T cell death and memory

Effector and memory CD4+ and CD8+ T cells in the chronic infection process

T cell memory in comparison with B cell memory is not well understood. This review focuses on CD8+ and CD4+ memory T cells. In this article we try to define memory cells and also present models of memory T cells formation. We would also like to delineate their differentiation into distinct subsets. Long-lived memory T cells consist in two main subsets: TCM and TEM. Recent studies have shown that not all cells considered to be memory cells differentiate into TCM and TEM, but a small proportion of theses cells exhibit naive cells phenotype. Memory T cells constitute a heterogeneous population of cells. In this study we lay stress on characteristic of main memory T cells subsets and their alleged participation in immune response upon reexposure to the Ag.

Immunobiology of human cytomegalovirus: from bench to bedside

SUMMARY

Following primary infection, human cytomegalovirus (HCMV) establishes lifelong latency and periodically reactivates without causing symptoms in healthy individuals. In the absence of an adequate host-derived immune response, this fine balance of permitting viral reactivation without causing pathogenesis is disrupted, and HCMV can subsequently cause invasive disease and an array of damaging indirect immunological effects. Over the last decade, our knowledge of the immune response to HCMV infection in healthy virus carriers and diseased individuals has allowed us to translate these findings to develop better diagnostic tools and therapeutic strategies. The application of these emerging technologies in the clinical setting is likely to provide opportunities for better management of patients with HCMV-associated diseases.

Concurrent generation of effector and central memory CD8 T cells during vaccinia virus infection

It is generally thought that during the contraction phase of an acute anti-viral T cell reponse, the effector T cells that escape activation-induced cell death eventually differentiate into central memory T cells over the next several weeks. Here we report that antigen-specific CD8T cells with the phenotype and function of central memory cells develop concomitantly with effector T cells during vaccinia virus (vv) infection. As soon as 5 days after an intraperitoneal infection with vv, we could identify a subset of CD44^hi and CD62L⁺ vv-specific CD8 T cells in the peritoneal exudate lymphocytes. This population constituted approximately 10% of all antigen-specific T cells and like central memory T cells, they also expressed high levels of CCR7 and IL-7R but expressed little granzyme B. Importantly, upon adoptive transfer into naïve congenic hosts, CD62L⁺, but not CD62L⁻ CD8 T cells were able to expand and mediate a rapid recall response to a new vv challenge initiated 6 weeks after transfer, confirming that the CD62L⁺ vv-specific CD8 T cells are bonafide memory cells. Our results are thus consistent with the branched differentiation model, where effector and memory cells develop simultaneously. These results are likely to have implications in the context of vaccine design, particularly those based on vaccinia virus recombinants.

An antibody combination that targets activated T cells extends graft survival in sensitized recipients

Memory T cells are the very essence of adaptive immunity with their rapid and efficient response to antigen rechallenge and long-term persistence. However, it is becoming increasingly evident that when primed with self or transplanted tissue, these cells play a key role in causing and perpetuating tissue damage. Furthermore, current treatments, which efficiently control the naive response, have limited effects on primed T cells. We have used a treatment based on a combination of antibodies specific for molecules expressed by activated T lymphocytes to selectively remove these cells. This approach, which we termed multi-hit therapy, leads to cumulative binding of antibodies to the target T cells and a striking prolongation of skin graft survival in presensitized recipients in a stringent skin transplant model. The findings are consistent with the depletion of graft-specific CD4+ and CD8+ T cells, although other modes of action, such as T-cell regulation and altered migration could play a role. In conclusion, our therapeutic strategy controls primed T cells which are a major driving force in the pathology of many autoimmune diseases and in transplant rejection.

Serpins in T cell immunity

Serine protease inhibitors (serpins) are a family of proteins that are important in the regulation of several biological processes. This mainly involves the inhibition of serine proteases, although some serpins inhibit a different class of proteases or even function without inhibitory activity. In contrast to other protease inhibitor families, serpins inhibit their target proteases by a specific mechanism, which depends on a change in conformation. This review primarily focuses on one subgroup of serpins--ovalbumin (ov)-serpins. Different than most members of the family, this group of serpins lacks secretion signal sequences and therefore, mainly functions intracellularly. In addition to expression in most normal tissues, ov-serpins can be found in multiple different cells of the immune system. Interestingly, expression of ov-serpins in these cells is tightly regulated, indicating a role for these serpins in the regulation of immune responses. The role of serpins in the immune response will be the topic of this review.

Clinical implications of discordant viral and immune outcomes following protease inhibitor containing antiretroviral therapy for HIV-infected children

Many HIV-infected children treated with protease inhibitors (PI) reconstitute immunity despite viral breakthrough predicting disease progression. We studied a unique cohort of PI treated children with advanced disease who demonstrated sustained CD4 T cell counts but median post therapy viral load rebounded to >4.0 log(10) copies/ml. Phylogenetic relationships between pre- and post-therapy viruses reveals significant bottlenecks for quasispecies with natural polymorphisms mapping outside of protease active site providing selective advantage for emergence. Among discordant subjects post-therapy viruses fell into two phenotypes; high viral loads (median >5.0 log(10) copies/ml) and attenuated post-therapy replication (median <4.0 log(10) copies/ml). Both groups showed similar degrees of CD4 T cell immune reconstitution and were similar to children who optimally suppressed virus to <400 copies/ml. Both high fit and low fit discordant response groups showed high reconstitution of naïve CD4 CD45RA T cells (median 388 and 357 cells/microl, respectively). Naïve T cells increases suggest virus replicating under PI selective pressure do not impair thymic output. If therapeutic options are limited, selection of therapy which allows immune reconstitution despite suboptimal viral control may be beneficial. This novel paradigm for virus/host interactions may lead to therapeutic approaches to attenuate viral pathogenesis.

Pathogen proliferation governs the magnitude but compromises the function of CD8 T cells

CD8+ T cell memory is critical for protection against many intracellular pathogens. However, it is not clear how pathogen virulence influences the development and function of CD8+ T cells. Salmonella typhimurium (ST) is an intracellular bacterium that causes rapid fatality in susceptible mice and chronic infection in resistant strains. We have constructed recombinant mutants of ST, expressing the same immunodominant Ag OVA, but defective in various key virulence genes. We show that the magnitude of CD8+ T cell response correlates directly to the intracellular proliferation of ST. Wild-type ST displayed efficient intracellular proliferation and induced increased numbers of OVA-specific CD8+ T cells upon infection in mice. In contrast, mutants with defective Salmonella pathogenicity island II genes displayed poor intracellular proliferation and induced reduced numbers of OVA-specific CD8+ T cells. However, when functionality of the CD8+ T cell response was measured, mutants of ST induced a more functional response compared with the wild-type ST. Infection with wild-type ST, in contrast to mutants defective in pathogenicity island II genes, induced the generation of mainly effector-memory CD8+ T cells that expressed little IL-2, failed to mediate efficient cytotoxicity, and proliferated poorly in response to Ag challenge in vivo. Taken together, these results indicate that pathogens that proliferate rapidly and chronically in vivo may evoke functionally inferior memory CD8+ T cells which may promote the survival of the pathogen.

