Central Memory Subsets Research Articles

Naive CD4+ T Cells Exert Superior Alloreactive Capacity Than Central Memory CD4+ T Cells in Fully HLA-Matched Setting

Abstract 4702 Background:Allogeneic stem cell transplantation provides donor-derived mature T cells which are involved in post-transplant immune reactions including engraftment, graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) activity, and thus play a major role in determining clinical outcome. In a prior clinical study, we showed that receiving a high percentage of CD4+CCR7+ T cells that includes naive and central memory (CM) subsets, was correlated with increased incidence and severity of acute GVHD. In a recent update of our results on 126 patients, we confirmed our previous results with a particular impact of CD4+ naive subset on acute GVHD development. The aim of the present study was to investigate in vitro the alloreactive response of CD4+CCR7+CD45RA+ naïve T cells and CD4+CCR7+CD45RAneg central memory T cells in HLA-A, -B, -C, -DRB1 and -DQB1 allele matched setting (so called 10/10 match) Materials and methods:The alloreactivity was investigated by mixed lymphocyte dendritic cell reaction using five HLA-identical healthy male and female sibling pairs to include at least a H-Y mismatch. Stimulators were mature dendritic cells (derived from monocytes of the male sibling) co-cultured with each one of the three highly purified CD4+ T cell subsets (naive, central memory and effector memory) from the female sibling. Alloreactive response was assessed by 3H thymidine incorporation at day 5, and functionally at day 4, 6 and 10 by IFN-gamma ELISpot and measurement of Th1/Th2/Th17 cytokines in co-culture supernatants. Results:Four out of five sibling pairs developed an alloreactive response to mHAs. Maximal proliferation was supported by the CCR7+CD45RA+ naive CD4+ T cells with proliferation indices from 1.75 to 3.85. This proliferation was accompanied by a functional differentiation: only naive CD4+ T cells were able to produce significant amounts of IL-6, TNF-alpha and IFN-gamma at day 6 and day 10 (120 to 174 IFN-gamma spots at day 10). Conclusion:This study demonstrates the superior capacity of naive CD4+ T cells to mount a primary alloreactive response as compared to central memory T cells. Their proliferative response associated with a pro-inflammatory differentiation makes naive CD4+ T cells potential acute GVHD inducers. These in vitro results confirm what we have observed in clinical studies and may also lend support to approaches of selective T cell depletion for GVHD prevention. Disclosures:No relevant conflicts of interest to declare.

Immune Profile of Pediatric Renal Transplant Recipients following Alemtuzumab Induction

The incidence of developing circulating anti-human leukocyte antigen antibodies and the kinetics of T cell depletion and recovery among pediatric renal transplant recipients who receive alemtuzumab induction therapy are unknown. In a collaborative endeavor to minimize maintenance immunosuppression in pediatric renal transplant recipients, we enrolled 35 participants from four centers and treated them with alemtuzumab induction therapy and a steroid-free, calcineurin-inhibitor-withdrawal maintenance regimen. At 3 months after transplant, there was greater depletion of CD4(+) than CD8(+) T cells within the total, naive, memory, and effector memory subsets, although depletion of the central memory subset was similar for CD4(+) and CD8(+) cells. Although CD8(+) T cells recovered faster than CD4(+) subsets overall, they failed to return to pretransplant levels by 24 months after transplant. There was no evidence for greater recovery of either CD4(+) or CD8(+) memory cells than naïve cells. Alemtuzumab relatively spared CD4(+)CD25(+)FoxP3(+) regulatory T cells, resulting in a rise in their numbers relative to total CD4(+) cells and a ratio that remained at least at pretransplant levels throughout the study period. Seven participants (20%) developed anti-human leukocyte antigen antibodies without adversely affecting allograft function or histology on 2-year biopsies. Long-term follow-up is underway to assess the potential benefits of this regimen in children.

