Bcl6 acts as an amplifier for the generation and proliferative capacity of central memory CD8+ T cells

Central memory CD8(+) T cells (T(CM)) are considered to be more efficient than effector ones (T(EM)) for mediating protective immunity. The molecular mechanism involved in the generation of these cells remains elusive. Because Bcl6 plays a role in the generation and maintenance of memory CD8(+) T cells, we further examined this role in the process in relation to T(CM) and T(EM) subsets. In this study, we show that T(CM) and T(EM) were functionally identified in CD62L(+) and CD62L(-) memory (CD44(+)Ly6C(+)) CD8(+) T cell subsets, respectively. Although T(CM) produced similar amounts of IFN-gamma and IL-2 to T(EM) after anti-CD3 stimulation, the cell proliferation capacity after stimulation and tissue distribution profiles of T(CM) differed from those of T(EM). Numbers of T(CM) were greatly reduced and elevated in spleens of Bcl6-deficient and lck-Bcl6 transgenic mice, respectively, and those of T(EM) were constant in nonlymphoid organs of these same mice. The majority of Ag-specific memory CD8(+) T cells in spleens of these mice 10 wk after immunization were T(CM), and the number correlated with Bcl6 expression in T cells. The proliferation of Ag-specific memory CD8(+) T cells upon secondary stimulation was dramatically up-regulated in lck-Bcl6 transgenic mice, and the adoptive transfer experiments with Ag-specific naive CD8(+) T cells demonstrated that some of the up-regulation was due to the intrinsic effect of Bcl6 in the T cells. Thus, Bcl6 is apparently a crucial factor for the generation and secondary expansion of T(CM).     

Human effector memory CD4+ T cells directly recognize allogeneic endothelial cells in vitro and in vivo

The frequency of circulating alloreactive human memory T cells correlates with allograft rejection. Memory T cells may be divided into effector memory (T(EM)) and central memory (T(CM)) cell subsets, but their specific roles in allograft rejection are unknown. We report that CD4+ T(EM) (CD45RO+ CCR7- CD62L-) can be adoptively transferred readily into C.B-17 SCID/bg mice and mediate the destruction of human endothelial cells (EC) in vascularized human skin grafts allogeneic to the T cell donor. In contrast, CD4+ T(CM) (CD45RO+ CCR7+ CD62L+) are inefficiently transferred and do not mediate EC injury. In vitro, CD4+ T(EM) secrete more IFN-gamma within 48 h in response to allogeneic ECs than do T(CM). In contrast, T(EM) and T(CM) secrete comparable amounts of IFN-gamma in response to allogeneic monocytes (Mo). In the same cultures, both T(EM) and T(CM) produce IL-2 and proliferate in response to IFN-gamma-treated allogeneic human EC or Mo, but T(CM) respond more vigorously in both assays. Blockade of LFA-3 strongly inhibits both IL-2 and IFN-gamma secretion by CD4+ T(EM) cultured with allogeneic EC but only minimally inhibits responses to allogeneic Mo. Blockade of CD80 and CD86 strongly inhibits IL-2 but not IFN-gamma production by in response to allogeneic EC or Mo. Transduction of EC to express B7-2 enhances allogeneic T(EM) production of IL-2 but not IFN-gamma. We conclude that human CD4+ T(EM) directly recognize and respond to allogeneic EC in vitro by secreting IFN-gamma and that this response depends on CD2 but not CD28. Consistent with EC activation of effector functions, human CD4+ T(EM) can mediate allogeneic EC injury in vivo.     

Differential requirements for OX40 signals on generation of effector and central memory CD4+ T cells

