Conditioning of the injection site with CpG enhances the migration of adoptively transferred dendritic cells and endogenous CD8+ T-cell responses

Machine Learning-Based Single Cell and Integrative Analysis Reveals That Baseline mDC Predisposition Correlates With Hepatitis B Vaccine Antibody Response

Vaccination to prevent infectious disease is one of the most successful public health interventions ever developed. And yet, variability in individual vaccine effectiveness suggests that a better mechanistic understanding of vaccine-induced immune responses could improve vaccine design and efficacy. We have previously shown that protective antibody levels could be elicited in a subset of recipients with only a single dose of the hepatitis B virus (HBV) vaccine and that a wide range of antibody levels were elicited after three doses. The immune mechanisms responsible for this vaccine response variability is unclear. Using single cell RNA sequencing of sorted innate immune cell subsets, we identified two distinct myeloid dendritic cell subsets (NDRG1-expressing mDC2 and CDKN1C-expressing mDC4), the ratio of which at baseline (pre-vaccination) correlated with the immune response to a single dose of HBV vaccine. Our results suggest that the participants in our vaccine study were in one of two different dendritic cell dispositional states at baseline – an NDRG2-mDC2 state in which the vaccine elicited an antibody response after a single immunization or a CDKN1C-mDC4 state in which the vaccine required two or three doses for induction of antibody responses. To explore this correlation further, genes expressed in these mDC subsets were used for feature selection prior to the construction of predictive models using supervised canonical correlation machine learning. The resulting models showed an improved correlation with serum antibody titers in response to full vaccination. Taken together, these results suggest that the propensity of circulating dendritic cells toward either activation or suppression, their “dispositional endotype” at pre-vaccination baseline, could dictate response to vaccination.

Oncolytic virotherapy enhances the efficacy of a cancer vaccine by modulating the tumor microenvironment

The efficacy of cancer vaccines has been limited by the immunosuppressive tumor microenvironment, which can be alleviated by immune checkpoint inhibitor (ICI) therapy. Here, we tested if oncolytic viruses (OVs), similar to ICI, can also synergize with cancer vaccines by modulating the tumor microenvironment. VSV‐GP, a chimeric vesicular stomatitis virus (VSV) pseudotyped with the glycoprotein (GP) of the lymphocytic choriomeningitis virus, is a promising new OV candidate. Here, we show that in mouse B16‐OVA melanoma, combination treatment of VSV‐GP with an ovalbumin (OVA) peptide‐loaded dendritic cell (DC) vaccine (DCVacc) significantly enhanced survival over the single agent therapies, although both DCVacc and DCVacc/VSV‐GP treatments induced comparable levels of OVA‐specific CD8 T cell responses. Virus replication was minimal so that direct viral oncolysis in B16‐OVA did not contribute to this synergism. The strong therapeutic effect of the DCVacc/VSV‐GP combination treatment was associated with high numbers of tumor‐infiltrating, highly activated T cells and the relative reduction of regulatory T cells in treated and contra‐lateral nontreated tumors. Accordingly, depletion of CD8 T cells but not natural killer cells abrogated the therapeutic effect of DCVacc/VSV‐GP supporting the crucial role of CD8 T cells. In addition, a drastic increase in several proinflammatory cytokines was observed in VSV‐GP‐treated tumors. Taken together, OVs, similar to ICI, have the potential to markedly increase the efficacy of cancer vaccines by alleviating local immune suppression in the tumor microenvironment.

What's new?

Cancer vaccine efficacy has been limited by the immunosuppressive tumor microenvironment. By inducing cancer cell death with the release of tumor‐related antigens, oncolytic viruses may have an adjuvant effect. Here, the authors show that a combination of the oncolytic rhabdovirus VSV‐GP and a dendritic cell vaccine is highly effective in the treatment of mouse melanoma, most likely because VSV‐GP reprograms the tumor microenvironment to enhance the effectivity of the vaccine‐induced immune response. Oncolytic viruses have the potential to dramatically increase the efficacy of cancer vaccines by alleviating local immune suppression in the tumor microenvironment.

