Epistemic_Statements  

CORD-19:12d35c12218f230c49f4dc892814ba9f1037f251 JSONTXT 8 Projects

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Id Subject Object Predicate Lexical cue
T1 393-605 Epistemic_statement denotes Despite enormous advances in understanding the attributes of a protective mucosal antiviral immune response, current vaccines continue to fail in effectively generating long-lived protective CD8 + Tcell immunity.
T2 763-944 Epistemic_statement denotes In recent years, the selective manipulation of specific costimulatory pathways, which are critical in regulating T-cell-mediated immune responses, has generated increasing interest.
T3 1238-1407 Epistemic_statement denotes In this review, we highlight these new findings with a particular emphasis on their potential as immunological adjuvants to enhance poxvirus-based CD8 + T-cell vaccines.
T4 1615-1862 Epistemic_statement denotes Consequently, the body's respiratory mucosal surfaces contain a complex array of immune regulatory mechanisms that ensures, at least in healthy individuals, a quiescent and non-inflammatory environment that maintains optimal tissue function (1-3).
T5 1863-2188 Epistemic_statement denotes However, once a pathogen establishes an infection or the regulatory mechanisms fail, a rapid cascade of events leads to the production of inflammatory cytokines that recruit immune cells in an attempt to eradicate the ensuing pathogen/antigenic stimuli while minimizing the impact on the physiological function of the tissue.
T6 2189-2457 Epistemic_statement denotes This ideal conclusion, however, often does not occur, as many human pathogens have evolved virulence and immune modulatory mechanisms that circumvent and disrupt mucosal immune responses resulting in tissue pathology, clinical disease, and possible long-term sequelae.
T7 2907-3241 Epistemic_statement denotes Yet, despite the continued success and widespread use of respiratory pathogen vaccines, Mycobacterium tuberculosis (TB) and a multitude of respiratory viral infections continue to cause significant morbidity and result in millions of futile deaths each year (7) (8) (9) [World Health Organization (WHO) 2004 Global Burden of Disease].
T8 3242-3344 Epistemic_statement denotes Influenza virus alone causes seasonal epidemics that can affect 10-20% of the global population (10) .
T9 3345-3609 Epistemic_statement denotes Recent estimates suggest that seasonal influenza viral infections are responsible for between 250,000 to 500,000 deaths annually, which can increase during pandemics caused by the emergence of a novel re-assortment viral strain (WHO 2004 Global Burden of Disease).
T10 3812-4129 Epistemic_statement denotes In addition to influenza virus, parainfluenza virus, respiratory syncytial virus (RSV), meta-pneumonia virus, severe acute respiratory syndrome coronavirus (SARS-CoV), rhinovirus, measles, and adenovirus are endemic within the human population and can establish acute respiratory tract infection (11) (12) (13) (14) .
T11 4246-4517 Epistemic_statement denotes Ominously, the public health impact of respiratory infections is likely to increase in the near future due to aging global populations, increasing antibiotic resistance (in the case of TB and pneumococcus) and altering social attitudes toward vaccination (14) (15) (16) .
T12 4518-4994 Epistemic_statement denotes Moreover, the continuing emergence of novel respiratory viruses (through antigenic recombination events and zoonosis), such as the 2009 H1N1 influenza A virus strain, highly pathogenic avian influenza viruses, SARS coronavirus and human cases of monkeypox (11, 17, 18) , taken together with the continued concern of bio-terrorism (anthrax and smallpox) (19, 20) adds to the urgent need to better understand the pathogenesis of respiratory viruses and mechanisms of protection.
T13 5395-5694 Epistemic_statement denotes We then examine how attenuated poxviruses have been developed over the past three decades as candidate vaccines for a variety of mucosal pathogens and discuss how future efforts should focus on understanding in molecular terms why live non-attenuated vaccines result in better CD8 + T-cell immunity.
T14 5695-5961 Epistemic_statement denotes In the final section, we discuss how members of tumor necrosis factor receptor (TNFR)/TNF superfamily, specifically, OX40 (CD134) and its binding partner OX40L (CD252), are rapidly emerging as key players in the development of protective CD8 + T-cell memory in lung.
T15 6676-6863 Epistemic_statement denotes However, in the context of highly pathogenic or rapidly mutating viruses that target mucosal surfaces such as the respiratory tract, this approach has proven far less successful (6, 21) .
T16 6864-7018 Epistemic_statement denotes The limitations of generating solely immunoglobulin-mediated protection are highlighted by the necessity to annually develop a seasonal influenza vaccine.
T17 7465-7679 Epistemic_statement denotes This continual antigen drift or evolution also explains, in part, the difficulty in developing an effective vaccine against other intracellular pathogens such as human immunodeficiency virus (HIV) and malaria (6) .
