Red blood cells upregulate cytoprotective proteins and the labile iron pool in dividing human T cells despite a reduction in oxidative stress

We have recently reported that red blood cells (RBC) promote T cell growth and survival by inhibiting activation-induced T cell death. In the present study, we have examined parameters of oxidative stress and intracellular iron in activated T cells and correlated these data with the expression of ferritin, heme oxygenase-1 (HO-1), and the transferrin receptor CD71. T cells growing in the presence of RBC had reduced levels of reactive oxygen species (ROS) and oxidatively modified proteins, suggesting that RBC efficiently counteracted ROS production on the activated T cells. Flow cytometry and immunodetection demonstrated that T cells dividing in the presence of RBC had increased levels of intracellular ferritin rich in L-subunits and HO-1 along with a downmodulation in CD71 expression. Finally, using the fluorescent iron indicator calcein and flow cytometry analysis, we were able to show that a relative amount of the labile iron pool (LIP) was upregulated in T cells growing in the presence of RBC. These findings are consistent with a typical response to iron overload. However, neither heme compounds nor ferric iron reproduced the levels of expansion and survival of T cells induced by intact RBC. Altogether, these data suggest that RBC inhibit apoptosis of activated T cells by a combination of ROS scavenging and upregulation of cytoprotective proteins such as ferritin and HO-1, which may counteract a possible toxic effect of the increased intracellular free iron.     

Variation in the CD4+ and CD8+ populations in lymph nodes does not reflect that in the blood during SIVMNE/E11S infection of macaques.

The decline in the CD4% and CD4/CD8 ratios have been compared in lymph nodes and blood from SIVMNE/E11S infected rhesus macaques. The results indicate that loss from the LN CD4+ cell pool does not occur until CD4/CD8 ratios of less than 0.5 is reached in blood. These changes also correlate with the ability to isolate virus from the blood and the transition of CD45RAhi to highly activated CD45RAlo CD8+ cells both of which may play a role in eliminating CD4+ cells. In end-stage disease, CD8+ cells also decline in LN and mitogen responsiveness no longer exists in any nodes. Interestingly at this stage, the circulating CD8% increases significantly and represents the only source of functional T cells remaining in the body.     

Skin homing (cutaneous lymphocyte-associated antigen-positive) CD8+ T cells respond to superantigen and contribute to eosinophilia and IgE production in atopic dermatitis.

In allergic inflammations of the skin, activation of CD4+ T cells was demonstrated to play an important role; however, a minor role for CD8+ T cells is implied. In the present study, we compared cutaneous lymphocyte-associated Ag (CLA)-expressing CD4+ and CD8+ subsets, which were isolated from peripheral blood and lesional skin biopsies in atopic dermatitis (AD) patients. We demonstrated that CD8+CLA+ T cells proliferate in response to superantigen and are as potent as CD4+CLA+ T cells in IgE induction and support of eosinophil survival. In atopic skin inflammation, the existence of high numbers of CD4+ and CD8+ T cells was demonstrated by immunohistochemistry and by culturing T cells from skin biopsies. In peripheral blood, both CD4+ and CD8+ subsets of CLA+CD45RO+ T cells were in an activated state in AD. The in vivo-activated CLA+ T cells of both subsets spontaneously released an IL-5- and IL-13-dominated Th2 type cytokine pattern. This was confirmed by intracytoplasmic cytokine staining immediately after isolation of the cells from peripheral blood. In consequence, both CD4+ and CD8+, CLA+ memory/effector T cells induced IgE production by B cells mainly by IL-13, and enhanced eosinophil survival in vitro by delaying eosinophil apoptosis, mainly by IL-5. These results indicate that in addition to the CD4+ subset, the CD8+CLA+ memory/effector T cells are capable of responding to superantigenic stimulation and play an important role in the pathogenesis of AD.     

