glycosyltransferases and transport signal chimeras has been demonstrated to represent an efficient tool to alter cell- and species-specific glycosylation (Grabenhorst and Conradt, 1999. J. Biol. Chem. 274, 36107-36116). In order to reduce alphagal-epitope synthesis selected chimeric glycosyltransferases were constructed by fusing Golgi-signal sequences for compartment-specific localization with the catalytic domain of alpha2,3-sialyltransferase (ST3). Stable expression of these constructs in these cells resulted in a significant reduced alphagal-epitope synthesis, and moreover, a release of retroviral vectors showing an up to 3.5-fold increase in serum stability. Thus, our results suggest that the stably transfected cells stably transfected with chimeric glycosyltransferases compete efficiently with endogenous alpha1,3-galactosyltransferase. This approach allows favored glycodesign and we anticipate the applicability of such improved retroviral vectors produced by glycosylation engineered host cells for in vivo gene therapy and, furthermore, suggest the therapeutic benefit of this technology for xenotransplantation.

The Evolution of Alloimmunity and the Genesis of Adaptive Immunity

Infectious agents select for host immune responses that destroy infectious nonself yet maintain tolerance to self. Here we propose that retroviruses and other host-antigen associated pathogens (HAAPs) select for the genetic, biochemical, and cell biological properties of alloimmunity, also known as the histocompatibility or tissue rejection response. This hypothesis predicts the major observations regarding histocompatibility responses, including: (i) their existence in animals as diverse as sponges and humans; (ii) extreme polymorphism and balanced allele frequencies at histocompatibility loci, including the human MHC and blood group loci; (iii) the frequency dependent selection of histocompatibility alleles; (iv) the ancient age of many alloantigenic polymorphisms; (v) the high ratio of nonsynonymous mutations to synonymous mutations at histocompatibility loci; (vi) disassortative mating based on MHC alleles; (vii) the inability to explain the existence and continuing selection of histocompatibility alleles by other more conventional biochemical and genetic paradigms; and (viii) the susceptibility of HAAPs, particularly retroviruses such as HIV (human immunodeficiency virus), to histocompatibility reactions. In addition, the hypothesis that HAAPs select the forms and molecules of alloimmunity offers simple explanations for the evolution of histocompatibility systems over time, the initial selection of hypervariable immune mechanisms, and the genesis of adaptive immunity.

Natural antibodies prevent in vivo transmission of porcine islet-derived endogenous retrovirus to human cells

The discovery of porcine endogenous retroviruses (PERV) has raised concerns regarding the safety of porcine xenotransplantation. However, transmission of PERV had not been observed in humans exposed to porcine tissue. We examined whether PERV derived from porcine pancreatic islet cells could infect human cells in vivo and the role of natural antibodies in inhibiting PERV infection. In vivo infective potential of PERV was studied in SCID mice reconstituted with human peripheral blood leucocytes. Porcine islets were transplanted under the kidney capsule. PERV infection was determined by analyzing PERV gene expression in graft infiltrating lymphocytes (GIL) harvested 21 days posttransplantation. Mice were administered normal human serum prior to and 2 days posttransplantation to study their role in protection of human cells against PERV infection. PERV genes were expressed in all porcine tissues examined, including purified porcine islets. PERV expression was detected in GILs from three of five human-SCID mice. Administration of human serum blocked PERV infection in GILs in five of five human-SCID mice. These results indicate that PERV from porcine islets can infect human cells in vivo. Normal human serum blocks transmission of retrovirus in vivo, suggesting that natural xenoreactive antibodies can prevent PERV infection.

