A distinct role for ICOS-mediated co-stimulatory signaling in CD4+ and CD8+ T cell subsets

While the ligand of inducible co-stimulator (ICOS), B7 homologous protein, is widely expressed in somatic cells, B7-1 and B7-2 expression is mainly limited to lymphoid organs. Thus, the activation of T cells through ICOS without a CD28-mediated signal may occur in physiological situations. In order to gain a better understanding of the role of the ICOS co-stimulatory signal in immune responses, we studied the cellular response of T cells to beads coated with anti-ICOS or anti-CD28, plus sub-optimal anti-CD3 mAb. We demonstrate that while CD28 ligation induced expansion of both CD4+ and CD8+ populations, ICOS ligation only resulted in the expansion of CD8+ T cells, and induced apoptosis in the CD4+ T cell population. It was found that IL-2 is critically required for CD8+ T cell expansion triggered by ICOS ligation, whereas it had only a limited effect on the expansion of CD4+ T cells. This distinct reactivity of CD4+ and CD8+ T cell populations to exogenous IL-2 strongly correlates with the expression level of IL-2 receptor beta-chain, CD122, on T cells. Furthermore, we defined a small but distinct population of memory phenotype CD4+ T cells that constitutively express ICOS. Interestingly, while naive CD4+ T cells were unable to produce IL-2, ICOS-expressing T cells produced a substantial amount of IL-2 by stimulation with anti-ICOS/CD3 beads, suggesting that IL-2, which is indispensable for CD8+ T cell expansion, is produced by this ICOS-expressing T cell population. These results provide evidence indicating that the ICOS co-stimulatory signal plays a distinct role in the development of CD4+ and CD8+ T cell-mediated immune responses.     

In vivo depletion of CD4+CD25+ regulatory T cells in cats

To establish a characterized model of regulatory T cell (Treg) depletion in the cat we assessed the kinetics of depletion and rebound in peripheral and central lymphoid compartments after treatment with anti-CD25 antibody as determined by cell surface markers and FOXP3 mRNA expression. An 82% decrease in circulating CD4+CD25+ Tregs was observed by day 11 after treatment. CD4+CD25+ cells were also reduced in the thymus (69%), secondary lymphoid tissues (66%), and gut (67%). Although CD4+CD25+ cells rebound by day 35 post-treatment, FOXP3 levels remain depressed suggesting anti-CD25 antibody treatment has a sustainable diminutive effect on the Treg population. To determine whether CD25+ Treg depletion strategies also deplete activated CD25+ effector cells, cats were immunized with feline immunodeficiency virus (FIV) p24-GST recombinant protein, allowing them to develop a measurable memory response, prior to depletion with anti-CD25 antibody. Anti-FIV p24-GST effector cell activity in peripheral blood after depletion was sustained as determined by antigen-specific T cell proliferation and humoral responses against FIV p24-GST with an ELISA for antigen-specific feline IgG. Furthermore, development of an anti-mouse response in Treg-depleted cats was similar to control levels indicating the retained capacity to respond to a novel antigen. We conclude that despite alterations in CD25+ cell levels during depletion, the feline immune system remains functional. We demonstrate here a model for the study of disease pathogenesis in the context of reduced numbers of immunosuppressive CD4+CD25+ Tregs throughout the feline immune system.     

CD4+ T cell help improves CD8+ T cell memory by retained CD27 expression

CD4+ T cell help during the priming of CD8+ T lymphocytes imprints the capacity for optimal secondary expansion upon re-encounter with antigen. Helped memory CD8+ T cells rapidly expand in response to a secondary antigen exposure, even in the absence of T cell help and, are most efficient in protection against a re-infection. In contrast, helpless memory CTL can mediate effector function, but secondary expansion is reduced. How CD4+ T cells instruct CD8+ memory T cells during priming to undergo efficient secondary expansion has not been resolved in detail. Here, we show that memory CTL after infection with lymphocytic choriomeningitis virus are CD27(high) whereas memory CTL primed in the absence of CD4+ T cell have a reduced expression of CD27. Helpless memory CTL produced low amounts of IL-2 and did not efficiently expand after restimulation with peptide in vitro. Blocking experiments with monoclonal antibodies and the use of CD27(-/-) memory CTL revealed that CD27 ligation during restimulation increased autocrine IL-2 production and secondary expansion. Therefore, regulating CD27 expression on memory CTL is a novel mechanism how CD4+ T cells control CTL memory.     

