Dr Oliver Bannard

Research Area: Immunology
Technology Exchange: Cellular immunology, Flow cytometry and Immunohistochemistry
Scientific Themes: Immunology & Infectious Disease
Keywords: B cell Immunology, Germinal Center Responses and Adaptive Immunity
Germinal center (GC) B cells and T cells (blue) cluster within the B cell follicle (grey). GCs contain two distinct zones, known as the light zone and the dark zone, that cells move back and forth between. The light zone is identifiable by the presence of follicular dendritic cells (red), while the dark zone contains a dense network of CXCL12-expressing reticular cells (green). Movement of GC B cells between these zones is associated with switching between centrocyte and centroblast phenotypes.

Germinal center (GC) B cells and T cells (blue) cluster within the B cell follicle (grey). GCs ...

The GC dark zone is the principle site of somatic hypermutation and mitosis. Mitotic cells are identifiable by phospho-histone H3 staining (red). Zoomed images of the boxed cells are shown below. Selection is thought to occur in the light zone while cells are at the centrocyte stage.

The GC dark zone is the principle site of somatic hypermutation and mitosis. Mitotic cells are ...

A simplified graphic model for GC responses. Our recent findings suggest that the switching of GC B cells between centroblast (dark zone) and centrocyte (light zone) stages is determined by an intrinsic cellular program involving a timer component. The transitioning between these stages prepares cells to engage in the processes associated with their respective zones.

A simplified graphic model for GC responses. Our recent findings suggest that the switching of GC B ...

The adaptive immune system learns from primary exposures to pathogens to help prevent secondary infections of the same or similar kinds. One of the key ways by which this is achieved is through the production of specific antibodies – secreted proteins, made by terminally differentiated B cells (plasma cells), that bind to foreign objects such as viruses and bacteria to prevent their infecting host cells and to promote their clearance from the body. Most effective vaccines depend upon antibodies for the protection that they confer, however the processes determining the quality of the antibodies generated during an immune response are incompletely understood. We are investigating the biology of antibody development.

Our main research interest is in determining the mechanisms controlling germinal center reactions. Germinal centers are unique transient structures that form within the B cell follicles of lymphoid tissues during immune responses and are the principle sites of antibody affinity maturation and B cell receptor diversification. Random point mutations are introduced into the immunoglobulin (antibody) genes of germinal center B cells for the purpose of refining their specificity for cognate antigen. Rare B cells in which mutations lead to increases in antibody affinity capture more antigen through their membrane receptors and present more peptide-MHCII on their surface, allowing them to out-compete neighboring cells in acquiring “help” from limiting numbers of follicular helper T cells. The quality of the “help” received is also likely to be reflective of the amount of peptide antigen presented. Affinity maturation occurs through many iterative rounds of mutation and selection. The benefits of affinity maturation are great enough to justify the risks associated with genome mutagenesis, however complex regulation of GC responses is needed because off-target mutations can and do cause lymphomas.

The switching of germinal center B cells between mutagenic (centroblast) and selection (centrocyte) stages is determined by an intrinsic cellular program involving a “timer”, however the molecular mechanisms controlling this behavior are not known and are a focus of our research. We also are invested in understanding the types of specialized adaptations that germinal center B cells have evolved to allow them to cope with the unique demands associated with frequently and repetitively changing receptor specificity while simultaneously ensuring that selection is stringent and efficient. We hope to gain a better understanding of the dynamics of the mutation and selection processes and to determine what signals contribute to them. Our approaches include developing new in vivo mouse models that allow us to interrogate the behavior of GC B cells in their native unperturbed environment. The medical value of this research is that it may lead to a better understanding of how to promote immunity, prevent autoimmunity and identify druggable targets for cancers.

There are no collaborations listed for this principal investigator.

Bannard O, Cyster JG. 2017. Germinal centers: programmed for affinity maturation and antibody diversification. Curr Opin Immunol, 45 pp. 21-30. | Show Abstract | Read more

The seminal discovery by Eisen that antibodies undergo improvements in antigen-binding affinity over the course of an immune response led to a long running search for the underlying mechanism. Germinal centers in lymphoid organs are now recognized to be critically involved in this phenomenon, known as antibody affinity maturation. As well as improving in affinity for specific epitopes, some antibody responses maintain or even increase their breadth of antigen-recognition over time. This has led to another intense line of research aimed at understanding how broadly neutralizing anti-pathogen responses are generated. Recent work indicates that germinal centers also play an important role in the diversification process. We discuss current understanding of how germinal centers are programmed to support both affinity maturation and antibody diversification.