Complement regulatory proteins are incorporated into lentiviral vectors and protect particles against complement inactivation

Lentiviral vectors pseudotyped with G glycoprotein from vesicular stomatitis virus (VSV-G) and baculovirus gp64 are inactivated by human complement. The extent of vector inactivation in serum from individual donors was examined and results showed wide donor-dependent variation in complement sensitivity for VSV-G-pseudotyped lentivectors. Amphotropic envelope (Ampho)-pseudotyped vectors were generally resistant to serum from all donors, while gp64-pseudotyped vectors were inactivated but showed less donor-to-donor variation than VSV-G. In animal sera, the vectors were mostly resistant to inactivation by rodent complement, whereas canine complement caused a moderate reduction in titer. In a novel advance for the lentiviral vector system, human complement-resistant-pseudotyped lentivector particles were produced through incorporation of complement regulatory proteins (CRPs). Decay accelerating factor (DAF)/CD55 provided the most effective protection using this method, while membrane cofactor protein (MCP)/CD46 showed donor-dependent protection and CD59 provided little or no protection against complement inactivation. Unlike previous approaches using CRPs to produce complement-resistant viral vectors, CRP-containing lentivectors particles were generated for this study without engineering the CRP molecules. Thus, through overexpression of native DAF/CD55 in the viral producer cell, an easy method was developed for generation of lentiviral vectors that are almost completely resistant to inactivation by human complement. Production of complement-resistant lentiviral particles is a critical step toward use of these vectors for in vivo gene therapy applications.

Characterization of HIV-1 vectors with gammaretrovirus envelope glycoproteins produced from stable packaging cells

We have recently described a novel, stable human immunodeficiency virus type 1 (HIV-1) vector packaging system, STAR. High-titre HIV-1 vectors bearing gammaretrovirus envelopes (Env) are continuously produced from STAR cells. Here we compare the properties of such vectors, with the amphotropic murine leukaemia virus (MLV-A) Env, a modified gibbon ape leukaemia virus (GALV) Env and two modified versions of the cat endogenous retrovirus RD114 Env, produced from STAR cells, to transiently produced HIV-1 vectors with vesicular stomatitis virus G protein (VSV-G). Our results indicate that gammaretrovirus pseudotypes from STAR cells are relatively stable at 37 degrees C and are resistant to inactivation by freeze/thaw cycling or incubation with human sera. HIV-1(VSV-G) was, however, sensitive to freeze/thaw when harvested in serum-free media and was readily inactivated in human sera. Furthermore, the titre of 'gamma-retrovirus' pseudotypes, but not HIV-1(VSV-G), could be increased by the use of a combination of polybrene and spinoculation. All pseudotypes could be efficiently concentrated, but soluble gammaretrovirus Env could act as an inhibitor of infection.

Optimal modes and targets of gene therapy in transplantation

Genetic modification strategies have the potential to improve outcome following cell/organ transplantation. A unique opportunity in transplantation is that gene therapies need not be restricted to in vivo approaches and that ex vivo genetic modification of cell and/or organs can be of value. Improvements in vector design, production, and delivery should enhance transfection efficiency and optimize gene expression. Herein, we discuss potential modes of gene therapy, focusing on viral, liposome, or naked DNA-based systems for gene delivery. We suggest gene therapy targets taking into consideration the essential constituents of anti-allograft repertory. In addition to strategies that may have salutary effects in mitigating the threat of acute rejection, we suggest genetic strategies for minimizing ischemia/reperfusion injury as well as for the perennial problem of progressive functional loss of the transplanted organ. Data from pre-clinical transplant models support the idea that gene therapy may improve allograft function and survival. We are optimistic that gene therapy will be of clinical value in the near future in the management of recipients of allografts; we believe that genetic strategies would be essential for successful breaching of the formidable challenge of xenotransplantation.

