Dendritic cell-T cell interactions in the generation and maintenance of CD8 T cell memory

Sec22b-dependent antigen cross-presentation is a significant contributor of T cell priming during infection with the parasite Trypanosoma cruzi

Antigen cross-presentation is a vital mechanism of dendritic cells and other antigen presenting cells to orchestrate the priming of cytotoxic responses towards killing of infected or cancer cells. In this process, exogenous antigens are internalized by dendritic cells, processed, loaded onto MHC class I molecules and presented to CD8⁺ T cells to activate them. Sec22b is an ER-Golgi Intermediate Compartment resident SNARE protein that, in partnership with sintaxin4, coordinates the recruitment of the transporter associated with antigen processing protein and the peptide loading complex to phagosomes, where antigenic peptides that have been proteolyzed in the cytosol are loaded in MHC class I molecules and transported to the cell membrane. The silencing of Sec22b in dendritic cells primary cultures and conditionally in dendritic cells of C57BL/6 mice, critically impairs antigen cross-presentation, but neither affects other antigen presentation routes nor cytokine production and secretion. Mice with Sec22b conditionally silenced in dendritic cells (Sec22b^-/-) show deficient priming of CD8⁺ T lymphocytes, fail to control tumor growth, and are resistant to anti-checkpoint immunotherapy. In this work, we show that Sec22b^-/- mice elicit a deficient specific CD8⁺ T cell response when challenged with sublethal doses of Trypanosoma cruzi trypomastigotes that is associated with increased blood parasitemia and diminished survival.

Spatial, temporal and molecular dynamics of swine influenza virus-specific CD8 tissue resident memory T cells

For the first time we have defined naïve, central memory, effector memory and differentiated effector porcine CD8 T cells and analyzed their distribution in lymphoid and respiratory tissues after influenza infection or immunization, using peptide-MHC tetramers of three influenza nucleoprotein (NP) epitopes. The hierarchy of response to the three epitopes changes during the response in different tissues. Most NP-specific CD8 T cells in broncho-alveolar lavage (BAL) and lung are tissue resident memory cells (TRM) that express CD69 and downregulate CD45RA and CCR7. NP-specific cells isolated from BAL express genes characteristic of TRM, but gene expression differs at 7, 21 and 63 days post infection. In all tissues the frequency of NP-specific CD8 cells declines over 63 days almost to background levels but is best maintained in BAL. The kinetic of influenza specific memory CD8 T cell in this natural host species differs from that in small animal models.

How Does B Cell Antigen Presentation Affect Memory CD4 T Cell Differentiation and Longevity?

Dendritic cells are the antigen presenting cells that process antigens effectively and prime the immune system, a characteristic that have gained them the spotlights in recent years. B cell antigen presentation, although less prominent, deserves equal attention. B cells select antigen experienced CD4 T cells to become memory and initiate an orchestrated genetic program that maintains memory CD4 T cells for life of the individual. Over years of research, we have demonstrated that low levels of antigens captured by B cells during the resolution of an infection render antigen experienced CD4 T cells into a quiescent/resting state. Our studies suggest that in the absence of antigen, the resting state associated with low-energy utilization and proliferation can help memory CD4 T cells to survive nearly throughout the lifetime of mice. In this review we would discuss the primary findings from our lab as well as others that highlight our understanding of B cell antigen presentation and the contributions of the MHC Class II accessory molecules to this outcome. We propose that the quiescence induced by the low levels of antigen presentation might be a mechanism necessary to regulate long-term survival of CD4 memory T cells and to prevent cross-reactivity to autoantigens, hence autoimmunity.