Age-related increase in the fraction of CD27-CD4+ T cells and IL-4 production as a feature of CD4+ T cell differentiation in vivo.

The influence of ageing on phenotype and function of CD4+ T cells was studied by comparing young (19-28 years of age) and aged (75-84 years of age) donors that were selected using the SENIEUR protocol to exclude underlying disease. An age-related increase was observed in the relative number of memory cells, not only on the basis of a decreased CD45RA and increased CD45RO expression, but also on the basis of a decrease in the fraction of CD27+CD4+ T cells. Our observation that the absolute number of CD45RO+CD4+ T cells was increased, while absolute numbers of CD27-CD4+ T cells remained unchanged in aged donors, indicates that the latter subset does not merely reflect the size of the CD45RO+CD4+ T cell pool. The increased fraction of memory cells in the aged was functionally reflected in an increased IL-4 production and T cell proliferation, when cells were activated with the combination of anti-CD2 and anti-CD28, whereas IL-2 production was comparable between both groups. No differences were observed with respect to proliferative T cell responses or IL-2 production using plate-bound anti-CD3 or phytohaemagglutinin (PHA). The observation that IL-4 production correlated with the fraction of memory cells in young donors but not in aged donors suggests different functional characteristics of this subset in aged donors.     

Anti-CD3 priming generates heterogeneous antigen-specific memory CD4 T cells

Anti-CD3 activation of peripheral T cells is used in adoptive immunotherapy for cancer and HIV infection, but the long-term fate of anti-CD3-primed T cells in vivo is not known. In this study, we demonstrate that anti-CD3-mediated activation of influenza hemagglutinin (HA)-specific TCR-transgenic CD4 T cells results in generation of a long-lived HA-specific memory CD4 T cell population when transferred into lymphocyte-deficient and intact mouse hosts. This anti-CD3-primed memory population is indistinguishable from HA peptide-primed memory CD4 T cells in terms of phenotype, rapid recall function, and enhanced proliferative capacity. Moreover, anti-CD3 priming generates phenotypically heterogeneous memory subsets in lymphoid and non-lymphoid sites. Our results suggest that anti-CD3 has potential efficacy in generating memory responses in adoptive immunotherapies and vaccines and that the tissue distribution and maintenance of heterogeneous lymphoid and non-lymphoid memory T cell subsets are a stochastic process that can occur independent of antigen or TCR specificity.     

CD4+ CD25+调节性T细胞AICD机制的研究

目的探讨CD4^＋CD25^＋调节性T细胞活化诱导的细胞死亡（AICD）发生的机制。方法CD4^＋CD25^＋T细胞以磁性细胞分离器（MACS）从BALB／c小鼠或DO11．10小鼠的静息T细胞分离纯化。体外细胞增殖抑制实验证实其免疫调节作用。CD4^＋CD25^＋T细胞的AICD以CD3／CD28单克隆抗体活化或以特异性OVA323-339肽、抗原提呈细胞活化等两种方法获得。CD4^＋CD25^＋T细胞凋亡相关基因的表达通过实时定量PCR检测。流式细胞仪检测细胞的凋亡率。进一步观察FasL中和抗体、TRAIL中和抗体及caspase抑制剂zVAD-fmk对CD4^＋CD25^＋T细胞凋亡的影响。结果MACS成功分离CD4^＋CD25^＋T细胞，纯度可达98％，该细胞可特异性表达Foxp3基因，能明显抑制效应性T细胞的体外增殖。CD3／CD28抗体以及OVA特异性抗原活化8d的CD4^＋CD25^＋调节性T细胞AICD达39％～45％。活化前后的CD4^＋CD25^＋调节性T细胞死亡受体家族表达发生明显变化；FasL、TRAIL中和抗体及zVAD-fmk可明显抑制CD4^＋CD25^＋调节性T细胞的凋亡。结论FasL／Fas及其他凋亡相关分子可能参与了CD4^＋CD25^＋调节性T细胞的凋亡。     

Dendritic cells rapidly undergo apoptosis in vitro following culture with activated CD4+ Valpha24 natural killer T cells expressing CD40L

