Establishment of the reversible peptide-major histocompatibility complex (pMHC) class I Histamer technology: tool for visualization and selection of functionally active antigen-specific CD8(+) T lymphocytes

Rapid and sustained T cell-based immunotherapy against invasive fungal disease via a combined two step procedure

Introduction

Aspergillus fumigatus (Asp) infections constitute a major cause of morbidity and mortality in patients following allogeneic hematopoietic stem cell transplantation (HSCT). In the context of insufficient host immunity, antifungal drugs show only limited efficacy. Faster and increased T-cell reconstitution correlated with a favorable outcome and a cell-based therapy approach strongly indicated successful clearance of fungal infections. Nevertheless, complex and cost- or time-intensive protocols hampered their implementation into clinical application.

Methods

To facilitate the clinical-scale manufacturing process of Aspergillus fumigatus-specific T cells (ATCs) and to enable immediate (within 24 hours) and sustained (12 days later) treatment of patients with invasive aspergillosis (IA), we adapted and combined two complementary good manufacturing practice (GMP)-compliant approaches, i) the direct magnetic enrichment of Interferon-gamma (IFN-γ) secreting ATCs using the small-scale Cytokine Secretion Assay (CSA) and ii) a short-term in vitro T-cell culture expansion (STE), respectively. We further compared stimulation with two standardized and commercially available products: Asp-lysate and a pool of overlapping peptides derived from different Asp-proteins (PepMix).

Results

For the fast CSA-based approach we detected IFN-γ⁺ ATCs after Asp-lysate- as well as PepMix-stimulation but with a significantly higher enrichment efficiency for stimulation with the Asp-lysate when compared to the PepMix. In contrast, the STE approach resulted in comparably high ATC expansion rates by using Asp-lysate or PepMix. Independent of the stimulus, predominantly CD4⁺ helper T cells with a central-memory phenotype were expanded while CD8⁺ T cells mainly showed an effector-memory phenotype. ATCs were highly functional and cytotoxic as determined by secretion of granzyme-B and IFN-γ.

Discussion

For patients with IA, the immediate adoptive transfer of IFN-γ⁺ ATCs followed by the administration of short-term in vitro expanded ATCs from the same donor, might be a promising therapeutic option to improve the clinical outcome.

Antigen-Specific T Cells and SARS-CoV-2 Infection: Current Approaches and Future Possibilities

COVID-19, a significant global health threat, appears to be an immune-related disease. Failure of effective immune responses in initial stages of infection may contribute to development of cytokine storm and systemic inflammation with organ damage, leading to poor clinical outcomes. Disease severity and the emergence of new SARS-CoV-2 variants highlight the need for new preventative and therapeutic strategies to protect the immunocompromised population. Available data indicate that these people may benefit from adoptive transfer of allogeneic SARS-CoV-2-specific T cells isolated from convalescent individuals. This review first provides an insight into the mechanism of cytokine storm development, as it is directly related to the exhaustion of T cell population, essential for viral clearance and long-term antiviral immunity. Next, we describe virus-specific T lymphocytes as a promising and efficient approach for the treatment and prevention of severe COVID-19. Furthermore, other potential cell-based therapies, including natural killer cells, regulatory T cells and mesenchymal stem cells are mentioned. Additionally, we discuss fast and effective ways of producing clinical-grade antigen-specific T cells which can be cryopreserved and serve as an effective "off-the-shelf" approach for rapid treatment of SARS-CoV-2 infection in case of sudden patient deterioration.

Is It Feasible to Use CMV-Specific T-Cell Adoptive Transfer as Treatment Against Infection in SOT Recipients?

During the last decade, many studies have demonstrated the role of CMV specific T-cell immune response on controlling CMV replication and dissemination. In fact, it is well established that transplanted patients lacking CMV-specific T-cell immunity have an increased occurrence of CMV replication episodes and CMV-related complications. In this context, the use of adoptive transfer of CMV-specific T-cells has been widely investigated and applied to Hematopoietic Stem Cell Transplant patients and may be useful as a therapeutic alternative, to reconstitute the CMV specific T-cell response and to control CMV viremia in patients receiving a transplantation. However, only few authors have explored the use of T-cell adoptive transfer in SOT recipients. We propose a novel review in which we provide an overview of the impact of using CMV-specific T-cell adoptive transfer on the control of CMV infection in SOT recipients, the different approaches to stimulate, isolate and expand CMV-specific T-cells developed over the years and a discussion of the possible use of CMV adoptive cellular therapy in this SOT population. Given the timeliness and importance of this topic, we believe that such an analysis will provide important insights into CMV infection and its treatment/prevention.