Altered Proportions of Naïve, Central Memory and Terminally Differentiated Central Memory Subsets among CD4+ and CD8+ T Cells Expressing CD26 in Patients with Type 1 Diabetes

Type 1 diabetes is an autoimmune process predominantly T-cell mediated. CD26 plays a role in T-cell costimulation, migration, memory development, thymic maturation and emigration patterns. In peripheral blood from 55 patients with type 1 diabetes and 20 healthy controls, CD4(+) and CD8(+) T cells expressing CD26 were differentiated into naïve (N, CD45RA(+)CCR7(+)), central memory (CM, CD45RA(-)CCR7(+)), effector memory (EM, CD45RA(-)CCR7(-)), and terminally differentiated effector memory (TEMRA, CD45RA(+)CCR7(-)). In type 1 diabetes, CD4(+) and CD8(+) T cells expressing CD26 showed a distinctive differentiation profile: percentages and absolute numbers of CM and N cells were reduced, whereas those of TEMRA cells were markedly increased. The indices of intermediate- and long-term glycaemic control were associated negatively with the number of CM and N cells while positively with the number of TEMRA cells. The considerable accumulation of TEMRA T cells in our patients suggests life-long stimulation by protracted antigen exposure (viruses, other agents or residual self-antigens?) or a homeostatic defect in the regulation/contraction of immune responses.

Determinants of Successful CD8+ T-Cell Adoptive Immunotherapy for Large Established Tumors in Mice

Adoptive cell transfer (ACT) of tumor infiltrating or genetically engineered T cells can cause durable responses in patients with metastatic cancer. Multiple clinically modifiable parameters can comprise this therapy, including cell dose and phenotype, in vivo antigen restimulation, and common gamma-chain (γ(c)) cytokine support. However, the relative contributions of each these individual components to the magnitude of the antitumor response have yet to be quantified. To systematically and quantitatively appraise each of these variables, we employed the Pmel-1 mouse model treating large, established B16 melanoma tumors. In addition to cell dose and magnitude of in vivo antigen restimulation, we also evaluated the relative efficacy of central memory (T(CM)), effector memory (T(EM)), and stem cell memory (T(SCM)) subsets on the strength of tumor regression as well as the dose and type of clinically available γ(c) cytokines, including IL-2, IL-7, IL-15, and IL-21. We found that cell dose, T-cell differentiation status, and viral vaccine titer each were correlated strongly and significantly with the magnitude of tumor regression. Surprisingly, although the total number of IL-2 doses was correlated with tumor regression, no significant benefit to prolonged (≥6 doses) administration was observed. Moreover, the specific type and dose of γ(c) cytokine only moderately correlated with response. Collectively, these findings elucidate some of the key determinants of successful ACT immunotherapy for the treatment of cancer in mice and further show that γ(c) cytokines offer a similar ability to effectively drive antitumor T-cell function in vivo.

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.

Characteristics and PD-1 expression of peripheral CD4+CD127loCD25hiFoxP3+ Treg cells in chronic HCV infected-patients

BackgroundBoth regulatory T cells (Tregs) and PD-1/PD-L1 pathway were critically involved in HCV viral persistence. However, the association between them was not well investigated. Herein, we aimed to investigate the distributional profiles of Tregs subsets and association between PD-1 expression on these subsets and development of HCV long-term persistence.MethodsCD45RA and CD27 were employed to separate peripheral Tregs as naïve/central memory/effector memory/effector subsets. The phenotypic characteristics and PD-1 expression of Tregs were studied by flow cytometry.ResultsIn the present study, the majority of Tregs was identified as central memory phenotype in chronic hepatitis C patients compared with nearly equal contribution of naïve and central memory subsets in healthy individuals. PD-1 expression was elevated in all CD4+ T cell subset in chronic HCV infected patients, including Tregs. Of note, higher level of PD-1 expression was found on TEM- and effector-Treg than naïve- and TCM-Tregs subsets. The ratio of TEM-Tregs/naive-Tregs and TEM-Tregs/TCM-Tregs regarding to PD-1 MFI were significantly lower in CHC patients compared to controls.ConclusionsOur study indicated that distinctive characteristics of PD-1 expression on Tregs in HCV infection suggests associated with impaired adaptive immunity as well as viral long-term persistence. The cross talk between Treg cells and PD-1 induced inhibition in chronic HCV infection deserved further exploration for HCV infection associated immune pathogenesis.

