A PBMC-Based System to Assess Human T Cell Responses to Influenza Vaccine Candidates In Vitro

Induction of an immune response by a nonreplicating adenoviruses-based formulation versus a commercial pseudo-SARS-CoV-2 vaccine

Screening for effective vaccines requires broad studies on their immunogenicity in vitro and ex vivo . We used a PBMC-based system to assess changes in CD4+ T cells, CD8+ T cells, and CD19+ B cells upon stimulation with different combinations of antigens and adjuvants. We studied the activation mechanism using flow cytometry and two different adenoviral adjuvants characterized by the presence or absence of costimulatory ligands for the ICOS and CD40 receptors. Our studies identified the cellular targets and molecular mechanisms driving ongoing switched-antibody diversification. Class-switched memory B cells were the main precursor cells (95.03% ± 0.38 vs. mock 82.33% ± 0.45, P < 0.05) after treatment with the immunogenic formula: adenovirus armed (MIX1) or not (MIX2) with the ICOS and CD40 ligand, the recombinant receptor binding domain (rRBD), and Lentifect™ SARS-CoV-2 spike-pseudotyped lentivirus (GeneCopoeia, USA). Bcell class-switching towards the IgG+IgM+- positive phenotypes was noted (~50-fold increase vs. mock, P < 0.05). A significant increase was observed in the CD8+TEM population of the MIX1 (~2-fold, P < 0.05) and MIX2 (~4.7-fold, P < 0.05) treated samples. CD8+TEMRA increased when PBMCs were treated with MIX2 (9.63% ± 0.90, P < 0.05) vs. mock (2.63% ± 1.96). Class-switched memory B cells were the dominant antigen-specific cells in primary reactions. We indicated a correlation between the protection offered by vaccine regimens and their ability to induce high frequencies of multifunctional T cells.

A nonadjuvanted HLA-restricted peptide vaccine induced both T and B cell immunity against SARS-CoV-2 spike protein

During COVID-19 pandemic, cases of postvaccination infections and restored SARS-CoV-2 virus have increased after full vaccination, which might be contributed to by immune surveillance escape or virus rebound. Here, artificial linear 9-mer human leucocyte antigen (HLA)-restricted UC peptides were designed based on the well-conserved S2 region of the SARS-CoV-2 spike protein regardless of rapid mutation and glycosylation hindrance. The UC peptides were characterized for its effect on immune molecules and cells by HLA-tetramer refolding assay for HLA-binding ability, by HLA-tetramer specific T cell assay for engaged cytotoxic T lymphocytes (CTLs) involvement, by HLA-dextramer T cell assay for B cell activation, by intracellular cytokine release assay for polarization of immune response, Th1 or Th2. The specific lysis activity assay of T cells was performed for direct activation of cytotoxic T lymphocytes by UC peptides. Mice were immunized for immunogenicity of UC peptides in vivo and immunized sera was assay for complement cytotoxicity assay. Results appeared that through the engagement of UC peptides and immune molecules, HLA-I and II, that CTLs elicited cytotoxic activity by recognizing SARS-CoV-2 spike-bearing cells and preferably secreting Th1 cytokines. The UC peptides also showed immunogenicity and generated a specific antibody in mice by both intramuscular injection and oral delivery without adjuvant formulation. In conclusion, a T-cell vaccine could provide long-lasting protection against SARS-CoV-2 either during reinfection or during SARS-CoV-2 rebound. Due to its ability to eradicate SARS-CoV-2 virus-infected cells, a COVID-19 T-cell vaccine might provide a solution to lower COVID-19 severity and long COVID-19.