Human Valpha24 natural killer T (Valpha24NKT) cells are activated by alpha-glycosylceramide-pulsed dendritic cells (DCs) in a CD1d-dependent and T-cell receptor-mediated manner. There are two major subpopulations of Valpha24NKT cells, CD4- CD8- Valpha24NKT and CD4+ Valpha24NKT cells. We have recently shown that activated CD4- CD8- Valpha24NKT cells have cytotoxic activity against DCs, but knowledge of the molecules responsible for cytotoxicity of Valpha24NKT cells is currently limited. We aimed to investigate whether CD4+ Valpha24NKT cells also have cytotoxic activity against DCs and to determine the mechanisms underlying any observed cytotoxic activity. We demonstrated that activated CD4+ Valpha24NKT cells [CD40 ligand (CD40L) -positive] have cytotoxic activity against DCs (strongly CD40-positive), but not against monocytes (weakly CD40-positive) or phytohaemagglutinin blast T cells (CD40-negative), and that apoptosis of DCs significantly contributes to the observed cytotoxicity. The apoptosis of DCs following culture with activated CD4+ Valpha24NKT cells, but not with resting CD4+ Valpha24NKT cells (CD40L-negative), was partially inhibited by anti-CD40L mAb. Direct ligation of CD40 on the DCs by the anti-CD40 antibody also induced apoptosis of DCs. Our results suggest that CD40-CD40L interaction plays an important role in the induction of apoptosis of DCs following culture with activated CD4+ Valpha24NKT cells. The apoptosis of DCs from normal donors, triggered by the CD40-CD40L interaction, may contribute to the homeostatic regulation of the normal human immune system, preventing the interminable activation of activated CD4+ Valpha24NKT cells by virtue of apoptosis of DCs.     

Induction of CD95 ligand expression on T lymphocytes and B lymphocytes and its contribution to apoptosis of CD95-up-regulated CD4+ T lymphocytes in macaques by infection with a pathogenic simian/human immunodeficiency virus

Using an established SIV/HIV-C2/1-infected cynomolgus monkey model displaying stable CD4+ T cell depletion, the kinetics of apoptosis and the levels of expression of CD95 membrane-associated CD95L on lymphocytes were investigated to test the involvement of the CD95/CD95L system in CD4+ T lymphocyte loss in vivo. Rapid depletion of CD4+ T cells occurred up to 2 weeks after infection, with chronic CD4+ T lymphopenia thereafter. During the initial CD4+ T cell loss, which was accompanied by viraemia, about 90% of the peripheral CD4+ T cell subset underwent spontaneous apoptotic cell death during 24 h of culture. Increased expression of CD95 was observed on both CD4+ and CD8+ T cell subsets, with CD95 expression on CD8+ cells declining rapidly, but high CD95 expression being maintained on CD4+ cells. Since CD95L was expressed on CD8+ T cells, B cells and to a lesser extent on CD4+ T cells, this suggests that CD95-mediated apoptosis might be controlled in an autocrine/paracrine fashion.     

The effect of anti-CD4 on helper function of CD4,45RA+ versus CD4,45RO+ T cells.

Here we have investigated and compared the effects of anti-CD4 on helper function of CD4,45RA+ versus CD4,45RO+ T cells. Only CD4,45RO+ cells, but not CD4,45RA+ cells were able to promote B cell differentiation resulting in immunoglobulin production in vitro (IgM as well as IgG) which could be inhibited by anti-CD4 MoAbs (MAX.16H5 and T151). In pokeweed mitogen (PWM)-induced B cell proliferation a similar pattern of responsiveness was obtained. When we studied the anti-CD4 effects on cytokine production in T cells stimulated in mixed lymphocyte reaction (MLR) or by mitogens, we found that neither IL-2 nor IL-4 production was dramatically influenced by anti-CD4 in CD4,45RO+ cells. This led us to the conclusion that the inhibitory effect of anti-CD4 on B cell proliferation and immunoglobulin secretion was not due to inhibition of cytokine production. To clarify this point, we investigated the ability of anti-CD4 to inhibit conjugate formation between B and T cells. It was found that CD4,45RO+ T cells formed more conjugates than CD4,45RA+ cells, and that only the conjugate formation by CD4,45RO+ T cells was inhibited by anti-CD4. These results suggest that (i) anti-CD4 inhibits T helper functions primarily by affecting CD4,45RO+ cells, and (ii) this effect is probably mediated by contact inhibition in the early phase of T-B collaboration.     

