Peripheral blood mononuclear cells of HIV-infected patients contain CD8 T cells that form conjugates with and kill HIV-infected autologous CD4 T cells

Peripheral blood mononuclear cells (PBMC) of untreated, HIV-infected patients contain HIV-specific CD8 T cells as well as their corresponding targets, HIV-infected CD4 T cells. To determine if CD4 T-cell depletion in HIV-infected patients may result from autologous CD8–CD4 T-cell interaction, CD8 and CD4 T cells procured from PBMC of acute and chronic untreated HIV-infected patients were sorted and co-incubated. Formation of CD8-CD4 T-cell conjugates was observed by fluorescence microscopy. Apoptosis of CD4 T cells in conjugation was recorded by digitized images and was further observed and measured by FACS using Annexin staining. Perforin expression in the CD8 T cells was measured using intracellular monoclonal perforin antibody staining. HIV DNA in the conjugated CD4 T cells was detected by in situ PCR. We found that 6·1 ± 0·5% of CD4 T cells from acute HIV-infected patients and 3·0 ± 0·5% from chronic HIV-infected patients formed CD8–CD4 T-cell conjugates. Annexin binding and cell morphology typical of apoptosis were observed in the conjugated CD4 T cells. The majority of CD8 T cells that had conjugated to CD4 T cells expressed perforin. The conjugated CD4 T cells exhibited nuclear HIV DNA. CD8 T cells and HIV-infected CD4 T cells, both procured from the PBMC of untreated HIV-infected patients, form conjugates. Apoptotic lytic activity has been observed in the conjugated CD4 T cells. We propose that CD4 T-cell annihilation in HIV-infected patients results, at least in part, from the interactions of perforin-rich CD8 T cells with autologous, HIV-infected CD4 T cells.     

Comparison of activation marker and TCR V beta gene product expression by CD4+ and CD8+ T cells in peripheral blood and lymph nodes from HIV-infected patients.

Since lymphoid organs constitute the site of active and progressive HIV disease, analysis of their lymphocytes may provide more accurate information on T cell abnormalities than that obtained from studying peripheral blood lymphocytes. The objective of this study was to compare the expressions of activation markers and T cell receptor (TCR) V beta gene products by CD4+ and CD8+ T cells in lymph nodes (LN) and peripheral blood (PB) from healthy individuals and asymptomatic HIV-infected patients to determine whether anomalies that could be identified at the HIV replication site could support the hypothesis of T cell activation by HIV-encoded antigens or superantigens. CD4+ and CD8+ T cells in paired LN and PB obtained from six healthy controls and five asymptomatic HIV-infected individuals were analysed by flow cytometry, using anti-CD38, anti-HLA-DR and 13 anti-V beta MoAbs that cover, approximately, 45% of the T cell repertoire. Analysis of T cell activation marker expression indicated that the percentages of CD4+ and CD8+ T cells bearing CD38 or CD38 and HLA-DR molecules were higher in patients than in controls and, in patients, higher in LN than in PB. Comparison between the V beta repertoires of CD4+ and CD8+ T cells in LN and PB showed that, in each healthy individual, a limited number of V beta families expressed by CD4+ or CD8+ T cells had different repartition in LN and PB, whereas in each HIV+ patient, more V beta families exhibited different distributions and these differences recurred among certain V beta segments, such as V beta 5.3 and V beta 21 in the CD4+ T cell population and V beta 5.2/5.3, V beta 12 and V beta 21 in the CD8+ T cell population. Taken together, these data argue for a skewed TCR repertoire in HIV infection and sustained activation of T cells by HIV-encoded antigens at the site of HIV replication, and further demonstrate that a high proportion of CD4+ T cells are in an activation state that may, indirectly, participate in their functional abnormalities.     

