School of Biomedical Sciences - Research Publications
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ItemInduction of antigen-specific effector-phase tolerance following vaccination against a previously ignored B-cell lymphoma(WILEY, 2011-07-01)The mechanisms of immune evasion during haematological malignancies are poorly understood. As lymphomas grow in lymphoid organs, it would be expected that if these lymphomas express neo-antigens they should be readily detected by the immune system. To test this assumption, we generated a new non-Hodgkin B-cell lymphoma model expressing the model tumour neo-antigen Ovalbumin (OVA), and analysed the endogenous antigen-specific CD8(+) T-cell response that it elicited in recipient mice. The OVA+ lymphoma cells were eliminated by cytotoxic T lymphocytes (CTL) in mice that had been previously vaccinated against OVA. In contrast, the immune system of naïve mice ignored the malignant cells even though these continuously expressed and presented OVA on their MHC class I molecules. This state of ignorance could be overcome by therapeutic vaccination, which led to the expansion of endogenous anti-OVA-specific CD8(+) T cells. However, the cytotoxic and interferon-γ secretion capacity of these T cells were impaired. The tumour model that we describe thus reproduces several key aspects of human lymphoma; tumor ignorance can be broken by vaccination but the ensuing immune response remains ineffective. This model can be exploited to further understand the mechanisms of lymphoma immunoevasion and devise effective immunotherapy.
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ItemTargeting antigen to bone marrow stromal cell-2 expressed by conventional and plasmacytoid dendritic cells elicits efficient antigen presentation(WILEY-BLACKWELL, 2013-03-01)Bone marrow stromal cell-2 (BST-2) has major roles in viral tethering and modulation of interferon production. Here we investigate BST-2 as a receptor for the delivery of antigen to dendritic cells (DCs). We show that BST-2 is expressed by a panel of mouse and human DC subsets, particularly under inflammatory conditions. The outcome of delivering antigen to BST-2 expressed by steady state and activated plasmacytoid DC (pDC) or conventional CD8(+) and CD8(-) DCs was determined. T-cell responses were measured for both MHC class I (MHCI) and MHC class II (MHCII) antigen presentation pathways in vitro. Delivering antigen via BST-2 was compared with that via receptors DEC205 or Siglec-H. We show that despite a higher antigen load and faster receptor internalisation, when antigen is delivered to steady state or activated pDC via BST-2, BST-2-targeted activated conventional DCs present antigen more efficiently. Relative to DEC205, BST-2 was inferior in its capacity to deliver antigen to the MHCI cross-presentation pathway. In contrast, BST-2 was superior to Siglec-H at initiating either MHCI or MHCII antigen presentation. In summary, BST-2 is a useful receptor to target with antigen, given its broad expression pattern and ability to access both MHCI and MHCII presentation pathways with relative efficiency.
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ItemHepatitis B virus-like particles access major histocompatibility class I and II antigen presentation pathways in primary dendritic cells(ELSEVIER SCI LTD, 2013-04-26)Virus-like particles (VLPs) represent high density displays of viral proteins that efficiently trigger immunity. VLPs composed of the small hepatitis B virus envelope protein (HBsAgS) are useful vaccine platforms that induce humoral and cellular immune responses. Notably, however, some studies suggest HBsAgS VLPs impair dendritic cell (DC) function. Here we investigated HBsAgS VLP interaction with DC subsets and antigen access to major histocompatibility complex (MHC) class I and II antigen presentation pathways in primary DCs. HBsAgS VLPs impaired plasmacytoid DC (pDC) interferon alpha (IFNα) production in response to CpG in vitro, but did not alter conventional DC (cDC) or pDC phenotype when administered in vivo. To assess cellular immune responses, HBsAgS VLPs were generated containing the ovalbumin (OVA) model epitopes OVA(257-264) and OVA(323-339) to access MHCI and MHCII antigen presentation pathways, respectively; both in vitro and following immunisation in vivo. HBsAgS VLP-OVA(257-264) elicited CTL responses in vivo that were not enhanced by inclusion of an additional MHCII helper epitope. HBsAgS VLP-OVA(257-264) administered in vivo was cross-presented by CD8(+) DCs, but not CD8(-) DCs. Therefore, HBsAgS VLPs can deliver antigen to both MHCI and MHCII antigen presentation pathways in primary DCs and promote cytotoxic and helper T cell priming despite their suppressive effect on pDCs.
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ItemRapid Deletion and Inactivation of CTLs upon Recognition of a Number of Target Cells over a Critical Threshold(AMER ASSOC IMMUNOLOGISTS, 2013-10-01)Initiation of CTL responses against foreign pathogens also primes anti-self CTLs. Mechanisms of CTL inactivation inhibit anti-self CTLs to prevent tissue damage. These mechanisms are exploited by pathogens and tumors to evade the immune response, and present a major hurdle to adoptive CTL therapies. It is unclear whether CTL inactivation is Ag specific and, if so, which APCs are involved. Potential candidates include the target cells themselves, dendritic cells, myeloid-derived suppressor cells, and macrophages. In this study, we show that lymphoma-specific CTLs are rapidly deleted in an Ag-specific manner after adoptive transfer into lymphoma-bearing mice, and the surviving CTLs are functionally impaired. The only APCs responsible were the target cells directly presenting Ag, notwithstanding the presence of myeloid-derived suppressor cells, and CD8(+) dendritic cells cross-presenting tumor Ag. The capacity to inactivate CTLs critically depended on the number of tumor/target cells; small numbers of targets were readily killed, but a large number caused quick deletion and functional inactivation of the CTLs. Application of mild, noninflammatory, and nonlymphoablative chemotherapy to specifically reduce tumor burden before CTL injection prevented CTL deletion and inactivation and allowed eradication of tumor. Our results advocate the use of adoptive CTL therapy soon after mild chemotherapy. They also suggest a simple mechanism for Ag-specific impairment of anti-self CTLs in the face of an active anti-foreign CTL response.