Cellular traffic through afferent lymphatic vessels

The lymphatic system has long been known to serve as a highway for migrating leukocytes from peripheral tissue to draining lymph nodes (dLNs) and back to circulation, thereby contributing to the induction of adaptive immunity and immunesurveillance. Lymphatic vessels (LVs) present in peripheral tissues upstream of a first dLN are generally referred to as afferent LVs. In contrast to migration through blood vessels (BVs), the detailed molecular and cellular requirements of cellular traffic through afferent LVs have only recently started to be unraveled. Progress in our ability to track the migration of lymph-borne cell populations, in combination with cutting-edge imaging technologies, nowadays allows the investigation and visualization of lymphatic migration of endogenous leukocytes, both at the population and at the single-cell level. These studies have revealed that leukocyte trafficking through afferent LVs generally follows a step-wise migration pattern, relying on the active interplay of numerous molecules. In this review, we will summarize and discuss current knowledge of cellular traffic through afferent LVs. We will first outline how the structure of the afferent LV network supports leukocyte migration and highlight important molecules involved in the migration of dendritic cells (DCs), T cells and neutrophils, i.e. the most prominent cell types trafficking through afferent LVs. Additionally, we will describe how tumor cells hijack the lymphatic system for their dissemination to draining LNs. Finally, we will summarize and discuss our current understanding of the functional significance as well as the therapeutic implications of cell traffic through afferent LVs.

Migration of dendritic cells to the lymph nodes and its enhancement to drive anti-tumor responses

Better prognoses associated with increased T cell infiltration of tumors, as seen with chimeric antigen receptor (CAR) T cell therapies and immune checkpoint inhibitors, portray the importance and potential of the immune system in controlling tumors. This has rejuvenated the field of cancer immunotherapy leading to an increasing number of immunotherapies developed for cancer patients. Dendritic Cells (DCs) vaccines represent an appealing option for cancer immunotherapy since DCs have the ability to circumvent tolerance to tumors by its adjuvant properties and to induce memory T cells that can become persistent after initial tumor clearance to engage potential metastatic tumors. In the past, DC-based cancer vaccines have elicited only poor clinical response in cancer patients, which can be attributed to complex and a multitude of issues associated with generation, implementing, delivery of DC vaccine and their potential interaction with effector cells. The current review mainly focuses on migration/trafficking of DCs, as one of the key issues that affect the success of DC-based cancer vaccines, and discusses strategies to enhance it for cancer immunotherapy. Additionally, impact of maturation, route of DC delivery and negative effects of tumor microenvironment (TME) on DC homing to LN are reviewed. Moreover, strategies to increase the expression of genes involved in Lymph node homing, preconditioning of the vaccination site, enhancing lymph node ability to attract and receive DCs, while limiting negative impact of TME on DC migration are discussed.

Functional Specialization of Skin Dendritic Cell Subsets in Regulating T Cell Responses

Dendritic cells (DC) are a heterogeneous family of professional antigen-presenting cells classically recognized as most potent inducers of adaptive immune responses. In this respect, Langerhans cells have long been considered to be prototypic immunogenic DC in the skin. More recently this view has considerably changed. The generation of in vivo cell ablation and lineage tracing models revealed the complexity of the skin DC network and, in particular, established the existence of a number of phenotypically distinct Langerin⁺ and negative DC populations in the dermis. Moreover, by now we appreciate that DC also exert important regulatory functions and are required for the maintenance of tolerance toward harmless foreign and self-antigens. This review summarizes our current understanding of the skin-resident DC system in the mouse and discusses emerging concepts on the functional specialization of the different skin DC subsets in regulating T cell responses. Special consideration is given to antigen cross-presentation as well as immune reactions toward contact sensitizers, cutaneous pathogens, and tumors. These studies form the basis for the manipulation of the human counterparts of the murine DC subsets to promote immunity or tolerance for the treatment of human disease.