Bannard O, McGowan SJ, Ersching J, Ishido S, Victora GD, Shin J-S, Cyster JG. 2016. Ubiquitin-mediated fluctuations in MHC class II facilitate efficient germinal center B cell responses. J Exp Med, 213 (6), pp. 993-1009. | Show Abstract | Read more

Antibody affinity maturation occurs in germinal centers (GCs) through iterative rounds of somatic hypermutation and selection. Selection involves B cells competing for T cell help based on the amount of antigen they capture and present on their MHC class II (MHCII) proteins. How GC B cells are able to rapidly and repeatedly transition between mutating their B cell receptor genes and then being selected shortly after is not known. We report that MHCII surface levels and degradation are dynamically regulated in GC B cells. Through ectopic expression of a photoconvertible MHCII-mKikGR chimeric gene, we found that individual GC B cells differed in the rates of MHCII protein turnover. Fluctuations in surface MHCII levels were dependent on ubiquitination and the E3 ligase March1. Increases in March1 expression in centroblasts correlated with decreases in surface MHCII levels, whereas CD83 expression in centrocytes helped to stabilize MHCII at that stage. Defects in MHCII ubiquitination caused GC B cells to accumulate greater amounts of a specific peptide-MHCII (pMHCII), suggesting that MHCII turnover facilitates the replacement of old complexes. We propose that pMHCII complexes are periodically targeted for degradation in centroblasts to favor the presentation of recently acquired antigens, thereby promoting the fidelity and efficiency of selection.

Rodda LB, Bannard O, Ludewig B, Nagasawa T, Cyster JG. 2015. Phenotypic and Morphological Properties of Germinal Center Dark Zone Cxcl12-Expressing Reticular Cells. J Immunol, 195 (10), pp. 4781-4791. | Show Abstract | Read more

The germinal center (GC) is divided into a dark zone (DZ) and a light zone (LZ). GC B cells must cycle between these zones to achieve efficient Ab affinity maturation. Follicular dendritic cells (FDCs) are well characterized for their role in supporting B cell Ag encounter in primary follicles and in the GC LZ. However, the properties of stromal cells supporting B cells in the DZ are relatively unexplored. Recent work identified a novel stromal population of Cxcl12-expressing reticular cells (CRCs) in murine GC DZs. In this article, we report that CRCs have diverse morphologies, appearing in open and closed networks, with variable distribution in lymphoid tissue GCs. CRCs are also present in splenic and peripheral lymph node primary follicles. Real-time two-photon microscopy of Peyer's patch GCs demonstrates B cells moving in close association with CRC processes. CRCs are gp38(+) with low to undetectable expression of FDC markers, but CRC-like cells in the DZ are lineage marked, along with FDCs and fibroblastic reticular cells, by CD21-Cre- and Ccl19-Cre-directed fluorescent reporters. In contrast to FDCs, CRCs do not demonstrate dependence on lymphotoxin or TNF for chemokine expression or network morphology. CRC distribution in the DZ does require CXCR4 signaling, which is necessary for GC B cells to access the DZ and likely to interact with CRC processes. Our findings establish CRCs as a major stromal cell type in the GC DZ and suggest that CRCs support critical activities of GC B cells in the DZ niche through Cxcl12 expression and direct cell-cell interactions.

Dos Santos LI, Galvão-Filho B, de Faria PC, Junqueira C, Dutra MS, Teixeira SMR, Rodrigues MM, Ritter G, Bannard O, Fearon DT et al. 2015. Blockade of CTLA-4 promotes the development of effector CD8+ T lymphocytes and the therapeutic effect of vaccination with an attenuated protozoan expressing NY-ESO-1. Cancer Immunol Immunother, 64 (3), pp. 311-323. | Show Abstract | Read more

The development of cancer immunotherapy has long been a challenge. Here, we report that prophylactic vaccination with a highly attenuated Trypanosoma cruzi strain expressing NY-ESO-1 (CL-14-NY-ESO-1) induces both effector memory and effector CD8(+) T lymphocytes that efficiently prevent tumor development. However, the therapeutic effect of such a vaccine is limited. We also demonstrate that blockade of Cytotoxic T Lymphocyte Antigen 4 (CTLA-4) during vaccination enhances the frequency of NY-ESO-1-specific effector CD8(+) T cells producing IFN-γ and promotes lymphocyte migration to the tumor infiltrate. As a result, therapy with CL-14-NY-ESO-1 together with anti-CTLA-4 is highly effective in controlling the development of an established melanoma.