Clonal analysis of CD4 mediated accessory function on the effector activity of human CD4+ T cell subsets

Background: It has been reported for the peripheral T cell repertoire that CD4 molecules may enhance adhesion between T cells and antigen presenting cells and, through their physical association with T cell antigen receptors, contribute to signal transduction. Objective: The aims of this study were to determine if the modulation of CD4 molecules had differential effects on T cell recognition, antigen induced cytokine (IL-4 and IFNγ), release and the induction of specific anergy for human TH-0, TH-1 and TH-2 cells. Methods: A panel of anti-CD4 antibodies was examined for its ability to modulate T cell proliferation, cytokine production and tolerance induction in house dust mite (TH-0 and TH-2) and influenza haemagglutinin (TH-1) specific human CD4+ T cell clones all restricted by DRB1^*1101 and isolated from dust mite allergic individuals. Results: We observed that anti-CD4 antibodies may inhibit or enhance antigen mediated T cell proliferation, which may reflect the differential requirements of T cells for selective functions of CD4. Furthermore, IFNγ and IL-4 production was differentially modulated depending on the specificity of the anti-CD4 antibody and the clone of T cells. However, pretreatment of T cells with anti-CD4 antibody alone neither induced nor enhanced the susceptibility of T cells to peptide mediated anergy. Conclusion: Antigen recognition by different subsets of human CD4+ T cells has differential requirements on CD4, whereas the induction of specific anergy appeared to be independent of the functions of CD4 molecules. Antigen induced IFNγ production was more susceptible than IL-4 to the inhibitory effects of anti-CD4 antibodies. Furthermore, it appeared that certain anti-CD4 antibodies can dissociate antigen induced IFNγ and IL-4 production, and may downregulate IFNγ synthesis without inhibiting antigen dependent proliferation.     

Peripheral blood extrathymic CD4(+)CD8(+) T cells with high cytotoxic activity are from the same lineage as CD4(+)CD8(-) T cells in cynomolgus monkeys

We have previously reported that CD4/CD8 double-positive (DP) T cells with the resting memory phenotype are present in the periphery of healthy cynomolgus monkeys. In the present study, we performed functional studies on the T cells. The expression of CD4 and CD8 on DP, CD4 single-positive (SP) or CD8 SP T cells was stable in cultures with either mitogen or anti-CD3 antibody stimulation. In spite of lacking CD28 expression, DP T cells showed similar proliferative ability and apoptosis sensitivity to CD4 SP and CD8 SP T cells. DP T cells showed both helper and cytotoxic activities. Although the helper activity of DP T cells was lower than that of CD4 SP T cells, cytotoxic activity was comparable to that of CD8 SP T cells. Fresh DP T cells killed target cells mainly by the perforin-granzyme pathway. In addition, fresh DP T cells expressed a high level of mRNA for IFN-gamma and produced a high level of IFN-gamma when they were activated by anti-CD3 antibody ligation. On the other hand, several expanded DP T cell clones shared TCR V(beta) with expanded CD4 SP T cell clones, strongly suggesting that those two corresponding clones with DP and CD4 SP phenotypes might be derived from the same ancestor T cell. These results showed that the DP T cells are a novel T cell subset with functions overlapping with those of CD4 SP and CD8 SP T cells, and that they might play protective and regulatory roles in secondary immune response in cynomolgus monkeys.     

Long-term in vivo depletion of functional CD4+ T lymphocytes from calves requires both thymectomy and anti-CD4 monoclonal antibody treatment