Engagement of SLAMF2/CD48 prolongs the time frame of effective T cell activation by supporting mature dendritic cell survival

Signaling lymphocyte activation molecule family (SLAMF)2/CD48 is a coactivator and adhesion molecule on cells with hematopoietic origin. It ligates mainly SLAMF4 on effector/memory CD8(+) T cells and NK cells, suggesting a potential role during viral infection, with SLAMF2 acting as a ligand to activate SLAMF4-bearing cells. The ability of SLAMF2 to signal on its own after it is engaged and the functional consequences are largely unknown. We found that cytosolic DNA-activated dendritic cells (DCs) upregulate the expression of SLAMF2 molecules. Using anti-SLAMF2 Ab and SLAMF4 recombinant protein, we found that SLAMF2 engagement activates immature DCs and, more interestingly, prolongs the survival of DNA-activated DCs by inhibiting IFN-β production and IFN-β-induced apoptosis and promotes the production of the granzyme B inhibitor protease inhibitor-9. Thus, SLAMF2 can serve as a survival molecule for DNA-activated DCs during their interaction with SLAMF4-expressing cytotoxic T cells. Based on our results, we propose that SLAMF2 engagement regulates adaptive immune responses by providing longer access of putative APCs to virus-specific effector T cells by prolonging the time frame of effective stimulation.

High-risk human papillomavirus E6 inhibits monocyte differentiation to Langerhans cells

High-risk human papillomaviruses (HPVs) cause a variety of malignancies of the mucosal epithelium. However, the local immune evasion strategies used by HPV-transformed cells remain unclear. Here, we examined the effect of HPV-positive cancer cells on human peripheral blood monocytes, which are precursors of Langerhans cells, key antigen-presenting cells in the squamous epithelium. HPV-positive cervical cancer cells and HPV-E6 expressing cells inhibited monocyte differentiation to Langerhans cells in a contact-dependent manner. Unlike Langerhans cells, monocytes that differentiated in the presence of HPV16 E6-expressing cells exhibited high levels of endocytic activity. Our results suggest that cells infected by high-risk HPV evade immune surveillance by blocking the differentiation of monocytes into competent antigen presenting cells.

Inhibitory receptors are expressed by Trypanosoma cruzi-specific effector T cells and in hearts of subjects with chronic Chagas disease

We had formerly demonstrated that subjects chronically infected with Trypanosoma cruzi show impaired T cell responses closely linked with a process of T cell exhaustion. Recently, the expression of several inhibitory receptors has been associated with T cell dysfunction and exhaustion. In this study, we have examined the expression of the cytotoxic T lymphocyte antigen 4 (CTLA-4) and the leukocyte immunoglobulin like receptor 1 (LIR-1) by peripheral T. cruzi antigen-responsive IFN-gamma (IFN-γ)-producing and total T cells from chronically T. cruzi-infected subjects with different clinical forms of the disease. CTAL-4 expression was also evaluated in heart tissue sections from subjects with severe myocarditis. The majority of IFN-γ-producing CD4⁺ T cells responsive to a parasite lysate preparation were found to express CTLA-4 but considerably lower frequencies express LIR-1, irrespective of the clinical status of the donor. Conversely, few IFN-γ-producing T cells responsive to tetanus and diphtheria toxoids expressed CTLA-4 and LIR-1. Polyclonal stimulation with anti-CD3 antibodies induced higher frequencies of CD4⁺CTAL-4⁺ T cells in patients with severe heart disease than in asymptomatic subjects. Ligation of CTLA-4 and LIR-1 with their agonistic antibodies, in vitro, reduces IFN-γ production. Conversely, CTLA-4 blockade did not improved IFN-γ production in response to T. cruzi antigens. Subjects with chronic T. cruzi infection had increased numbers of CD4⁺LIR-1⁺ among total peripheral blood mononuclear cells, relative to uninfected individuals and these numbers decreased after treatment with benznidazole. CTLA-4 was also expressed by CD3⁺ T lymphocytes infiltrating heart tissues from chronically infected subjects with severe myocarditis. These findings support the conclusion that persistent infection with T. cruzi leads to the upregulation of inhibitory receptors which could alter parasite specific T cell responses in the chronic phase of Chagas disease.