CD8+ T cells and not CD4+ T cells are hyporesponsive to CD28- and CD40L-mediated activation in HIV-infected subjects

T cell dysfunction in HIV-infected subjects could be the consequence of altered sensitivity of CD4⁺ or CD8⁺ T cells to various costimulatory signals. Therefore, we studied proliferation and cytokine production in highly purified CD8⁺ and CD4⁺ T cells from HIV-infected and HIV⁻ subjects, induced by co-activation via cell-bound CD80, CD86 and CD40 or by allo-activation. Regardless of the nature of the first and the costimulatory signal, CD8⁺ T cells from patients proliferated consistently less than controls, while responses from CD4⁺ T cells were similar in patients and controls. This phenomenon was observed after ligation of CD28 combined with anti-CD3 or phorbol myristate acetate (PMA), but also after allogeneic stimulation and after activation by CD40 and anti-CD3. Anti-CD3 combined with CD80 or CD86 induced a mixed Th1/Th2-type cytokine profile in both CD4⁺ and CD8⁺ T cells from controls, whereas anti-CD3 plus CD40 induced only low levels of Th2-type cytokines and no interferon-gamma (IFN-γ) in CD4⁺ T cells. Compared with controls, CD4⁺ T cells from patients produced slightly lower levels of IL-10 but equal amounts of IFN-γ, IL-4 and IL-5, while CD8⁺ T cells from patients produced less of all cytokines tested. In conclusion, responses of purified CD4⁺ T cells from HIV⁺ subjects to various costimulatory pathways are relatively intact, whereas CD8⁺ T cells are hyporesponsive at the level of proliferation and cytokine production. A generalized intrinsic CD8⁺ T cell failure might contribute to viral and neoplastic complications of HIV infection.     

雷公藤甲素对诱导CD4+、CD8+T细胞凋亡的作用

目的 探讨雷公藤甲素对ＣＤ４＾＋、ＣＤ８＾＋Ｔ细胞凋亡的作用。方法 分离后的正常人外周血ＣＤ４＾＋、ＣＤ８＾＋Ｔ细胞在外培养条件下,加入雷公藤甲素处理,然后用３末端脱氧核苷酸基（ＴｄＴ）介导的ｄＵＴＰ缺口末端标记（ＴＵＮＥＬ）检测凋亡细胞。结果 雷公藤甲素处理后ＣＤ４和ＣＤ８＾＋细胞凋亡率比对照组显著增加,但ＣＤ４＾＋、ＣＤ８＾＋Ｔ细胞凋亡率则针显著差别。结论 雷公藤甲素诱导诱活化的ＣＤ４＾＋、Ｃ     

CD8+ CD28− T cells in vertically HIV-infected children

To evaluate whether vertical HIV infection interferes with the expression of CD28 on T lymphocytes, 25 HIV-infected children and 29 seroreverted children born to HIV⁺ mothers were studied. The percentage of CD28⁻ cells among CD8⁺ T lymphocytes was higher in HIV-infected children than in controls (P < 0.001). In fact, in HIV-infected children, this percentage was elevated from the first year of life, while in healthy seroreverted children, the proportion of CD28⁻ cells among CD8⁺ cells rose progressively with age (r = 0.49; P = 0.008). In HIV⁺ children, the CD8⁺ CD28⁻, but not CD8⁺ CD28⁺ cell proportion was significantly correlated with immunological markers of disease progression, such as CD4⁺ cell loss (r = −0.65; P < 0.001) and the level of in vitro spontaneous lymphocyte apoptosis (r = 0.53; P = 0.03).     