Topical CpG adjuvantation of a protein-based vaccine induces protective immunity to Listeria monocytogenes

Robust CD8(+) T cell responses are essential for immune protection against intracellular pathogens. Using parenteral administration of ovalbumin (OVA) protein as a model antigen, the effect of the Toll-like receptor 9 (TLR9) agonist, CpG oligodeoxynucleotide (ODN) 1826, as an adjuvant delivered either topically, subcutaneously, or intramuscularly on antigen-specific CD8(+) T cell responses in a mouse model was evaluated. Topical CpG adjuvant increased the frequency of OVA-specific CD8(+) T cells in the peripheral blood and in the spleen. The more effective strategy to administer topical CpG adjuvant to enhance CD8(+) T cell responses was single-dose administration at the time of antigen injection with a prime-boost regimen. Topical CpG adjuvant conferred both rapid and long-lasting protection against systemic challenge with recombinant Listeria monocytogenes expressing the cytotoxic T lymphocyte (CTL) epitope of OVA(257-264) (strain Lm-OVA) in a TLR9-dependent manner. Topical CpG adjuvant induced a higher proportion of CD8(+) effector memory T cells than parenteral administration of the adjuvant. Although traditional vaccination strategies involve coformulation of antigen and adjuvant, split administration using topical adjuvant is effective and has advantages of safety and flexibility. Split administration of topical CpG ODN 1826 with parenteral protein antigen is superior to other administration strategies in enhancing both acute and memory protective CD8(+) T cell immune responses to subcutaneous protein vaccines. This vaccination strategy induces rapid and persistent protective immune responses against the intracellular organism L. monocytogenes.

Treg depletion followed by intracerebral CpG-ODN injection induce brain tumor rejection

Using brain lymphoma model, we demonstrate that immunotherapy combining Treg depletion (using anti-CD25 mAb PC61) followed by intracranial CpG-ODN administration induced tumor rejection in all treated mice and led to the establishment of a memory antitumor immune response in 60% of them. This protective effect was associated with a recruitment of NK cells and, to a lesser extent, of dendritic cells, B cells and T lymphocytes. NK cell depletion abolished the protective effect of the treatment, confirming a major role of NK cells in brain tumor elimination. Each treatment used alone failed to protect brain tumor bearing mice, revealing the therapeutic benefit of combining Treg depletion and local CpG-ODN injection.

Initial afferent lymphatic vessels controlling outbound leukocyte traffic from skin to lymph nodes

Tissue drains fluid and macromolecules through lymphatic vessels (LVs), which are lined by a specialized endothelium that expresses peculiar differentiation proteins, not found in blood vessels (i.e., LYVE-1, Podoplanin, PROX-1, and VEGFR-3). Lymphatic capillaries are characteristically devoid of a continuous basal membrane and are anchored to the ECM by elastic fibers that act as pulling ropes which open the vessel to avoid edema if tissue volume increases, as it occurs upon inflammation. LVs are also crucial for the transit of T lymphocytes and antigen presenting cells from tissue to draining lymph nodes (LN). Importantly, cell traffic control across lymphatic endothelium is differently regulated under resting and inflammatory conditions. Under steady-state non-inflammatory conditions, leukocytes enter into the lymphatic capillaries through basal membrane gaps (portals). This entrance is integrin-independent and seems to be mainly guided by CCL21 chemokine gradients acting on leukocytes expressing CCR7. In contrast, inflammatory processes in lymphatic capillaries involve a plethora of cytokines, chemokines, leukocyte integrins, and other adhesion molecules. Importantly, under inflammation a role for integrins and their ligands becomes apparent and, as a consequence, the number of leukocytes entering the lymphatic capillaries multiplies several-fold. Enhancing transmigration of dendritic cells en route to LN is conceivably useful for vaccination and cancer immunotherapy, whereas interference with such key mechanisms may ameliorate autoimmunity or excessive inflammation. Recent findings illustrate how, transient cell-to-cell interactions between lymphatic endothelial cells and leukocytes contribute to shape the subsequent behavior of leukocytes and condition the LV for subsequent trans-migratory events.