Regulatory dendritic cells program generation of interleukin-4–producing alternative memory CD4 T cells with suppressive activity

The heterogeneity and mechanisms for the generation of CD4 memory T (CD4 Tm) cells remain elusive. Distinct subsets of dendritic cells (DCs) have been found to regulate a distinct T-helper (Th)–cell subset differentiation by influencing cytokine cues around CD4 T cells; however, whether and how the regulatory DC subset can regulate Tm-cell differentiation remains unknown. Further, there is no ideal in vitro experimental system with which to mimic the 3 phases of the CD4 T-cell immune response (expansion, contraction, memory generation) and/or to culture CD4 Tm cells for more than a month. By analyzing CD4 T cells programmed by long-term coculture with regulatory DCs, we identified a population of long-lived CD4 T cells with a CD44hiCD62L−CCR7− effector memory phenotype and rapid, preferential secretion of the Th2 cytokines interleukin-4 (IL-4), IL-5, IL-10, and IL-13 after antigenic stimulation. These regulatory DC-programmed Tm cells suppress CD4 T-cell activation and proliferation in vitro via IL-10 and inhibit the delayed-type hypersensitivity response once infused in vivo. We also identify their natural counterpart, which is up-regulated by regulatory DC transfusion and negatively regulates the recall response in vivo. Different from interferon-γ–producing conventional Tm cells, these IL-4–producing CD4 Tm cells act as alternative Tm cells with a regulatory function, suggesting a new way of negative immune regulation by memory T cells.

Dendritic cells reveal a broad range of MHC class I epitopes for HIV-1 in persons with suppressed viral load on antiretroviral therapy

Background

HIV-1 remains sequestered during antiretroviral therapy (ART) and can resume high-level replication upon cessation of ART or development of drug resistance. Reactivity of memory CD8⁺ T lymphocytes to HIV-1 could potentially inhibit this residual viral replication, but is largely muted by ART in relation to suppression of viral antigen burden. Dendritic cells (DC) are important for MHC class I processing and presentation of peptide epitopes to memory CD8⁺ T cells, and could potentially be targeted to activate memory CD8⁺ T cells to a broad array of HIV-1 epitopes during ART.

Principal Findings

We show for the first time that HIV-1 peptide-loaded, CD40L-matured DC from HIV-1 infected persons on ART induce IFN gamma production by CD8⁺ T cells specific for a much broader range and magnitude of Gag and Nef epitopes than do peptides without DC. The DC also reveal novel, MHC class I restricted, Gag and Nef epitopes that are able to induce polyfunctional T cells producing various combinations of IFN gamma, interleukin 2, tumor necrosis factor alpha, macrophage inhibitory protein 1 beta and the cytotoxic de-granulation molecule CD107a.

Significance

There is an underlying, broad antigenic spectrum of anti-HIV-1, memory CD8⁺ T cell reactivity in persons on ART that is revealed by DC. This supports the use of DC-based immunotherapy for HIV-1 infection.

[Relationship between the phenotypes and functions of peripheral blood dendritic cells and the different spleen deficiency syndrome types in patients with chronic hepatitis B]

OBJECTIVE

To study the phenotypes and functions of dendritic cells (DCs) derived from peripheral blood monocytes of chronic hepatitis B (CHB) patients with different traditional Chinese medicine (TCM) syndrome types, and to explore the relationship between TCM syndrome type and DC functions.

METHODS

Sixty CHB patients were included in this study. All the CHB patients were divided into spleen deficiency and liver stagnation, spleen deficiency and dampness-heat and deficiency of both spleen and kidney groups according to TCM syndrome diagnosis standard. There were 20 cases in each group, and ten healthy people were included as normal control. The volunteer's peripheral blood was collected for monocyte separation, biochemical test and hepatitis B virus DNA loads detection. DCs were induced and isolated from peripheral blood monocytes, and then the expressions of surface markers CD80, CD86, CD1a and HLA-DR were detected by flow cytometric analysis method. Interleukin-10 (IL-10) production of the DCs was quantified by enzyme-linked immunosorbent assay.

RESULTS

The proliferation of DCs in the CHB patients was slower than that in the healthy volunteers (P<0.05). The expressions of DC surface molecules such as CD80, CD86, and CD1a were obviously decreased in the CHB patients as compared with those in the healthy volunteers (P<0.05). More over, expressions of DC surface molecules were different among CHB patients with different TCM syndrome types. The positive expressions of CD80, CD1a, and HLA-DR in the CHB patients with spleen deficiency and liver stagnation were obviously higher than those in the CHB patients with deficiency of both spleen and kidney (P<0.05), and the CD1a expression in the CHB patients with spleen deficiency and dampness-heat was higher than that in the CHB patients with deficiency of both spleen and kidney (P<0.05). In DC culture supernatant, the IL-10 concentration of the CHB patients with deficiency of both spleen and kidney was higher than that of the CHB patients with spleen deficiency and liver stagnation (P<0.05), and the IL-10 concentrations of the CHB patients with different TCM syndrome types were higher than that of the healthy volunteers (P<0.05).

