Antigen-armed antibodies targeting B lymphoma cells effectively activate antigen-specific CD4+ T cells

Comparison of methods generating antibody-epitope conjugates for targeting cancer with virus-specific T cells

Therapeutic antibody-epitope conjugates (AECs) are promising new modalities to deliver immunogenic epitopes and redirect virus-specific T-cell activity to cancer cells. Nevertheless, many aspects of these antibody conjugates require optimization to increase their efficacy. Here we evaluated different strategies to conjugate an EBV epitope (YVL/A2) preceded by a protease cleavage site to the antibodies cetuximab and trastuzumab. Three approaches were taken: chemical conjugation (i.e. a thiol-maleimide reaction) to reduced cysteine side chains, heavy chain C-terminal enzymatic conjugation using sortase A, and genetic fusions, to the heavy chain (HC) C-terminus. All three conjugates were capable of T-cell activation and target-cell killing via proteolytic release of the EBV epitope and expression of the antibody target was a requirement for T-cell activation. Moreover, AECs generated with a second immunogenic epitope derived from CMV (NLV/A2) were able to deliver and redirect CMV specific T-cells, in which the amino sequence of the attached peptide appeared to influence the efficiency of epitope delivery. Therefore, screening of multiple protease cleavage sites and epitopes attached to the antibody is necessary. Taken together, our data demonstrated that multiple AECs could sensitize cancer cells to virus-specific T cells.

T cell-mediated immunity during Epstein-Barr virus infections in children

Epstein-Barr virus (EBV) infection is extremely common worldwide, with approximately 90% of adults testing positive for EBV antibodies. Human are susceptible to EBV infection, and primary EBV infection typically occurs early in life. EBV infection can cause infectious mononucleosis (IM) as well as some severe non-neoplastic diseases, such as chronic active EBV infection (CAEBV) and EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH), which can have a heavy disease burden. After primary EBV infection, individuals develop robust EBV-specific T cell immune responses, with EBV-specific CD8⁺ and part of CD4⁺ T cells functioning as cytotoxic T cells, defending against virus. Different proteins expressed during EBV's lytic replication and latent proliferation can cause varying degrees of cellular immune responses. Strong T cell immunity plays a key role in controlling infection by decreasing viral load and eliminating infected cells. However, the virus persists as latent infection in EBV healthy carriers even with robust T cell immune response. When reactivated, it undergoes lytic replication and then transmits virions to a new host. Currently, the relationship between the pathogenesis of lymphoproliferative diseases and the adaptive immune system is still not fully clarified and needs to be explored in the future. Investigating the T cell immune responses evoked by EBV and utilizing this knowledge to design promising prophylactic vaccines are urgent issues for future research due to the importance of T cell immunity.

Quantum leap of monoclonal antibody (mAb) discovery and development in the COVID-19 era

In recent years the global market for monoclonal antibodies (mAbs) became a multi-billion-dollar business. This success is mainly driven by treatments in the oncology and autoimmune space. Instead, development of effective mAbs against infectious diseases has been lagging behind. For years the high production cost and limited efficacy have blocked broader application of mAbs in the infectious disease space, which instead has been dominated for almost a century by effective and cheap antibiotics and vaccines. Only very few mAbs against RSV, anthrax, Clostridium difficile or rabies have reached the market. This is about to change. The development of urgently needed and highly effective mAbs as preventive and therapeutic treatments against a variety of pathogens is gaining traction. Vast advances in mAb isolation, engineering and production have entirely shifted the cost-efficacy balance. MAbs against devastating diseases like Ebola, HIV and other complex pathogens are now within reach. This trend is further accelerated by ongoing or imminent health crises like COVID-19 and antimicrobial resistance (AMR), where antibodies could be the last resort. In this review we will retrace the history of antibodies from the times of serum therapy to modern mAbs and lay out how the current run for effective treatments against COVID-19 will lead to a quantum leap in scientific, technological and health care system innovation around mAb treatments for infectious diseases.

Sensitization of Tumors for Attack by Virus-Specific CD8+ T-Cells Through Antibody-Mediated Delivery of Immunogenic T-Cell Epitopes

Anti-tumor immunity is limited by a number of factors including the lack of fully activated T-cells, insufficient antigenic stimulation and the immune-suppressive tumor microenvironment. We addressed these hurdles by developing a novel class of immunoconjugates, Antibody-Targeted Pathogen-derived Peptides (ATPPs), which were designed to efficiently deliver viral T-cell epitopes to tumors with the aim of redirecting virus-specific memory T-cells against the tumor. ATPPs were generated through covalent binding of mature MHC class I peptides to antibodies specific for cell surface-expressed tumor antigens that mediate immunoconjugate internalization. By means of a cleavable linker, the peptides are released in the endosomal compartment, from which they are loaded into MHC class I without the need for further processing. Pulsing of tumor cells with ATPPs was found to sensitize these for recognition by virus-specific CD8+ T-cells with much greater efficiency than exogenous loading with free peptides. Systemic injection of ATPPs into tumor-bearing mice enhanced the recruitment of virus-specific T-cells into the tumor and, when combined with immune checkpoint blockade, suppressed tumor growth. Our data thereby demonstrate the potential of ATPPs as a means of kick-starting the immune response against “cold” tumors and increasing the efficacy of checkpoint inhibitors.