T18 7900-8154 Epistemic_statement denotes This continued dilemma has led to the general acceptance that to develop effective vaccines against these types of intracellular pathogens, a combination of immunoglobulin and a long-lasting memory CD8 + T-cell response must be generated (24) (25) (26) .
T19 8380-8532 Epistemic_statement denotes This would be an ideal strategy in the context of a virus that rapidly mutated its external antigens while maintaining more conserved internal antigens.
T20 8533-8754 Epistemic_statement denotes Strictly speaking, CD8 + T cells cannot afford protection against infection per se but can mediate faster viral clearance and provide a substantial degree of protection against challenge with a lethal dose of virus (14) .
T21 9091-9203 Epistemic_statement denotes To date, however, the development of effective T-cell vaccines against many respiratory viruses remains elusive.
T22 9204-9484 Epistemic_statement denotes In the past 10 years, immunologists have provided vaccinologists with valuable information on the regulatory mechanisms that govern not only the efficient generation of CD8 + T-cell responses in the lung but also how different memory CD8 + T-cell subsets are maintained over time.
T23 9485-9603 Epistemic_statement denotes The current challenge is to apply this knowledge in our endeavors to develop safe and effective CD8 + T-cell vaccines.
T24 10201-10443 Epistemic_statement denotes Upon viral recognition, a complex interplay between these distinct detection systems results in the activation of an array of transcription factors that culminates in the production of antiviral cytokines and inflammatory mediators (14, 28) .
T25 10897-11065 Epistemic_statement denotes These models have shown the crucial role CD8 + T cells play in controlling viral titers during primary infection and generating protection against subsequent infection.
T26 11542-11708 Epistemic_statement denotes Intravital LN microscopy studies suggest that antigen-bearing DCs migrate to and localize in the vicinity of the high endothelial venules (HEVs) (34) (35) (36) (37) .
T27 11853-12195 Epistemic_statement denotes The relatively rare antigen-specific T cells are subsequently selected through Tcell receptor (TCR)/major histocompatibility complex class I (MHC I) engagement and undergo 11 to 15 rounds of clonal expansion, resulting in a large population of antigenspecific effector CD8 + T cells observed during the peak of the primary response (14, 38) .
T28 12524-12754 Epistemic_statement denotes Homeostatic CD8 + Tcell clone frequency, specific antigenic peptide abundance, and presentation kinetics can collectively influence the development and relative frequency of dominant and subdominant CD8 + T-cell populations (39) .
T29 13108-13382 Epistemic_statement denotes The migration of CD8 + T cells to the lung tissue and airways does not appear to be dependent on antigen, although infiltrating CD8 + T cells must acquire a sufficient level of activation to downregulate LN homing receptors and acquire lung homing chemokine receptors (40) .
T30 13737-13848 Epistemic_statement denotes Recent data also suggest that IL-15 mediates the migration of effector CD8 + T cells to the lung airways (44) .
T31 13849-14124 Epistemic_statement denotes Together, these data support a two-hit model for promoting effective CD8 + T\[cell responses: a first hit in the lymph node that primes T-cell proliferation and migration to the site of infection, and a second hit that provides a survival signal to the effector T cell (42) .
T32 15079-15382 Epistemic_statement denotes Two major subtypes of memory CD8 + T cells have been defined based on the expression of CD62L (also know as L-selectin), a 'homing receptor' for leukocytes to enter secondary lymphoid tissues via HEVs, and CCR7, a chemokine receptor that supports trafficking through secondary lymphoid tissue (46) (Fig.
T33 15638-15859 Epistemic_statement denotes Considerable interest has been focused on elucidating functional differences between these memory T cell subsets and their capacity to confer protection against secondary infection (24, 32, (47) (48) (49) (50) (51) (52) .
T34 15860-16058 Epistemic_statement denotes After secondary encounter with antigen, T EM cells can be stimulated by respiratory DCs without the requirement for further division and can demonstrate rapid cytokine production and lytic activity.
T35 16299-16664 Epistemic_statement denotes Based on these observations, it has been proposed that T EM cells participate directly in the initiation of protective memory responses by rapidly producing effector molecules (perforin, granzyme and antiviral cytokines) at the site of antigen encounter, whilst T CM cells contribute to the maintenance and/or amplification of the overall secondary T cell response.
T36 16665-16878 Epistemic_statement denotes Therefore, the specific subset of memory CD8 T cells generated by vaccination may critically determine the ultimate effectiveness of vaccine induced immune protection against a natural respiratory viral infection.