Memory T cells can be divided into effector memory (T(EM)) and central memory (T(CM)) subsets based on their effector function and homing characteristics. Although previous studies have demonstrated that TCR and cytokine signals mediate the generation of the two memory subsets of CD8(+) T cells, the mechanisms for generation of the CD4(+) T(EM) and T(CM) cell subsets are unknown. We found that OX40-deficient mice showed a marked reduction in the number of CD4(+) T(EM) cells, whereas the number of CD4(+) T(CM) cells was normal. Adoptive transfer experiments using Ag-specific CD4(+) T cells revealed that OX40 signals during the priming phase were indispensable for the optimal generation of the CD4(+) T(EM), but not the CD4(+) T(CM) population. In a different transfer experiment with in vitro established CD4(+)CD44(high)CD62L(low) (T(EM) precursor) and CD4(+)CD44(high)CD62L(high) (T(CM) precursor) subpopulations, OX40-KO T(EM) precursor cells could not survive in the recipient mice, whereas wild-type T(EM) precursor cells differentiated into both T(EM) and T(CM) cells. In contrast, T(CM) precursor cells mainly produced T(CM) cells regardless of OX40 signals, implying the dispensability of OX40 for generation of T(CM) cells. Nevertheless, survival of OX40-KO T(EM) cells was partially rescued in lymphopenic mice. During in vitro recall responses, the OX40-KO T(EM) cells that were generated in lymphopenic recipient mice showed impaired cytokine production, suggesting an essential role for OX40 not only on generation but also on effector function of CD4(+) T(EM) cells. Collectively, the present results indicate differential requirements for OX40 signals on generation of CD4(+) T(EM) and T(CM) cells.     

Suppression of memory CD8 T cell generation and function by tryptophan catabolism

Dendritic cell-derived indoleamine 2,3-dioxygenase (IDO) suppresses naive T cell proliferation and induces their apoptosis by catalyzing tryptophan, and hence is essential for the maintenance of peripheral tolerance. However, it is not known whether memory T cells are subject to the regulation by IDO-mediated tryptophan catabolism, as memory T cells respond more rapidly and vigorously than their naive counterparts and are resistant to conventional costimulatory blockade. In this study, we present the evidence that memory CD8+ T cells are susceptible to tryptophan catabolism mediated by IDO. We found that overexpression of IDO in vivo attenuated the generation of both central memory CD8+ T cells (T(CM)) and effector memory CD8+ T cells (T(EM)) while suppressing IDO activity promoted their generation. Moreover, IDO overexpression suppressed the effector function of T(CM) cells or T(CM) cell-mediated allograft rejection as well as their proliferation in vivo. Interestingly, T(CM) cells were resistant to apoptosis induced by tryptophan catabolism. However, IDO overexpression did not suppress the effector function of T(EM) cells or T(EM) cell-mediated allograft rejection, suggesting that T(EM) cells, unlike T(CM) cells, do not require tryptophan for their effector function once they are generated. This study provides insight into the mechanisms underlying the differential regulation of memory T cell responsiveness and has clinical implications for vaccination or tolerance induction.     

Lack of ICAM-1 on APCs during T cell priming leads to poor generation of central memory cells

ICAM-1/LFA-1 interactions are known to enhance T cell/APC interactions and to promote T cell activation and cytokine secretion. We have analyzed the consequences of ICAM-1-mediated signaling on the generation of memory T cell subsets. We report that lack of ICAM-1 on APCs, but not on T cells, leads to poor T cell activation and proliferation in vitro and in vivo, and that the defect can be compensated by Ag dose, exogenous IL-2, additional costimulation, and by increasing responder T cell density on APCs. ICAM-1-null mice do not respond to immunization with OVA peptide, but immunization with OVA or with Salmonella typhimurium leads to good T cell proliferation 7-10 days later, and clearance of a challenge infection is equivalent to that of wild-type mice. However, when followed over time, recall proliferation and antibacterial immunity decay rapidly in ICAM-1-null mice, while recall cytokine responses are unaffected. The decline in immunity is not related to poor survival of T cells activated on ICAM-1-null APCs, or to poor generation of effectors in ICAM-1-null mice. Phenotypic analysis of T cells stimulated on ICAM-1-null APCs reveals preferential generation of CD44(high) CD62L(low) effector memory cells (T(EM)) over CD44(high) CD62L(high) central memory cells (T(CM)). Further, while the proportion of naive:memory T cells is similar in unmanipulated wild-type and ICAM-1-null mice, there is an accumulation of T(EM) cells, and a high T(EM):T(CM) ratio in aging ICAM-1-null mice. Together, the data indicate that signaling through LFA-1 during T cell activation may be involved in commitment to a proliferation-competent memory pool.     