CONCLUSION

During the pathogenic course of CHB, the phenotypes and functions of DCs are different in CHB patients with different TCM syndrome types. It suggests that there is a correlation between TCM syndrome type and body immunity function.

Geography and plumbing control the T cell response to infection

The orchestrated movement of cells of the immune system is essential to generation of productive responses leading to protective memory development. Recent advances have allowed the direct microscopic visualization of lymphocyte and antigen-presenting cell migration and interaction during immune response initiation and progression. These studies have defined important characteristics of the microanatomy of lymphocyte movement, particularly in the lymph node. Moreover, the ability to track endogenous antigen-specific T cells has revealed a coordinated pathway of CD8 T cell movement in the spleen following primary and secondary infection. As a consequence, the local anatomy of secondary lymphoid tissues during infection has emerged as a critical regulator of immunity. While some of the factors responsible for the migratory cues instructing immune cell movement have been identified, much remains to be learned. Here, we provide a brief overview of studies examining CD8 T cell localization during the immune response to infection in the context of our current understanding of immune system structure.

The requirement of CD80, CD86, and ICAM-1 on the ability of adjuvant formulations to potentiate antibody responses to a Plasmodium falciparum blood-stage vaccine

Many adjuvants are known to enhance expression of co-stimulatory and adhesion molecules secondarily to the activation of immune cells. Whether interactions via these molecules are obligatory in adjuvants' ability to potentiation vaccine immunogenicity is less clear. We investigated the ability of eight adjuvant formulations to potentiate the immunogenicity of a malaria vaccine in mice deficient in the prominent co-stimulatory molecules, CD80 and CD86; and the adhesion ligand, ICAM-1. While no adjuvants could bypass co-stimulatory requirements, more formulations exhibited dependency for CD86 than for CD80. In CD80 or CD86 KO mice, formulations with the saponin derivative, QS21 could efficiently default to the other B7 molecule. This effect was dominant over other adjuvant constituents. The requirement for ICAM-1 could be readily bypassed using adjuvant formulations containing immunomodulators; whereas this was not the case with emulsion-type adjuvants in which reduction in adjuvanticity was associated with decreases in antigen-specific IFN-gamma responses. These studies may help to guide the formulation of vaccine adjuvants to maintain effectiveness in hosts with altered immunological environment that often result from infections.

CC chemokine receptor 5 and CXC chemokine receptor 6 expression by lung CD8+ cells correlates with chronic obstructive pulmonary disease severity

Chronic obstructive pulmonary disease (COPD) is a progressive disease associated with a cellular inflammatory response. CD8(+) T cells are implicated in COPD pathogenesis, and their numbers significantly correlate with the degree of airflow limitation. Dendritic cells (DCs) are important sentinel immune cells, but little is known about their role in initiating and maintaining the CD8 T-cell response in COPD. To investigate the mechanisms for CD8(+) T-cell recruitment to the lung, we used resected human lung tissue to analyze chemokine receptor expression by CD8(+) T cells and chemokine production by CD1a(+) DCs. Among 11 surveyed chemokine receptors, only CC chemokine receptor (CCR5), CXC chemokine receptor (CXCR) 3, and CXCR6 correlated with COPD severity as defined by criteria from the Global Initiative for Chronic Obstructive Lung Disease. The CD8(+) T cells displayed a Tc1, CD45RA(+) effector memory phenotype. CD1a(+) DCs produced the respective ligands for CCR5 and CXCR3, CCL3 and CXCL9, and levels correlated with disease severity. CD1a(+) DCs also constitutively expressed the CXCR6 ligand, CXCL16. In conclusion, we have identified major chemokine elements that potentially mediate CD8(+) T-cell infiltration during COPD progression and demonstrated that CD1a(+) mucosal-associated DCs may sustain CD8(+) T-cell recruitment/retention. Chemokine targeting may prove to be a viable treatment approach.