T37 17216-17501 Epistemic_statement denotes There is substantial clinical evidence to suggest that protective T cell immunity does not last for more than a couple of years after resolution of a natural infection or vaccination, unless the response is boosted by re-exposure to the same or cross-reactive antigens (57) (58) (59) .
T38 17708-17931 Epistemic_statement denotes This decline in protective T cell immunity occurs despite the fact that the numbers of virus-specific memory CD8 T cells in the lymphoid tissues (T CM cells) remain relatively high for the life span of the animal (61, 62) .
T39 17932-18207 Epistemic_statement denotes These studies suggest that in the context of a respiratory viral infection, T CM cells may not respond, expand, or relocate (to the lung) sufficiently quickly to provide immediate protection against disease caused by reinfection (or live pathogen challenge post vaccination).
T40 18208-18416 Epistemic_statement denotes More recent studies have indicated that at one-month post infection, the total numbers of virus-specific T EM cells in the lung are substantially higher than the number of T CM cells in the draining LNs (62).
T41 18417-18750 Epistemic_statement denotes However, detailed kinetic studies have revealed that despite stable numbers of memory CD8 T cells in the lymphoid organs, the numbers of lung-and airwayresident memory CD8 T cells following a primary Sendai virus or influenza infection gradually decline over the first three to six months before stabilizing at very low levels (62) .
T42 18751-18949 Epistemic_statement denotes Interestingly, this decline and stabilization in the number of memory CD8 T cells in the lung directly correlates with a progressive decline in T cell-mediated protection from a secondary challenge.
T43 19512-19541 Epistemic_statement denotes This will be discussed below.
T44 19542-19799 Epistemic_statement denotes Despite continued disagreement on the precise details of how memory T cell generation occurs, most people accept that the amplitude of a memory T cell pool generated after viral clearance is dictated by the magnitude of the primary effector T cell response.
T45 20036-20180 Epistemic_statement denotes The primary determinant of the effector CD8 T cell size appears to be a function of the initial amount of antigen present during T cell priming.
T46 20181-20396 Epistemic_statement denotes It has been shown that brief periods of antigenic stimulation or antigen availability during priming favor the enrichment of T CM cells, whereas prolonged periods support T EM cell generation ( Figure 2 ) (24, 46) .
T47 20397-20722 Epistemic_statement denotes This has important implications for vaccine development against respiratory viruses; for example, the level and time of antigen exposure that can be provided by attenuated vaccines, non-replicating vectors, DNA vaccines, or protein subunit vaccines might be significantly less than those provided by livereplicating vaccines.
T48 20723-20904 Epistemic_statement denotes This is likely to be linked to the capacity of replicating vaccines to divide multiple times and disseminate faster, thus increasing the amount and the duration of antigen exposure.
T49 20905-21172 Epistemic_statement denotes As will be discussed in more detail below, one of the key questions in inducing large effector-cell burst size for new vaccines will be to define the precise mechanisms that regulate the formation of effector T cells in the context of high or persisting antigen load.
T50 21303-21432 Epistemic_statement denotes Initial data from mouse models suggested that T cell memory was short lived in the absence of periodic exposure to antigen (64) .
T51 21433-21623 Epistemic_statement denotes However, more recent evidence has challenged this idea and suggested that the number of T CM cells can be sustained in the absence of both specific antigen and MHC molecules (65) (66) (67) .
T52 21624-21867 Epistemic_statement denotes Further experimental evidence now suggests that a T CM memory pool is maintained, at least in part, through periodic slow cell division and continuous replacement of cells, a process commonly referred to as homeostatic proliferation (68, 69) .
T53 22085-22239 Epistemic_statement denotes Two different (although not mutually exclusive) models have been proposed to explain the longevity of T EM cells in the absence of re-exposure to antigen.
T54 22240-22430 Epistemic_statement denotes Initial studies suggested that T EM cell populations in the lung airways are maintained in an antigen-independent manner by continual recruitment of new cells from the circulation (40, 70) .
T55 22431-22655 Epistemic_statement denotes The rate of memory cell recruitment was shown to be extremely rapid, resulting in replacement of 90 % of the population every 10 days and that this can be maintained for periods over one year following viral clearance (70) .
T56 22656-22927 Epistemic_statement denotes More recent studies extended these observations by demonstrating that antigen can persist in the lung draining LNs for several weeks after influenza virus clearance and that this residual antigen contributes to the maintenance of T EM cells in the lung airways (71, 72) .
T57 22928-23095 Epistemic_statement denotes However, a small number of circulating memory CD8 T cells generated after influenza virus infection can migrate to the airways in the absence of cognate antigen (73) .
T58 23483-23669 Epistemic_statement denotes Thus, it is clear that the role of persisting antigen after vaccination is a crucial point that has to be addressed during an effective T cell vaccine design against respiratory viruses.