Functional Impairment of Central Memory CD4 T Cells Is a Potential Early Prognostic Marker for Changing Viral Load in SHIV-Infected Rhesus Macaques

In HIV infection there is a paucity of literature about the degree of immune dysfunction to potentially correlate and/or predict disease progression relative to CD4+ T cells count or viral load. We assessed functional characteristics of memory T cells subsets as potential prognostic markers for changing viral loads and/or disease progression using the SHIV-infected rhesus macaque model. Relative to long-term non-progressors with low/undetectable viral loads, those with chronic plasma viremia, but clinically healthy, exhibited significantly lower numbers and functional impairment of CD4+ T cells, but not CD8+ T cells, in terms of IL-2 production by central memory subset in response to PMA and ionomycine (PMA+I) stimulation. Highly viremic animals showed impaired cytokine-production by all T cells subsets. These results suggest that functional impairment of CD4+ T cells in general, and of central memory subset in particular, may be a potential indicator/predictor of chronic infection with immune dysfunction, which could be assayed relatively easily using non-specific PMA+I stimulation.

Human effector CD8+ T cells derived from naive rather than memory subsets possess superior traits for adoptive immunotherapy

AbstractCluster of differentiation (CD)8+ T cells exist as naive, central memory, and effector memory subsets, and any of these populations can be genetically engineered into tumor-reactive effector cells for adoptive immunotherapy. However, the optimal subset from which to derive effector CD8+ T cells for patient treatments is controversial and understudied. We investigated human CD8+ T cells and found that naive cells were not only the most abundant subset but also the population most capable of in vitro expansion and T-cell receptor transgene expression. Despite increased expansion, naive-derived cells displayed minimal effector differentiation, a quality associated with greater efficacy after cell infusion. Similarly, the markers of terminal differentiation, killer cell lectin-like receptor G1 and CD57, were expressed at lower levels in cells of naive origin. Finally, naive-derived effector cells expressed higher CD27 and retained longer telomeres, characteristics that suggest greater proliferative potential and that have been linked to greater efficacy in clinical trials. Thus, these data suggest that naive cells resist terminal differentiation, or “exhaustion,” maintain high replicative potential, and therefore may be the superior subset for use in adoptive immunotherapy.

Clinical Scale Central Memory T Cell Enrichment for Adoptive T Cell Therapy

AbstractAbstract 5180The adoptive transfer of genetically engineered lymphocytes is a promising strategy to treat cancer. However, the efficacy of adoptive immunotherapy in humans is often limited and the critical parameters for the in vivo efficacy remain poorly defined. One aspect may be the limited survival time and self renewal capacity of transferred T cells in vivo.Antigen-experienced memory T cells (TM) can be divided further into central memory (TCM) and effector memory (TEM) subsets. CD8+ TEM lack CCR7/CD62L, migrate preferentially to peripheral tissues, and exhibit immediate effector function, whereas CD8+ TCM express CD62L and CCR7, which promote migration into LNs. TCM proliferate rapidly if re-exposed to antigen and there is evidence that T cell lines derived from TCM have increased persistence and functionality in vivo. Thus TCM might be a superior starting population for T cell therapy using transduced T cells.We have developed a GMP compatible sorting strategy for TCM allowing their selective transduction and large-scale expansion. TCM cell were isolated by a sequential depletion of CD45RA+ and CD4+ and subsequent enrichment of CD62L+ cells using the CliniMACS® Plus Instrument. CD8+ TCM from peripheral blood of cancer patients were obtained in large numbers from leukapheresis products and genetically engineered with tumor-specific TCRs. After expansion in vitro to numbers sufficient for patient treatment the TCM population retained high CD62L expression. This protocol can be the basis for clinical studies on the efficiency of TCM derived T cell lines in T cell therapy against tumors. Disclosures:Casati:Miltenyi Biotec: Employment. Schmitz:Miltenyi Biotec: Employment. Assenmacher:m: Employment. Scheffold:Miltenyi Biotec: Employment.

