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

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.

Virotherapy in Germany-Recent Activities in Virus Engineering, Preclinical Development, and Clinical Studies

Virotherapy research involves the development, exploration, and application of oncolytic viruses that combine direct killing of cancer cells by viral infection, replication, and spread (oncolysis) with indirect killing by induction of anti-tumor immune responses. Oncolytic viruses can also be engineered to genetically deliver therapeutic proteins for direct or indirect cancer cell killing. In this review—as part of the special edition on “State-of-the-Art Viral Vector Gene Therapy in Germany”—the German community of virotherapists provides an overview of their recent research activities that cover endeavors from screening and engineering viruses as oncolytic cancer therapeutics to their clinical translation in investigator-initiated and sponsored multi-center trials. Preclinical research explores multiple viral platforms, including new isolates, serotypes, or fitness mutants, and pursues unique approaches to engineer them towards increased safety, shielded or targeted delivery, selective or enhanced replication, improved immune activation, delivery of therapeutic proteins or RNA, and redirecting antiviral immunity for cancer cell killing. Moreover, several oncolytic virus-based combination therapies are under investigation. Clinical trials in Germany explore the safety and potency of virotherapeutics based on parvo-, vaccinia, herpes, measles, reo-, adeno-, vesicular stomatitis, and coxsackie viruses, including viruses encoding therapeutic proteins or combinations with immune checkpoint inhibitors. These research advances represent exciting vantage points for future endeavors of the German virotherapy community collectively aimed at the implementation of effective virotherapeutics in clinical oncology.

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.

Retargeting adenoviruses for therapeutic applications and vaccines

Adenoviruses (Ads) are robust vectors for therapeutic applications and vaccines, but their use can be limited by differences in their in vitro and in vivo pharmacologies. This review emphasizes that there is not just one Ad, but a whole virome of diverse viruses that can be used as therapeutics. It discusses that true vector targeting involves not only retargeting viruses, but importantly also detargeting the viruses from off-target cells.