Wang X, Rodda LB, Bannard O, Cyster JG. 2014. Integrin-mediated interactions between B cells and follicular dendritic cells influence germinal center B cell fitness. J Immunol, 192 (10), pp. 4601-4609. | Show Abstract | Read more

Integrin-ligand interactions between germinal center (GC) B cells and Ag-presenting follicular dendritic cells (FDCs) have been suggested to play central roles during GC responses, but their in vivo requirement has not been directly tested. In this study, we show that, whereas integrins αLβ2 and α4β1 are highly expressed and functional on mouse GC B cells, removal of single integrins or their ligands had little effect on B cell participation in the GC response. Combined β2 integrin deficiency and α4 integrin blockade also did not affect the GC response against a particulate Ag. However, the combined integrin deficiency did cause B cells to be outcompeted in splenic GC responses against a soluble protein Ag and in mesenteric lymph node GC responses against gut-derived Ags. Similar findings were made for β2-deficient B cells in mice lacking VCAM1 on FDCs. The reduced fitness of the GC B cells did not appear to be due to decreased Ag acquisition, proliferation rates, or pAKT levels. In summary, our findings provide evidence that αLβ2 and α4β1 play overlapping and context-dependent roles in supporting interactions with FDCs that can augment the fitness of responding GC B cells. We also find that mouse GC B cells upregulate αvβ3 and adhere to vitronectin and milk-fat globule epidermal growth factor VIII protein. Integrin β3-deficient B cells contributed in a slightly exaggerated manner to GC responses, suggesting this integrin has a regulatory function in GC B cells.

Bannard O, Horton RM, Allen CDC, An J, Nagasawa T, Cyster JG. 2013. Germinal center centroblasts transition to a centrocyte phenotype according to a timed program and depend on the dark zone for effective selection. Immunity, 39 (5), pp. 912-924. | Show Abstract | Read more

Germinal center (GC) B cells cycle between the dark zone (DZ) and light zone (LZ) during antibody affinity maturation. Whether this movement is necessary for GC function has not been tested. Here we show that CXCR4-deficient GC B cells, which are restricted to the LZ, are gradually outcompeted by WT cells indicating an essential role for DZ access. Remarkably, the transition between DZ centroblast and LZ centrocyte phenotypes occurred independently of positioning. However, CXCR4-deficient cells carried fewer mutations and were overrepresented in the CD73(+) memory compartment. These findings are consistent with a model where GC B cells change from DZ to LZ phenotype according to a timed cellular program but suggest that spatial separation of DZ cells facilitates more effective rounds of mutation and selection. Finally, we identify a network of DZ CXCL12-expressing reticular cells that likely support DZ functions.

Baumjohann D, Kageyama R, Clingan JM, Morar MM, Patel S, de Kouchkovsky D, Bannard O, Bluestone JA, Matloubian M, Ansel KM, Jeker LT. 2013. The microRNA cluster miR-17∼92 promotes TFH cell differentiation and represses subset-inappropriate gene expression. Nat Immunol, 14 (8), pp. 840-848. | Show Abstract | Read more

Follicular helper T cells (TFH cells) are the prototypic helper T cell subset specialized to enable B cells to form germinal centers (GCs) and produce high-affinity antibodies. We found that expression of microRNAs (miRNAs) by T cells was essential for TFH cell differentiation. More specifically, we show that after immunization of mice with protein, the miRNA cluster miR-17∼92 was critical for robust differentiation and function of TFH cells in a cell-intrinsic manner that occurred regardless of changes in proliferation. In a viral infection model, miR-17∼92 restrained the expression of genes 'inappropriate' to the TFH cell subset, including the direct miR-17∼92 target Rora. Removal of one Rora allele partially 'rescued' the inappropriate gene signature in miR-17∼92-deficient TFH cells. Our results identify the miR-17∼92 cluster as a critical regulator of T cell-dependent antibody responses, TFH cell differentiation and the fidelity of the TFH cell gene-expression program.