CD8+ T cell responses in bronchoalveolar lavage fluid and peripheral blood mononuclear cells of infants with severe primary respiratory syncytial virus infections

A protective role for CD8+ T cells during viral infections is generally accepted, but little is known about how CD8+ T cell responses develop during primary infections in infants, their efficacy, and how memory is established after viral clearance. We studied CD8+ T cell responses in bronchoalveolar lavage (BAL) samples and blood of infants with a severe primary respiratory syncytial virus (RSV) infection. RSV-specific CD8+ T cells with an activated effector cell phenotype: CD27+CD28+CD45RO+CCR7-CD38+HLA-DR+Granzyme B+CD127- could be identified in BAL and blood. A high proportion of these CD8+ T cells proliferated and functionally responded upon in vitro stimulation with RSV Ag. Thus, despite the very young age of the patients, a robust systemic virus-specific CD8+ T cell response was elicited against a localized respiratory infection. RSV-specific T cell numbers as well as the total number of activated effector type CD8+ T cells peaked in blood around day 9-12 after the onset of primary symptoms, i.e., at the time of recovery. The lack of a correlation between RSV-specific T cell numbers and parameters of disease severity make a prominent role in immune pathology unlikely, in contrast the T cells might be involved in the recovery process.     

CD127与T淋巴细胞

CD127是IL-7受体α链,T淋巴细胞对IL-7的特异性应答主要通过CD127的表达实现的。CD127在胸腺细胞向T淋巴细胞的发育过程、成熟T细胞内环境稳态的维持、病毒感染后T细胞的免疫应答及记忆性T细胞的分化及幸存等方面发挥重要的作用。在整个T淋巴细胞生命周期中仅有两个阶段缺乏CD127的表达：即双阳性CD4+CD8+T细胞及激活的T细胞。近期,随着对CD127研究的不断深入,发现CD127在作为记忆性T细胞及调节性T细胞特异性的表面标记物方面也发挥着重要作用。本文简要介绍了CD127在T淋巴细胞生命周期的不同阶段所发挥的调节作用及其机制。     

A previously unrecognized large fraction of cytotoxic lymphocyte precursors is present in CD4+ human peripheral blood T cells

We describe a limiting dilution (LD) culture system in which cell sorter-purified CD4+ (and CD8+) peripheral blood T cells are cocultured with irradiated, anti-CD3 mab-producing OKT3 hybridoma cells. Under these conditions, one out of 2-3 CD4+ (and CD8+) T cells is induced to clonal proliferation. In striking contrast to previously described LD culture systems, every growing CD4+ cell clone displayed cytotoxic activity when tested in a lectin-facilitated 51Cr release assay against P815 target cells. This contrasts with the development of cytotoxic CD4+ T cells in alloantigen-stimulated LD cultures, where only one out of 15-20 proliferating CD4+ cells killed P815 in the presence of PHA, and one out of 300-500 proliferating CD4+ cells displayed alloantigen-specific cytotoxic activity. Furthermore, we have established antigen-specific proliferating CD4+ T cell clones which do not exert antigen-specific cytotoxicity but can be cytotoxic when crosslinked to target cells via lectin or monoclonal antibody (anti-CD3, anti-TCR). Our results show that a previously unrecognized large fraction (at least 30-50%) of all peripheral blood CD4+ T cells can give rise to cytotoxic effector cells. The mode of CD4+ T cell activation (OKT3 hybridoma versus alloantigen) thus determines whether the intrinsic cytotoxic capacity of CD4+ T cells is functionally activated or not.     

Regression of Epstein-Barr virus-induced B-cell transformation in vitro involves virus-specific CD8+ T cells as the principal effectors and a novel CD4+ T-cell reactivity

T-cell memory to Epstein-Barr virus (EBV) was first demonstrated through regression of EBV-induced B-cell transformation to lymphoblastoid cell lines (LCLs) in virus-infected peripheral blood mononuclear cell (PBMC) cultures. Here, using donors with virus-specific T-cell memory to well-defined CD4 and CD8 epitopes, we reexamine recent reports that the effector cells mediating regression are EBV latent antigen-specific CD4+ and not, as previously assumed, CD8+ T cells. In regressing cultures, we find that the reversal of CD23+ B-cell proliferation was always coincident with an expansion of latent epitope-specific CD8+, but not CD4+, T cells; furthermore CD8+ T-cell clones derived from regressing cultures were epitope specific and reproduced regression when cocultivated with EBV-infected autologous B cells. In cultures of CD4-depleted PBMCs, there was less efficient expansion of these epitope-specific CD8+ T cells and correspondingly weaker regression. The data are consistent with an effector role for epitope-specific CD8+ T cells in regression and an auxiliary role for CD4+ T cells in expanding the CD8 response. However, we also occasionally observed late regression in CD8-depleted PBMC cultures, though again without any detectable expansion of preexisting epitope-specific CD4+ T-cell memory. CD4+ T-cell clones derived from such cultures were LCL specific in gamma interferon release assays but did not recognize any known EBV latent cycle protein or derived peptide. A subset of these clones was also cytolytic and could block LCL outgrowth. These novel effectors, whose antigen specificity remains to be determined, may also play a role in limiting virus-induced B-cell proliferation in vitro and in vivo.     