Apoptosis regulators Fas and Bim cooperate in shutdown of chronic immune responses and prevention of autoimmunity

Apoptotic death of T lymphocytes is critical for shutdown of immune responses and hemopoietic cell homeostasis. Both death receptor (Fas) activation and mitochondrial apoptosis triggered by the BH3-only protein Bim have been implicated in the killing of antigen-stimulated T cells. We examined mice lacking the gene encoding Bim (Bcl2l11) and with the inactivating lpr mutation in the gene encoding Fas (Fas), designated Bcl2l11(-/-)Fas(lpr/lpr) mice. Shutdown of an acute T cell response to herpes simplex virus involved only Bim with no contribution by Fas, whereas both pathways synergized in killing antigen-stimulated T cells in chronic infection with murine gamma-herpesvirus. Bcl2l11(-/-)Fas(lpr/lpr) mice developed remarkably enhanced and accelerated fatal lymphadenopathy and autoimmunity compared to mice lacking only one of these apoptosis inducers. These results identify critical overlapping roles for Fas and Bim in T cell death in immune response shutdown and prevention of immunopathology and thereby resolve a long-standing controversy.

Regulation of T cell survival through coronin-1-mediated generation of inositol-1,4,5-trisphosphate and calcium mobilization after T cell receptor triggering

T cell homeostasis is essential for the functioning of the vertebrate immune system, but the intracellular signals required for T cell homeostasis are largely unknown. We here report that the WD-repeat protein family member coronin-1, encoded by the gene Coro1a, is essential in the mouse for T cell survival through its promotion of Ca2+ mobilization from intracellular stores. Upon T cell receptor triggering, coronin-1 was essential for the generation of inositol-1,4,5-trisphosphate from phosphatidylinositol-4,5-bisphosphate. The absence of coronin-1, although it did not affect T cell development, resulted in a profound defect in Ca2+ mobilization, interleukin-2 production, T cell proliferation and T cell survival. We conclude that coronin-1, through activation of Ca2+ release from intracellular stores, is an essential regulator of peripheral lymphocyte survival.

BH3-only protein Puma contributes to death of antigen-specific T cells during shutdown of an immune response to acute viral infection

During acute T cell immune responses to viral infection, antigen-specific T cells first proliferate and differentiate into effector cells, but after pathogen clearance most are deleted by apoptosis. The developmentally programmed death of antigen-specific T cells during shutdown of a T cell response is mediated by the Bcl-2-regulated apoptotic pathway and partly depends on the proapoptotic BH3-only protein Bim. However, loss of Bim enhanced survival of antigen-activated T cells to a lesser extent than Bcl-2 overexpression, indicating that other proapoptotic factors must contribute to T cell killing. In this study, we investigated the contributions of several BH3-only proteins to the shutdown of an acute T cell immune response in vivo. After infection with human herpes simplex virus (HSV-1), mice lacking Noxa, Bid, or Bad had a normal increase and subsequent decline in the numbers of antigen-specific CD8(+) T cells. In contrast, Puma-deficient mice showed an abnormally prolonged persistence of antigen-specific CD8(+) T cells in the spleen, associated with enhanced in vitro survival of these cells in the absence of cytokines. Puma was dispensable for viral clearance and also did not play a role in proliferation or activation of HSV-1-specific CD8(+) T cells in vivo. Collectively, these findings show that Puma contributes to the death of antigen-specific T cells during shutdown of an immune response.

Loss of IL-7 receptor alpha on CD4+ T cells defines terminally differentiated B cell-helping effector T cells in a B cell-rich lymphoid tissue

IL-7 plays important roles in development and homeostatic proliferation of lymphocytes. IL-7 uses a receptor composed of IL-7Ralpha (CD127) and the common gamma-chain (CD132) to transmit its signal. It has been unknown how CD127 is regulated during Th cell differentiation to the B cell-helping T cell lineage. In this study, we report that loss of CD127 defines terminally differentiated B cell-helping effector T cells in human tonsils. Although naive CD4(+) T cells uniformly express CD127, the memory/effector (non-FOXP3(+)) CD4(+) T cells are divided into CD127(+) and CD127(-) cells. The CD127(-) T cells are exclusively localized within the germinal centers where B cells become plasma and memory B cells, whereas CD127(+) T cells are found in T cell areas and the area surrounding B cell follicles. Consistently, the CD127(-) T cells highly express the B cell zone homing receptor CXCR5 with concomitant loss of CCR7. Compared with CD127(+) memory T cells, CD127(-) T cells have considerably shorter telomeres, do not proliferate in response to IL-7, and are prone to cell death. The CD127(-) T cells produce a large amount of the B cell follicle-forming chemokine CXCL13 upon stimulation with B cells and Ags. Most importantly, they are highly efficient in helping B cells produce Igs of all isotypes in a manner dependent on CD40L and ICOS and inducing activation-induced cytidine deaminase and Ig class switch recombination. The selective loss of CD127 on the B cell-helping effector T cells would have implications in regulation and termination of Ig responses.

Extent of stimulation controls the formation of memory CD8 T cells

Only a small fraction of effector CD8 T cells survives to become long-lived memory cells, whereas the majority of them die after an acute infection. What controls the formation of memory CD8 T cells remains mostly unknown. In this study, we showed CD8 T cells primed earlier during vaccinia viral infection received stronger stimulation, divided more extensively, and survived better than those primed later, leading to generation of a larger memory pool. Despite differentiation into effectors, the late-primed CD8 T cells lacked full cell division, displayed increased apoptosis, and failed to develop into memory cells, suggesting that the extent of stimulation influences the survival of effector CD8 T cells. We further demonstrated that the extent of stimulation, which included both the duration and the levels of antigenic stimulation/costimulation, during priming determined the formation of memory CD8 T cells via controlling the extent of Akt activation, and functional suppression of Akt led to defective CD8 memory formation in vivo. Collectively, our data suggest that the extent of stimulation controls CD8 memory formation via activation of Akt and may provide important insights into the design of effective vaccines.

A comparison of random vs. chemotaxis-driven contacts of T cells with dendritic cells during repertoire scanning

Generating adaptive immunity after infection or immunization requires physical interactions within a lymph node (LN) T-zone between antigen-bearing dendritic cells (DCs) that arrive from peripheral tissues and rare cognate T cells entering via high endothelial venules (HEVs). This interaction results in activation of cognate T cells, expansion of that T cell lineage and their exit from the LN T-zone via efferent lymphatics (ELs). How antigen-specific T cells locate DCs within this complex environment is controversial, and both random T cell migration and chemotaxis have been proposed. We developed an agent-based computational model of a LN that captures many features of T cell and DC dynamics observed by two-photon microscopy. Our simulations matched in vivo two-photon microscopy data regarding T cell speed, short-term directional persistence of motion and cell motility. We also obtained in vivo data regarding density of T cells and DCs within a LN and matched our model environment to measurements of the distance from HEVs to ELs. We used our model to compare chemotaxis with random motion and showed that chemotaxis increased total number of T cell DC contacts, but decreased unique contacts, producing fewer activated T cells. Our results suggest that, within a LN T-zone, a random search strategy is optimal for a rare cognate T cell to find its DC match and maximize production of activated T cells.