Schmidt TH, Bannard O, Gray EE, Cyster JG. 2013. CXCR4 promotes B cell egress from Peyer's patches. J Exp Med, 210 (6), pp. 1099-1107. | Show Abstract | Read more

Peyer's patches (PPs) play a central role in supporting B cell responses against intestinal antigens, yet the factors controlling B cell passage through these mucosal lymphoid tissues are incompletely understood. We report that, in mixed chimeras, CXCR4-deficient B cells accumulate in PPs compared with their representation in other lymphoid tissues. CXCR4-deficient B cells egress from PPs more slowly than wild-type cells, whereas CXCR5-deficient cells egress more rapidly. The CXCR4 ligand, CXCL12, is expressed by cells adjacent to lymphatic endothelial cells in a zone that abuts but minimally overlaps with the CXCL13(+) follicle. CXCR4-deficient B cells show reduced localization to these CXCL12(+) perilymphatic zones, whereas CXCR5-deficient B cells preferentially localize in these regions. By photoconverting KikGR-expressing cells within surgically exposed PPs, we provide evidence that naive B cells transit PPs with an approximate residency half-life of 10 h. When CXCR4 is lacking, KikGR(+) B cells show a delay in PP egress. In summary, we identify a CXCL12(hi) perilymphatic zone in PPs that plays a role in overcoming CXCL13-mediated retention to promote B cell egress from these gut-associated lymphoid tissues.

Bannard OM, Cyster JG. 2012. Immunology. When less signaling is more. Science, 336 (6085), pp. 1120-1121. | Show Abstract | Read more

Negative regulation of B cell receptor signaling may contribute to B cell selection and cell fate determination in germinal centers.

Mackay LK, Wakim L, van Vliet CJ, Jones CM, Mueller SN, Bannard O, Fearon DT, Heath WR, Carbone FR. 2012. Maintenance of T cell function in the face of chronic antigen stimulation and repeated reactivation for a latent virus infection. J Immunol, 188 (5), pp. 2173-2178. | Show Abstract | Read more

Persisting infections are often associated with chronic T cell activation. For certain pathogens, this can lead to T cell exhaustion and survival of what is otherwise a cleared infection. In contrast, for herpesviruses, T cells never eliminate infection once it is established. Instead, effective immunity appears to maintain these pathogens in a state of latency. We used infection with HSV to examine whether effector-type T cells undergoing chronic stimulation retained functional and proliferative capacity during latency and subsequent reactivation. We found that latency-associated T cells exhibited a polyfunctional phenotype and could secrete a range of effector cytokines. These T cells were also capable of mounting a recall proliferative response on HSV reactivation and could do so repeatedly. Thus, for this latent infection, T cells subjected to chronic Ag stimulation and periodic reactivation retain the ability to respond to local virus challenge.

Bannard O, Kraman M, Fearon DT. 2010. Cutting edge: Virus-specific CD8+ T cell clones and the maintenance of replicative function during a persistent viral infection. J Immunol, 185 (12), pp. 7141-7145. | Show Abstract | Read more

Persistent viral infections induce the differentiation and accumulation of large numbers of senescent CD8(+) T cells, raising the possibility that repetitive stimulation drives clones of T cells to senesce. It is therefore unclear whether T cell responses are maintained by the self-renewal of Ag-experienced peripheral T cell subsets or by the continuous recruitment of newly generated naive T cells during chronic infections. Using a transgenic mouse model that permits the indelible marking of granzyme B-expressing cells, we found that T cells primed during the initial stages of a persistent murine γ-herpes infection persisted and continued to divide during a latent phase of up to 7 mo. Such cells maintained an ability to extensively replicate in response to challenge with influenza virus expressing the same Ag. Therefore, Ag-experienced, virus-specific CD8(+) T cell populations contain a subset that maintains replicative potential, despite long-term, persistent antigenic stimulation.