In vivo depletion of lymphocyte subsets is a direct approach used for dissection of the mechanisms of protective immunity. Long-term in vivo depletion of bovine T lymphocyte subpopulations with monoclonal antibody (mAb) treatment alone has been difficult to achieve. The objective of this study was to determine whether both thymectomy and anti-CD4 mAb treatment would optimize long-term in vivo depletion of functional bovine CD4+ T lymphocytes. Calves were thymectomized and treated with high doses of anti-CD4 mAb (approximately 5 mg/kg) over 4 days followed by subsequent lower doses (approximately 0.3 mg/kg) administered twice weekly for an additional 7 weeks. Depletion of CD4+ T lymphocytes from blood, spleen and peripheral lymph nodes was significantly improved in thymectomized calves compared to thymus-intact anti-CD4 mAb-treated calves. Significant differences in percentages of CD4+ T lymphocytes between thymectomized and thymus-intact calves were sustained for the duration of the 8-week study. Depletion of CD4+ T lymphocytes from thymectomized calves resulted in complete abrogation of lymphoproliferative responses to ovalbumin. In addition, thymectomized calves treated with anti-CD4 mAb had significantly reduced immunoglobulin G1 and no detectable immunoglobulin G2 ovalbumin-specific antibody responses compared to thymus-intact anti-CD4 mAb-treated calves. The results of this study demonstrate that both thymectomy and treatment with anti-CD4 mAb are required for long-term in vivo depletion of functional bovine CD4+ T lymphocytes.     

人类CD8+记忆T细胞体外扩增方法的研究

 目的： 研究体外扩增人类CD8+记忆T细胞的新方法,为抗病毒与抗肿瘤的过继性免疫治疗提供新的手段。方法：将anti-CD3抗体、anti-CD28抗体、CD70、白细胞介素（IL）-2、IL-7和IL-15进行排列组合,设计出63种刺激方式,对体外分离得到的正常人外周血CD8+ T细胞进行体外扩增;培养14 d后进行细胞计数,并检测CD8+ T细胞的纯度以及CD8+中枢记忆T细胞（TCM）和CD8+效应记忆T细胞（TEM）所占的比例,进而计算出CD8+ T细胞、CD8+ TCM和CD8+ TEM的体外扩增倍数,从而确定理想的刺激方法。结果：体外扩增CD8+ T细胞、CD8+ TCM和CD8+ TEM的理想刺激方式均为anti-CD3抗体、IL-2和IL-7三者的组合;该刺激方式使3种细胞在培养14 d后分别扩增了13.19、13.28和15.27倍。结论：Anti-CD3抗体、IL-2和IL-7三者的组合,是刺激人类CD8+记忆T细胞体外扩增的相对理想方法。     

CTLA-4 x Ig converts naive CD4+CD25- T cells into CD4+CD25+ regulatory T cells

CTLA-4 x Ig was originally designed as an immunosuppressive agent capable of interfering with the co-stimulation of T cells. In the present study, we demonstrate that CTLA-4 x Ig, in combination with TCR ligation, has the additional capacity to convert naive CD4+CD25- T cells into Foxp3+ regulatory T (T(reg)) cells, as well as to expand their numbers. The CD4+CD25+Foxp3+ T(reg) generated by CTLA-4 x Ig treatment in vitro potently suppress effector T cells. Extending this in vivo, we show that systemic administration of CTLA-4 x Ig increases the percentage of CD4+CD25(hi)Foxp3+ cells within mixed lymphocyte reaction-induced murine lymph nodes. Significantly, the in vitro conversion of naive CD4+CD25- T cells into T(reg) cells is antigen-presenting cell (APC) dependent. This finding, together with the further observation that this conversion can also be driven in vitro by an antibody that engages B7-2 ligand, suggests that CTLA-4 x Ig-driven T(reg) induction may be predicated upon active CTLA-4 x Ig to B7-2 signaling within APC, which elicits from them T(reg)-inducing potential. These findings extend CTLA-4 x Ig's functional repertoire, and at the same time, reinforce the concept that T cell anergy and active suppression are not entirely distinct processes and may be linked by some common molecular triggers.     

Immobilized anti-CD3 mAb induces anergy in murine naive and memory CD4+ T cells in vitro

The induction of non-responsiveness in resting murine CD4+ T cells was investigated using immobilized anti-CD3 mAb. Incubation of freshly isolated CD4+ T cells with immobilized anti-CD3 mAb led to apoptosis in 40-60% cells. The surviving cells were profoundly non-responsive to subsequent mitogenic stimulation. The non-responsive state was characterized by a lack of IL-2 production and hyper-responsiveness to added IL-2, but was not explained by further activation-induced cell death. The induction of non-responsiveness was not due to modulation of the TCR-CD3 complex, and required partial activation of the T cells in that it was accompanied by an increase in cell size and was inhibited by addition of cyclosporin A. Finally, analysis of anti-CD3-mediated responses in naive and memory CD4+ T cells, separated on the basis of CD44 expression, showed that both naive and memory T cells have similar sensitivity to immobilized anti-CD3 mAb-induced activation, apoptosis and anergy. These results demonstrate that TCR-CD3 engagement on freshly isolated resting CD4+ naive and memory T cells, In the absence of co-stimulation, as achieved by plastic-immobilized anti-CD3 mAb, induces both anergy and cell death.      