Altered T cell memory and effector cell development in chronic lymphatic filarial infection that is independent of persistent parasite antigen

Chronic lymphatic filarial (LF) infection is associated with suppression of parasite-specific T cell responses that persist even following elimination of infection. While several mechanisms have been implicated in mediating this T cell specific downregulation, a role for alterations in the homeostasis of T effector and memory cell populations has not been explored. Using multiparameter flow cytometry, we investigated the role of persistent filarial infection on the maintenance of T cell memory in patients from the filarial-endemic Cook Islands. Compared to filarial-uninfected endemic normals (EN), microfilaria (mf) positive infected patients (Inf) had a reduced CD4 central memory (T(CM)) compartment. In addition, Inf patients tended to have more effector memory cells (T(EM)) and fewer effector cells (T(EFF)) than did ENs giving significantly smaller T(EFF):T(EM) ratios. These contracted T(CM) and T(EFF) populations were still evident in patients previously mf+ who had cleared their infection (CLInf). Moreover, the density of IL-7Rα, necessary for T memory cell maintenance (but decreased in T effector cells), was significantly higher on memory cells of Inf and CLInf patients, although there was no evidence for decreased IL-7 or increased soluble IL7-Rα, both possible mechanisms for signaling defects in memory cells. However, effector cells that were present in Inf and CLInf patients had lower percentages of HLA-DR suggesting impaired function. These changes in T cell populations appear to reflect chronicity of infection, as filarial-infected children, despite the presence of active infection, did not show alterations in the frequencies of these T cell phenotypes. These data indicate that filarial-infected patients have contracted T(CM) compartments and a defect in effector cell development, defects that persist even following clearance of infection. The fact that these global changes in memory and effector cell compartments do not yet occur in infected children makes early treatment of LF even more crucial.     

A novel role of CD30/CD30 ligand signaling in the generation of long-lived memory CD8+ T cells

Memory CD8+ T cells can be divided into two subsets, central memory (T(CM)) and effector memory (T(EM)) CD8+ T cells. We found that CD30, a member of the TNFR-associated factor (TRAF)-linked TNFR superfamily, signaling is involved in differentiation of long-lived CD8+ T(CM) cells following Listeria monocytogenes infection. Although CD8+ T(EM) cells transiently accumulated in the nonlymphoid tissues of CD30 ligand (CD153-/-) mice after infection, long-lived memory CD8+ T(CM) cells were poorly generated in these mice. CCR7 mRNA expression was down-regulated in CD8+ T cells of the spleen of CD153-/- mice in vivo and the expression was up-regulated in CD8+ T(EM) cells by anti-CD30 mAb cross-linking in vitro. These results suggest that CD30/CD30 ligand signaling plays an important role in the generation of long-lived memory CD8+ T cells at least partly by triggering homing receptors for T(CM) cells.     

Antigen-specific central memory CD4+ T lymphocytes produce multiple cytokines and proliferate in vivo in humans

The function of Ag-specific central (T(CM)) and effector (T(EM)) memory CD4+ T lymphocytes remains poorly characterized in vivo in humans. Using CD154 as a marker of Ag-specific CD4+T cells, we studied the differentiation of memory subsets following anti-hepatitis B immunization. Hepatitis B surface Ag (HBs)-specific memory CD4+T cells were heterogeneous and included T(CM) (CCR7+CD27+) and T(EM) (CCR7(-)CD27(+/-)). HBs-specific T(CM) and T(EM) shared the capacity to produce multiple cytokines, including IL-2 and IFN-gamma. Several years postimmunization, approximately 10% of HBs-specific memory CD4+ T cells were in cycle (Ki67+) and the proliferating cells were CCR7+. These results suggest that the model of functional specialization of T(CM) and T(EM) cannot be applied to protein vaccine Ags and support the concept that T(CM) are capable of self-renewal and contribute to maintain the pool of memory cells.     

Molecular signatures distinguish human central memory from effector memory CD8 T cell subsets

Memory T cells are heterogeneous in terms of their phenotype and functional properties. We investigated the molecular profiles of human CD8 naive central memory (T(CM)), effector memory (T(EM)), and effector memory RA (T(EMRA)) T cells using gene expression microarrays and phospho-protein-specific intracellular flow cytometry. We demonstrate that T(CM) have a gene expression and cytokine signaling signature that lies between that of naive and T(EM) or T(EMRA) cells, whereas T(EM) and T(EMRA) are closely related. Our data define the molecular basis for the different functional properties of central and effector memory subsets. We show that T(EM) and T(EMRA) cells strongly express genes with known importance in CD8 T cell effector function. In contrast, T(CM) are characterized by high basal and cytokine-induced STAT5 phosphorylation, reflecting their capacity for self-renewal. Altogether, our results distinguish T(CM) and T(EM)/T(EMRA) at the molecular level and are consistent with the concept that T(CM) represent memory stem cells.     