Defective integration of activating signals derived from the T cell receptor (TCR) and costimulatory molecules in both CD4+ and CD8+ T lymphocytes of common variable immunodeficiency (CVID) patients

CVID is characterized by hypogammaglobulinaemia and impaired antibody production. Previous studies demonstrated defects at the T cell level. In the present study the response of purified CD4⁺ and CD8⁺ T lymphocytes to stimulation with anti-TCR monoclonal antibody (the first signal) in combination with anti-CD4 or anti-CD8, anti-CD2 and anti-CD28 MoAbs (the costimulatory signals) was investigated. Both CD4⁺ and CD8⁺ T cells from the patients showed significantly reduced IL-2 release following stimulation via TCR and costimulation via CD4 or CD8 and CD2, respectively. However, normal IL-2 production following TCR plus phorbol myristate acetate (PMA) costimulation and normal expression of an early activation marker, CD69, after TCR + CD28 stimulation indicated that TCR was able to transduce a signal. Furthermore, both IL-2 and IL-4 release were impaired in CD4⁺ lymphocytes following TCR + CD28 stimulation. In addition, stimulation via TCR + CD28 resulted in significantly decreased expression of CD40 ligand in the patients. These results suggest that the integration of activating signals derived from the TCR and costimulatory molecules is defective in CVID patients; the defect is not confined to costimulation via a single molecule, or restricted to cells producing Thl-type cytokines such as IL-2, and is expressed in both CD4⁺ and CD8⁺T cell subsets.     

Functionality of CD4+ and CD8+ T cells from tonsillar tissue

For many years, tonsillectomy has been used routinely in children to treat chronic or recurrent acute tonsillitis. Palatine tonsils are secondary lymphoid organs and the major barrier protecting the digestive and respiratory tracts from potential invasive microorganisms. They have been used as sources of lymphoid tissue; however, despite the hundreds of papers published on tonsillectomy, no studies addressing the functionality of the CD4(+) and CD8(+) T cells from chronically infected tonsils have yet been published. The aim of this study was to analyse the functionality of the CD4(+) and CD8(+) T cells with respect to tonsillar tissue. We used an affordable approach to measure the frequency of antigen-specific CD4(+) T cells, the direct ex-vivo cytotoxicity of CD8(+) T cells, memory T cell phenotype, cytokine profile and DC phenotype. Our results demonstrate that CD4(+) and CD8(+) T cells from tonsillar tissue are totally functional, as shown by their ability to produce cytokines, to degranulate and to differentiate into effector-memory T cells.     

Activation of CD4+ T cells by delivery of the B7 costimulatory signal on bystander antigen-presenting cells (trans-costimulation)

Increasing evidence in both murine and human systems suggests that the interaction of the T cell surface antigens CD28/CTLA4 with their ligand B7 on the antigen-presenting cells (APC) is the critical costimulatory pathway involved in the induction of maximal T cell activation and the prevention of induction of anergy. It has also been demonstrated that efficient induction of clonal expansion of normal CD4⁺ T cells requires the delivery of the T cell receptor (TCR) ligand and costimulation by the same APC. We demonstrate here that normal murine CD4⁺ T cells can be efficiently activated by soluble anti-CD3 cross-linked by fixed macrophages and by a costimulatory signal delivered by a bystander APC, B7-transfected L cells. The major factor which determined the ability of an APC to provide costimulation in “trans” was the level of cell surface B7 expression. The requirement for B7 costimulation appears to be at initial stage of TCR engagement since optimal T cell activation was only observed when TCR triggering and B7 costimulatory activity were delivered at same time by different APC. Induction of maximal proliferation of both naive CD45RB^hi and memory CD45RB^lo CD4⁺ T cells was B7 dependent and both populations of cells responded equally well to the B7 costimulation delivered in “trans”. Furthermore, trans-costimulation provided by B7 transfected L cells efficiently prevented the induction of anergy in normal murine CD4⁺ T cells induced by anti-CD3 cross-linked by fixed-resting macrophages. Addition of exogenous interleukin-2 (IL-2) and IL-7 to the primary culture in the absence of B7-transfected L cells or addition of IL-2 to the culture containing the B7 transfectant and CTLA4Ig completely prevented the induction of hyporesponsiveness. These findings raise the possibility that in certain pathological states, CD4⁺ T cells in vivo may be activated by costimulation delivered by bystander APC.     