T59 24053-24127 Epistemic_statement denotes These approaches however have obvious logistical and economic limitations.
T60 24128-24396 Epistemic_statement denotes Thus, in order to fully realize the potential benefits of attenuated vaccines or simple protein/peptide immunizations it will be of great interest to identify specific molecules and/or pathways that can be targeted to safely lower the activation threshold for antigen.
T61 24397-24538 Epistemic_statement denotes Currently, intradermal, intramuscular, oral, intranasal, intravaginal, and even rectal routes of immunization are under active investigation.
T62 24539-24754 Epistemic_statement denotes Accumulating evidence from many research groups has confirmed that the route of immunization is critical in determining both qualitative and quantitative aspects of a vaccine induced immune response (74) (75) (76) .
T63 24755-25061 Epistemic_statement denotes With regards to T cell vaccines against respiratory viruses, recent studies support the concept that long-lived CD8 T cells can be detected in the lung after mucosal, but not systemic immunization, suggesting that the maintenance of memory T cells are also dependent on the particular route of vaccination.
T64 25887-26079 Epistemic_statement denotes Furthermore, they demonstrated that the inability of intraperitoneally primed memory CD8 T cells to access residual antigen could be corrected by a subsequent intranasal virus infection (78) .
T65 26410-26500 Epistemic_statement denotes Several approaches have been used to elicit protective CD8 T cell responses (25, 79, 80) .
T66 27203-27467 Epistemic_statement denotes The focus of the remaining sections of this review center around the poxvirus-based vectors listed in Table 1 , and more specifically how the pursuit of safer vaccines has paradoxically resulted in largely ineffective CD8 T cell vaccines against mucosal pathogens.
T67 27822-27997 Epistemic_statement denotes The concept of utilizing live-attenuated poxviruses as an immunizing agent against respiratory viruses can be traced back to the global smallpox eradication program (82, 83) .
T68 27998-28155 Epistemic_statement denotes The strategy for this program involved mass vaccination with VACV, an antigenically similar virus to the etiological agent of smallpox disease Variola major.
T69 28720-29008 Epistemic_statement denotes It was the ability of these VACV strains to induce robust humoral and cell mediated immunity (82, 83, 85 ) that led to the World Health Organization declaring the eradication of smallpox in 1980 and shortly thereafter routine vaccination with VACV could be discontinued in most countries.
T70 29508-29730 Epistemic_statement denotes Furthermore, poxviruses have the potential to be administered by different routes, such as intradermal, intramuscular, oral, intranasal, intravaginal, and intrarectal routes to generate immunoglobulin and T cell responses.
T71 30015-30202 Epistemic_statement denotes The VACV strain most extensively utilized in animal models has been the highly virulent Western Reserve (WR) strain, which was derived from the NYCBOH strain by multiple passages in mice.
T72 30319-30606 Epistemic_statement denotes Moreover, the well-documented severe, albeit rare, complications following vaccination with first generation VACV strains, and the increasing number of immune compromised individuals have raised legitimate concerns about their widespread use as a vaccine-delivery system in humans (84) .
T73 30607-30888 Epistemic_statement denotes Thus, during the past three decades, a major focus of research has been on developing novel, highly attenuated, recombinant VACV strains (rVACV) that demonstrate significantly improved safety profiles and can be used in humans as potential vaccines candidates (83, 84) (Table 1) .
T74 30889-31105 Epistemic_statement denotes As briefly mentioned above, the safety concerns surrounding the WR and first-generation VACV-based vaccine candidates have been addressed through the development of highly attenuated VACV strains (83, 84) (Table 1 ).
T75 31439-31556 Epistemic_statement denotes Both virus vectors are extremely safe and can be used in young children and immuno-compromised individuals (84, 96) .
T76 31801-32020 Epistemic_statement denotes In recent years, MVA, NYVAC and ALVAC have all been utilized, with varying degrees of success, as promising vaccine vectors for many infectious diseases including influenza, SARS, HIV, HSV, TB and malaria (81, 84, 99) .
T77 32381-32652 Epistemic_statement denotes Despite a small number of clinical trials providing promising preliminary evidence for CD8 T cell induction (101, 102) , unfortunately, many trials demonstrate a limited induction of antigen specific CD8 T cell against the infectious disease or cancer target of interest.
T78 33616-33735 Epistemic_statement denotes This response, however, rapidly declined over time, reaching pre-vaccination levels by week 52 post-vaccination (109) .
T79 33736-34023 Epistemic_statement denotes This is consistent with an earlier preclinical study that demonstrated MVA induced T cell responses are followed several weeks later by a dramatic (20-40 fold) contraction, a phenomenon that also occurred with DNA-poxvirus regimens in which NYVAC and ALVAC were used for boosting (110) .