Peptide-activated double-negative T cells can prevent autoimmune type-1 diabetes development

Autoimmune diseases may develop because of defective maturation, activation, differentiation and function of regulatory T cells. Previous studies have shown that exposure to donor antigen activates peripheral TCRalphabeta+CD3+CD4-CD8-NK1.1-, double-negative (DN) T cells, which specifically suppress anti-donor T cells and enhance survival of skin and heart grafts from allogeneic and xenogeneic donors. However, the role of DN T cells in preventing T cell-mediated autoimmune disease is unknown. Here, we analyzed the ability of DN T cells to recognize peptides expressed on self MHC and to suppress peptide-reactive CD8+ T cells, using the P14 mouse model that expresses a transgenic TCR specific for gp33 peptide presented on self MHC class I-Db. We found that injection of gp33 peptide resulted in increased DN and decreased CD8+ T cell numbers in the lymph nodes when compared to untreated mice. Injection of gp33, but not TCR-non-specific AV peptide, increased expression of T cell activation markers on DN T cells. Moreover, gp33-activated DN T cells suppressed proliferation of syngeneic CD8+ T cells via killing activated CD8+ T cells in an antigen-specific fashion in vitro. Furthermore, transferring gp33-activated DN T cells inhibited the development of autoimmune diabetes, suggesting that DN T cells may provide a novel therapy for T cell-mediated autoimmune diseases.

Immune memory, immune oblivion: a lesson from Funes the memorious

We commonly think of the immune system as having a memory. However, memory is always accompanied by a complementary process of oblivion. Is there immune oblivion? In this theoretical paper, I address this question and suggest that oblivion is an integral aspect of memorization. In this context, I suggest that immune memory is an orchestration of reversible and irreversible processes of biological computation through feedback loops. Drawing on the linguistic metaphor, I inquire into the implications of this idea for a better understanding of immune memory and immune deficiency among the elderly.

A reduced antigen load in vivo, rather than weak inflammation, causes a substantial delay in CD8+ T cell priming against Mycobacterium bovis (bacillus Calmette-Guérin)

Regardless of the dose of Ag, Ag presentation occurs rapidly within the first few days which results in rapid expansion of the CD8+ T cell response that peaks at day 7. However, we have previously shown that this rapid priming of CD8+ T cells is absent during infection of mice with Mycobacterium bovis (bacillus Calmette-Guérin (BCG)). In this study, we have evaluated the mechanisms responsible for the delayed CD8+ T cell priming. Because BCG replicates poorly and survives within phagosomes we considered whether 1) generation of reduced amounts of Ag or 2) weaker activation by pathogen-associated molecular patterns (PAMPs) during BCG infection is responsible for the delay in CD8+ T cell priming. Using rOVA-expressing bacteria, our results indicate that infection of mice with BCG-OVA generates greatly reduced levels of OVA, which are 70-fold lower in comparison to the levels generated during infection of mice with Listeria monocytogenes-expressing OVA. Furthermore, increasing the dose of OVA, but not PAMP signaling during BCG-OVA infection resulted in rapid Ag presentation and consequent expansion of the CD8+ T cell response, indicating that the generation of reduced Ag levels, not lack of PAMP-associated inflammation, was responsible for delayed priming of CD8+ T cells. There was a strong correlation between the relative timing of Ag presentation and the increase in the level of OVA in vivo. Taken together, these results reveal that some slowly replicating pathogens, such as mycobacteria, may facilitate their chronicity by generating reduced Ag levels which causes a substantial delay in the development of acquired immune responses.

Memory generation and maintenance of CD8+ T cell function during viral persistence

During infection with viruses that establish latency, the immune system needs to maintain lifelong control of the infectious agent in the presence of persistent Ag. By using a gamma-herpesvirus (gammaHV) infection model, we demonstrate that a small number of virus-specific central-memory CD8+ T cells develop early during infection, and that virus-specific CD8+T cells maintain functional and protective capacities during chronic infection despite low-level Ag persistence. During the primary immune response, we show generation of CD8+ memory T cell precursors expressing lymphoid homing molecules (CCR7, L-selectin) and homeostatic cytokine receptors (IL-7alpha, IL-2/IL-15beta). During long-term persistent infection, central-memory cells constitute 20-50% of the virus-specific CD8+ T cell population and maintain the expression of L-selectin, CCR7, and IL-7R molecules. Functional analyses demonstrate that during viral persistence: 1) CD8+ T cells maintain TCR affinity for peptide/MHC complexes, 2) the functional avidity of CD8+ T cells measured as the capacity to produce IFN-gamma is preserved intact, and 3) virus-specific CD8+ T cells have in vivo killing capacity. Next, we demonstrate that at 8 mo post-virus inoculation, long-term CD8+ T cells are capable of mediating a protective recall response against the establishment of gammaHV68 splenic latency. These observations provide evidence that functional CD8+ memory T cells can be generated and maintained during low-load gammaHV68 persistence.

Multiple immunizations with adenovirus and MVA vectors improve CD8+ T cell functionality and mucosal homing

Recombinant adenovirus vectors and MVA vectors were used in prime boost vaccine regimens to address the impact of repeated immunizations on transgene product-specific CD8(+) T cell frequencies, phenotypes, function, and localization. We show that a regimen with three immunizations incorporating MVA, human adenovirus serotype 5 and chimpanzee-derived adenoviruses serotype 68 or 7 yields high transgene product-specific CD8(+) T cell frequencies in spleen, blood, lymph nodes, and peritoneal lavage. Furthermore, upon triple immunization increased frequencies of transgene-specific T cells were measured at mucosal sites such as mesenteric lymph nodes, intestinal epithelium, and Peyer's patches. Multiple dose vaccine regimens that markedly increase functionally active transgene-specific T cells and target them to the appropriate ports of entry may be important in protection against pathogens such as HIV-1.

Role of the indigenous microbiota in maintaining the virus-specific CD8 memory T cells in the lung of mice infected with murine cytomegalovirus

The potent role of indigenous microbiota in maintaining murine CMV (MCMV)-specific memory T cells, which were measured by multimer staining, was investigated using germfree (GF) mice. When the BALB/c mice bred under specific pathogen-free (SPF) conditions were i.p. infected with 0.2 LD(50) of MCMV, high frequencies of CD69(+)/CD44(+) MCMV-specific CD8 T cells were noted in the lungs even at 6-12 mo after infection (11.1 +/- 3.2 and 9.8 +/- 0.9%, respectively). In contrast, even though the viral load and expression levels of mRNA of such cytokines as IL-2, IL-7, IL-15, and IFN-gamma in the lungs of MCMV-infected GF mice were comparable to those of infected SPF mice, the frequencies of MCMV-specific CD8 T cells in the lungs of infected GF mice were kept lower than 1% at 6-12 mo after infection. In addition, the reconstitution of microbiota of MCMV-infected GF mice by orally administering a fecal suspension prepared from SPF mice restored the frequencies of both CD8(+)/multimer(+) and CD8(+)/multimer(-) T cells to levels similar to those found in SPF mice. These results suggested the indigenous microbiota to play a crucial role in the expansion and maintenance of viral-specific CD8 memory T cells, probably by cross-reactivity between the antigenic epitope of the MCMV-specific memory T cells and the variety of peptides derived from the members of the microbiota. Such cross-reactivity may thus be a major feature of those cells.