HIV gag‐specific immune response mediated by double negative (CD3+CD4−CD8−) T cells in HIV‐exposed seronegative individuals

Double negative (DN) T cells are CD3⁺, CD4^?, CD8^? cells with either T‐cell receptors (TCR) αβ or TCR γδ whose importance on protection against HIV infection is unknown. Since HIV‐exposed seronegative individuals correspond to an ideal group in whom correlates of protection are expected, the role of these cells was studied in 13 HIV‐serodiscordant couples in a stable relationship and reporting unprotected sexual intercourses. HIV‐specific immune responses mediated by DN T‐cells were evaluated by measuring intracellular IFNγ and MIP1β (CCL4) production in response to HIV‐Gag peptides. Thirty‐five healthy controls not exposed to HIV were tested similarly and used to define a threshold for positive responses. Interestingly, Gag‐specific DN T‐cell responses were found in 3/13 (23%) HIV‐exposed seronegative individuals (Group A), involving both DN/αβ⁺ and DN/γδ⁺ T‐cells through MIP1β and IFNγ production. 4/13 (30%) of partners infected with HIV (Group B) also showed Gag‐specific responses but were mediated exclusively by DN/γδ⁺ T‐cells, mainly through IFNγ production. DN T‐cells in Group A individuals can display differential HIV‐specific immune responses, which might contribute to the low susceptibility to infection with HIV shown by individuals in Group A. J. Med. Virol. 85:200–209, 2013. © 2012 Wiley Periodicals, Inc.     

Regulation of allergen-induced bone marrow eosinophilopoiesis: role of CD4+ and CD8+ T cells

BACKGROUND: The mechanisms of the distant stimulation of the bone marrow (BM) after airway allergen exposure remain largely obscure. T cells have been implicated in allergic airway inflammation but their role in allergen-induced BM eosinophilopoiesis is poorly understood. The aim of this study was to determine the role of CD4(+) and CD8(+) T cells in allergen-induced BM eosinophilopoiesis. METHODS: Ovalbumin (OVA)-sensitized wild type (WT), CD4 knockout (CD4-/-) and CD8 knockout (CD8-/-) mice were exposed intranasally to OVA or saline. Bromo-deoxyuridine (BrdU) was used to label newly produced cells. Bone marrow, blood and bronchoalveolar lavage (BAL) were sampled 24 h after the final exposure. Immunostaining for newly produced eosinophils (i.e. BrdU(+)/MBP(+)) and BM eosinophil progenitor [CD34(+)/CD45(+)/interleukin-5 (IL-5)Ralpha(+)] cells was performed. RESULTS: The number of newly produced BM eosinophils (BrdU(+)/MBP(+) cells) was significantly reduced in allergen exposed CD4-/- or CD8-/- mice compared with allergen exposed WT mice, which was followed by a subsequent decrease in newly produced blood and airway eosinophils. Furthermore, BM eosinophil progenitors were significantly reduced in allergen exposed CD4-/- and CD8-/- mice compared with WT mice. Finally, serum IL-5 and Bronchoalveolar lavage fluid eotaxin-2 levels were abolished in allergen exposed CD4-/- mice to levels seen in saline exposed WT mice. CONCLUSIONS: These data suggests that both CD4(+) and CD8(+) T cells have a regulatory role in allergen-induced BM eosinophilopoiesis, whereas CD4(+) T cells are obligatory for allergen-induced airway eosinophilia. The subsequent traffic of eosinophils to the airways is likely to be at least partly regulated by a CD4(+) T-cell-dependent local airway eotaxin-2 production.     