Progress in EBV Vaccines

The Epstein-Barr virus (EBV) is a ubiquitous pathogen that imparts a significant burden of disease on the human population. EBV is the primary cause of infectious mononucleosis and is etiologically linked to the development of numerous malignancies. In recent years, evidence has also been amassed that strongly implicate EBV in the development of several autoimmune diseases, including multiple sclerosis. Prophylactic and therapeutic vaccination has been touted as a possible means of preventing EBV infection and controlling EBV-associated diseases. However, despite several decades of research, no licensed EBV vaccine is available. The majority of EBV vaccination studies over the last two decades have focused on the major envelope protein gp350, culminating in a phase II clinical trial that showed soluble gp350 reduced the incidence of IM, although it was unable to protect against EBV infection. Recently, novel vaccine candidates with increased structural complexity and antigenic content have been developed. The ability of next generation vaccines to safeguard against B-cell and epithelial cell infection, as well as to target infected cells during all phases of infection, is likely to decrease the negative impact of EBV infection on the human population.

Immunogenic particles with a broad antigenic spectrum stimulate cytolytic T cells and offer increased protection against EBV infection ex vivo and in mice

The ubiquitous Epstein-Barr virus (EBV) is the primary cause of infectious mononucleosis and is etiologically linked to the development of several malignancies and autoimmune diseases. EBV has a multifaceted life cycle that comprises virus lytic replication and latency programs. Considering EBV infection holistically, we rationalized that prophylactic EBV vaccines should ideally prime the immune system against lytic and latent proteins. To this end, we generated highly immunogenic particles that contain antigens from both these cycles. In addition to stimulating EBV-specific T cells that recognize lytic or latent proteins, we show that the immunogenic particles enable the ex vivo expansion of cytolytic EBV-specific T cells that efficiently control EBV-infected B cells, preventing their outgrowth. Lastly, we show that immunogenic particles containing the latent protein EBNA1 afford significant protection against wild-type EBV in a humanized mouse model. Vaccines that include antigens which predominate throughout the EBV life cycle are likely to enhance their ability to protect against EBV infection.

Human herpesviruses are tremendously successful pathogens that establish lifelong infection in a substantial proportion of the population. The oncogenic γ-herpesvirus EBV, like other herpesviruses, expresses a plethora of open-reading frames throughout its multifaceted life cycle. We have developed a prophylactic vaccine candidate in the form of immunogenic particles that contain several EBV antigens. This is in stark contrast to the vast majority of EBV vaccines candidates that contain only one or two EBV antigens. Our immunogenic particles were shown capable of stimulating several EBV-specific T-cell clones in vitro. The immunogenic particles were also capable of expanding cytolytic EBV-specific T cells ex vivo and provided a protective benefit in vivo when used as a prophylactic vaccine.

Antibodies conjugated with viral antigens elicit a cytotoxic T cell response against primary CLL ex vivo

Chronic lymphocytic leukemia (CLL) is the most frequent B cell malignancy in Caucasian adults. The therapeutic armamentarium against this incurable disease has recently seen a tremendous expansion with the introduction of specific pathway inhibitors and innovative immunotherapy. However, none of these approaches is curative and devoid of side effects. We have used B-cell-specific antibodies conjugated with antigens (AgAbs) of the Epstein-Barr virus (EBV) to efficiently expand memory CD4⁺ cytotoxic T lymphocytes (CTLs) that recognized viral epitopes in 12 treatment-naive patients with CLL. The AgAbs carried fragments from the EBNA3C EBV protein that is recognized by the large majority of the population. All CLL cells pulsed with EBNA3C-AgAbs elicited EBV-specific T cell responses, although the intensity varied across the patient collective. Interestingly, a large proportion of the EBV-specific CD4⁺ T cells expressed granzyme B (GrB), perforin, and CD107a, and killed CLL cells loaded with EBV antigens with high efficiency in the large majority of patients. The encouraging results from this preclinical ex vivo study suggest that AgAbs have the potential to redirect immune responses toward CLL cells in a high percentage of patients in vivo and warrant the inception of clinical trials.