Virus-Specific T Cells for the Immunocompromised Patient

While progress has been made in the treatment of both hematologic cancers and solid tumors, chemorefractory or relapsed disease often portends a dismal prognosis, and salvage chemotherapy or radiation expose patients to intolerable toxicities and may not be effective. Hematopoietic stem cell transplant offers the promise of cure for many patients, and while mismatched, unrelated or haploidentical donors are increasingly available, the recipients are at higher risk of severe immunosuppression and immune dysregulation due to graft versus host disease. Viral infections remain a primary cause of severe morbidity and mortality in this patient population. Again, many therapeutic options for viral disease are toxic, may be ineffective or generate resistance, or fail to convey long-term protection. Adoptive cell therapy with virus-specific T cells (VSTs) is a targeted therapy that is efficacious and has minimal toxicity in immunocompromised patients with CMV and EBV infections in particular. Products have since been generated specific for multiple viral antigens (multi-VST), which are not only effective but also confer protection in 70–90% of recipients when used as prophylaxis. Notably, these products can be generated from either virus-naive or virus-experienced autologous or allogeneic sources, including partially matched HLA-matched third-party donors. Obstacles to effective VST treatment are donor availability and product generation time. Banking of third-party VST is an attractive way to overcome these constraints and provide products on an as-needed basis. Other developments include epitope discovery to broaden the number of viral antigens targets in a single product, the optimization of VST generation from naive donor sources, and the modification of VSTs to enhance persistence and efficacy in vivo.

β2-microglobulin gene duplication in cetartiodactyla remains intact only in pigs and possibly confers selective advantage to the species

Several β2-microglobulin (B2M) -bound protein complexes undertake key roles in various immune system pathways, including the neonatal Fc receptor (FcRn), cluster of differentiation 1 (CD1) protein, non-classical major histocompatibility complex (MHC), and well-known MHC class I molecules. Therefore, the duplication of B2M may lead to an increase in the biological competence of organisms to the environment. Based on the pig genome assembly SSC10.2, a segmental duplication of ~45.5 kb, encoding the entire B2M protein, was identified in pig chromosome 1. Through experimental validation, we confirmed the functional duplication of the B2M gene with a completely identical coding sequence between two copies in pigs. Considering the importance of B2M in the immune system, we performed the phylogenetic analysis of B2M duplication in ten mammalian species, confirming the presence of B2M duplication in cetartioldactyls, like cattle, sheep, goats, pigs and whales, but non-cetartiodactyl species, like mice, cats, dogs, horses, and humans. The density of long interspersed nuclear element (LINE) at the edges of duplicated blocks (39 to 66%) was found to be 2 to 3-fold higher than the average (20.12%) of the pig genome, suggesting its role in the duplication event. The B2M mRNA expression level in pigs was 12.71 and 7.57 times (2-ΔΔCt values) higher than humans and mice, respectively. However, we were unable to experimentally demonstrate the difference in the level of B2M protein because species specific anti-B2M antibodies are not available. We reported, for the first time, the functional duplication of the B2M gene in animals. The identification of partially remaining duplicated B2M sequences in the genomes of only cetartiodactyls indicates that the event was lineage specific. B2M duplication could be beneficial to the immune system of pigs by increasing the availability of MHC class I light chain protein, B2M, to complex with the proteins encoded by the relatively large number of MHC class I heavy chain genes in pigs. Further studies are necessary to address the biological meaning of increased expression of B2M.

Preservation of Antigen-Specific Functions of αβ T Cells and B Cells Removed from Hematopoietic Stem Cell Transplants Suggests Their Use As an Alternative Cell Source for Advanced Manipulation and Adoptive Immunotherapy

Hematopoietic stem cell transplantation is standard therapy for numerous hematological diseases. The use of haploidentical donors, sharing half of the HLA alleles with the recipient, has facilitated the use of this procedure as patients can rely on availability of a haploidentical donor within their family. Since HLA disparity increases the risk of graft-versus-host disease, T-cell depletion has been used to remove alloreactive lymphocytes from the graft. Selective removal of αβ T cells, which encompass the alloreactive repertoire, combined with removal of B cells to prevent EBV-related lymphoproliferative disease, proved safe and effective in clinical studies. Depleted αβ T cells and B cells are generally discarded as by-products. Considering the possible use of donor T cells for donor lymphocyte infusions or for generation of pathogen-specific T cells as mediators of graft-versus-infection effect, we tested whether cells in the discarded fractions were functionally intact. Response to alloantigens and to viral antigens comparable to that of unmanipulated cells indicated a functional integrity of αβ T cells, in spite of the manipulation used for their depletion. Furthermore, B cells proved to be efficient antigen-presenting cells, indicating that antigen uptake, processing, and presentation were fully preserved. Therefore, we propose that separated αβ T lymphocytes could be employed for obtaining pathogen-specific T cells, applying available methods for positive selection, which eventually leads to indirect allodepletion. In addition, these functional T cells could undergo additional manipulation, such as direct allodepletion or genetic modification.