Elite Controllers Display Higher Activation on Central Memory CD8 T Cells Than HIV Patients Successfully on HAART

T cell activation plays an important role in driving CD4 depletion during the course of HIV infection. There is scarce information about activation of different T cell subsets in HIV(+) individuals experiencing distinct disease progression. The activation of different CD4(+) and CD8(+) T cell subsets and its contribution to total T cell activation were examined measuring CD38 expression by flow cytometry in 120 HIV-infected individuals and 9 uninfected healthy controls. HIV-infected patients were divided into four groups: 11 elite controllers (EC), 14 viremic controllers (VC), 61 antiretroviral-naive typical progressors (TP), and 34 progressors with viral suppression (VS) under antiretroviral therapy. EC displayed significantly greater activation levels than VS, with a higher contribution of central memory subsets to the activation of total CD8 T cells (p = 0.002). The activation of central memory CD8(+) T cells significantly correlated with viral load in TP regardless of CD4 counts. In contrast with VS, proviral load was undetectable in all EC. Compared to VS, EC display abnormal and higher activation levels of different CD8(+) T cell subsets. Factors other than the size of the viral reservoir should explain the high level of activation of central memory CD8(+) T cells characteristically seen in HIV(+) individuals with spontaneous control of viral replication.

TH2 heterogeneity: Does function follow form?

T(H)2 immune responses are required for the 2 fundamental pathological processes characteristic of allergic disease: IgE-mediated hypersensitivity and eosinophilic inflammation. The 3 established T(H)2 cytokines, IL-4, IL-5, and IL-13, each play a nonredundant role in allergic disease pathology. The recent explosion of T(H) subpopulations combined with the wide availability of polychromatic cytokine staining has facilitated the discovery of T(H)2 lineage heterogeneity. In this article we review T(H)2 heterogeneity and ask the following question: At what point do these subpopulations graduate from in vitro curiosities to immunologically robust therapeutic targets? We propose criteria to establish a T-cell subset as a biologically relevant entity and address the evidence to support these T(H)2 subpopulations having a unique function or specific contribution to allergic pathology or host defense.

Expression of CD35 on subsets of human peripheral CD8+ T-cells (138.18)

Abstract There is now considerable evidence that CD8+ T cell reactions can promote or suppress autoreactivity. The type of response is not only dictated by the TCR but also by other cellular receptors. Also known, is that natural deficiencies of certain complement components are associated with autoimmune responses. The potential link between complement and CD8+ T-cells was explored by examining several subsets for the expression of the complement receptor CD35. Mononuclear cells were purified from the peripheral blood of ten donors and further enriched for CD8+ T-cells by either positive or negative selection using immunomagnetic beads, and analyzed for the presence of CD35 by flow cytometry. Upon inspection, 6-12% expressed CD35 and were negative for CD56. Of the CD35+ cells, approximately 65% were found in the naïve subset (CCR7+CD45RA+), 15% in the CD45RA effector memory subset (CCR7-CD45RA+), and 10% in the central memory (CCR7+CD45RA-) and effector memory (CCR7-CD45RA-) subsets. Next, using plate-bound antibodies against CD3 and CD35, in vitro activation experiments were done followed by analysis of several T-cell responses. The results showed a substantial increase in cytokine secretion and intracellular granzyme production with minimal effect on cellular proliferation, compared to TCR cross-linking alone. These data imply that the CD8+ T-cells, which express CD35, modulate T-cell responsiveness following co-engagement of the TCR and CD35.

P16-28. The first year: early correlates of long-term HIV progression

Background SIV studies reveal dramatic, systemic destruction of CD4+ T-cells in acute disease; this, and early levels of central memory (TCM) subsets predict progression to death independently of viral load. Similar data are not available for HIV, because samples from early disease are rare and long, untreated follow-up is usually not possible. We analyzed a large cohort of confirmed seroconverters to test whether T-cell and viral dynamics in early disease predict longterm progression.