Engineered CD8+ cytotoxic T cells with fiber-modified adenovirus-mediated TNF-alpha gene transfection counteract immunosuppressive interleukin-10-secreting lung metastasis and solid tumors

T-cell suppression derived from tumor-secreted immunosuppressive interleukin (IL)-10 becomes a major barrier to CD8+ T-cell immunotherapy of tumors. Tumor necrosis factor-alpha (TNF-alpha) is a multifunctional cytokine capable of activating T and dendritic cells (DCs) and counteracting IL-10-mediated DC inhibition and regulatory T-cell-mediated immune suppression. In this study, we constructed a recombinant adenovirus (MF)AdVTNF with fiber-gene modified by RGD insertion into the viral knob's H1 loop and a melanoma cell line B16(OVA/IL-10) engineered to express ovalbumin (OVA) and to secrete IL-10 (2.2 ng/ml/10(6) cells/24 h). We transfected OVA-specific CD8+ T cells with (MF)AdVTNF, and found a fivefold increase in transgene human TNF-alpha secretion (4.3 ng/ml/10(6) cells/24 h) by the engineered CD8+ T(TNF) cells transfected with (MF)AdVTNF, compared to that (0.8 ng/ml/10(6) cells/24 h) by CD8+ T cells transfected with the original AdVTNF without viral fiber modification. The engineered CD8+ T(TNF) cells exhibited enhanced cytotoxicity and elongated survival in vivo after adoptive transfer. TNF-alpha derived from both the donor CD8+ T cells and the host cells plays an important role in donor CD8+ T-cell survival in vivo after adoptive transfer. We also demonstrated that the transfected B16(OVA/IL-10) tumor cells secreting IL-10 are more resistant to in vivo CD8+ T-cell therapy than the original B16(OVA) tumor cells without IL-10 expression. Interestingly, the engineered CD8+ T(TNF) cells secreting transgene-coded TNF-alpha, but not the control CD8+ T(control) cells without any transgene expression eradicated IL-10-secreting 12-day lung micrometastasis in all 10/10 mice and IL-10-secreting solid tumors ( approximately 5 mm in diameter) in 6/10 mice. Transfer of the engineered CD8+ T(TNF) cells further induced both donor- and host-derived memory CD8+ T cells, leading to a stronger long-term antitumor immunity against the IL-10-secreting B16(OVA/IL-10) tumor cell challenges. Therefore, CD8+ T cells engineered to secrete TNF-alpha may be useful when designing strategies for adoptive T-cell therapy of solid tumors.

Toward a multiscale model of antigen presentation in immunity

A functioning immune system and the process of antigen presentation in particular encompass events that occur at multiple length and time scales. Despite a wealth of information in the biological literature regarding each of these scales, no single representation synthesizing this information into a model of the overall immune response as it depends on antigen presentation is available. In this article, we outline an approach for integrating information over relevant biological and temporal scales to generate such a representation for major histocompatibility complex class II-mediated antigen presentation. In addition, we begin to address how such models can be used to answer questions about mechanisms of infection and new strategies for treatment and vaccines.

Lymphopenia-induced proliferation of donor T cells reduces their capacity for causing acute graft-versus-host disease

OBJECTIVE

T cells that undergo lymphopenia-induced proliferation (LIP) are characterized by greater effector and anti-tumor function than naïve T cells. But the ability of these T cells in causing graft-versus-host disease (GVHD) is not known.

METHODS

We tested the hypothesis that donor T cells that had undergone LIP would cause more severe GVHD than naïve T cells by utilizing well-characterized murine experimental models of allogeneic bone marrow transplantation (BMT).

RESULTS

Contrary to our hypothesis, LIP of donor T cells under either noninflammatory or irradiated conditions caused significantly reduced GVHD as determined by survival, clinical, pathologic, and biochemical parameters than naïve T cells. Compared to naïve donor T cells, LIP T cells demonstrated reduced expansion in vivo and in vitro after allogeneic BMT. The reduction in GVHD mortality and severity was observed across multiple strains after allogeneic BMT. In vivo mechanistic studies by cell depletion demonstrated an increase in the CD44(hi) "memory" phenotype T cells and not the CD4(+)CD25(+) T cell subset to be critical for the reduction in GVHD.

CONCLUSIONS

These data demonstrate that LIP of T cells regulates acute GVHD severity in contrast to their ability to cause increased allograft rejection, autoimmunity, or anti-tumor immunity.

Functional roles of immature dendritic cells in impaired immunity of solid tumour and their targeted strategies for provoking tumour immunity

Dendritic cells play a crucial role in initiating tumour immunity as well as in the immune response for invading foreign pathogens such as bacteria and viruses. For bacterial and viral infections, the immature dendritic cells (iDCs) residing in peripheral tissues are efficiently activated and matured by pathogen signals for performing the immune response. In contrast, for self-antigens, the naive T cells are not activated by iDCs but proceed to anergy/deletion, and the generation of regulatory T cells for immune tolerance. The induction of immune response and tolerance is regulated strictly by iDCs as the sensor for homeostasis of immune response in the host. Despite the identification of some tumour antigens, tumour immunity is not provoked successfully. Even though there are some critical obstacles to inhibit effective tumour immunity, tumour cells are able to exploit the functional roles of iDCs for tumour progression, which are induced by tumour-derived soluble factors such as vascular endothelial growth factor (VEGF) and functionally modulated in the microenvironment. The iDCs still remain as the critical target for provoking tumour immunity. In this review, the functional roles of tumour-associated iDCs and the strategy for targeting iDCs in effective tumour immunity for the cancer patient are discussed.

Acquisition of antigen presentasome (APS), an MHC/costimulatory complex, is a checkpoint of memory T-cell homeostasis

Immunologic memory is associated with the activation and expansion of antigen-specific T cells, followed by clonal deletion and survival of a small number of memory T cells. This study establishes that effector and rested memory T cells can acquire major histocompatibility complex (MHC)/CD80 molecules (antigen presentasome [APS]) upon activation in vitro and after vaccination in vivo. We demonstrate for the first time that acquisition of APS by rested memory T cells is correlated with increased levels of apoptosis in vivo and up-regulation of caspase-3, bcl-x, bak, and bax in our in vitro studies. Moreover, our results demonstrate that memory T cells with acquired APS can indeed become cytotoxic T lymphocytes and kill other cells through perforin-mediated lysis. In addition, they retained the production of interferon gamma and T-helper 2 (Th2) type cytokines. The acquisition of APS by memory T cells might be an important checkpoint leading to the clonal deletion of the majority of effector T cells, possibly allowing the surviving cells to become long-term memory cells by default.

Development, trafficking, and function of memory T-cell subsets

The precise mechanisms that govern memory T-cell lineage commitment during an immune response continue to be the subject of intense scrutiny. The existence of memory T-cell subsets defined by location, function, and phenotype adds an additional layer of complexity to the overall memory T-cell population. In this review, the integration of memory subset development and migration and the functional consequences of specific tissue localization are discussed.