Improved efficacy of dendritic cell-based immunotherapy by cutaneous laser illumination

PURPOSE

The present study investigates a convenient laser-based approach to enhance dendritic cell (DC) migration and improve DC-based immunotherapy in murine models.

EXPERIMENTAL DESIGN

Influence of laser illumination on dermal tissue microenvironment and migration of DCs following intradermal injection were determined by whole-mount immunohistochemistry, transmission electron microscope, and flow cytometry. We also investigated in vivo expansion of CTLs by flow cytometry, CTL activity by in vitro CTL assay, and antitumor efficacy of DC immunization following cutaneous laser illumination in both preventive and therapeutic tumor models.

RESULTS

Laser illumination was found to significantly enlarge perforations in the perilymphatic basement membrane, disarray collagen fibers, and disrupt cell-matrix interactions in the dermis. The altered dermal tissue microenvironment permitted more efficient migration of intradermally injected DCs from the dermis to the draining lymph nodes (dLN). Laser illumination also slightly but significantly enhanced the expression of costimulatory molecule CD80 and MHC I on inoculated DCs. As a result, more vigorous expansion of tumor-specific IFN-γ(+)CD8(+) T lymphocytes and enhanced CTL activity against 4T1 but not irrelevant tumor cells were obtained in the laser-treated group over the control group. Laser-augmented DC immunization also completely abrogated early growth of 4T1 tumor and B16F10 melanoma in preventive tumor models and significantly extended the survival of 4T1-resected mice in a therapeutic tumor model.

CONCLUSION

These data suggest a simple, safe, laser-based approach to significantly enhance DC-based immunotherapy.

The capsule of Porphyromonas gingivalis leads to a reduction in the host inflammatory response, evasion of phagocytosis, and increase in virulence

Periodontal disease is a chronic oral inflammatory disease that is triggered by bacteria such as Porphyromonas gingivalis. P. gingivalis strains exhibit great heterogeneity, with some strains being encapsulated while others are nonencapsulated. Although the encapsulated strains have been shown to be more virulent in a mouse abscess model, so far the role of the capsule in P. gingivalis interactions with host cells is not well understood and its role in virulence has not been defined. Here, we investigated the contribution of the capsule to triggering a host response following microbial infection, as well as its protective role following bacterial internalization by host phagocytic cells with subsequent killing, using the encapsulated P. gingivalis strain W50 and its isogenic nonencapsulated mutant, PgC. Our study shows significant time-dependent upregulation of the expression of various groups of genes in macrophages challenged with both the encapsulated and nonencapsulated P. gingivalis strains. However, cells infected with the nonencapsulated strain showed significantly higher upregulation of 9 and 29 genes at 1 h and 8 h postinfection, respectively, than cells infected with the encapsulated strain. Among the genes highly upregulated by the nonencapsulated PgC strain were ones coding for cytokines and chemokines. Maturation markers were induced at a 2-fold higher rate in dendritic cells challenged with the nonencapsulated strain for 4 h than in dendritic cells challenged with the encapsulated strain. The rates of phagocytosis of the nonencapsulated P. gingivalis strain by both macrophages and dendritic cells were 4.5-fold and 7-fold higher, respectively, than the rates of phagocytosis of the encapsulated strain. On the contrary, the survival of the nonencapsulated P. gingivalis strain was drastically reduced compared to the survival of the encapsulated strain. Finally, the encapsulated strain exhibited greater virulence in a mouse abscess model. Our results indicate that the P. gingivalis capsule plays an important role in aiding evasion of host immune system activation, promoting survival of the bacterium within host cells, and increasing virulence. As such, it is a major virulence determinant of P. gingivalis.