CD52 is a novel costimulatory molecule for induction of CD4+ regulatory T cells

We previously reported that 4C8 monoclonal antibody (mAb) provides a costimulatory signal to human CD4+ T cells and consequently induces regulatory T (Treg) cells, which are hypo-responsive and suppress the polyclonal response of bystander CD4+ cells in a contact-dependent manner. In this study, we identified the antigen of 4C8 mAb as CD52. Costimulation with Campath-1H, a humanized anti-CD52 mAb, also induced Treg cells. Anti-CD52-induced Treg cells suppressed the proliferation of both CD4+ and CD8+ T cells provided with polyclonal or allogeneic stimulation. When Treg cells were induced from Staphylococcal enterotoxin B (SEB) treated cells, they suppressed the response to SEB more efficiently than that to another superantigen, SEA. Furthermore, anti-CD52-induced Treg cells could be expanded by culture with IL-2 followed by CD52-costimulation, and co-injection of expanded Treg cells suppressed lethal xenogeneic graft versus host disease (GvHD) reactions in SCID mice caused by human peripheral blood mononuclear cells (PBMCs).     

Cytotoxic T lymphocyte antigen-4-dependent down-modulation of costimulatory molecules on dendritic cells in CD4+ CD25+ regulatory T-cell-mediated suppression

We have previously demonstrated that CD4+ CD25+ natural regulatory T cells (Treg cells) induce down-modulation of CD80 and CD86 (B7) molecules on dendritic cells (DCs) in vitro. In this report we show that the extent of down-modulation is functionally significant because Treg-cell conditioned DCs induced poor T-cell proliferation responses. Further, we report that down-modulation was induced rapidly and was inhibited by blocking cytotoxic T lymphocyte antigen-4 (CTLA-4), which is constitutively expressed by the Treg cells. Even though Treg cells have previously been reported to kill antigen-presenting cells, the down-modulation was not due to selective killing of DCs expressing high level of the costimulatory molecules. We propose that Treg cells down-modulate B7-molecules on DCs in a CTLA-4-dependent way, thereby enhancing suppression of T-cell activity.     

In vivo elimination of viral superantigen-activated CD4+ T cells: apoptosis occurs at a distance from the activation site

Local injection of mouse mammary tumor virus (MMTV) induces a local immune response, with activation of viral superantigen (vSAG)-specific T cell subsets followed by their clonal deletion. We investigated the fate of vSAG-reactive T cells following footpad injection of MMTV(SW) to mice. Activated T cells accumulated in draining lymph nodes. However, we demonstrated that apoptosis did not occur at the activation site, on the contrary of what has been shown after bacterial SAG activation. Although activated T cells were already shown to have the capacity to migrate to the gut, the fate of gut homing cells remains unclear. We demonstrate that the number of vSAG-specific T cells activated in the periphery was increasing in the follicles of gut-associated lymphoid organs, together with the number of apoptotic cell clusters. These results strongly suggested that gut-associated lymphoid tissue was the specific graveyard for apoptotic vSAG-activated CD4 T cells.     

Activated CD4+ CD25+ T cells suppress antigen-specific CD4+ and CD8+ T cells but induce a suppressive phenotype only in CD4+ T cells

CD4(+) CD25(+) regulatory T cells are increasingly recognized as central players in the regulation of immune responses. In vitro studies have mostly employed allogeneic or polyclonal responses to monitor suppression. Little is known about the ability of CD4(+) CD25(+) regulatory T cells to suppress antigen-specific immune responses in humans. It has been previously shown that CD4(+) CD25(+) regulatory T cells anergize CD4(+) T cells and turn them into suppressor T cells. In the present study we demonstrate for the first time in humans that CD4(+) CD25(+) T cells are able to inhibit the proliferation and cytokine production of antigen specific CD4(+) and CD8(+) T cells. This suppression only occurs when CD4(+) CD25(+) T cells are preactivated. Furthermore, we could demonstrate that CD4(+) T-cell clones stop secreting interferon-gamma (IFN-gamma), start to produce interleukin-10 and transforming growth factor-beta after coculture with preactivated CD4(+) CD25(+) T cells and become suppressive themselves. Surprisingly preactivated CD4(+) CD25(+) T cells affect CD8(+) T cells differently, leading to reduced proliferation and reduced production of IFN-gamma. This effect is sustained and cannot be reverted by exogenous interleukin-2. Yet CD8(+) T cells, unlike CD4(+) T cells do not start to produce immunoregulatory cytokines and do not become suppressive after coculture with CD4(+) CD25(+) T cells.     