Approaches for monitoring of non virus-specific and virus-specific T-cell response in solid organ transplantation and their clinical applications

Opportunistic viral infections are still a major complication following solid organ transplantation. Immune monitoring may allow the identification of patients at risk of infection and, eventually, the modulation of immunosuppressive strategies. Immune monitoring can be performed using virus-specific and non virus-specific assays. This article describes and summarizes the pros and cons of the different technical approaches. Among the assays based on non virus-specific antigens, the enumeration of T-cell subsets, the quantification of cytokines and chemokines and the quantification of intracellular adenosine triphosphate following mitogen stimulation are described and their clinical applications to determine the risk for viral infection are discussed. In addition, current specific methods available for monitoring viral-specific T-cell responses are summarized, such as peptide-MHC multimer staining, intracellular cytokine staining, enzyme-linked immunospot and virus-specific IFN-γ ELISA assays, and their clinical applications to determine the individual risk for opportunistic viral infections with human cytomegalovirus, Epstein-Barr virus and polyoma BK virus are discussed. The standardization of the procedure, the choice of the antigen(s) and the criteria to define cut-off values for positive responses are needed for some of these approaches before their implementation in the clinic. Nevertheless, immune monitoring combined with virological monitoring in transplant recipients is increasingly regarded as a helpful tool to identify patients at risk of infection as well as to assess treatment efficacy.

Selection of adenovirus-specific and Epstein-Barr virus-specific T cells with major histocompatibility class I streptamers under Good Manufacturing Practice (GMP)-compliant conditions

BACKGROUND AIMS

Despite antiviral drug therapies, human adenovirus (HAdV), cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infections still contribute substantially to transplant-related death of patients after hematopoietic stem cell transplantation. Earlier clinical studies demonstrated successful adoptive transfer of magnetically selected CMV-specific T cells via removable, and thus Good Manufacturing Practice-compliant, major histocompatibility class I streptamers. Thus, the primary focus of the present study was the selection of HAdV-streptamer+ T cells, although in three experiments, EBV-streptamer+ T cells were also selected.

METHODS

Cells from leukaphereses of healthy donors were prepared in large (1-6 × 10(9)) and small (25 × 10(6)) cell batches. Whereas the larger batch was directly labeled with streptamers to select HAdV- and/or EBV-specific T cells (large-scale), the smaller batch was used to generate in vitro virus-specific T-cell lines before streptamer labeling for streptamer selection (small-scale). Isolation of HAdV- and/or EBV-specific T cells was performed with the use of the CliniMACS device.

RESULTS

The purity of HAdV- and EBV-streptamer+ T cells among CD3+ cells, obtained from large-scale selection, was up to 6.7% and 44%, respectively. If HAdV- and EBV-streptamers were applied simultaneously, the purity of antigen-specific T cells reached up to 50.7%. A further increase in purity reaching up to 98% was achieved by small-scale selection of HAdV-specific T cells. All final products fulfilled the microbiological and chemical release criteria. Interferon-γ-response indicating functional activity was seen in 6 of 9 HAdV and 2 of 3 EBV large-scale selections and in 2 of 3 HAdV small-scale selections.

CONCLUSIONS

HAdV-streptamers were shown to be clinically feasible for few patients after the large-scale approach but for larger patient numbers if combined with EBV-streptamers or after the small-scale approach.

Adenovirus infections in immunocompetent and immunocompromised patients

Human adenoviruses (HAdVs) are an important cause of infections in both immunocompetent and immunocompromised individuals, and they continue to provide clinical challenges pertaining to diagnostics and treatment. The growing number of HAdV types identified by genomic analysis, as well as the improved understanding of the sites of viral persistence and reactivation, requires continuous adaptions of diagnostic approaches to facilitate timely detection and monitoring of HAdV infections. In view of the clinical relevance of life-threatening HAdV diseases in the immunocompromised setting, there is an urgent need for highly effective treatment modalities lacking major side effects. The present review summarizes the recent progress in the understanding and management of HAdV infections.