Viral vector-based therapeutic HPV vaccines

Replication-defective viral vector vaccines have several advantages over conventional subunit vaccines, including potent antibody responses, cellular responses critical for eliminating pathogen-infected cells, and the induction of highly immunogenic and durable immune responses without adjuvants. The Human papillomavirus (HPV), a microorganism with over 200 genotypes, plays a crucial role in inducing human tumors, with the majority of HPV-related malignancies expressing HPV proteins. Tumors associated with HPV infection, most of which result from HPV16 infection, include those affecting the cervix, anus, vagina, penis, vulva, and oropharynx. In recent years, the development of therapeutic HPV vaccines utilizing viral vectors for the treatment of premalignant lesions or tumors caused by HPV infection has experienced rapid growth, with numerous research pipelines currently underway. Simultaneously, screening for optimal antigens requires more basic research and more optimized methods. In terms of preclinical research, we present the various models used to assess vaccine efficacy, highlighting their respective advantages and disadvantages. Further, we present current research status of therapeutic vaccines using HPV viral vectors, especially the indications, initial efficacy, combination drugs, etc. In general, this paper summarizes current viral vector therapeutic HPV vaccines in terms of HPV infection, antigen selection, vectors, efficacy evaluation, and progress in clinical trials.

Comparison of media for a human peripheral blood mononuclear cell-based in vitro vaccine evaluation system

Purpose

Human peripheral blood mononuclear cell (PBMC)-based in vitro systems can be of great value in the development and assessment of vaccines but require the right medium for optimal performance of the different cell types present. Here, we compare three commonly used media for their capacity to support innate and adaptive immune responses evoked in PBMCs by Toll-like receptor (TLR) ligands and whole inactivated virus (WIV) influenza vaccine.

Materials and Methods

Human PBMCs were cultured for different periods of time in Roswell Park Memorial Institute (RPMI), Dulbecco's minimal essential medium (DMEM), or Iscove's modified DMEM (IMDM) supplemented with 10% fetal calf serum. The viability of the cells was monitored and their responses to TLR ligands and WIV were assessed.

Results

With increasing days of incubation, the viability of PBMCs cultured in RPMI or IMDM was slightly higher than that of cells cultured in DMEM. Upon exposure of the PBMCs to TLR ligands and WIV, RPMI was superior to the other two media in terms of supporting the expression of genes related to innate immunity, such as the TLR adaptor protein gene MyD88 (myeloid differentiation factor 88), the interferon (IFN)-stimulated genes MxA (myxovirus resistance protein 1) and ISG56 (interferon-stimulated gene 56), and the leukocyte recruitment chemokine gene MCP1 (monocyte chemoattractant protein-1). RPMI also performed best with regard to the activation of antigen-presenting cells. As for adaptive immunity, when stimulated with WIV, PBMCs cultured in RPMI or IMDM contained higher numbers of IFNγ-producing T cells and secreted more immunoglobulin G than PBMCs cultured in DMEM.

Conclusion

Taken together, among the different media assessed, RPMI was identified as the optimal medium for a human PBMC-based in vitro vaccine evaluation system.

Proceedings of the Online Conference "Vaccines and Vaccination during and Post COVID Pandemics" (7-9 December 2022)

The COVID-19 pandemic put focus on various aspects of vaccine research and development. These include mass vaccination strategies, vaccination compliance and hesitancy, acceptance of novel vaccine approaches, preclinical and animal models used to assess vaccine safety and efficacy, and many other related issues. These issues were addressed by the international online conference "Vaccines and Vaccination During and Post COVID Pandemics" (VAC&VAC 2022) held on the platform of Riga Stradins University, Riga, Latvia. Conference was supported by the International Society for Vaccines, the National Cancer Institute "Fondazione Pascale" (Naples, Italy), and the scientific journal VACCINES (mdpi). VAC&VAC 2022 attracted nearly 150 participants from 14 countries. This report summarizes conference presentations and their discussion. Sessions covered the topics of (1) COVID-19 vaccine development, evaluation, and attitude towards these vaccines, (2) HPV and cancer vaccines, (3) progress and challenges of HIV vaccine development, (4) new and re-emerging infectious threats, and (5) novel vaccine vehicles, adjuvants, and carriers. Each session was introduced by a plenary lecture from renowned experts from leading research institutions worldwide. The conference also included sessions on research funding and grant writing and an early career researcher contest in which the winners received monetary awards and a chance to publish their results free of charge in the special issue of VACCINES covering the meeting.