Regulatory function of cytomegalovirus-specific CD4CD27CD28 T cells

CMV infection is characterized by high of frequencies of CD27⁻CD28⁻ T cells. Here we demonstrate that CMV-specific CD4⁺CD27⁻CD28⁻ cells are regulatory T cells (T_R). CD4⁺CD27⁻CD28⁻ cells sorted from CMV-stimulated PBMC of CMV-seropositive donors inhibited de novo CMV-specific proliferation of autologous PBMC in a dose-dependent fashion. Compared with the entire CMV-stimulated CD4⁺ T-cell population, higher proportions of CD4⁺CD27⁻CD28⁻ T_R expressed FoxP3, TGFβ, granzyme B, perforin, GITR and PD-1, lower proportions expressed CD127 and PD1-L and similar proportions expressed CD25, CTLA4, Fas-L and GITR-L. CMV-CD4⁺CD27⁻CD28⁻ T_R expanded in response to IL-2, but not to CMV antigenic restimulation. The anti-proliferative effect of CMV-CD4⁺CD27⁻CD28⁻ T_R significantly decreased after granzyme B or TGFβ inhibition. The CMV-CD4⁺CD27⁻CD28⁻ T_R of HIV-infected and uninfected donors had similar phenotypes and anti-proliferative potency, but HIV-infected individuals had higher proportions of CMV-CD4⁺CD27⁻CD28⁻ T_R. The CMV-CD4⁺CD27⁻CD28⁻ T_R may contribute to the downregulation of CMV-specific and nonspecific immune responses of CMV-infected individuals.     

Polyfunctional response by ImmTAC (IMCgp100) redirected CD8+ and CD4+ T cells

The success of immune system‐based cancer therapies depends on a broad immune response engaging a range of effector cells and mechanisms. Immune mobilizing monoclonal T cell receptors (TCRs) against cancer (ImmTAC™ molecules: fusion proteins consisting of a soluble, affinity enhanced TCR and an anti‐CD3 scFv antibody) were previously shown to redirect CD8⁺ and CD4⁺ T cells against tumours. Here we present evidence that IMCgp100 (ImmTAC recognizing a peptide derived from the melanoma‐specific protein, gp100, presented by HLA‐A*0201) efficiently redirects and activates effector and memory cells from both CD8⁺ and CD4⁺ repertoires. Using isolated subpopulations of T cells, we find that both terminally differentiated and effector memory CD8⁺ T cells redirected by IMCgp100 are potent killers of melanoma cells. Furthermore, CD4⁺ effector memory T cells elicit potent cytotoxic activity leading to melanoma cell killing upon redirection by IMCgp100. The majority of T cell subsets belonging to both the CD8⁺ and CD4⁺ repertoires secrete key pro‐inflammatory cytokines (tumour necrosis factor‐α, interferon‐γ, interleukin‐6) and chemokines (macrophage inflammatory protein‐1α‐β, interferon‐γ‐inducible protein‐10, monocyte chemoattractant protein‐1). At an individual cell level, IMCgp100‐redirected T cells display a polyfunctional phenotype, which is a hallmark of a potent anti‐cancer response. This study demonstrates that IMCgp100 induces broad immune responses that extend beyond the induction of CD8⁺ T cell‐mediated cytotoxicity. These findings are of particular importance because IMCgp100 is currently undergoing clinical trials as a single agent or in combination with check point inhibitors for patients with malignant melanoma.     