The descent of memory T-cell subsets

The immune system has evolved by continuously increasing its complexity to provide the host with an advantage over infectious agents. The development of immunological memory engenders long-lasting protection and lengthens the lifespan of the host. The generation of subsets of memory T cells with distinct homing and functional properties increases our defensive capabilities. However, the developmental relationship of memory T-cell subsets is a matter of debate. In this Opinion article, in light of recent developments, we suggest that it is probable that two distinct lineages comprise the memory CD8+ T-cell population generated in response to infection.

Delayed expansion and contraction of CD8+ T cell response during infection with virulent Salmonella typhimurium

Ag presentation to CD8(+) T cells often commences immediately after infection, which facilitates their rapid expansion and control of infection. Subsequently, the primed cells undergo rapid contraction. We report that this paradigm is not followed during infection with virulent Salmonella enterica, serovar Typhimurium (ST), an intracellular bacterium that replicates within phagosomes of infected cells. Although susceptible mice die rapidly (approximately 7 days), resistant mice (129 x 1SvJ) harbor a chronic infection lasting approximately 60-90 days. Using rOVA-expressing ST (ST-OVA), we show that T cell priming is considerably delayed in the resistant mice. CD8(+) T cells that are induced during ST-OVA infection undergo delayed expansion, which peaks around day 21, and is followed by protracted contraction. Initially, ST-OVA induces a small population of cycling central phenotype (CD62L(high)IL-7Ralpha(high)CD44(high)) CD8(+) T cells. However, by day 14-21, majority of the primed CD8(+) T cells display an effector phenotype (CD62L(low)IL-7Ralpha(low)CD44(high)). Subsequently, a progressive increase in the numbers of effector memory phenotype cells (CD62L(low)IL-7Ralpha(high)CD44(high)) occurs. This differentiation program remained unchanged after accelerated removal of the pathogen with antibiotics, as majority of the primed cells displayed an effector memory phenotype even at 6 mo postinfection. Despite the chronic infection, CD8(+) T cells induced by ST-OVA were functional as they exhibited killing ability and cytokine production. Importantly, even memory CD8(+) T cells failed to undergo rapid expansion in response to ST-OVA infection, suggesting a delay in T cell priming during infection with virulent ST-OVA. Thus, phagosomal lifestyle may allow escape from host CD8(+) T cell recognition, conferring a survival advantage to the pathogen.

Inflaming the CD8+ T cell response

Although inflammatory cytokines induced by infection or vaccination with adjuvants have long been known to stimulate optimal antigen-presenting cell function, recent evidence indicates that some inflammatory cytokines also act directly on the responding T cells to control their response to infection. Here, we review the evidence that specific inflammatory cytokines act to control the magnitude of expansion, the degree of contraction, and the rate of memory cell development. These data may suggest new strategies for manipulating vaccine efficacy in the quest to protect against pathogenic microbes.

Cutting edge: latecomer CD8 T cells are imprinted with a unique differentiation program

Factors that influence T cell responses, such as Ag load, APCs, costimulatory molecules, and cytokines, dramatically change during the course of an immune response. We observed that antiviral CD8 T cells were not recruited from circulation simultaneously, but over a period of 3-4 days. Consequently, locally resident T cells and those that entered secondary lymphoid tissue later were primed in very different environments. The cells recruited later in the response were imprinted with a unique differentiation program, such that their magnitude of proliferation was reduced and their kinetics of expansion was delayed. In addition, we found that the "latecomer" CD8 T cells displayed a unique surface phenotype indicative of reduced stimulation but were not preferentially recruited into the surviving pool of memory cells. This finding demonstrates that the timing of recruitment of individual T cell clones determines the population dynamics of the subsequent immune response.

Activated mouse T cells downregulate, process and present their surface TCR to cognate anti-idiotypic CD4+ T cells

The ability of activated T cells to present foreign antigens through the MHC class II pathway has been shown in the case of human, rat and mouse T cells. In the present study, the ability of activated T cells to present their endogenous TCR in association with MHC class II molecules to CD4+ T cells was shown. Upon activation mouse T cells downregulate their surface TCR, which are degraded into peptides in endosomal/lysosomal compartments. The idiopeptides (peptides derived from the variable region of the TCR) are presented to cognate anti-idiotypic CD4+ T cells, resulting in activation and proliferation of these cells. Interaction of idiotypic and anti-idiotypic T cells brought about by presentation of TCR idiopeptide may have important implications for T-cell vaccination and perpetuation of T-cell memory not requiring persisting antigen or long-lived memory cells.

Idiotypic T cells specific for Morbillivirus nucleocapsid protein process and present their TCR to cognate anti-idiotypic CD8+ T cells

CD8(+) T cells are activated by the presentation of antigenic peptide through MHC class I molecules. Newly synthesized proteins formed as defective ribosomal products (DRiPs) can act as a major source of antigenic peptides for MHC class I presentation pathway. Majority of these peptides are generated from the intracellular degradation of self antigens. In the present study, we have shown that newly synthesized T cell receptor (TCR) beta chains formed as DRiPs in T cells are ubiquitinated and degraded by the proteasomes. These TCR-DRiPs are processed and presented by activated T cells to cognate anti-idiotypic CD8(+) T cells. Presentation of TCR idiopeptide (peptide derived from the variable region of idiotypic TCR) by activated T cells leads to Bcl-2 expression and cytokine secretion by anti-idiotypic CD8(+) T cells. Presentation of intracellular antigen by T cells may have important implications in immunoregulation, control of lymphotropic virus infection and autoimmune diseases.

The dissection of CD8 T cells during liver-stage infection

Multiple injections of gamma-radiation-attenuated Plasmodium sporozoites (gamma-spz) can induce long-lived, sterile immunity against pre-erythrocytic stages of malaria. Malaria antigen (Ag)-specific CD8 T cells that produce IFN-gamma are key effector cells in this model of protection. Although there have been numerous reports dealing with gamma-spz-induced CD8 T cells in the spleen, CD8 T cells most likely confer protection by targeting infected hepatocytes. Consequently, in this chapter we discuss observations and hypotheses concerning CD8 T cell responses that occur in the liver after an encounter with the Plasmodium parasite. Protracted protection against pre-erythrocytic stages requires memory CD8 T cells and we discuss evidence that gamma-spz-induced immunity is indeed accompanied by the presence of intrahepatic CD44hi CD45RBlo CD62lo CD122lo effector memory (EM) CD8 T cells and CD44hi CD45RBhi CD621hi CD122hi central memory (CM) CD8 T cells. In addition, the EM CD8 T cells rapidly release IFN-gamma in response to spz challenge. The possible role of Kupffer cells in the processing of spz Ags and the production of cytokines is also considered. Finally, we discuss evidence that is consistent with a model whereby intrahepatic CM CD8 T cells are maintained by IL-15 mediated-homeostatic proliferation while the EM CD8 T cells are conscripted from the CM pool in response to a persisting depot of liver-stage Ag.