Interleukin 2 and interleukin 10 function synergistically to promote CD8+ T cell cytotoxicity,which is suppressed by regulatory T cells in breast cancer

The precise role of interleukin (IL)-10 in breast cancer is not clear. Previous studies suggested a tumor-promoting role of IL-10 in breast cancer, whereas recent discoveries that IL-10 activated and expanded tumor-resident CD8⁺ T cells challenged the traditional view. Here, we investigated the role of IL-10 in HLA-A2-positive breast cancer patients with Grade III, Stage IIA or IIB in-situ and invasive ductal carcinoma, and compared it with that of IL-2, the canonical CD8⁺ T cell growth factor. We first observed that breast cancer patients presented higher serum levels of IL-2 and IL-10 than healthy controls. Upon prolonged TCR stimulation, peripheral blood CD8⁺ T cells from breast cancer patients tended to undergo apoptosis, which could be prevented by the addition of IL-2 and/or IL-10. The cytotoxicity of TCR-activated CD8⁺ T cells was also enhanced by exogenous IL-2 and/or IL-10. Interestingly, IL-2 and IL-10 demonstrated synergistic effects, since the enhancement in CD8⁺ T cell function when both cytokines were added was greater than the sum of the improvements mediated by each individual cytokine. IL-10 by itself could not promote the proliferation of CD8⁺ T cells but could significantly enhance IL-2-mediated promotion of CD8⁺ T cell proliferation. In addition, the cytotoxicity of tumor-infiltrating CD8⁺ T cells in breast tumor was elevated when both IL-2 and IL-10 were present but not when either one was absent. This synergistic effect was stopped by CD4⁺CD25⁺ regulatory T cells (Treg), which depleted IL-2 in a cell number-dependent manner. Together, these results demonstrated that IL-2 and IL-10 could work synergistically to improve the survival, proliferation, and cytotoxicity of activated CD8⁺ T cells, an effect suppressible by CD4⁺CD25⁺ Treg cells.     

Generation of lymphokine-activated killer activity in T cells. Possible regulatory circuits.

CD4+ and CD8+ T cells do not develop significant lymphokine-activated killer (LAK) activity when PBL are cultured with IL-2 or even when they are activated with a T cell stimulus such as OKT3 mAb. The possibility that a T cell regulatory mechanism prevents the development of LAK activity by CD4+ or CD8+ cells in OKT3 mAb and IL-2 cultures was tested by depleting CD8+ or CD4+ cells from PBL before stimulation with OKT3 and IL-2. Under these conditions, the remaining CD4+ and CD8+ cells were able to generate non-MHC-restricted lysis of NK-resistant tumor targets. Our data suggested that a regulatory signal was present in the culture to prevent the development of lytic function by T cells. T cells removed from the PBL cultures were, upon culture with IL-2, able to generate high LAK activity, suggesting that inhibition of the CD4+ or CD8+ T cell-mediated LAK activity was an active ongoing process, which blocked the lysis at the level of the activated cell and not the precursor cell. Mixing experiments demonstrated that the CD4+ or the CD8+ cells isolated from the PBL cultures were able to inhibit the development of lytic function in the CD4-depleted and CD8-depleted cultures. Transforming growth factor-beta (TGF-beta) has been shown to block LAK activity of NK cells in IL-2-stimulated cultures. When TGF-beta was added to CD4(+)- or CD8(+)-depleted cultures, it also inhibited LAK activity of T cells in a dose-dependent fashion, without interfering with T cell growth. Lytic activity returned to activated levels when TGF-beta was removed from the culture medium, thereby demonstrating the reversibility of TGF-beta inhibition.     

Expression and function of the B and T lymphocyte attenuator (BTLA/CD272) on human T cells

Co-signal receptors provide crucial activating or attenuating signals for T cells. The B and T lymphocyte attenuator (BTLA/CD272) is a third member of co-inhibitory receptors, which belongs to the CD28 immunoglobulin-superfamily. Using monoclonal antibodies (mAbs) against human BTLA, we show that BTLA is constitutively expressed on most CD4+ and CD8+ T cells and its expression progressively decreases upon T cell activation. Polarized Th1 and Th2 cells contained both BTLA-positive and BTLA-negative populations, but the extended culture diminished BTLA expression. Cross-linking BTLA with an agonistic mAb inhibited T cell proliferation and the production of the cytokines IFN-gamma and IL-10 in response to anti-CD3 stimulation. BTLA-mediated inhibition of T cell activation occurred during both primary CD4+ T cell responses and secondary CD4+ and CD8+ T cell responses, suggesting that BTLA ligation sends a constitutive "off" signal to T cells and thus might play an important role in the maintenance of T cell tolerance.     