N-glycan structures of pigeon IgG: a major serum glycoprotein containing Galalpha1-4 Gal termini

We had shown previously that all major glycoproteins of pigeon egg white contain Galalpha1-4Gal epitopes (Suzuki, N., Khoo, K. H., Chen, H. C., Johnson, J. R., and Lee, Y. C. (2001) J. Biol. Chem. 276, 23221-23229). We now report that Galalpha1-4Gal-bearing glycoproteins are also present in pigeon serum, lymphocytes, and liver, as probed by Western blot with Griffonia simplicifolia-I lectin (specific for terminal alpha-Gal) and anti-P1 (specific for Galalpha1-4Galbeta1-4GlcNAcbeta1-) monoclonal antibody. One of the major glycoproteins from pigeon plasma was identified as IgG (also known as IgY), which has Galalpha1-4Gal in its heavy chains. High pressure liquid chromatography, mass spectrometric (MS), and MS/MS analyses revealed that N-glycans of pigeon serum IgG included (i) high mannose-type (33.3%), (ii) disialylated biantennary complex-type (19.2%), and (iii) alpha-galactosylated complex-type N-glycans (47.5%). Bi- and tri-antennary oligosaccharides with bisecting GlcNAc and alpha1-6 Fuc on the Asn-linked GlcNAc were abundant among N-glycans possessing terminal Galalpha1-4Gal sequences. Moreover, MS/MS analysis identified Galalpha1-4Galbeta1-4Galbeta1-4GlcNAc branch terminals, which are not found in pigeon egg white glycoproteins. An additional interesting aspect is that about two-thirds of high mannose-type N-glycans from pigeon IgG were monoglucosylated. Comparison of the N-glycan structures with chicken and quail IgG indicated that the presence of high mannose-type oligosaccharides may be a characteristic of these avian IgG.

Specific history of heterologous virus infections determines anti-viral immunity and immunopathology in the lung

Having previously shown that previous immunity to one virus can influence the host response to a subsequent unrelated virus, we questioned whether the outcome to a given virus infection would be altered in similar or different ways by previous immunity to different viruses, and whether immunity to a given virus would have similar effects on all subsequent infections. In mouse models of respiratory viral infections, immunity to lymphocytic choriomeningitis virus (LCMV), murine cytomegalovirus (MCMV), or influenza A virus enhanced both Th1-type cytokine responses and viral clearance in the lung on vaccinia virus infection. A common pathological feature was the presence of chronic mononuclear infiltrates instead of the acute polymorphonuclear response seen in the infected nonimmune mice, but some pathologies such as enhanced bronchus-associated lymphoid tissue and bronchiolitis obliterans were unique for the immunizing virus, LCMV. Immunity to influenza virus influenced subsequent infections diversely, inhibiting vaccinia virus but enhancing LCMV and MCMV titers and completely altering cytokine profiles. Influenza virus immunity enhanced the mild mononuclear responses usually observed during acute infections with MCMV or LCMV in nonimmune mice, but unique features such as enhanced bronchiolization and mononuclear consolidation occurred during MCMV infection of influenza virus-immune mice. Heterologous immunity induced two patterns of disease outcome dependent on the specific virus infection sequence: improved, if the acute response switched from a neutrophilic to a lymphocytic response or worsened, if it switched from a mild to a severe lymphocytic response. Heterologous immunity thus occurs between many viruses, resulting in altered protective immunity and lung immunopathology, and this is influenced by the specific virus infection sequence.

Xenoreactive anti-Galalpha(1,3)Gal antibodies prevent porcine endogenous retrovirus infection of human in vivo

The discovery of porcine endogenous retroviruses (PERV) has raised concerns regarding the safety of pig to human xenotransplantation. In this study, we examined PERV infection of human cells in vivo. Furthermore, we examined the effect of human xenoreactive natural antibody on in vivo PERV infection. Human peripheral blood leukocyte reconstituted severe combined immunodeficiency mice were transplanted with porcine aortic endothelial cells (PAEC). PERV gene expression was readily detected in human leukocytes after transplantation. In contrast, human leukocytes harvested from mice treated with human serum or anti-Galalpha(1,3)Gal antibody prevented PERV infection in 6 of 8 mice. These results provide the first evidence that PERV can infect human cells in vivo and that natural xenoreactive antibody can prevent this infection.