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ItemInflammation Conditions Mature Dendritic Cells To Retain the Capacity To Present New Antigens but with Altered Cytokine Secretion Function(AMER ASSOC IMMUNOLOGISTS, 2014-10-15)Dendritic cells (DCs) are directly activated by pathogen-associated molecular patterns (PAMPs) and undergo maturation. Mature DCs express high levels of MHC class II molecules ("signal 1"), upregulate T cell costimulatory receptors ("signal 2"), and secrete "signal 3" cytokines (e.g., IL-12). Mature DCs efficiently present Ags linked to the activating PAMP and prime naive T cells. However, mature DCs downregulate MHC II synthesis, which prevents them from presenting newly encountered Ags. DCs can also be indirectly activated by inflammatory mediators released during infection (e.g., IFN). Indirectly activated DCs mature but do not present pathogen Ags (as they have not encountered the pathogen) and do not provide signal 3. Therefore, although they are probably generated in large numbers upon infection or vaccination, indirectly activated DCs are considered to play little or no role in T cell immunity. In this article, we show that indirectly activated DCs retain their capacity to present Ags encountered after maturation in vivo. They can also respond to PAMPs, but the previous encounter of inflammatory signals alters their cytokine (signal 3) secretion pattern. This implies that the immune response elicited by a PAMP is more complex than predicted by the examination of the immunogenic features of directly activated DCs, and that underlying inflammatory processes can skew the immune response against pathogens. Our observations have important implications for the design of vaccines and for the understanding of the interactions between simultaneous infections, or of infection in the context of ongoing sterile inflammation.
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ItemCriteria for Dendritic Cell Receptor Selection for Efficient Antibody-Targeted Vaccination(AMER ASSOC IMMUNOLOGISTS, 2015-03-15)Ab-targeted vaccination involves targeting a receptor of choice expressed by dendritic cells (DCs) with Ag-coupled Abs. Currently, there is little consensus as to which criteria determine receptor selection to ensure superior Ag presentation and immunity. In this study, we investigated parameters of DC receptor internalization and determined how they impact Ag presentation outcomes. First, using mixed bone marrow chimeras, we established that Ag-targeted, but not nontargeted, DCs are responsible for Ag presentation in settings of Ab-targeted vaccination in vivo. Next, we analyzed parameters of DEC205 (CD205), Clec9A, CD11c, CD11b, and CD40 endocytosis and obtained quantitative measurements of internalization speed, surface turnover, and delivered Ag load. Exploiting these parameters in MHC class I (MHC I) and MHC class II (MHC II) Ag presentation assays, we showed that receptor expression level, proportion of surface turnover, or speed of receptor internalization did not impact MHC I or MHC II Ag presentation efficiency. Furthermore, the Ag load delivered to DCs did not correlate with the efficiency of MHC I or MHC II Ag presentation. In contrast, targeting Ag to CD8(+) or CD8(-) DCs enhanced MHC I or MHC II Ag presentation, respectively. Therefore, receptor expression levels, speed of internalization, and/or the amount of Ag delivered can be excluded as major determinants that dictate Ag presentation efficiency in setting of Ab-targeted vaccination.
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ItemModulation of antigen presentation by intracellular trafficking(CURRENT BIOLOGY LTD, 2015-06-01)Processing and loading of antigen into major histocompatibility complex molecules (MHC) occurs in specific intracellular compartments. Accessing MHC loading compartments requires trafficking via specific pathways, some of which have yet to be fully characterized. For MHC I, cross-presentation involves antigen trafficking to a specialised compartment. We review the features of this compartment and how it is accessed by different mechanisms of antigen capture and internalization. We also summarize advances in understanding how antigen efficiently accesses the MHC II loading compartment, with particular focus on the role of autophagy. Understanding the mechanisms that control how antigen is trafficked to specific compartments for loading and presentation is crucial if these pathways are to be manipulated more effectively in settings of vaccination.
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ItemDifferential use of autophagy by primary dendritic cells specialized in cross-presentation(TAYLOR & FRANCIS INC, 2015-06-01)Antigen-presenting cells survey their environment and present captured antigens bound to major histocompatibility complex (MHC) molecules. Formation of MHC-antigen complexes occurs in specialized compartments where multiple protein trafficking routes, still incompletely understood, converge. Autophagy is a route that enables the presentation of cytosolic antigen by MHC class II molecules. Some reports also implicate autophagy in the presentation of extracellular, endocytosed antigen by MHC class I molecules, a pathway termed "cross-presentation." The role of autophagy in cross-presentation is controversial. This may be due to studies using different types of antigen presenting cells for which the use of autophagy is not well defined. Here we report that active use of autophagy is evident only in DC subtypes specialized in cross-presentation. However, the contribution of autophagy to cross-presentation varied depending on the form of antigen: it was negligible in the case of cell-associated antigen or antigen delivered via receptor-mediated endocytosis, but more prominent when the antigen was a soluble protein. These findings highlight the differential use of autophagy and its machinery by primary cells equipped with specific immune function, and prompt careful reassessment of the participation of this endocytic pathway in antigen cross-presentation.