T80 34500-34710 Epistemic_statement denotes These studies suggests that MVA in its current form may not be the most effective poxvirus vector for induction of strong and long-lasting protective CD8 T-cell responses in peripheral tissues such as the lung.
T81 34711-34945 Epistemic_statement denotes If one looks back in the literature it becomes evident that these somewhat disappointing clinical results with non-replicating highly attenuated poxviruses could have been predicted based on studies carried out more than 20 years ago.
T82 35373-35489 Epistemic_statement denotes The precise mechanism for this was not investigated in detail but it appeared to be independent of humoral immunity.
T83 35490-35839 Epistemic_statement denotes In summary, 30 years of increasing safety and regulatory concerns surrounding replication competent recombinant poxviruses has unfortunately resulted in the widespread use of vaccine delivery vectors that are ineffective at inducing robust and long-lived memory CD8 T cells necessary to confer protection against highly virulent respiratory viruses.
T84 35840-36080 Epistemic_statement denotes At the dawn of recombinant poxvirus-vaccine research, relatively little was known about the precise molecular mechanisms that govern the quantity, phenotype, and quality of memory T cells following infection with a live (replicating) virus.
T85 36973-37137 Epistemic_statement denotes As discussed previously, these limitations are logically related to antigen load, antigen persistence and the ability to effectively stimulate CD8 T cell responses.
T86 37138-37356 Epistemic_statement denotes Thus, a convincing argument can be made that a key challenge in utilizing attenuated poxvirus vectors to develop efficacious T cell vaccines is to define the molecular mechanisms that link virulence and immunogenicity.
T87 37357-37725 Epistemic_statement denotes Towards this end, several recent studies have indicated that key events during initial T cell priming, including inflammatory stimuli (24, 54) , co-stimulation (114), CD4 T cell help (115) , and the cytokine mileu (54), have long lasting programming effects on the quantity, phenotype, and quality of the memory T cells generated in response to a live viral infection.
T88 38044-38249 Epistemic_statement denotes It has been hypothesized that the co-evolution of pathogens and their hosts has been a major driving force behind the development of a highly sophisticated and extremely adaptable vertebrate immune system.
T89 38250-38564 Epistemic_statement denotes This co-evolution is clearly demonstrated by the fact that many large DNA viruses, such as poxviruses and herpesviruses, possess multiple homologues of cytokines, chemokines, or the associated receptors of these molecules, that can neutralize or modulate host immunity to favour the virus (116) (117) (118) (119) .
T90 38565-38835 Epistemic_statement denotes It is assumed that the main goal of these immune modulatory strategies is to enhance viral replication and survival, however it is highly plausible that there exists unknown consequences of viral immune evasion strategies and how these impact the host's immune response.
T91 38836-39103 Epistemic_statement denotes Could it be possible that certain molecular pathways that regulate alternative immune responses, such as those involved in autoimmunity, allergic or even anti-tumor responses, might have evolved or be differentially utilized as a consequence of viral evasion tactics.
T92 39980-40164 Epistemic_statement denotes Interestingly, there are a number of receptor-ligand pairs within the TNF/TNFR superfamily that are not constitutively expressed but are induced during specific inflammatory scenarios.
T93 40165-40309 Epistemic_statement denotes They are thought to provide 'late' signals that subtly regulate T cell responses in both a quantitative and qualitative manner (114, 120, 122) .
T94 40310-40448 Epistemic_statement denotes Why so many co-stimulatory molecules exist, with often apparently similar and overlapping functional attributes, remains to be determined.
T95 40677-40908 Epistemic_statement denotes It is of interest, that recent analysis of the teleost genome, an organism in which the first fully functional adaptive immune system was thought to have developed, has revealed the presence of many human TNF superfamily orthologs.
T96 40909-41048 Epistemic_statement denotes This provides evidence to suggest that many of the TNF superfamily members co-emerged around the same time as did antigen receptors (129) .
T97 41049-41203 Epistemic_statement denotes Interestingly, however, four ligands were not found to exist within the teleost genome, namely OX40L, CD70 (the ligand for CD27), GITRL, and CD30L (129) .
T98 41204-41498 Epistemic_statement denotes As briefly discussed above, these are important regulators of the later phases of T cell expansion and survival, leading to the hypothesis that these ligands may have arisen more recently to allow immune adaptation, plasticity and effective development of protective immunity against pathogens.
T99 41499-41715 Epistemic_statement denotes To test this hypothesis, we recently utilized several poxvirus infection models and investigated the use and role of select TNF/TNFR and Ig family members in initiating and sustaining protective CD8 T cell responses.