Requirement for CD4+ T cells in V beta 4+CD8+ T cell activation associated with latent murine gammaherpesvirus infection.

A CD8+ T cell lymphocytosis in the peripheral blood is associated with the establishment of latency following intranasal infection with murine gammaherpesvirus-68. Remarkably, a large percentage of the activated CD8+ T cells of mice expressing different MHC haplotypes express V beta 4+ TCR. Identification of the ligand driving the V beta 4+CD8+ T cell activation remains elusive, but there is a general correlation between V beta 4+CD8+ T cell stimulatory activity and establishment of latency in the spleen. In the current study, the role of CD4+ T cells in the V beta 4+CD8+ T cell expansion has been addressed. The results show that CD4+ T cells are essential for expansion of the V beta 4+CD8+ subset, but not other V beta subsets, in the peripheral blood. CD4+ T cells are required relatively late in the antiviral response, between 7 and 11 days after infection, and mediate their effect independently of IFN-gamma. Assessment of V beta 4+CD8+ T cell stimulatory activity using murine gammaherpesvirus-68-specific T cell hybridomas generated from latently infected mice supports the idea that CD4+ T cells control levels of the stimulatory ligand that drives the V beta 4+CD8+ T cells. As V beta 4+CD8+ T cell expansion also correlates with levels of activated B cells, these data raise the possibility that CD4+ T cell-mediated B cell activation is required for optimal expression of the stimulatory ligand. In addition, in cases of low ligand expression, there may also be a direct role for CD4+ T cell-mediated help for V beta 4+CD8+ T cells.     

Phenotypic and cytolytic activity of Macaca nemestrina natural killer cells isolated from blood and expanded in vitro

Natural killer (NK) cells from nonhuman primates have not been completely characterized, and methods for expanding nonhuman primates NK cells in vitro have been described only in rhesus species. The purpose of this report was to characterize NK cells in pigtail macaques (Macaca nemestrina), a species that is frequently used in studies of transplantation biology/immunology, virology, vaccine development, and reproductive biology. NK cells from Macaca nemestrina peripheral blood were best defined by the expression of CD16 and CD8alpha, and the absence of CD3. Subsets of these cells express CD56, NKp30, and NKp46. An enhanced ability to kill K562 cells was not present in fluorescence activated cell sorted (FACS)-purified CD16-/CD3+ and CD16-/CD56+ cells isolated from fresh peripheral blood. However, FACS-purified CD16+/CD3- and CD16+/CD56- cells were highly efficient killers of K562 cells. Macaca nemestrina NK cells can be expanded by in vitro culturing of FACS-purified CD16+/CD2-/CD3-/CD56- cells, or from peripheral blood cells depleted of cells expressing CD3, CD4, and HLA-DR. Cells in these cultures expand 70-fold after 21 days of culturing. After culturing, these cells express high levels of natural cytotoxicity receptors (NCRs) NKp30 and NKp46. NK cell populations obtained from FACS-purified CD16+/CD3-, CD16+/CD56- cells and CD3/CD4/HLA-DR-depleted cells were highly efficient killers of K562 cells. These data suggest that a population of highly enriched cytolytic NK cells can be obtained from purified CD16+/CD3- and CD16+/CD56- cells obtained from peripheral blood, as well as from cells that have been cultured and expanded from peripheral blood that is depleted of CD3/CD4/HLA-DR-expressing cells.     