Lack of in vivo compartmentalization among HIV-1 infected naïve and memory CD4+ T cell subsets

Viral compartmentalization between naïve and memory CD4(+) T cell subsets has been described, but only for individuals who were receiving antiretroviral therapy (ART). We present here an extensive analysis of the viral quasispecies residing in the naïve, central and effector memory CD4(+) T cell subsets in a number of therapy naïve individuals and representing an array of HIV-1 subtypes. We longitudinally analyzed subset-specific infection and evolution in a subtype B infected individual who switches from CCR5 to dual CCR5/CXCR4 coreceptor usage. We show that the central memory subset, the predominantly infected subset, harbors a more diverse viral population compared to the others. Through sequence analysis of the env C2V3 region we demonstrate a lack of viral compartmentalization among all subsets. Upon coreceptor switch we observe a pronounced increase in the infection level of the naïve population. Our findings emphasize the importance of all CD4(+) T cell subsets to viral evolution.

HIV infection-associated immune activation occurs by two distinct pathways that differentially affect CD4 and CD8 T cells

HIV infection is characterized by a brisk immune activation that plays an important role in the CD4 depletion and immune dysfunction of patients with AIDS. The mechanism underlying this activation is poorly understood. In the current study, we tested the hypothesis that this activation is the net product of two distinct pathways: the inflammatory response to HIV infection and the homeostatic response to CD4 T cell depletion. Using ex vivo BrdU incorporation of PBMCs from 284 patients with different stages of HIV infection, we found that CD4 proliferation was better predicted by the combination of CD4 depletion and HIV viral load (R(2) = 0.375, P < 0.001) than by either parameter alone (CD4 T cell counts, R(2) = 0.202, P < 0.001; HIV viremia, R(2) = 0.302, P < 0.001). Interestingly, CD8 T cell proliferation could be predicted by HIV RNA levels alone (R(2) = 0.334, P < 0.001) and this predictive value increased only slightly (R(2) = 0.346, P < 0.001) when CD4 T cell depletion was taken into account. Consistent with the hypothesis that CD4 T cell proliferation is driven by IL-7 as a homeostatic response to CD4 T cell depletion, levels of phosphorylated STAT-5 were found to be elevated in naive subsets of CD4 and CD8 T cells from patients with HIV infection and in the central memory subset of CD4 T cells. Taken together these data demonstrate that at least two different pathways lead to immune activation of T cells in patients with HIV infection and these pathways differentially influence CD4 and CD8 T cell subsets.

Impaired Initiation of Contact Hypersensitivity by FTY720

FTY720 inhibits lymphocyte emigration from lymphoid organs to peripheral blood by binding one of the sphingosine-1-phosphate (S1P) receptors, S1P(1). We investigated the effects of FTY720 in relation to murine contact hypersensitivity (CHS). CHS was impaired by FTY720 when administered during the sensitization but not the elicitation phase. Consistently, adoptive transfer of immunized lymph node cells from mice treated with FTY720 during the sensitization phase was virtually incapable of inducing CHS response in recipients. FTY720 decreased the number of blood CD44(-)-naive T cells markedly and that of CD44(+) memory T cells modestly. Among memory T cells, the CD62L(-) effector memory subset was more resistant to FTY720 than the CD62L(+) central memory subset. Accordingly, the level of S1P chemotactic response was high in naive T cells, marginal in effector memory T cells, and very low in central memory T cells. Consistently, the S1P(1) mRNA expression level was much lower in memory T cells than in naive T cells. These findings demonstrate that S1P-S1P(1) signaling is essential for recirculation of naive T cells. FTY720 seems to decrease the incidence of interactions between antigen-loaded dendritic cells and circulating naive T-cell clones in the lymph nodes, thereby depressing the sensitization of naive T cells in CHS.