Bannard O, Kraman M, Fearon D. 2009. Pathways of memory CD8+ T-cell development. Eur J Immunol, 39 (8), pp. 2083-2087. | Show Abstract | Read more

CD8(+) T-cell responses must have at least two components, a replicative cell type that proliferates in the secondary lymphoid tissue and that is responsible for clonal expansion, and cytotoxic cells with effector functions that mediate the resolution of the infection in the peripheral tissues. To confer memory, the response must also generate replication-competent T cells that persist in the absence of antigen after the primary infection is cleared. The current models of memory differentiation differ in regards to whether or not memory CD8(+) T cells acquire effector functions during their development. In this review we discuss the existing models for memory development and the consequences that the recent finding that memory CD8(+) T cells may express granzyme B during their development has for them. We propose that memory CD8(+) T cells represent a self-renewing population of T cells that may acquire effector functions but that do not lose the naïve-like attributes of lymphoid homing, antigen-independent persistence or the capacity for self-renewal.

Bannard O, Kraman M, Fearon DT. 2009. Secondary replicative function of CD8+ T cells that had developed an effector phenotype. Science, 323 (5913), pp. 505-509. | Show Abstract | Read more

Models of the differentiation of memory CD8+ T cells that replicate during secondary infections differ over whether such cells had acquired effector function during primary infections. We created a transgenic mouse line that permits mapping of the fate of granzyme B (gzmB)-expressing CD8+ T cells and their progeny by indelibly marking them with enhanced yellow fluorescent protein (EYFP). Virus-specific CD8+ T cells express gzmB within the first 2 days of a primary response to infection with influenza, without impairment of continued primary clonal expansion. On secondary infection, virus-specific CD8+ T cells that became EYFP+ during a primary infection clonally expand as well as all virus-specific CD8+ T cells. Thus, CD8+ T cells that have acquired an effector phenotype during primary infection may function as memory cells with replicative function.

Bannard O, Cyster JG. 2017. Germinal centers: programmed for affinity maturation and antibody diversification. Curr Opin Immunol, 45 pp. 21-30. | Show Abstract | Read more

The seminal discovery by Eisen that antibodies undergo improvements in antigen-binding affinity over the course of an immune response led to a long running search for the underlying mechanism. Germinal centers in lymphoid organs are now recognized to be critically involved in this phenomenon, known as antibody affinity maturation. As well as improving in affinity for specific epitopes, some antibody responses maintain or even increase their breadth of antigen-recognition over time. This has led to another intense line of research aimed at understanding how broadly neutralizing anti-pathogen responses are generated. Recent work indicates that germinal centers also play an important role in the diversification process. We discuss current understanding of how germinal centers are programmed to support both affinity maturation and antibody diversification.

Bannard O, McGowan SJ, Ersching J, Ishido S, Victora GD, Shin J-S, Cyster JG. 2016. Ubiquitin-mediated fluctuations in MHC class II facilitate efficient germinal center B cell responses. J Exp Med, 213 (6), pp. 993-1009. | Show Abstract | Read more

Antibody affinity maturation occurs in germinal centers (GCs) through iterative rounds of somatic hypermutation and selection. Selection involves B cells competing for T cell help based on the amount of antigen they capture and present on their MHC class II (MHCII) proteins. How GC B cells are able to rapidly and repeatedly transition between mutating their B cell receptor genes and then being selected shortly after is not known. We report that MHCII surface levels and degradation are dynamically regulated in GC B cells. Through ectopic expression of a photoconvertible MHCII-mKikGR chimeric gene, we found that individual GC B cells differed in the rates of MHCII protein turnover. Fluctuations in surface MHCII levels were dependent on ubiquitination and the E3 ligase March1. Increases in March1 expression in centroblasts correlated with decreases in surface MHCII levels, whereas CD83 expression in centrocytes helped to stabilize MHCII at that stage. Defects in MHCII ubiquitination caused GC B cells to accumulate greater amounts of a specific peptide-MHCII (pMHCII), suggesting that MHCII turnover facilitates the replacement of old complexes. We propose that pMHCII complexes are periodically targeted for degradation in centroblasts to favor the presentation of recently acquired antigens, thereby promoting the fidelity and efficiency of selection.