T100 42940-43193 Epistemic_statement denotes Similar differences were observed at the peak (days seven and eight) of the initial effector CD8 T cell response, implying that altered molecular regulation at this phase of the response could explain the difference in size of the memory pool generated.
T101 43194-43535 Epistemic_statement denotes To highlight the importance of CD8 T cells in protecting against subsequent viral encounter, MHC class-II-deficient mice (MHC II −/− ), that lack CD4 T cells and therefore can not generate VACV-specific humoral immunity, were vaccinated with WR, Lister, and NYCBOH and challenged 70 days later with a lethal intranasal dose of VACV-WR (76) .
T102 44154-44315 Epistemic_statement denotes In humans, immunization with live-attenuated VACV (Lister or NYCBOH) elicits what was previously thought to be a good memory CD8 T cell response (85, 131, 132) .
T103 44316-44604 Epistemic_statement denotes The VACVspecific memory CD8 T cell pool has been shown to persist for many years in the majority of vaccine recipients, however recent observations have highlighted a rapid decline in memory CD8 T cell numbers does occur in a significant group of individuals over time (133) (134) (135) .
T104 44605-44740 Epistemic_statement denotes This raised concerns as to whether optimal long-lived CD8 T cell immunity can in fact be generated using first generation VACV strains.
T105 44741-44910 Epistemic_statement denotes Our data provides considerable evidence to warrant these concerns as vaccination using the virulent VACV-WR promoted far superior numbers of protective memory CD8 cells.
T106 44911-45112 Epistemic_statement denotes This result raised the question as to whether a specific molecular mechanism exists that is engaged during an infection with the virulent WR strain but not the attenuated Lister or NYCBOH VACV strains.
T107 45113-45278 Epistemic_statement denotes If alternate molecular control mechanisms are evident, they could potentially be harnessed to enhance CD8 T cell responses generated by attenuated poxvirus vaccines.
T108 45834-46058 Epistemic_statement denotes In our initial studies we found that the development of high numbers of effector CD8 T cells capable of producing both IFNγ and TNFα was strongly impaired when OX40 was lacking on a CD8 T cell responding to VACV (124, 136) .
T109 46578-46768 Epistemic_statement denotes Most interestingly, OX40 driven induction of lung-resident memory CD8 T cells correlated directly with a robust protection against a highly lethal intranasal infection with VV-WR (76, 136) .
T110 47336-47473 Epistemic_statement denotes In light of these studies, we postulated whether the differential engagement of OX40 applies to other T cell stimulatory receptors (76) .
T111 47474-47795 Epistemic_statement denotes In this regard, recent data from our group and others have shown that in addition to OX40, CD28 (a co-stimulatory receptor in the Ig superfamily) (137, 138) and CD27 (another TNFR family member) (139) , can be utilized during a VACV-WR infection and each can contribute to the generation of effector CD8 T cell responses.
T112 48068-48250 Epistemic_statement denotes In contrast to our OX40 studies, we found that CD28 was indispensible for optimal effector CD8 T cell generation regardless of whether mice were infected with Lister or NYCBOH (76) .
T113 48251-48394 Epistemic_statement denotes However, similar to OX40, deficiency in CD27 resulted in impaired CD8 T cell responses to WR but little or no defect to Lister or NYCBOH (76) .
T114 48585-48799 Epistemic_statement denotes CD28-deficient mice exhibited defective memory CD8 T cell generation in response to Lister and NYCBOH but interestingly not to WR, even though CD28 was required for an optimal effector response to this virus (76) .
T115 48800-48949 Epistemic_statement denotes This indicates that in response to VACV-WR infection, there exists a CD28-dependent phase of CD8 T cell priming followed by a CD28-independent phase.
T116 48950-49187 Epistemic_statement denotes CD27 signaling has previously been shown to prolong CD8 T cell survival beyond the effector phase of the immune response and thus serves to increase the number of memory cells by inhibiting effector T cell death (124, (142) (143) (144) .
T117 49415-49680 Epistemic_statement denotes These results support a model in which a temporal sequence of events is necessary for optimal virus-specific CD8 T cell proliferation, survival and memory generation, brought about by a specific sequential engagement of costimulatory molecules CD28, OX40, and CD27.
T118 49681-49985 Epistemic_statement denotes In summary, we show that viral virulence and evasion strategies that impact viral replication, dissemination and invariably the inflammatory milieu, can lead to differential use of co-stimulatory receptors for T cells which dictate the magnitude and effectiveness of the CD8 T cell response ( Figure 3 ).
T119 49986-50323 Epistemic_statement denotes Furthermore, these data are of high potential significance to vaccination, and promote the notion that the use of attenuated viruses may not elicit the best long-term T cell memory because they do not allow molecules such as OX40 and CD27 or their ligands, that may have evolved for the purpose of promoting T cell memory, to be engaged.