Multimer monitoring of CMV-specific T cells in research and in clinical applications

Multimer monitoring has become a standard technique for detection of antigen-specific T cells. The term "multimer" refers to a group of reagents based on the multimerisation of molecules in order to raise avidity and thus stabilize binding to their ligand. Multimers for detection of antigen-specific T-cell responses are based on major histocompatibility complex class I peptide complexes. Multimer staining enables fast and direct visualization of antigen-specific T cells; thus, it is widely applied to assess antiviral immunity, e.g., monitor patients in vaccination trials or confirm purity of cell products for adoptive transfer. Assessment of T-cell immunity against persistent pathogens like cytomegalovirus (CMV) is of major importance in immunosuppressed patients. Recent advancements of multimers facilitate reversible labeling and allow isolation of epitope-specific T cells for adoptive transfer. Here, we give an overview on the different multimers and their applications, with an emphasis on CMV-specific T-cell responses.

CMV-, EBV- and ADV-specific T cell immunity: screening and monitoring of potential third-party donors to improve post-transplantation outcome

Adoptive immunotherapy with virus-specific T lymphocytes can efficiently reconstitute antiviral immunity against cytomegalovirus (CMV), Epstein-Barr virus (EBV), and adenovirus (ADV) without causing acute toxicity or increasing the risk of graft-versus-host disease. To gain insight into antiviral T cell repertoires and to identify the most efficient antigens for immunotherapy, the frequencies of CMV-, EBV- and ADV-specific T cells in 204 HLA-typed healthy donors were assessed using viral peptides and peptide pools. Confirmatory testing for CMV serology by Western blot technique revealed 19 of 143 (13%) false-positive results. We observed highly significant individual and overall differences in T cell frequencies against CMV, EBV, and ADV antigens, whereas antigen-specific T cells were detected in 100% of CMV- seropositive donors, 73% of EBV- seropositive donors, and 73% of ADV-seropositive donors. At least 124 (61%) potential T cell donors were identified for each virus. Among the tested antigens, frequencies for CMVpp65 and EBVBZLF1 peptide pools were highest. Short-term in vitro peptide stimulation revealed that a donor response to a certain ADV- and EBV-derived peptide may not be determined without prior stimulation. A modified granzyme B ELISpot was used to detect T cell specificity and alloreactivity. Treatment with allogeneic virus-specific cytotoxic T lymphocytes from seropositive third-party donors may be a feasible therapeutic option for infections following cord-blood stem cell transplantation or hematopoietic stem cell transplantation from virus-seronegative donors.

Adoptive T-cell immunotherapy from third-party donors: characterization of donors and set up of a T-cell donor registry

Infection with and reactivation of human cytomegalovirus (CMV), Epstein-Barr virus (EBV), and adenovirus (ADV) are frequent and severe complications in immunocompromised recipients after hematopoietic stem cell transplantation (HSCT) or solid organ transplantation (SOT). These serious adverse events are associated with significant morbidity and mortality. Donor lymphocyte infusions (DLIs) are often used to treat both viral infections and leukemia relapses after transplantation but are associated with potentially life-threatening graft-versus-host disease (GvHD). Adoptive immunotherapy with virus-specific cytotoxic effector T cells (CTLs) derived from seropositive donors can rapidly reconstitute antiviral immunity after HSCT and organ transplantation. Therefore, it can effectively prevent the clinical manifestation of these viruses with no significant acute toxicity or increased risk of GvHD. In conditions, where patients receiving an allogeneic cord blood (CB) transplant or a transplant from a virus-seronegative donor and since donor blood is generally not available for solid organ recipients, allogeneic third party T-cell donors would offer an alternative option. Recent studies showed that during granulocyte colony-stimulating factor (G-CSF) mobilization, the functional activity of antiviral memory T cells is impaired for a long period. This finding suggests that even stem cell donors may not be the best source of T cells. Under these circumstances, partially human leukocyte antigen (HLA)-matched virus-specific CTLs from healthy seropositive individuals may be a promising option. Therefore, frequency assessments of virus-specific memory T cells in HLA-typed healthy donors as well as in HSCT/SOT donors using a high throughput T-cell assay were performed over a period of 4 years at Hannover Medical School. This chapter will address the relevance and potential of a third-party T-cell donor registry and will discuss its clinical implication for adoptive T-cell immunotherapy.