Rodda LB, Bannard O, Ludewig B, Nagasawa T, Cyster JG. 2015. Phenotypic and Morphological Properties of Germinal Center Dark Zone Cxcl12-Expressing Reticular Cells. J Immunol, 195 (10), pp. 4781-4791. | Show Abstract | Read more

The germinal center (GC) is divided into a dark zone (DZ) and a light zone (LZ). GC B cells must cycle between these zones to achieve efficient Ab affinity maturation. Follicular dendritic cells (FDCs) are well characterized for their role in supporting B cell Ag encounter in primary follicles and in the GC LZ. However, the properties of stromal cells supporting B cells in the DZ are relatively unexplored. Recent work identified a novel stromal population of Cxcl12-expressing reticular cells (CRCs) in murine GC DZs. In this article, we report that CRCs have diverse morphologies, appearing in open and closed networks, with variable distribution in lymphoid tissue GCs. CRCs are also present in splenic and peripheral lymph node primary follicles. Real-time two-photon microscopy of Peyer's patch GCs demonstrates B cells moving in close association with CRC processes. CRCs are gp38(+) with low to undetectable expression of FDC markers, but CRC-like cells in the DZ are lineage marked, along with FDCs and fibroblastic reticular cells, by CD21-Cre- and Ccl19-Cre-directed fluorescent reporters. In contrast to FDCs, CRCs do not demonstrate dependence on lymphotoxin or TNF for chemokine expression or network morphology. CRC distribution in the DZ does require CXCR4 signaling, which is necessary for GC B cells to access the DZ and likely to interact with CRC processes. Our findings establish CRCs as a major stromal cell type in the GC DZ and suggest that CRCs support critical activities of GC B cells in the DZ niche through Cxcl12 expression and direct cell-cell interactions.

Bannard O, Horton RM, Allen CDC, An J, Nagasawa T, Cyster JG. 2013. Germinal center centroblasts transition to a centrocyte phenotype according to a timed program and depend on the dark zone for effective selection. Immunity, 39 (5), pp. 912-924. | Show Abstract | Read more

Germinal center (GC) B cells cycle between the dark zone (DZ) and light zone (LZ) during antibody affinity maturation. Whether this movement is necessary for GC function has not been tested. Here we show that CXCR4-deficient GC B cells, which are restricted to the LZ, are gradually outcompeted by WT cells indicating an essential role for DZ access. Remarkably, the transition between DZ centroblast and LZ centrocyte phenotypes occurred independently of positioning. However, CXCR4-deficient cells carried fewer mutations and were overrepresented in the CD73(+) memory compartment. These findings are consistent with a model where GC B cells change from DZ to LZ phenotype according to a timed cellular program but suggest that spatial separation of DZ cells facilitates more effective rounds of mutation and selection. Finally, we identify a network of DZ CXCL12-expressing reticular cells that likely support DZ functions.

Schmidt TH, Bannard O, Gray EE, Cyster JG. 2013. CXCR4 promotes B cell egress from Peyer's patches. J Exp Med, 210 (6), pp. 1099-1107. | Show Abstract | Read more

Peyer's patches (PPs) play a central role in supporting B cell responses against intestinal antigens, yet the factors controlling B cell passage through these mucosal lymphoid tissues are incompletely understood. We report that, in mixed chimeras, CXCR4-deficient B cells accumulate in PPs compared with their representation in other lymphoid tissues. CXCR4-deficient B cells egress from PPs more slowly than wild-type cells, whereas CXCR5-deficient cells egress more rapidly. The CXCR4 ligand, CXCL12, is expressed by cells adjacent to lymphatic endothelial cells in a zone that abuts but minimally overlaps with the CXCL13(+) follicle. CXCR4-deficient B cells show reduced localization to these CXCL12(+) perilymphatic zones, whereas CXCR5-deficient B cells preferentially localize in these regions. By photoconverting KikGR-expressing cells within surgically exposed PPs, we provide evidence that naive B cells transit PPs with an approximate residency half-life of 10 h. When CXCR4 is lacking, KikGR(+) B cells show a delay in PP egress. In summary, we identify a CXCL12(hi) perilymphatic zone in PPs that plays a role in overcoming CXCL13-mediated retention to promote B cell egress from these gut-associated lymphoid tissues.

