Priming of CD8 T cells by adenoviral vectors is critically dependent on B7 and dendritic cells but only partially dependent on CD28 ligation on CD8 T cells

Adenovirus vector and mRNA vaccines: Mechanisms regulating their immunogenicity

Replication-incompetent adenovirus (Ad) vector and mRNA-lipid nanoparticle (LNP) constructs represent two modular vaccine platforms that have attracted substantial interest over the past two decades. Due to the COVID-19 pandemic and the rapid development of multiple successful vaccines based on these technologies, there is now clear real-world evidence of the utility and efficacy of these platforms. Considerable optimization and refinement efforts underpin the successful application of these technologies. Despite this, our understanding of the specific pathways and processes engaged by these vaccines to stimulate the immune response remains incomplete. This review will synthesize our current knowledge of the specific mechanisms by which CD8⁺ T cell and antibody responses are induced by each of these vaccine platforms, and how this can be impacted by specific vaccine construction techniques. Key gaps in our knowledge are also highlighted, which can hopefully focus future studies.

A phase I study of an adenoviral vector delivering a MUC1/CD40-ligand fusion protein in patients with advanced adenocarcinoma

Cancer vaccines as immunotherapy for solid tumours are currently in development with promising results. We report a phase 1 study of Ad-sig-hMUC1/ecdCD40L (NCT02140996), an adenoviral-vector vaccine encoding the tumour-associated antigen MUC1 linked to CD40 ligand, in patients with advanced adenocarcinoma. The primary objective of this study is safety and tolerability. We also study the immunome in vaccinated patients as a secondary outcome. This trial, while not designed to determine clinical efficacy, reports an exploratory endpoint of overall response rate. The study meets its pre-specified primary endpoint demonstrating safety and tolerability in a cohort of 21 patients with advanced adenocarcinomas (breast, lung and ovary). The maximal dose of the vaccine is 1 ×10¹¹ viral particles, with no dose limiting toxicities. All drug related adverse events are of low grades, most commonly injection site reactions in 15 (71%) patients. Using exploratory high-dimensional analyses, we find both quantitative and relational changes in the cancer immunome after vaccination. Our data highlights the utility of high-dimensional analyses in understanding and predicting effective immunotherapy, underscoring the importance of immune competency in cancer prognosis.

Design and Immunological Validation of Macaca fascicularis Papillomavirus Type 3 Based Vaccine Candidates in Outbred Mice: Basis for Future Testing of a Therapeutic Papillomavirus Vaccine in NHPs

Persistent human papillomavirus (HPV) infections are causative for cervical neoplasia and carcinomas. Despite the availability of prophylactic vaccines, morbidity and mortality induced by HPV are still too high. Thus, an efficient therapy, such as a therapeutic vaccine, is urgently required. Herein, we describe the development and validation of Macaca fascicularis papillomavirus type 3 (MfPV3) antigens delivered via nucleic-acid and adenoviral vectors in outbred mouse models. Ten artificially fused polypeptides comprising early viral regulatory proteins were designed and optionally linked to the T cell adjuvant MHC-II-associated invariant chain. Transfected HEK293 cells and A549 cells transduced with recombinant adenoviruses expressing the same panel of artificial antigens proved proper and comparable expression, respectively. Immunization of outbred CD1 and OF1 mice led to CD8+ and CD4+ T cell responses against MfPV3 antigens after DNA- and adenoviral vector delivery. Moreover, in vivo cytotoxicity of vaccine-induced CD8+ T cells was demonstrated in BALB/c mice by quantifying specific killing of transferred peptide-pulsed syngeneic target cells. The use of the invariant chain as T cell adjuvant enhanced the T cell responses regarding cytotoxicity and in vitro analysis suggested an accelerated turnover of the antigens as causative. Notably, the fusion-polypeptide elicited the same level of T-cell responses as administration of the antigens individually, suggesting no loss of immunogenicity by fusing multiple proteins in one vaccine construct. These data support further development of the vaccine candidates in a follow up efficacy study in persistently infected Macaca fascicularis monkeys to assess their potential to eliminate pre-malignant papillomavirus infections, eventually instructing the design of an analogous therapeutic HPV vaccine.