Signs of immunosenescence correlate with poor outcome of mRNA COVID-19 vaccination in older adults

Vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is effective in preventing COVID-19 hospitalization and fatal outcome. However, several studies indicated that there is reduced vaccine effectiveness among older individuals, which is correlated with their general health status^1,2. How and to what extent age-related immunological defects are responsible for the suboptimal vaccine responses observed in older individuals receiving SARS-CoV-2 messenger RNA vaccine, is unclear and not fully investigated^1,3-5. In this observational study, we investigated adaptive immune responses in adults of various ages (22-99 years old) receiving 2 doses of the BNT162b2 mRNA vaccine. Vaccine-induced Spike-specific antibody, and T and memory B cell responses decreased with increasing age. These responses positively correlated with the percentages of peripheral naïve CD4⁺ and CD8⁺ T cells and negatively with CD8⁺ T cells expressing signs of immunosenescence. Older adults displayed a preferred T cell response to the S2 region of the Spike protein, which is relatively conserved and a target for cross-reactive T cells induced by human 'common cold' coronaviruses. Memory T cell responses to influenza virus were not affected by age-related changes, nor the SARS-CoV-2-specific response induced by infection. Collectively, we identified signs of immunosenescence correlating with the outcome of vaccination against a new viral antigen to which older adults are immunologically naïve. This knowledge is important for the management of COVID-19 infections in older adults.

Phenotypic characteristics of peripheral immune cells of Myalgic encephalomyelitis/chronic fatigue syndrome via transmission electron microscopy: A pilot study

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex chronic multi-systemic disease characterized by extreme fatigue that is not improved by rest, and worsens after exertion, whether physical or mental. Previous studies have shown ME/CFS-associated alterations in the immune system and mitochondria. We used transmission electron microscopy (TEM) to investigate the morphology and ultrastructure of unstimulated and stimulated ME/CFS immune cells and their intracellular organelles, including mitochondria. PBMCs from four participants were studied: a pair of identical twins discordant for moderate ME/CFS, as well as two age- and gender- matched unrelated subjects-one with an extremely severe form of ME/CFS and the other healthy. TEM analysis of CD3/CD28-stimulated T cells suggested a significant increase in the levels of apoptotic and necrotic cell death in T cells from ME/CFS patients (over 2-fold). Stimulated Tcells of ME/CFS patients also had higher numbers of swollen mitochondria. We also found a large increase in intracellular giant lipid droplet-like organelles in the stimulated PBMCs from the extremely severe ME/CFS patient potentially indicative of a lipid storage disorder. Lastly, we observed a slight increase in platelet aggregation in stimulated cells, suggestive of a possible role of platelet activity in ME/CFS pathophysiology and disease severity. These results indicate extensive morphological alterations in the cellular and mitochondrial phenotypes of ME/CFS patients' immune cells and suggest new insights into ME/CFS biology.

Assessing the Immunomodulatory Effect of Size on the Uptake and Immunogenicity of Influenza- and Hepatitis B Subunit Vaccines In Vitro

Viral subunit vaccines are a safer and more tolerable alternative to whole inactivated virus vaccines. However, they often come with limited efficacy, necessitating the use of adjuvants. Using free and particle-bound viral antigens, we assessed whether size affects the uptake of those antigens by human monocyte-derived dendritic cells (Mo-DCs) and whether differences in uptake affect their capacity to stimulate cytokine production by T cells. To this end, influenza antigens and hepatitis B surface antigen (HBsAg) were covalently conjugated to polystyrene particles of 500 nm and 3 μm. Cellular uptake of the antigens, either unconjugated or conjugated, and their capacity to stimulate T cells within a population of human peripheral blood mononuclear cells (PBMCs) were measured by flow cytometry. Conjugation of both antigens to particles significantly increased their uptake by Mo-DCs. Moreover, both the 500 nm and 3 μm influenza conjugates induced significantly higher numbers of cytokine-producing CD4⁺ T cells and induced increased production of the pro-inflammatory cytokines IFNγ and TNFα. In contrast, conjugation of HBsAg to particles did not notably affect the T cell response. In conclusion, conjugation of antigen to 500 nm and 3 μm particles leads to increased antigen uptake by human Mo-DCs, although the capacity of such conjugates to induce T cell stimulation likely depends on the immunological status of the PBMC donor.