Splenic dendritic cell subsets prime and boost CD8 T cells and are involved in the generation of effector CD8 T cells

The ability of the dendritic cell (DC) subsets, CD8alpha+ and CD8alpha- DCs, to initiate a CD8 T cell response or to activate memory CD8 T cells and generate effector CD8 T cells has been controversial. In this study, we analyse the capacity of splenic DC subsets to induce CD8 T cell responses to a CD8 T cell epitope (pb9) of a malaria antigen. The administration of peptide-pulsed CD8alpha- or CD8alpha+ DCs primes and boosts a primed CD8 T cell response against the malaria epitope. In vitro, depletion of CD11c(+) DCs from mouse splenocytes, immunised with recombinant vaccinia virus Ankara (MVA) expressing pb9 epitope, significantly reduced the generation of pb9-specific IFNgamma producing effector CD8 T cells, indicating that splenic DCs are involved in the development of pb9-specific IFNgamma producing effector cells. Taken together, this result shows that both DC subsets have the ability to prime and boost CD8 T cell responses and are involved in the activation of memory CD8 T cells.     

Nipah virus infects specific subsets of porcine peripheral blood mononuclear cells

Nipah virus (NiV), a zoonotic paramyxovirus, is highly contagious in swine, and can cause fatal infections in humans following transmission from the swine host. The main viral targets in both species are the respiratory and central nervous systems, with viremia implicated as a mode of dissemination of NiV throughout the host. The presented work focused on the role of peripheral blood mononuclear cells (PBMC) in the viremic spread of the virus in the swine host. B lymphocytes, CD4-CD8-, as well as CD4+CD8- T lymphocytes were not permissive to NiV, and expansion of the CD4+CD8- cells early post infection was consistent with functional humoral response to NiV infection observed in swine. In contrast, significant drop in the CD4+CD8- T cell frequency was observed in piglets which succumbed to the experimental infection, supporting the hypothesis that antibody development is the critical component of the protective immune response. Productive viral replication was detected in monocytes, CD6+CD8+ T lymphocytes and NK cells by recovery of infectious virus in the cell supernatants. Virus replication was supported by detection of the structural N and the non-structural C proteins or by detection of genomic RNA increase in the infected cells. Infection of T cells carrying CD6 marker, a strong ligand for the activated leukocyte cell adhesion molecule ALCAM (CD166) highly expressed on the microvascular endothelial cell of the blood-air and the blood-brain barrier may explain NiV preferential tropism for small blood vessels of the lung and brain.     

Co-culture of human CD34+ cells with mesenchymal stem cells increases the survival of CD34+ cells against the 5-aza-deoxycytidine- or trichostatin A-induced cell death

It has been suggested that epigenetic regulation plays an important role in maintaining the stemness and lineage differentiation of hematopoietic stem cells (HSCs), 5-aza-deoxycytidine (aza-D) and Trichostatin A (TSA) being candidate additives for HSC ex vivo expansion. Although they have potent activity to maintain the stemness, they can also cause serious cell death. This study examined the effects of mesenchymal stem cells (MSCs) on the maintenance of CD34+ cells driven by aza-D and TSA in culture with the combined cytokines of thrombopoietin, flt-3 ligand, stem cell factor, interleukin-3, and interleukin-6. In cultures without MSCs, although aza-D and TSA retained the CD34 frequency 4 to 8 times more than in the cytokines alone, a large portion of cells underwent apoptotic cell death. Consequently, CD34+ cell expansion could not be achieved in any condition without MSCs. In cultures with MSCs, the total cell number was higher in aza-D or TSA than in any conditions in the cultures without MSCs. The CD34 frequency was also similar to the level in the cultures in aza-D or TSA without the MSCs. These results suggest that a co-culture of CD34+ cells with the MSCs might not simply deliver the proliferation signals but also stemness and survival signals, and overlap the action of epigenetic regulators.     

CD8+ T cells inhibit HIV replication in naturally infected CD4+ T cells. Evidence for a soluble inhibitor

This study describes the inhibitory effect exerted by activated CD8+ T cells on the replication of HIV in naturally infected CD4+ T cells. Highly purified CD4+ T cells from asymptomatic HIV seropositive individuals were stimulated with anti-TCR mAb-coated beads in the presence of IL-2. HIV was subsequently reproducibly isolated in cell supernatants from all study participants (53 cultures from 42 individuals). Both autologous and allogeneic CD8+ T cells from asymptomatic HIV seropositive and healthy HIV seronegative individuals inhibited the replication of HIV in these cultures in a dose-dependent manner. CD8+ T cells from patients with AIDS showed reduced or no such inhibitory activity. The inhibitory effect was not dependent on direct cell-cell contact: an inhibitory effect was exerted by CD8+ T cells across a semipermeable membrane, and an inhibitory activity was also exerted by the cell-free supernatants from activated CD8+ T cells. These results suggest that activated CD8+ T cells secrete a soluble inhibitor of HIV replication.     