Dynamic differentiation of activated human peripheral blood CD8+ and CD4+ effector memory T cells

Two functionally different memory T cell subsets were originally defined based on their different CCR7 expression profile, but the lineage relationship between these subsets referred to as central memory T cells (T(CM)) and effector memory T cells (T(EM)), is not resolved. A prevalent model proposes a linear progressive differentiation from T(CM) to T(EM). Our results demonstrate that on activation, human CCR7-CD62L- peripheral blood CD8+ and CD4+ T(EM) cells exhibit a dynamic differentiation, involving transient as well as stable changes to T(CM) phenotype and properties. Whereas the larger fraction of T(EM) cells increases expression of effector molecules, such as perforin or IFN-gamma, a smaller fraction first acquires CCR7 expression. We demonstrate that this acquisition of lymph node homing potential is associated with strong proliferation similar to that of activated T(CM) cells. After proliferation, most of these cells lose CCR7 expression again and acquire effector functions (e.g., perforin production). A small proportion (approximately 6%), however, maintain phenotypic and functional T(CM) properties over a long time interval. These results suggest that T(EM) cells provide immediate effector function by a fraction of cells as well as self-renewal by others through up-regulation of CCR7 followed by either secondary peripheral effector function or long term maintenance of T(CM)-like properties.     

Functional properties and lineage relationship of CD8+ T cell subsets identified by expression of IL-7 receptor alpha and CD62L

Three major subsets of Ag-experienced CD8+ T cells have been identified according to their expression of CD62L and CD127. These markers are associated with central memory T cells (CD62L+ CD127+), effector memory T cells (CD162L- CD127+), and effector T cells (CD62L- CD127-). In this study we characterized the development of these three populations during acute and chronic viral infections and after immunization with virus-like particles and determined their lineage relation and functional and protective properties. We found that the balance between the three subsets was critically regulated by the availability of Ag and time. After initial down-regulation of CD127, the responding CD8+ T cell population down-regulated CD62L and re-expressed CD127. Dependent on Ag availability, the cells then further differentiated into CD62L- CD127- effector cells or, in the absence of Ag, re-expressed CD62L to become central memory T cells. Although all three populations efficiently produced effector cytokines such as IFN-gamma, CD62L- CD127- effector cells exhibited the highest ex vivo lytic potential. In contrast, CD62L+ CD127+ central memory T cells most efficiently produced IL-2 and proliferated extensively in vitro and in vivo upon antigenic restimulation. Strikingly, only effector and effector memory, but not central memory, T cells were able to protect against peripheral infection with vaccinia virus, whereas central memory T cells were most potent at protecting against systemic infection with lymphocytic choriomeningitis virus, indicating that the antiviral protective capacities of specific CD8+ T cell subsets are closely related to the nature of the challenging pathogen.     

GB Virus C Infection Is Associated with Altered Lymphocyte Subset Distribution and Reduced T Cell Activation and Proliferation in HIV-Infected Individuals