T120 50324-50606 Epistemic_statement denotes This provides a hypothetical model that might in part explain the abundance of such stimulatory receptors for T cells, and demonstrate that molecular plasticity can occur during anti-viral responses where certain immune mechanisms thought non-essential could become highly relevant.
T121 50607-50828 Epistemic_statement denotes Contrary to our VACV-WR studies, but similar to the data with VACV-Lister and VACV-NYCBOH discussed above, the regulation of CD8 T cell responses in other viral settings is variably dependent on OX40 and OX40L signalling.
T122 51183-51455 Epistemic_statement denotes However, recent studies investigating the impact of OX40/OX40L signalling on memory and recall CD8 T cell responses demonstrated a reduction in the number and secondary expansion of memory CD8 T cells in the lung, despite not influencing initial CD8 T cell priming (148) .
T123 51625-51733 Epistemic_statement denotes Collectively these data suggest that no two viruses initiate the same combination of costimulatory pathways.
T124 51734-51929 Epistemic_statement denotes This raises many questions surrounding the specific signals that initiate the 'program' of co-stimulatory pathways required for induction, maintenance and recall of memory CD8 T cell populations.
T125 52216-52403 Epistemic_statement denotes Furthermore, the inflammatory signature initiated by a specific virus strain or the presence of virus specific virulence factors may also authorize particular co-stimulatory interactions.
T126 52404-52571 Epistemic_statement denotes APC derived cytokines such as IL-1, IL-2, IL-12, and TNFα have been shown to influence the extent and length of co-stimulatory receptors/ligand expression (114, 124) .
T127 52775-52909 Epistemic_statement denotes Furthermore the CD40 engagement, TLR ligation and IL-18 derived signals can also regulate the expression of OX40L on APCs (114, 140) .
T128 52910-53151 Epistemic_statement denotes In summary, the extent of viral replication, in terms of peak titre and tissue tropism, and the unique inflammatory signature of a specific viral infection is likely to influence the use of a specific combination of co-stimulatory molecules.
T129 53152-53432 Epistemic_statement denotes Further studies to investigate the spatial and temporal expression profiles of both co-stimulatory ligands and receptors in different viral settings will almost certainly add to our understanding and help in the development of safe yet effective vaccines against viral infections.
T130 53433-54077 Epistemic_statement denotes Accumulating evidence from our laboratory and others support the notion that a critical component of any future CD8 T cell vaccine against highly virulent respiratory viruses must be the capacity to (1) promote robust expansion of naïve precursor T cells reactive with viral antigenic peptides; (2) allow a high frequency of these virus-specific effector T cells to survive over time as memory T cells; (3) allow high numbers of these memory cells to persist in the lung parenchyma and airways in the absence of persisting antigen; and (4) to retain high effector function in order to provide optimal surveillance against subsequent infections.
T131 54078-54249 Epistemic_statement denotes As alluded to earlier, replication-defective highly attenuated poxvirus vectors, although extremely safe, are unlikely to satisfy a number of these important requirements.
T132 54609-54806 Epistemic_statement denotes Our studies, highlighted above, suggest that attenuated VACV-vaccine strains will not elicit the most effective CD8 T cell memory responses in the lungs due to the lack of OX40 and CD27 engagement.
T133 54807-54964 Epistemic_statement denotes Therefore, we investigated whether engagement of OX40 would boost the response to attenuated VACV vaccine strains by treating with an agonist antibody (76) .
T134 55138-55248 Epistemic_statement denotes This was observed regardless of whether vaccination was via the intraperitoneal or dermal scarification route.
T135 56392-56726 Epistemic_statement denotes It should be stressed that prevention of weight loss during the first seven days of infection is extremely difficult to achieve, especially with such high challenge doses (x 300 LD 50 ) that were used in our experiments, and therefore an important demonstration of the utility of agonistically targeting OX40 in anti-viral protection.
T136 56727-56895 Epistemic_statement denotes More interestingly, targeting OX40 induced almost complete protection in mice immunized with a low dose of B8R 20-27 that alone was ineffective at preventing lethality.
T137 57001-57235 Epistemic_statement denotes As before, the extent of protection directly correlated with the number of IFN-γ producing B8Rspecific memory CD8 cells that were generated in the lung after OX40 engagement, and the number that accumulated after intranasal infection.
T138 58102-58370 Epistemic_statement denotes Collectively, our studies demonstrate that intraperitoneal infection with attenuated VACV vaccine strains or subcutaneous vaccination of a viral peptide in the presence of an agonistic OX40 antibody can generate long-lasting memory CD8 T cell that persist in the lung.