Bannard OM, Cyster JG. 2012. Immunology. When less signaling is more. Science, 336 (6085), pp. 1120-1121. | Show Abstract | Read more

Negative regulation of B cell receptor signaling may contribute to B cell selection and cell fate determination in germinal centers.

Mackay LK, Wakim L, van Vliet CJ, Jones CM, Mueller SN, Bannard O, Fearon DT, Heath WR, Carbone FR. 2012. Maintenance of T cell function in the face of chronic antigen stimulation and repeated reactivation for a latent virus infection. J Immunol, 188 (5), pp. 2173-2178. | Show Abstract | Read more

Persisting infections are often associated with chronic T cell activation. For certain pathogens, this can lead to T cell exhaustion and survival of what is otherwise a cleared infection. In contrast, for herpesviruses, T cells never eliminate infection once it is established. Instead, effective immunity appears to maintain these pathogens in a state of latency. We used infection with HSV to examine whether effector-type T cells undergoing chronic stimulation retained functional and proliferative capacity during latency and subsequent reactivation. We found that latency-associated T cells exhibited a polyfunctional phenotype and could secrete a range of effector cytokines. These T cells were also capable of mounting a recall proliferative response on HSV reactivation and could do so repeatedly. Thus, for this latent infection, T cells subjected to chronic Ag stimulation and periodic reactivation retain the ability to respond to local virus challenge.

Bannard O, Kraman M, Fearon DT. 2010. Cutting edge: Virus-specific CD8+ T cell clones and the maintenance of replicative function during a persistent viral infection. J Immunol, 185 (12), pp. 7141-7145. | Show Abstract | Read more

Persistent viral infections induce the differentiation and accumulation of large numbers of senescent CD8(+) T cells, raising the possibility that repetitive stimulation drives clones of T cells to senesce. It is therefore unclear whether T cell responses are maintained by the self-renewal of Ag-experienced peripheral T cell subsets or by the continuous recruitment of newly generated naive T cells during chronic infections. Using a transgenic mouse model that permits the indelible marking of granzyme B-expressing cells, we found that T cells primed during the initial stages of a persistent murine γ-herpes infection persisted and continued to divide during a latent phase of up to 7 mo. Such cells maintained an ability to extensively replicate in response to challenge with influenza virus expressing the same Ag. Therefore, Ag-experienced, virus-specific CD8(+) T cell populations contain a subset that maintains replicative potential, despite long-term, persistent antigenic stimulation.

Bannard O, Kraman M, Fearon D. 2009. Pathways of memory CD8+ T-cell development. Eur J Immunol, 39 (8), pp. 2083-2087. | Show Abstract | Read more

CD8(+) T-cell responses must have at least two components, a replicative cell type that proliferates in the secondary lymphoid tissue and that is responsible for clonal expansion, and cytotoxic cells with effector functions that mediate the resolution of the infection in the peripheral tissues. To confer memory, the response must also generate replication-competent T cells that persist in the absence of antigen after the primary infection is cleared. The current models of memory differentiation differ in regards to whether or not memory CD8(+) T cells acquire effector functions during their development. In this review we discuss the existing models for memory development and the consequences that the recent finding that memory CD8(+) T cells may express granzyme B during their development has for them. We propose that memory CD8(+) T cells represent a self-renewing population of T cells that may acquire effector functions but that do not lose the naïve-like attributes of lymphoid homing, antigen-independent persistence or the capacity for self-renewal.

Bannard O, Kraman M, Fearon DT. 2009. Secondary replicative function of CD8+ T cells that had developed an effector phenotype. Science, 323 (5913), pp. 505-509. | Show Abstract | Read more

Models of the differentiation of memory CD8+ T cells that replicate during secondary infections differ over whether such cells had acquired effector function during primary infections. We created a transgenic mouse line that permits mapping of the fate of granzyme B (gzmB)-expressing CD8+ T cells and their progeny by indelibly marking them with enhanced yellow fluorescent protein (EYFP). Virus-specific CD8+ T cells express gzmB within the first 2 days of a primary response to infection with influenza, without impairment of continued primary clonal expansion. On secondary infection, virus-specific CD8+ T cells that became EYFP+ during a primary infection clonally expand as well as all virus-specific CD8+ T cells. Thus, CD8+ T cells that have acquired an effector phenotype during primary infection may function as memory cells with replicative function.

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