A Salmonella Typhi ghost induced by the E gene of phage φX174 stimulates dendritic cells and efficiently activates the adaptive immune response

Previously, we genetically engineered a Salmonella Typhi bacterial ghost (STG) as a novel inactivated vaccine candidate against typhoid fever. The underlying mechanism employed by the ghost in stimulating the adaptive immune response remains to be investigated. In this study, we aimed to evaluate the immunostimulatory effect of STG on mouse bone marrow-derived dendritic cells (BMDCs) and its activation of the adaptive immune response in vitro. Immature BMDCs were stimulated with STG, which efficiently stimulated maturation events in BMDCs, as indicated by upregulated expressions of CD40, CD80, and major histocompatibility complex class II molecules on CD11⁺ BMDCs. Immature BMDCs responded to STG stimulation by significantly increasing the expression of interleukin (IL)-6, which might indicate the induction of dendritic cell maturation in vivo (p < 0.05). In addition, ghost-stimulated murine BMDCs showed significant expressions of interferon gamma and IL-4, which can drive the development of Th1 and Th2 cells, respectively, in co-cultured CD4⁺ T cells in vitro. These results suggest that STG can effectively stimulate maturation of BMDCs and facilitate subsequent immune responses via potent immunomodulatory cytokine responses.

Improved Induction of Anti-Melanoma T Cells by Adenovirus-5/3 Fiber Modification to Target Human DCs

To mount a strong anti-tumor immune response, non T cell inflamed (cold) tumors may require combination treatment encompassing vaccine strategies preceding checkpoint inhibition. In vivo targeted delivery of tumor-associated antigens (TAA) to dendritic cells (DCs), relying on the natural functions of primary DCs in situ, represents an attractive vaccination strategy. In this study we made use of a full-length MART-1 expressing C/B-chimeric adenoviral vector, consisting of the Ad5 capsid and the Ad3 knob (Ad5/3), which we previously showed to selectively transduce DCs in human skin and lymph nodes. Our data demonstrate that chimeric Ad5/3 vectors encoding TAA, and able to target human DCs in situ, can be used to efficiently induce expansion of functional tumor-specific CD8⁺ effector T cells, either from a naïve T cell pool or from previously primed T cells residing in the melanoma-draining sentinel lymph nodes (SLN). These data support the use of Ad3-knob containing viruses as vaccine vehicles for in vivo delivery. “Off-the-shelf” DC-targeted Ad vaccines encoding TAA could clearly benefit future immunotherapeutic approaches.

Infectious Sporozoites of Plasmodium berghei Effectively Activate Liver CD8α+ Dendritic Cells

Immunization with radiation-attenuated sporozoites (RAS) shown to confer complete sterile protection against Plasmodia liver-stage (LS) infection that lasts about 6 to 9 months in mice. We have found that the intermittent infectious sporozoite challenge to immune mice following RAS vaccination extends the longevity of sterile protection by maintaining CD8⁺ T cell memory responses to LS infection. It is reported that CD8α⁺ dendritic cells (DCs) are involved in the induction of LS-specific CD8⁺ T cells following RAS or genetically attenuated parasite (GAP) vaccination. In this study, we demonstrate that CD8α⁺ DCs respond differently to infectious sporozoite or RAS inoculation. The higher accumulation and activation of CD8α⁺ DCs was seen in the liver in response to infectious sporozoite 72 h postinoculation and found to be associated with higher expression of chemokines (CCL-20 and CCL-21) and type I interferon response via toll-like receptor signaling in liver. Moreover, the infectious sporozoites were found to induce qualitative changes in terms of the increased MHCII expression as well as costimulatory molecules including CD40 on the CD8α⁺ DCs compared to RAS inoculation. We have also found that infectious sporozoite challenge increased CD40L-expressing CD4⁺ T cells, which could help CD8⁺ T cells in the liver through "licensing" of the antigen-presenting cells. Our results suggest that infectious sporozoite challenge to prior RAS immunized mice modulates the CD8α⁺ DCs, which might be shaping the fate of memory CD8⁺ T cells against Plasmodium LS infection.

A high frequency of CD8+CD28- T-suppressor cells contributes to maintaining stable graft function and reducing immunosuppressant dosage after liver transplantation

CD8⁺CD28^-T cells (CD8Ts) exert immunosuppressive effects in various autoimmune diseases. The current study was designed to investigate the role of defects in CD8Ts in liver transplantation (LT). The proportion of CD8Ts in peripheral blood was determined by flow cytometry. The mean proportion of CD8Ts was 23.39% in recipients with stable graft function and 16.64% in those with graft dysfunction following LT compared with 19.86% in the healthy cohort. After receiving enhanced immunosuppressive therapy, patients in the rejection group who achieved recovery of graft function showed an increase in the proportion of CD8Ts (from 17.39% to 25.55%), but those in the group with refractory graft dysfunction showed no significant change (12.49% to 10.30%). Furthermore, in the first year after LT, recipients longer removed in time from the LT date exhibited a higher proportion of CD8Ts. Patients benefited most from tacrolimus concentrations of 5-10 ng/ml in the first year after LT and 0-5 ng/ml thereafter. Moreover, the change in the proportion of CD8Ts (ΔCD8Ts) was significantly higher in recipients with stable graft function than in those with graft dysfunction. These results suggest that a high frequency of CD8Ts prevents rejection and contributes to reduce immunosuppressant dosage and even induces tolerance.