Level, phenotype and activation status of CD4+FoxP3+ regulatory T cells in patients chronically infected with human immunodeficiency virus and/or hepatitis C virus

CD4(+) regulatory T (T(reg)) cells have been involved in impaired immunity and persistence of viral infections. Herein, we report the level, phenotype and activation status of T(reg) cells in patients chronically infected with human immunodeficiency virus (HIV) and/or hepatitis C virus (HCV). Expression of CD25, CD45RA, CD27, CD127 and CD38 was assessed on these cells using polychromatic flow cytometry in 20 healthy controls, 20 HIV-monoinfected, 20 HCV-monoinfected and 31 HIV/HCV-co-infected patients. T(reg) cells were defined as CD4(+)forkhead box P3 (FoxP3)(+). The percentage of T(reg) cells was increased significantly in HIV patients compared with controls. Moreover, there was a significant inverse correlation between CD4 counts and T(reg) cell levels. Fewer than 50% of T(reg) cells expressed CD25, with differences in terms of CD127 expression between CD25(+) and CD25((-)) T(reg) cells. CD4(+)Foxp3(+) T(reg) cells displayed predominantly a central memory phenotype (CD45RA(-)CD27(+)), without differences between patients and healthy controls. Activated T(reg) cells were increased in HIV patients, particularly considering the central memory subset. In summary, HIV infection, but not HCV, induces an up-regulation of highly activated T(reg) cells, which increases in parallel with CD4 depletion. Hypothetically, this might contribute to the accelerated course of HCV-related liver disease in HIV-immunosuppressed patients.

Memory T cells in cancer immunotherapy: which CD8+ T‐cell population provides the best protection against tumours?

Cancer immunotherapy strategies often fail because of immunosuppressive mechanisms present in the tumour-bearing host. Adoptive T-cell transfer therapy circumvents this problem by activating tumour-specific CD8(+) T cells in vitro and transferring them back into the patient. Classically, effector T cells have been used in these studies because of their potent anti-tumour activity. However, it is becoming apparent that highly activated effector cells may become terminally differentiated, display impaired proliferation and survival in vivo, and mediate short-term anti-tumour effects. In contrast to effector cells, memory cells have enhanced proliferative potential and survival, and the potential to provide more robust and enduring protection against tumours. Here, we discuss key studies in the field of adoptive T-cell transfer, along with some of our own results relating to this area. Based on the body of existing research, it is clear that CD8(+) T cells with memory potential are superior to terminally differentiated effectors in mediating successful tumour clearance. Opinions remain divided as to whether the central memory or effector memory T-cell subset is capable of providing the best protection against tumours. We propose that as these cell types have different but complementary benefits for the anti-tumour immune response, the ideal cell population to use for adoptive T-cell transfer should consist of a heterogeneous mixture of memory cells.

Dynamics of T- and B-Lymphocyte Turnover in a Natural Host of Simian Immunodeficiency Virus

Increased lymphocyte turnover is a hallmark of pathogenic lentiviral infection. To investigate perturbations in lymphocyte dynamics in natural hosts with nonpathogenic simian immunodeficiency virus (SIV) infection, the nucleoside analog bromodeoxyuridine (BrdU) was administered to six naturally SIV-infected and five SIV-negative sooty mangabeys. As a measure of lymphocyte turnover, we estimated the mean death rate by fitting a mathematical model to the fraction of BrdU-labeled cells during a 2-week labeling and a median 10-week delabeling period. Despite significantly lower total T- and B-lymphocyte counts in SIV-infected sooty mangabeys than in SIV-negative mangabeys, the turnover rate of B lymphocytes and CD4(+) and CD8(+) T lymphocytes was not increased in the SIV-infected animals. A small, rapidly proliferating CD45RA(+) memory subset and a large, slower-proliferating CD45RA(-) central memory subset of CD4(+) T lymphocytes identified in the peripheral blood of sooty mangabeys also did not show evidence of increased turnover in the context of SIV infection. Independently of SIV infection, the turnover of CD4(+) T lymphocytes in sooty mangabeys was significantly higher (P < 0.01) than that of CD8(+) T lymphocytes, a finding hitherto not reported in rhesus macaques or humans. The absence of aberrant T-lymphocyte turnover along with an inherently high rate of CD4(+) T-lymphocyte turnover may help to preserve the pool of central memory CD4(+) T lymphocytes in viremic SIV-infected sooty mangabeys and protect against progression to AIDS.

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.