GBV-C infection is associated with prolonged survival and with reduced T cell activation in HIV-infected subjects not receiving combination antiretroviral therapy (cART). The relationship between GBV-C and T cell activation in HIV-infected subjects was examined. HIV-infected subjects on cART with non-detectable HIV viral load (VL) or cART naïve subjects were studied. GBV-C VL and HIV VL were determined. Cell surface markers of activation (CD38⁺/HLA-DR⁺), proliferation (Ki-67+), and HIV entry co-receptor expression (CCR5+ and CXCR4+) on total CD4+ and CD8+ T cells, and on naïve, central memory (CM), effector memory (EM), and effector CD4+ and CD8+ subpopulations were measured by flow cytometry. In subjects with suppressed HIV VL, GBV-C was consistently associated with reduced activation in naïve, CM, EM, and effector CD4+ cells. GBV-C was associated with reduced CD4+ and CD8+ T cell surface expression of activation and proliferation markers, independent of HIV VL classification. GBV-C was also associated with higher proportions of naïve CD4+ and CD8+ T cells, and with lower proportions of EM CD4+ and CD8+ T cells. In conclusion, GBV-C infection was associated with reduced activation of CD4+ and CD8+ T cells in both HIV viremic and HIV RNA suppressed patients. Those with GBV-C infection demonstrated an increased proportion of naive T cells and a reduction in T cell activation and proliferation independent of HIV VL classification, including those with suppressed HIV VL on cART. Since HIV pathogenesis is thought to be accelerated by T cell activation, these results may contribute to prolonged survival among HIV infected individuals co-infected with GBV-C. Furthermore, since cART therapy does not reduce T cell activation to levels seen in HIV-uninfected people, GBV-C infection may be beneficial for HIV-related diseases in those effectively treated with anti-HIV therapy.     

Stable CD8+ T cell memory during persistent Trypanosoma cruzi infection

CD8(+) T cell responses to persistent infections caused by intracellular pathogens are dominated by resting T effectors and T effector memory cells, with little evidence suggesting that a T central memory (T(CM)) population is generated. Using a model of Trypanosoma cruzi infection, we demonstrate that in contrast to the T effector/T effector memory phenotype of the majority of T. cruzi-specific CD8(+) T cells, a population of cells displaying hallmark characteristics of T(CM) cells is also present during long-term persistent infection. This population expressed the T(CM) marker CD127 and a subset expressed one or more of three other T(CM) markers: CD62L, CCR7, and CD122. Additionally, the majority of CD127(high) cells were KLRG1(low), indicating that they have not been repetitively activated through TCR stimulation. These CD127(high) cells were better maintained than their CD127(low) counterparts following transfer into naive mice, consistent with their observed surface expression of CD127 and CD122, which confer the ability to self-renew in response to IL-7 and IL-15. CD127(high) cells were capable of IFN-gamma production upon peptide restimulation and expanded in response to challenge infection, indicating that these cells are functionally responsive upon Ag re-encounter. These results are in contrast to what is typically observed during many persistent infections and indicate that a stable population of parasite-specific CD8(+) T cells capable of Ag-independent survival is maintained in mice despite the presence of persistent Ag.     

CD8+ T effector memory cells protect against liver-stage malaria

Identification of correlates of protection for infectious diseases including malaria is a major challenge and has become one of the main obstacles in developing effective vaccines. We investigated protection against liver-stage malaria conferred by vaccination with adenoviral (Ad) and modified vaccinia Ankara (MVA) vectors expressing pre-erythrocytic malaria Ags. By classifying CD8(+) T cells into effector, effector memory (T(EM)), and central memory subsets using CD62L and CD127 markers, we found striking differences in T cell memory generation. Although MVA induced accelerated central memory T cell generation, which could be efficiently boosted by subsequent Ad administration, it failed to protect against malaria. In contrast, Ad vectors, which permit persistent Ag delivery, elicit a prolonged effector T cell and T(EM) response that requires long intervals for an efficient boost. A preferential T(EM) phenotype was maintained in liver, blood, and spleen after Ad/MVA prime-boost regimens, and animals were protected against malaria sporozoite challenge. Blood CD8(+) T(EM) cells correlated with protection against malaria liver-stage infection, assessed by estimation of number of parasites emerging from the liver into the blood. The protective ability of Ag-specific T(EM) cells was confirmed by transfer experiments into naive recipient mice. Thus, we identify persistent CD8 T(EM) populations as essential for vaccine-induced pre-erythrocytic protection against malaria, a finding that has important implications for vaccine design.     