Molecular and Genomic Impact of Large and Small Lateral Dimension Graphene Oxide Sheets on Human Immune Cells from Healthy Donors

Graphene oxide (GO) is attracting great interest in biomedical sciences. The impact of GO on immune cells is one fundamental area of study that is often overlooked, but critical in terms of clinical translation. This work investigates the effects of two types of thoroughly characterized GO sheets, different in their lateral dimension, on human peripheral immune cells provided from healthy donors using a wide range of assays. After evaluation of cell viability, the gene expression was analyzed, following GO exposure on 84 genes related to innate and adaptive immune responses. Exposure to GO small sheets was found to have a more significant impact on immune cells compared to GO large sheets, reflected in the upregulation of critical genes implicated in immune responses and the release of cytokines IL1β and TNFα. These findings were further confirmed by whole-genome microarray analysis of the impact of small GO sheets on T cells and monocytes. Activation in both cell types was underlined by the overexpression of genes such as CXCL10 and receptor CXCR3. Significant energy-dependent pathway modulation was identified. These findings can potentially pave the foundations for further design of graphene that can be used for immune modulation applications, for example in cancer immunotherapy.

Skin vaccination with live virus vectored microneedle arrays induce long lived CD8(+) T cell memory

A simple dissolvable microneedle array (MA) platform has emerged as a promising technology for vaccine delivery, due to needle-free injection with a formulation that preserves the immunogenicity of live viral vectored vaccines dried in the MA matrix. While recent studies have focused largely on design parameters optimized to induce primary CD8(+) T cell responses, the hallmark of a vaccine is synonymous with engendering long-lasting memory. Here, we address the capacity of dried MA vaccination to programme phenotypic markers indicative of effector/memory CD8(+) T cell subsets and also responsiveness to recall antigen benchmarked against conventional intradermal (ID) injection. We show that despite a slightly lower frequency of dividing T cell receptor transgenic CD8(+) T cells in secondary lymphoid tissue at an early time point, the absolute number of CD8(+) T cells expressing an effector memory (CD62L(-)CD127(+)) and central memory (CD62L(+)CD127(+)) phenotype during peak expansion were comparable after MA and ID vaccination with a recombinant human adenovirus type 5 vector (AdHu5) encoding HIV-1 gag. Similarly, both vaccination routes generated CD8(+) memory T cell subsets detected in draining LNs for at least two years post-vaccination capable of responding to secondary antigen. These data suggest that CD8(+) T cell effector/memory generation and long-term memory is largely unaffected by physical differences in vaccine delivery to the skin via dried MA or ID suspension.

Liver-resident CD103+ dendritic cells prime antiviral CD8+ T cells in situ

The liver maintains a tolerogenic environment to avoid unwarranted activation of its resident immune cells upon continuous exposure to food and bacterially derived Ags. However, in response to hepatotropic viral infection, the liver's ability to switch from a hyporesponsive to a proinflammatory environment is mediated by select sentinels within the parenchyma. To determine the contribution of hepatic dendritic cells (DCs) in the activation of naive CD8(+) T cells, we first characterized resident DC subsets in the murine liver. Liver DCs exhibit unique properties, including the expression of CD8α (traditionally lymphoid tissue specific), CD11b, and CD103 markers. In both the steady-state and following viral infection, liver CD103(+) DCs express high levels of MHC class II, CD80, and CD86 and contribute to the high number of activated CD8(+) T cells. Importantly, viral infection in the Batf3(-/-) mouse, which lacks CD8α(+) and CD103(+) DCs in the liver, results in a 3-fold reduction in the proliferative response of Ag-specific CD8(+) T cells. Limiting DC migration out of the liver does not significantly alter CD8(+) T cell responsiveness, indicating that CD103(+) DCs initiate the induction of CD8(+) T cell responses in situ. Collectively, these data suggest that liver-resident CD103(+) DCs are highly immunogenic in response to hepatotropic viral infection and serve as a major APC to support the local CD8(+) T cell response. It also implies that CD103(+) DCs present a promising cellular target for vaccination strategies to resolve chronic liver infections.