Initiation and regulation of CD8+T cells recognizing melanocytic antigens in the epidermis: implications for the pathophysiology of vitiligo

Antigen-specific CD8+T lymphocytes play an important role in defense against cutaneous microbial infection and skin cancer as well as in the pathophysiology of autoimmune skin disease such as lupus erythematodes and vitiligo. We have explored the role of CD8+ cytotoxic T lymphocytes (CTL) in an experimental mouse model of vitiligo, a pigmentation disorder characterized by focal loss of melanocytes in the skin. Using genetic immunization techniques we found that pigment cells in the epidermis can be destroyed by CD8+ T cells specifically recognizing a single H2-Kb-binding peptide derived from the model melanocytic self antigen tyrosinase-related protein 2 (TRP2), a melanosomal enzyme involved in pigment synthesis. Experimental evidence suggests that peripheral tolerance of pigment cell-specific cytotoxic CD8+T cells is regulated in two steps. In the induction phase, stimulation and expansion of these T cells in vivo strictly depends on CD4+ T cell help. In the effector phase, autoimmune destruction of melanocytes in the skin depends on local inflammation facilitating the migration of T cells into the epidermis and supporting effector functions. Our results suggest that accidental stimulation of CD8+ CTL recognizing MHC class I-binding peptides derived from melanocytic proteins in the context of an inflammatory skin disease may play an important role in the pathophysiology of vitiligo. Further investigations will address the role of chemokines, chemokine receptors and adhesion molecules in this experimental system and will reveal the role of keratinocytes and Langerhans cells in regulating cutaneous CD8+ T cell responses.     

B cells activated by lipopolysaccharide,but not by anti-Ig and anti-CD40 antibody,induce anergy in CD8+ T cells: role of TGF-beta 1

B cells recognize Ag through their surface IgRs and present it in the context of MHC class II molecules to CD4(+) T cells. Recent evidence indicates that B cells also present exogenous Ags in the context of MHC class I to CD8(+) T cells and thus may play an important role in the modulation of CTL responses. However, in this regard, conflicting reports are available. One group of studies suggests that the interaction between B cells and CD8(+) T cells leads to the activation of the T cells, whereas other studies propose that it induces T cell tolerance. For discerning this dichotomy, we used B cells that were activated with either LPS or anti-Ig plus anti-CD40 Ab, which mimic the T-independent and T-dependent modes of B cell activation, respectively, to provide accessory signals to resting CD8(+) T cells. Our results show that, in comparison with anti-Ig plus anti-CD40 Ab-activated B cells, the LPS-activated B cells (LPS-B) failed to induce significant levels of proliferation, cytokine secretion, and cytotoxic ability of CD8(+) T cells. This hyporesponsiveness of CD8(+) T cells activated with LPS-B was significantly rescued by anti-TGF-beta1 Ab. Moreover, it was found that such hyporesponsive CD8(+) T cells activated with LPS-B had entered a state of anergy. Furthermore, LPS-B expresses a significantly higher level of TGF-beta1 on the surface, which caused the observed hyporesponsiveness of CD8(+) T cells. Therefore, this study, for the first time, provides a novel mechanism of B cell surface TGF-beta1-mediated hyporesponsiveness leading to anergy of CD8(+) T cells.     

4-1BB costimulation enhances HSV-1-specific CD8+ T cell responses by the induction of CD11c+CD8+ T cells

Since 4-1BB plays a predominant role in CD8+ T cell responses, we investigated the effects of 4-1BB triggering on the primary and memory CD8+ T responses to HSV-1 infection. 4-1BB was detected on 10-15% of CD4+ and CD8+ T cells following the infection. 4-1BB-positive T cells were in the proliferative mode and showed the enhanced expression of anti-apoptotic proteins. Agonistic anti-4-1BB treatment exerted preferential expansion of CD8+ T cells and gB/H-2Kb-positive CD8+ T cells, and enhanced cytotoxicity against HSV-1 that was mainly mediated by CD11c+CD8+ T cells. CD11c+CD8+ T cells were re-expanded following re-challenge with HSV-1 at post-infection day 50, indicating that CD11c+CD8+ phenotype was maintained in memory CD8+ T cell pool. Our studies demonstrated that 4-1BB stimulation enhanced both primary and memory anti-HSV-1 CD8+ T cell responses, which was mediated by a massive expansion of antigen-specific CD11c+CD8+ T cells.