免疫磁珠负性分离纯化小鼠脾脏CD8+ T细胞

目的 探讨小鼠脾脏CD8 T细胞的免疫磁珠负性分选方法,并对分选后所得细胞进行纯度、活力及功能检测.方法 以免疫磁珠负性分选法从小鼠脾脏细胞中分离CD8 T细胞,流式细胞术检测所得细胞的纯度,台盼蓝检测细胞活力并用ConA刺激检测增殖能力. 结果 经过流式细胞仪测定免疫磁珠负性分选后的小鼠脾脏CD8 T细胞纯度达到(91.6±3.6)%,台盼兰染色细胞活力为(94.9±3.2)%,ConA刺激72 h后有(56.3±1.7)%的细胞增殖.结论 免疫磁珠负性分选法能够分选出高纯度的CD8 T细胞,并且不影响分选靶细胞的细胞活力和功能.     

Lysis of CD4+ lymphocytes by non-HLA-restricted cytotoxic T lymphoe from HIV-infected individuals

Individuals infected with HIV have elevated numbers of total and activated CD8⁺ lymphocytes in peripheral blood. CD8⁺ lymphocytes from HIV-infected individuals have been shown to mediate non-human histocompatibility-linked antigen (HLA)-restricted suppression of viral replication, HLA-restricted killing of cells expressing HIV antigens, and killing of uninfected lymphocytes. We studied CD8⁽ T lymphocytes that lysed autologous CD4+ lymphocytes, hetcrologous CD4¹ lymphocytes from HIV-infected individuals and uninfected CD4⁺ lymphocytes. Killing in all cases required T cell receptor (TCR)-mediated recognition or triggering. However, these CD8 cytotoxic T lymphocytes (CTL) killed HLA class I mismatched CD4* lymphocytes and CD4⁴ lymphocytes treated with a MoAb against HLA-A, B and C antigens (PA2.6) which blocks HLA class I-restricted killing. HLA class H-negativc CD4* T lymphoma cells (CEM.NK^R) were also killed by anti-CD3 inhibited CTL. Stimulation of peripheral blood lymphocytes (PBL) from HIV-infected individuals, but not uninfected controls, with concanavalin A (Con A) and IL-2, induced non-HLA-restricted TCR aft¹, CD8^f CTL which lysed CD4⁺ lymphocytes. Activation ofCD4’lymphocytes increased their susceptibility to CD8^f CTL-mediated lysis. In HIV infection, a population of non-HLA-restricted CTL which lyse activated CD4⁺ lymphocytes is expanded. The expansion of CTL with unusual characteristics is interesting, because the stimulus for this expansion is unknown. CTL which recognize activated CD4⁺ cells could play a role in immune regulation and the pathogenesis of A IDS.     

CD4+ T cell-independent maintenance and expansion of memory CD8+ T cells derived from in vitro dendritic cell activation

CD4+ T cells are essential for the maintenance of CD8+ memory T (Tm) cells following acute infection, but the importance of CD4+ T cells for the maintenance and expansion of CD8+ Tm cells to non-infectious antigens remains mostly unknown. Here, we showed that ovalbumin (OVA)-specific CD8+ Tm cell precursors derived from in vitro stimulation of TCR transgenic OT I CD8+ T cells with OVA protein-pulsed bone marrow-derived dendritic cells (DCOVA) can give rise to functional CD8+ Tm cells after adoptively transferred into mice. These CD8+ Tm cells can be maintained and remain fully functional in CD4+ T cell-absent environments in vivo. Furthermore, CD4+ T cells are not essential for the expansion of these CD8+ Tm cells. Finally, these in vitro DCOVA-activated CD8+ Tm cells maintained in CD4-deficient mice are also able to confer fully protective immunity against a later challenge of OVA-expressing tumor cells. Collectively, these findings demonstrate that in contrast to acute infections, maintenance and expansion of CD8+ Tm cells after priming with OVA protein-pulsed dendritic cells are independent of CD4+ T cells.