Host-reactive CD8+ memory stem cells in graft-versus-host disease

Graft-versus-host disease (GVHD) is caused by alloreactive donor T cells that trigger host tissue injury. GVHD develops over weeks or months, but how this immune response is maintained over time is unknown. In mouse models of human GVHD, we identify a new subset of postmitotic CD44(lo)CD62L(hi)CD8(+) T cells that generate and sustain all allogeneic T-cell subsets in GVHD reactions, including central memory, effector memory and effector CD8(+) T cells, while self-renewing. These cells express Sca-1, CD122 and Bcl-2, and induce GVHD upon transfer into secondary recipients. The postmitotic CD44(lo)CD62L(hi)CD8(+) T cells persist throughout the course of GVHD, are generated in the initial phase in response to alloantigens and dendritic cells and require interleukin-15. Thus, their long life, ability to self-renew and multipotentiality define these cells as candidate memory stem cells. Memory stem cells will be important targets for understanding and influencing diverse chronic immune reactions, including GVHD.

Commensal microbiota alter the abundance and TCR responsiveness of splenic naïve CD4+ T lymphocytes

The epidemiologic risk of certain systemic immunologic diseases is affected by commensal or environmental microbiota, but the cellular basis of the "hygiene hypothesis" is poorly understood. In this study, we demonstrate that composition of the commensal microbiota affects the functional state of the peripheral naïve (CD62L(hi)CD44(lo)) T lymphocyte populations. Restricted flora (RF) mice (stably colonized with excess nonpathogenic Clostridium sp., and changes in other bacterial and fungal taxa) were distinguished after the neonatal period by a progressive deficiency in absolute numbers of naïve CD4+ and CD8+ T lymphocytes. SPF and RF mice had comparable levels of memory CD4+ and CD8+ T cells. This phenotype was attributable to the altered levels of certain commensals and their products, since germ-free mice had normal absolute numbers of splenic CD4+ and CD8+ T cells and their respective naïve and memory subsets. The naïve CD4+ T cell subset was functionally distinguished in RF mice versus SPF mice by TCR hyperresponsiveness, pro-inflammatory cytokine production, and increased activation-induced cell death. Biochemically, these traits were associated with higher basal phosphorylation of the TCR signaling proteins ZAP-70, Lck, and LAT. These findings indicate that enteric microbial products, through unknown cellular circuitry, influence steps in CD4 T cell differentiation moderating basal TCR signaling and immune responsiveness.

Antigenic stimulation specifically reactivates the replication of archived simian immunodeficiency virus genomes in chronically infected macaques

Human immunodeficiency virus/simian immunodeficiency virus (SIV) diversification is a direct consequence of viral replication and occurs principally in secondary lymphoid organs where CD4(+) T cells are activated and proliferate. However, the evolution of viral quasispecies may also be driven by various nonexclusive mechanisms, including adaptation to specific immune responses and modification of viral fitness. Analysis of viral quasispecies in SIV-infected macaques subjected to repeated antigenic stimulations allowed us to demonstrate transient expansions of SIV populations that were highly dependent upon activation of antigen-specific T cells. T-cell clones expanded in response to a particular antigen were infected by a specific viral population and persisted for prolonged periods. Upon a second stimulation by encounter with the same antigen, these specific genomes were at the origin of a new burst of replication, leading to rapid but transient replacement of the viral quasispecies in blood. Finally, longitudinal analysis of SIV sequence variation during and between antigenic stimulations revealed that viral evolution is mostly constrained to periods of strong immunological activity.

Species-specific inhibition of cerebral malaria in mice coinfected with Plasmodium spp

Recent epidemiological observations suggest that clinical evolution of Plasmodium falciparum infections might be influenced by the concurrent presence of another Plasmodium species, and such mixed-species infections are now known to occur frequently in residents of most areas of endemicity. We used mice infected with P. berghei ANKA (PbA), a model for cerebral malaria (CM), to investigate the influence of experimental mixed-species infections on the expression of this pathology. Remarkably, the development of CM was completely inhibited by the simultaneous presence of P. yoelii yoelii but not that of P. vinckei or another line of P. berghei. In the protected coinfected mice, the accumulation of CD8(+) T cells in the brain vasculature, a pivotal step in CM pathogenesis, was found to be abolished. Protection from CM was further found to be associated with species-specific suppression of PbA multiplication. These observations establish the concept of mixed Plasmodium species infections as potential modulators of pathology and open novel avenues to investigate mechanisms implicated in the pathogenesis of malaria.

Intestinal Fibroblast-Derived IL-10 Increases Survival of Mucosal T Cells by Inhibiting Growth Factor Deprivation- and Fas-Mediated Apoptosis

Mucosal T cells are essential to immune tolerance in the intestine, an organ constantly exposed to large amounts of dietary and bacterial Ags. We investigated whether local fibroblasts affect mucosal T cell survival, which is critical for maintenance of immune tolerance. Coculture with autologous fibroblasts significantly increased viability of mucosal T cells by inhibiting IL-2 deprivation- and Fas-mediated apoptosis, an effect that was both contact- and secreted product-dependent. Investigation of anti-apoptotic factors in the fibroblast-conditioned medium (FCM) revealed the presence of IL-10 and PGE2, but not IFN-beta, IL-2, or IL-15. Although recombinant IFN-beta, but not PGE2, effectively prevented T cell apoptosis, neutralizing Ab studies showed that only IL-10 blockade significantly increased T cells apoptosis, whereas neutralizing IFN-beta or IFN-alpha failed to inhibit the anti-apoptotic effect of FCM. To confirm that fibroblast-derived IL-10 was responsible for preserving mucosal T cell viability, IL-10 mRNA was demonstrated in fibroblasts by Southern blotting and RT-PCR. When FCM was submitted to HPLC fractionation, only the peak matching rIL-10 contained the anti-apoptotic activity, and this was eliminated by treatment with an IL-10-neutralizing Ab. Finally, when fibroblasts were transiently transfected with IL-10 antisense oligonucleotides, the conditioned medium lost its T cell anti-apoptotic effect, whereas medium from fibroblasts transfected with IFN-beta antisense oligonucleotides displayed the same anti-apoptotic activity of medium from untransfected fibroblasts. These results indicate that local fibroblast-derived IL-10 is critically involved in the survival of mucosal T cells, underscoring the crucial importance of studying organ-specific cells and products to define the mechanisms of immune homeostasis in specialized tissue microenvironments like the intestinal mucosa.

Recent thymic emigrants and subsets of naive and memory T cells in the circulation of patients with head and neck cancer

Apoptosis of circulating CD8+ T lymphocytes is a frequent finding in patients with cancer. T-cell output by the thymus or antigen-driven expansion of circulating T cells could compensate for apoptosis and thus normalize their homeostasis. We studied the frequency of recent thymic emigrants (RTE) identified by T-cell receptor excision circles (TREC) and of naive and memory T-cell subsets in peripheral blood samples obtained from 39 patients with head and neck cancer (HNC) and 33 age-matched controls (NC). TREC numbers were determined by real-time quantitative PCR, and CD8+CD45RO-CD27+ or CD4+CD45RO-CD27+ T-cell subsets were quantified by flow cytometry. Age-associated decreases in TREC numbers and proportions of naive CD8+ and CD4+ T-cell subsets were significantly greater in cancer patients than NC. In contrast, the memory compartment was expanded, with increased proportions of CD4+CD45RO+ but not CD8+CD45RO+ T cells, in cancer patients vs. NC. These alterations did not normalize in patients who were NED. The data suggest that lower thymic output combined with rapid turnover of naive CD8+ T cells account for altered lymphocyte homeostasis in HNC patients. The defect persists long after curative treatments and may contribute to immune cell dysregulation in patients with cancer.