Characterization of the functional properties of the voltage-gated potassium channel Kv1.3 in human CD4+ T lymphocytes

Previous studies have shown that central memory T (T(CM)) cells predominantly use the calcium-dependent potassium channel KCa3.1 during acute activation, whereas effector memory T (T(EM)) cells use the voltage-gated potassium channel Kv1.3. Because Kv1.3-specific pharmacological blockade selectively inhibited anti-CD3-mediated proliferation, whereas naive T cells and T(CM) cells escaped inhibition due to up-regulation of KCa3.1, this difference indicated a potential for selective targeting of the T(EM) population. We examined the effects of pharmacological Kv1.3 blockers and a dominant-negative Kv1.x construct on T cell subsets to assess the specific effects of Kv1.3 blockade. Our studies indicated both T(CM) and T(EM) CD4+ T cells stimulated with anti-CD3 were inhibited by charybdotoxin, which can block both KCa3.1 and Kv1.3, whereas margatoxin and Stichodactyla helianthus toxin, which are more selective Kv1.3 inhibitors, inhibited proliferation and IFN-gamma production only in the T(EM) subset. The addition of anti-CD28 enhanced proliferation of freshly isolated cells and rendered them refractory to S. helianthus, whereas chronically activated T(EM) cell lines appeared to be costimulation independent because Kv1.3 blockers effectively inhibited proliferation and IFN-gamma regardless of second signal. Transduction of CD4+ T cells with dominant-negative Kv1.x led to a higher expression of CCR7+ T(CM) phenotype and a corresponding depletion of T(EM). These data provide further support for Kv1.3 as a selective target of chronically activated T(EM) without compromising naive or T(CM) immune functions. Specific Kv1.3 blockers may be beneficial in autoimmune diseases such as multiple sclerosis in which T(EM) are found in the target organ.     

Cutting edge: L-selectin (CD62L) expression distinguishes small resting memory CD4+ T cells that preferentially respond to recall antigen

Naive CD4+ T cells use L-selectin (CD62L) expression to facilitate immune surveillance. However, the reasons for its expression on a subset of memory CD4+ T cells are unknown. We show that memory CD4+ T cells expressing CD62L were smaller, proliferated well in response to tetanus toxoid, had longer telomeres, and expressed genes and proteins consistent with immune surveillance function. Conversely, memory CD4+ T cells lacking CD62L expression were larger, proliferated poorly in response to tetanus toxoid, had shorter telomeres, and expressed genes and proteins consistent with effector function. These findings suggest that CD62L expression facilitates immune surveillance by programming CD4+ T cell blood and lymph node recirculation, irrespective of naive or memory CD4+ T cell phenotype.     

Naturally arising CD4+CD25+ regulatory T cells suppress the expansion of colitogenic CD4+CD44highCD62L- effector memory T cells

Naturally arising CD4+CD25+ regulatory T (T(R)) cells have been shown to prevent and cure murine T cell-mediated colitis. However, their exact mechanism of controlling colitogenic memory CD4+ T cells in in vivo systems excluding the initial process of naive T cell activation and differentiation has not been examined to date. Using the colitogenic effector memory (T(EM)) CD4+ cell-mediated colitis model induced by adoptive transfer of colitogenic CD4+CD44(high)CD62L(-) lamina propria (LP) T cells obtained from colitic CD4+CD45RB(high) T cell-transferred mice, we have shown in the present study that CD4+CD25+ T(R) cells are able not only to suppress the development of colitis, Th1 cytokine production, and the expansion of colitogenic LP CD4+ T(EM) cells but also to expand these cells by themselves extensively in vivo. An in vitro coculture assay revealed that CD4+CD25+ T(R) cells proliferated in the presence of IL-2-producing colitogenic LP CD4+ T(EM) cells at the early time point (48 h after culture), followed by the acquisition of suppressive activity at the late time point (96 h after culture). Collectively, these data suggest the distinct timing of the IL-2-dependent expansion of CD4+CD25+ T(R) cells and the their suppressive activity on colitogenic LP CD4+ T(EM) cells.     

The development of colitogenic CD4(+) T cells is regulated by IL-7 in collaboration with NK cell function in a murine model of colitis