Study of Oligonucleotides Access and Distribution in Human Peripheral Blood Mononuclear Cells

Therapeutic oligonucleotides have achieved great clinical interest since their approval as drug agents by regulatory agencies but their access and distribution in blood cells are not completely known. We evaluated by flow cytometry the ability of short fluorescent scramble oligonucleotides (ON*) to access human peripheral blood mononuclear cells (PBMC) after incubating with ON* during 1 h and 7 days of culture follow-up 'in vitro'. Blood samples were treated with chemically modified oligonucleotides (phosphorothioate backbone and 2' O-Me ends) to resist nuclease digestion under culture conditions. The ON* internalization was determined after discarding the membrane-associated fluorescence by trypan blue quenching. Whereas the oligonucleotide accessed neutrophils and monocytes rapidly, achieving their maximum in 1 h and 24 h, respectively, lymphocytes required 7 days to achieve the maximum (80% of cells) transfection. The ON*ability to access lymphocyte types (T, B, and NK) and T cell subtypes (CD4+, CD8+, and CD4-CD8-) were similar, with T cells being more accessible. Regulatory CD4+ and CD8+ T cells were classified in low and high Foxp3 expressers, whose expression proved not to alter the ON* internalization during the first hour, achieving 53% of CD4+Foxp3+ and 40% of CD8+Foxp3+ cells. Our results contribute to understanding and improving the management of therapeutic ONs.

Association of Flu specific and SARS-CoV-2 specific CD4 T cell responses in SARS-CoV-2 infected asymptomatic heath care workers

Influenza vaccination is widely advocated to avoid infection with influenza virus, a serious respiratory pathogen, and this was greatly emphasized during the raging COVID-19 epidemic. We conducted a study for baseline Flu specific immunity in a group of health care workers with documented past SARs-CoV-2 infection (designated COVID+) with mild or no symptoms and compared them with a control group that had not been infected with SARS CoV-2 (COVID-). Concurrently, we examined flu and SARS-CoV-2 specific T cell responses using the AIM (activation induced molecules) assay by flow cytometry. All COVID+ and 40% COVID- participants exhibited AIM responses to SARS-CoV-2 peptides, but only COVID+ were positive for SARs-CoV-2 antibody. Influenza HIN1 antigen specific CD4 T cells were found in 92% COVID+ and 76% COVID- participants and exhibited a strong direct correlation with SARS-CoV-2 specific CD4 T cells. This observation suggests that influenza specific T cell immunity may impact immune responses to SARS-CoV-2.

Overcoming scientific barriers in the transition from in vivo to non-animal batch testing of human and veterinary vaccines

INTRODUCTION

Before release, vaccine batches are assessed for quality to evaluate whether they meet the product specifications. Vaccine batch tests, in particular of inactivated and toxoid vaccines, still largely rely on in vivo methods. Improved vaccine production processes, ethical concerns, and suboptimal performance of some in vivo tests have led to the development of in vitro alternatives.

AREAS COVERED

This review describes the scientific constraints that need to be overcome for replacement of in vivo batch tests, as well as potential solutions. Topics include the critical quality attributes of vaccines that require testing, the use of cell-based assays to mimic aspects of in vivo vaccine-induced immune responses, how difficulties with testing adjuvanted vaccines in vitro can be overcome, the use of altered batches to validate new in vitro test methods, and how cooperation between different stakeholders is key to moving the transition forward.

EXPERT OPINION

For safety testing, many in vitro alternatives are already available or at an advanced level of development. For potency testing, in vitro alternatives largely comprise immunochemical methods that assess several, but not all critical vaccine properties. One-to-one replacement by in vitro alternatives is not always possible and a combination of methods may be required.