T139 58599-58750 Epistemic_statement denotes Several other groups have raised the possibility that triggering OX40 could enhance vaccination efficacy against other viral (and non viral) pathogens.
T140 59512-59611 Epistemic_statement denotes The use of an agonistic OX40 antibody and fusion proteins has also produced very promising results.
T141 60266-60514 Epistemic_statement denotes Collectively, these studies suggest that OX40 is a promising target for enhancing T cell responses against a variety of antigens, and that agonist reagents, to OX40, or OX40L encoded within a vaccine vector, might be useful in vaccination regimens.
T142 60515-60734 Epistemic_statement denotes This strategy could enable the highly desirable ability to retain the use of attenuated vaccines or simple peptide or protein immunization whilst promote both immunoglobulin and T cell components of the immune response.
T143 60885-61065 Epistemic_statement denotes Without doubt the greatest concern with enhancing CD8 T cell responses through the use of agonistic OX40 antibodies or vector encoded OX40L is a hyper-inflammatory immune response.
T144 61675-61816 Epistemic_statement denotes Direct interaction between viral pathogens and OX40 itself also raise concerns surrounding the targeting of OX40 to enhance T cell responses.
T145 61950-62141 Epistemic_statement denotes By replicating in and subsequently killing OX40 expressing cells, both FIV and HIV would preferentially deplete virus-specific T cells that would otherwise mediate antiviral immune responses.
T146 62142-62228 Epistemic_statement denotes T cell tropic viruses may also exploit the OX40-OX40L axis to aid their dissemination.
T147 62459-62696 Epistemic_statement denotes Intriguingly, a small number of ATL patients displayed OX40 dependent adhesion of leukemic cells to endothelial cells (184) , suggesting that virus-induced OX40 expression could enhance leukemic cell infiltration and viral dissemination.
T148 62697-62812 Epistemic_statement denotes Viruses can hijack transcriptional activation events triggered by OX40 to induce the expression of their own genes.
T149 62813-63037 Epistemic_statement denotes A number of viruses including cytomegalovirus (185, 186) and HIV (187) have NF-κB response elements incorporated into their genomes which can enhance viral reactivation, in the case of CMV, and viral replication (182, 188) .
T150 63038-63193 Epistemic_statement denotes The possible influence of OX40 on the replication, survival and/or reactivation from latency of viruses represents an interesting area for future research.
T151 63194-63318 Epistemic_statement denotes Finally, research into the potential pathogenicity of enhanced T cell responses upon natural virus re-exposure is necessary.
T152 63510-63737 Epistemic_statement denotes Consequently it would be necessary to determine the safe upper limit for the number of memory CD8 T cells desired and also whether maintaining large numbers of tissue resident (lung) memory CD8 T cells is detrimental over time.
T153 63738-64080 Epistemic_statement denotes In summary, although OX40 is a promising target for enhancing protection against infection and reducing viral-induced immunopathology, the positive effect OX40 may have on virus replication and survival in infected host cells raises new considerations for its manipulation, making the infectious status of the patient of paramount importance.
T154 64081-64320 Epistemic_statement denotes Accumulating evidence now indicates that targeting human OX40 and OX40L holds great promise for future vaccine strategies against highly virulent respiratory viruses and other unmet clinical infectious diseases such as HIV, Malaria and TB.
T155 64321-64634 Epistemic_statement denotes The literature discussed above provide compelling evidence to suggests the targeting of co-stimulatory pathways such as OX40/OX40L, or other similar molecules in this family, can promote robust expansion of antigen-specific effector T cells in response to safe attenuated VACV vaccine strains and peptide antigen.
T156 64888-65180 Epistemic_statement denotes There is no doubt that increasing our understanding of basic CD8 T cell biology and the dynamic regulatory influences the many co-stimulatory pathways have on the generation, phenotype, maintenance and re-activation of CD8 T cells will facilitate the development of novel CD8 T cell vaccines.
T157 65460-65625 Epistemic_statement denotes This will enable us to recapitulate the signature of a virulent virus whilst using a safe attenuated vaccine virus to promote life long CD8 T cell mediated immunity.
T158 67380-67597 Epistemic_statement denotes The model explains why the strongly replicating (live) vaccinia virus (VACV) Western Resrve strain (VACV-WR) results in better CD8 T cell immunity as compared with attenuated VACV strains (VACV-Lister or VACV-NYCBOH).
T159 67598-67849 Epistemic_statement denotes The level of virus replication, brought about by virulence and immune evasion tactics, can lead to differential use by a CD8 T cell of stimulatory receptors in the TNFR and Ig superfamilies, and that this dictates the magnitude of the T cell response.