Chemokines: control of primary and memory T-cell traffic

Motility is a hallmark of leukocytes, and breakdown in the control of migration contributes to many inflammatory diseases. Chemotactic migration of leukocytes largely depends on adhesive interaction with the substratum and recognition of a chemoattractant gradient. Chemokines are secreted proteins and have emerged as key controllers of integrin function and cell locomotion. Numerous distinct chemokines exist that target all types of leukocytes, including hematopoietic precursors, leukocytes of the innate immune system, as well as naive memory, and effector lymphocytes. The combinatorial diversity in responsiveness to chemokines ensures the proper tissue distribution of distinct leukocyte subsets under normal and pathological conditions. Inflammatory chemokines are readily detected in lesional tissue and local cellular infiltrates carry corresponding chemokine receptors. Blocking of inflammatory chemokines represents a promising strategy for the development of novel anti-inflammatory therapeutics. This review focuses on a separate class of chemokines, termed homeostatic chemokines, with steady-state production at diverse sites, including primary and secondary lymphoid tissues as well as peripheral (extralymphoid) tissues. More precisely, we discuss the chemokines involved in T-cell traffic during the initiation of adaptive immunity and compare the distinct migration properties of short-lived effector T cells and long-lived memory T cells. Memory T cells are currently classified according to the presence of the lymph node-homing receptor CCR7 into CCR7+ central memory T (T(CM)) cells and CCR7- effector memory T (T(EM)) cells. For better understanding memory T-cell function, we propose the distinction of a third category, termed peripheral immune surveillance T (T(PS)) cells, which typically reside in healthy peripheral tissues, such as skin, lung, and gastrointestinal tract. Localization and relocation of memory T cells is strictly related to their function in recall responses. Therefore, detailed knowledge of their generation and tissue distribution may help to design better vaccination strategies.

The role of BH3-only proteins in the immune system

Programmed cell death--also known as apoptosis--has a crucial role in the immune system of mammals and other animals. It removes useless cells and potentially dangerous cells, including lymphocytes, and is involved in killing pathogen-infected or damaged cells. Defects in this process have been found to cause or contribute to diseases of the immune system, including immunodeficiency, autoimmunity, lymphoma and leukaemia. This review describes BH3-only proteins, a pro-apoptotic subgroup of the BCL-2 family, and their role in the development and function of the immune system.

Dietary (n-3) Polyunsaturated Fatty Acids Do Not Affect the In Vivo Development and Function of Listeria-Specific CD4+ and CD8+ Effector and Memory/Effector T Cells in Mice

We previously reported that in a mouse model, a diet high in (n-3) PUFA diminishes host survival following an infection from Listeria monocytogenes, a gram-positive bacterial pathogen. In this study we investigated the impact of (n-3) PUFA on the adaptive immune response to L. monocytogenes. BALB/c mice were fed experimental diets either devoid of or rich in (n-3) PUFA from fish oil for 4 wk and then infected with 10(6) actA-deficient L. monocytogenes. At 7 and 35 d postchallenge, effector and memory/effector T cells in the spleen were enumerated by flow cytometry. Surprisingly, the number of Listeria-specific CD4(+) and CD8(+) effector and memory/effector T cells in the spleen was not affected by (n-3) PUFA. Also, the effector cells derived from mice fed either diet were equally capable of conferring protective immunity upon adoptive transfer to naive recipients. Despite our previous data, which demonstrated that (n-3) PUFA profoundly impaired host resistance to L. monocytogenes, pathogen-specific T cell responses were not substantially affected by dietary (n-3) PUFA.

Reducing the Stimulation of CD8+T Cells during Infection with Intracellular Bacteria Promotes Differentiation Primarily into a Central (CD62LhighCD44high) Subset

During infection with lymphocytic choriomeningitis virus, CD8(+) T cells differentiate rapidly into effectors (CD62L(low)CD44(high)) that differentiate further into the central memory phenotype (CD62L(high)CD44(high)) gradually. To evaluate whether this CD8(+) T cell differentiation program operates in all infection models, we evaluated CD8(+) T cell differentiation during infection of mice with recombinant intracellular bacteria, Listeria monocytogenes (LM) and Mycobacterium bovis (BCG), expressing OVA. We report that CD8(+) T cells primed during infection with the attenuated pathogen BCG-OVA differentiated primarily into the central subset that correlated to reduced attrition of the primed cells subsequently. CD8(+) T cells induced by LM-OVA also differentiated into central phenotype cells first, but the cells rapidly converted into effectors in contrast to BCG-OVA. Memory CD8(+) T cells induced by both LM-OVA as well as BCG-OVA were functional in that they produced cytokines and proliferated extensively in response to antigenic stimulation after adoptive transfer. During LM-OVA infection, if CD8(+) T cells were guided to compete for access to APCs, then they received reduced stimulation that was associated with increased differentiation into the central subset and reduced attrition subsequently. Similar effect was observed when CD8(+) T cells encountered APCs selectively during the waning phase of LM-OVA infection. Taken together, our results indicate that the potency of the pathogen can influence the differentiation and fate of CD8(+) T cells enormously, and the extent of attrition of primed CD8(+) T cells correlates inversely to the early differentiation of CD8(+) T cells primarily into the central CD8(+) T cell subset.

Expression of inhibitory KIR is confined to CD8+ effector T cells and limits their proliferative capacity

A subset of effector/memory CD8(+) T cells expresses natural killer cell receptors (NKR). Expression of inhibitory NKR at that stage of T cell differentiation is poorly understood. Interestingly, recent studies in mice indicated that transgenic expression of an inhibitory NKR induced the accumulation of memory T cells by inhibiting activation-induced cell death (AICD). To further understand the role of inhibitory NKR on T cells, we characterized the subset of human peripheral T cells expressing the inhibitory NKR, CD158b, and studied the modulation of antigen-driven T cell expansion by an endogenous inhibitory NKR. We found that CD158b expression was confined to a population of CD8(+)TCRalphabeta(+) effector T cells as defined by a CD45RA(+)CCR7(-) phenotype and high constitutive expression of granzyme B1. Few cells expressed the activating form CD158j in the absence of CD158b. Functionally, engagement of CD158b by MHC ligands diminished early TCR signaling, as well as AICD. However, the reduced AICD did not rescue cells for proliferation, since T cell expansion in the presence of CD158b triggering was impaired. Expression of inhibitory NKR on effector CD8(+) T cells may explain in part the poor replicative capacity of T cells at that stage of differentiation.

Sub-compartmentalization of the gastrointestinal (GI) immune system determined with microbeads that differ in release properties

Immunization of two specific regions of the murine GI tract of two types of mice with ovalbumin (OVA) encapsulated in microbeads with two different pH-sensitive coatings allowed a more precise analysis of this compartment of the mucosal immune system. Acute, chronic and pervasive immunization protocols were utilized in an attempt to stimulate specific types of immunity. Chronic immunization potentiated antibody isotypes influenced by type 2 T helper cells (T(h)2). Pervasive immunization of both regions of the GI tract mimicked chronic immunization, stimulating high levels of OVA-reactive IgE. Acute immunization was best able to potentiate isotypes influenced by type 1 T helper cells (T(h)1) and a sequential segregated immunization protocol allowed the targeting of T(h)1-like memory responses.