Immunocartography: Charting vaccine-driven immunity by applying single cell proteomics to an in vitro human model

The ability to measure immunomodulatory effects of a vaccine is crucial for novel vaccine design. While traditional animal models have been effective, a better understanding of the response in humans to new vaccines in pre-clinical development is critical for advancement to clinical trials. A translational methodology that can capture the complexity of a vaccine-driven response in a human model, which does not require human exposure, is needed. Here we have designed a platform that uses fresh human whole blood as a key component to study the adaptive immune memory response to vaccine formulations. The response is monitored by high-parameter single cell analysis using mass cytometry (Helios, CyTOF System), allowing for a rapid, in-depth characterization of antigen specific proliferation and expansion of preexisting memory T cells in concert with an innate adjuvant-driven response. In this work we demonstrate the capability of this platform to characterize biologically relevant changes in the cellular response across memory T-cells, B cells, monocytes, and NK cells, at an unprecedented level of detail. This approach that we call Immunocartography has the potential to transform the way new vaccines can be assessed before and throughout clinical development.

The impact of blood-processing time on the proteome of human peripheral blood mononuclear cells

Human peripheral blood mononuclear cells (PBMC) are key to several diagnostics assays and basic science research. Blood pre-analytical variations that occur before obtaining the PBMC fraction can significantly impact the assays results, including viability, composition, integrity, and gene expression changes of immune cells. With this as motivation, we performed a quantitative shotgun proteomics analysis using Isobaric Tag for Relative and Absolute Quantitation (iTRAQ 8plex) labeling to compare PBMC obtained from 24 h-stored blood at room temperature versus freshly isolated. We identified a total of 3195 proteins, of which 245 were differentially abundant (101 upregulated and 144 downregulated). Our results revealed enriched pathways of downregulated proteins related to exocytosis, localization, vesicle-mediated transport, cell activation, and secretion. In contrast, pathways related to exocytosis, neutrophil degranulation and activation, granulocyte activation, leukocyte degranulation, and myeloid leukocyte activation involved in immune response were enriched in upregulated proteins, which may indicate probable granulocyte contamination and activation due to blood storage time and temperature. Examples of upregulated proteins in the 24 h-PBMC samples are CAMP, S100A8, LTA4H, RASAL3, and S100A6, which are involved in an adaptive immune system and antimicrobial activity, proinflammatory mediation, aminopeptidase activities, and naïve T cells survival. Moreover, examples of downregulated proteins are NDUFA5, TAGLN2, H3C1, TUBA8, and CCT2 that are related to the cytoskeleton, cell junction, mitochondrial respiratory chain. In conclusion, the delay in blood-processing time directly impacts the proteomic profile of human PBMC, possibly through granulocyte contamination and activation.

Prospects of and Barriers to the Development of Epitope-Based Vaccines against Human Metapneumovirus

Human metapneumovirus (HMPV) is a major cause of respiratory illnesses in children, the elderly and immunocompromised patients. Although this pathogen was only discovered in 2001, an enormous amount of research has been conducted in order to develop safe and effective vaccines to prevent people from contracting the disease. In this review, we summarize current knowledge about the most promising experimental B- and T-cell epitopes of human metapneumovirus for the rational design of HMPV vaccines using vector delivery systems, paying special attention to the conservation of these epitopes among different lineages/genotypes of HMPV. The prospects of the successful development of an epitope-based HMPV vaccine are discussed in the context of recent findings regarding HMPV’s ability to modulate host immunity. In particular, we discuss the lack of data on experimental human CD4 T-cell epitopes for HMPV despite the role of CD4 lymphocytes in both the induction of higher neutralizing antibody titers and the establishment of CD8 memory T-cell responses. We conclude that current research should be focused on searching for human CD4 T-cell epitopes of HMPV that can help us to design a safe and cross-protective epitope-based HMPV vaccine.