We previously reported that IL-7(-/-)RAG(-/-) mice receiving naive T cells failed to induce colitis. Such abrogation of colitis may be associated with not only incomplete T cell maintenance due to the lack of IL-7, but also with the induction of colitogenic CD4(+) T cell apoptosis at an early stage of colitis development. Moreover, NK cells may be associated with the suppression of pathogenic T cells in vivo, and they may induce apoptosis of CD4(+) T cells. To further investigate these roles of NK cells, RAG(-/-) and IL-7(-/-)RAG(-/-) mice that had received naive T cells were depleted of NK cells using anti-asialo GM1 and anti-NK1.1 Abs. NK cell depletion at an early stage, but not at a later stage during colitogenic effector memory T cell (T(EM)) development, resulted in exacerbated colitis in recipient mice even in the absence of IL-7. Increased CD44(+)CD62L(-) T(EM) and unique CD44(-)CD62L(-) T cell subsets were observed in the T cell-reconstituted RAG(-/-) recipients when NK cells were depleted, although Fas, DR5, and IL-7R expressions in this subset differed from those in the CD44(+)CD62L(-) T(EM) subset. NK cell characteristics were the same in the presence or absence of IL-7 in vitro and in vivo. These results suggest that NK cells suppress colitis severity in T cell-reconstituted RAG(-/-) and IL-7(-/-)RAG(-/-) recipient mice through targeting of colitogenic CD4(+)CD44(+)CD62L(-) T(EM) and, possibly, of the newly observed CD4(+)CD44(-)CD62L(-) subset present at the early stage of T cell development.     

Naive, effector, and memory CD8 T cells in protection against pulmonary influenza virus infection: homing properties rather than initial frequencies are crucial.

The goal of adoptive immunotherapy is to target a high number of persisting effector cells to the site of a virus infection or tumor. In this study, we compared the protective value of hemagglutinin peptide-specific CD8 T cells generated from the clone-4 TCR-transgenic mice, defined by different stages of their differentiation, against lethal pulmonary influenza infection. We show that the adoptive transfer of high numbers of Ag-specific unprimed, naive CD8 T cells failed to clear the pulmonary virus titer and to promote host survival. The same numbers of in vitro generated primary Ag-specific Tc1 effector cells, producing high amounts of IFN-gamma, or resting Tc1 memory cells, generated from these effectors, were protective. Highly activated CD62Llow Tc1 effectors accumulated in the lung with rapid kinetics and most efficiently reduced the pulmonary viral titer early during infection. The resting CD62Lhigh naive and memory populations first increased in cell numbers in the draining lymph nodes. Subsequently, memory cells accumulated more rapidly and to a greater extent in the lung lavage as compared with naive cells. Thus, effector cells are most effective against a localized virus infection, which correlates with their ability to rapidly distribute at the infected tissue site. The finding that similar numbers of naive Ag-specific CD8 T cells are not protective supports the view that qualitative differences between the two resting populations, the naive and the memory population, may play a major role in their protective value against disease.     

Protective immunity induced with the RTS,S/AS vaccine is associated with IL-2 and TNF-α producing effector and central memory CD4 T cells

A phase 2a RTS,S/AS malaria vaccine trial, conducted previously at the Walter Reed Army Institute of Research, conferred sterile immunity against a primary challenge with infectious sporozoites in 40% of the 80 subjects enrolled in the study. The frequency of Plasmodium falciparum circumsporozoite protein (CSP)-specific CD4(+) T cells was significantly higher in protected subjects as compared to non-protected subjects. Intrigued by these unique vaccine-related correlates of protection, in the present study we asked whether RTS,S also induced effector/effector memory (T(E/EM)) and/or central memory (T(CM)) CD4(+) T cells and whether one or both of these sub-populations is the primary source of cytokine production. We showed for the first time that PBMC from malaria-non-exposed RTS,S-immunized subjects contain both T(E/EM) and T(CM) cells that generate strong IL-2 responses following re-stimulation in vitro with CSP peptides. Moreover, both the frequencies and the total numbers of IL-2-producing CD4(+) T(E/EM) cells and of CD4(+) T(CM) cells from protected subjects were significantly higher than those from non-protected subjects. We also demonstrated for the first time that there is a strong association between the frequency of CSP peptide-reactive CD4(+) T cells producing IL-2 and the titers of CSP-specific antibodies in the same individual, suggesting that IL-2 may be acting as a growth factor for follicular Th cells and/or B cells. The frequencies of CSP peptide-reactive, TNF-α-producing CD4(+) T(E/EM) cells and of CD4(+) T(E/EM) cells secreting both IL-2 and TNF-α were also shown to be higher in protected vs. non-protected individuals. We have, therefore, demonstrated that in addition to TNF-α, IL-2 is also a significant contributing factor to RTS,S/AS vaccine induced immunity and that both T(E/EM) and T(CM) cells are major producers of IL-2.