Role of tumor necrosis factor receptors in regulating CD8 T-cell responses during acute lymphocytic choriomeningitis virus infection

The role of tumor necrosis factor (TNF) in regulating various phases of the antiviral T-cell response is incompletely understood. Additionally, despite strong evidence ascribing a role for TNF in protecting against T-cell-dependent autoimmunity, the underlying mechanisms are still obscure. To address these issues, we have investigated the role of tumor necrosis factor receptors (TNFRs) I (p55R) and II (p75R) in regulating CD8 T-cell responses to lymphocytic choriomeningitis virus (LCMV) with wild-type, p55R-deficient (p55(-/-)), p75R-deficient (p75(-/-)), and p55R- and p75R-deficient (DKO) mice. Loss of p55R increased the number of memory CD8 T cells to only one of the two immunodominant epitopes, and p75R deficiency had a minimal impact on the T-cell response to LCMV. Strikingly, deficiency of both p55R and p75R had a more dramatic effect on the LCMV-specific CD8 T-cell response; in the DKO mice, as a sequel to enhanced expansion and a reduction in contraction of CD8 T cells, there was a substantial increase in the number of memory CD8 T cells (specific to the two immunodominant epitopes). While the majority of LCMV-specific memory CD8 T cells in wild-type mice were CD62Lhi CCR7hi (central memory), a major proportion of memory CD8 T cells in DKO mice were CD62Llo CCR7hi. TNFR deficiency did not affect the proliferative renewal of memory CD8 T cells. Taken together, these data suggested that TNFRs p55R and p75R have overlapping roles in downregulating CD8 T-cell responses and establishment of immune homeostasis during an acute viral infection.

Down-regulation of normal human T cell blast activation: roles of APO2L/TRAIL, FasL, and c- FLIP, Bim, or Bcl-x isoform expression

A systematic study was undertaken to characterize the role of APO 2 ligand/tumor necrosis factor-related apoptosis-inducing ligand (APO2L/TRAIL) and Fas ligand (FasL) together with the expression of several anti- or proapoptotic proteins in the down-regulation of normal human T cell responses. We have observed for the first time that the higher sensitivity of normal human T cell blasts to apoptosis and activation-induced cell death (AICD) as compared with naive T cells correlates with the increased expression of Bcl-x short (Bcl-xS) and Bim. T cell blasts die in the absence of interleukin 2 (IL-2) with no additional effect of death receptor ligation. In the presence of IL-2, recombinant APO2L/TRAIL or cytotoxic anti-Fas monoclonal antibodies induce rather inhibition of IL-2-dependent growth and not cell death on normal human T cell blasts. This observation is of physiological relevance, as supernatants from T cell blasts, pulse-stimulated with phytohemagglutinin (PHA) or through CD3 or CD59 ligation and containing bioactive APO2L/TRAIL and/or FasL expressed on microvesicles or direct CD3 or CD59 ligation, had the same effect. Cell death was only observed in the presence of cycloheximide or after a pulse through CD3 or CD59, correlating with a net reduction in cellular Fas-associated death domain-like IL-1beta-converting enzyme-inhibitory protein long (c-FLIPL) and c-FLIPS expression. We also show that death receptor and free radical generation contribute, at least partially, to AICD induced by PHA and also to the inhibition of IL-2-dependent cell growth by CD3 or CD59 ligation. Finally, we have also shown that T cell blasts surviving PHA-induced AICD are memory CD44high cells with increased c-FLIPS and Bcl-xL expression.

Transition of late-stage effector T cells to CD27+ CD28+ tumor-reactive effector memory T cells in humans after adoptive cell transfer therapy

In humans, the pathways of memory T-cell differentiation remain poorly defined. Recently, adoptive cell transfer (ACT) of tumor-reactive T lymphocytes to metastatic melanoma patients after nonmyeloablative chemotherapy has resulted in persistence of functional, tumor-reactive lymphocytes, regression of disease, and induction of melanocyte-directed autoimmunity in some responding patients. In the current study, longitudinal phenotypic analysis was performed on melanoma antigen-specific CD8+ T cells during their transition from in vitro cultured effector cells to long-term persistent memory cells following ACT to 6 responding patients. Tumor-reactive T cells used for therapy were generally late-stage effector cells with a CD27Lo CD28Lo CD45RA- CD62 ligand- (CD62L-) CC chemokine receptor 7- (CCR7-) interleukin-7 receptor alphaLo (IL-7RalphaLo) phenotype. After transfer, rapid up-regulation and continued expression of IL-7Ralpha in vivo suggested an important role for IL-7R in immediate and long-term T-cell survival. Although the tumor antigen-specific T-cell population contracted between 1 and 4 weeks after transfer, stable numbers of CD27+)CD28+ tumor-reactive T cells were maintained, demonstrating their contribution to the development of long-term, melanoma-reactive memory CD8+ T cells in vivo. At 2 months after transfer, melanoma-reactive T cells persisted at high levels and displayed an effector memory phenotype, including a CD27+ CD28+ CD62L- CCR7- profile, which may explain in part their ability to mediate tumor destruction.

Fate and function of anti-CD3/CD28-activated T cells following adoptive transfer: IL-2 promotes development of anti-tumor memory T cells in vivo

BACKGROUND

Adoptive immunotherapy with T cells activated through CD3 alone requires exogenous IL-2 for T-cell function and survival after transfer, but the in vivo cytokine requirement of T cells activated through CD3 and CD28 is unknown. We hypothesized that CD3/CD28-activated T cells, unlike those activated through CD3 alone, might develop into long-lived memory T cells, either with or without systemic IL-2.

METHODS

We used MHC class I-restricted TCR transgenic T cells from the OT-1 mouse, specific for the surrogate tumor Ag ovalbumin (OVA), to assess the trafficking kinetics, antigenic responsiveness and anti-tumor efficacy of dual-activated T cells in vivo as a function of IL-2 administration. At days 7, 14, and 28 after transfer, lymph node cells and splenocytes were examined for donor cell persistence and antigenic responsiveness by FACS and ELISA, respectively.

RESULTS

In IL-2-treated mice, donor CD8+ T cells persisted and developed a memory phenotype, based on CD44 and Ly6c expression at day 28, while mice given no IL-2 had fewer donor cells at all time points. OVA-specific release of IFN-gamma was higher from lymphocytes of IL-2-treated mice compared with no-IL-2 mice (P<0.02 at all time points). In mice challenged with an OVA-bearing subline of the AML leukemia model C1498, IL-2 did not confer added protection from tumor challenge at 1 or 2 weeks after adoptive transfer, but gave improved survival at 4 weeks post-transfer.

DISCUSSION

We conclude that exogenous IL-2 is not required for anti-tumor activity of CD3/CD28-activated CD8+ cells early after adoptive transfer, but promotes T-cell persistence that confers disease protection at more remote times.