Distinct roles for CD4 and CD8 as co-receptors in T cell receptor signalling

We demonstrate that CD4 and CD8 modify signals induced through the T cell receptor for antigen (TCRαβ) in distinct fashions. Pretreatment of CD4⁺ lymph node T cells with CD4-specific monoclonal antibody results in a tenfold inhibition of DNA synthesis induced by anti-TCRαβ. In contrast, pretreatment of CD8⁺ T cells with CD8-specific mAb has no effect on DNA synthesis subsequently induced through TCRαβ. While inhibiting late activation signals, pretreatment with anti-CD4 does not detectably alter the pattern of anti-TCRαβ-induced tyrosine phosphorylation of cellular proteins, nor subsequent Ca²⁺ mobilization. The distinct biological consequences of anti-CD4 and anti-CD8 pretreatment correlate with the differential association of their respective ligands with the cellular protein tyrosine kinase, p56^lck. While both T cell lineages contain similar levels of cellular p56^lck, tenfold more is associated with CD4 than with CD8. This difference is associated with the differential effects of pretreatment with anti-CD4 and anti-CD8 on the distribution and activity of p56^lck. Further, antibody-mediated aggregation of TCRαβ on CD4⁺ T cells induces the appearance of a p56^lck species with decreased mobility in sodium dodecylsulfate-polyacrylamide gel electrophoresis. This effect is observed in CD4⁺ T cells exclusively and involves the fraction of p56^lck which is not associated with CD4. The results presented here demonstrate that the signalling elements which couple the antigen receptor to second messenger-generating systems are under distinct physical and/or functional constraints in the two T cell lineages.     

The number of human peripheral blood CD4+ CD25high regulatory T cells increases with age

Ageing is associated with evidence of immune deficiency and dysregulation. Key changes in the immune system with ageing include a progressive reduction in naive T cell output associated with thymic involution and peripheral expansion of oligoclonal memory T cells. These features are associated with evidence of impaired immune responsiveness both in vitro and in vivo, termed immune senescence. CD4+ CD25+ T cells have recently been recognized as mediators of peripheral immune regulation and play a role in the control of autoimmune and pathogen-specific immune responses. The significance of CD4+ CD25+ regulatory T cells in the context of immunosenescence is not known. We have investigated the number, phenotype and function of CD4+ CD25+ T cells in healthy volunteers over a wide age range. We demonstrate that the number of CD4+ CD25+ and CD4+ CD25high T cells in healthy volunteers increases with age. In both age groups CD4+ CD25+ T cells showed a phenotype consistent with that described for regulatory T cells. Further analysis of CD4+ CD25high T cells in young and elderly donors showed equivalent expression of intracellular CTLA-4 and surface expression of activation markers. In vitro, functional titration assays of CD4+ CD25high T cells demonstrated equivalent regulatory function in both young and elderly donors, with suppression of proliferation and cytokine production in response to polyclonal T cell stimulation. These observations demonstrate an increase in peripheral blood CD4+ CD25high regulatory T cells associated with ageing. The relevance of these expanded cells in relation to the immune senescence seen in the elderly as yet remains unclear.     

A role for CD4+ but not CD8+ T cells in immunity to Schistosoma mansoni induced by 20 krad-irradiated and Ro 11-3128-terminated infections.

The role of CD4+ (L3/T4+) and CD8+ (Lyt-2+) T cells in immunity to Schistosoma mansoni induced by 20 krad-irradiated and Ro 11-terminated infections in mice was investigated directly by in vivo depletion of these subsets with cytotoxic rat monoclonal antibodies (mAb). Effective physical depletion was demonstrated by flow cytometric analysis and immunohistochemical staining. Functional depletion of helper activity following anti-CD4 treatment was indicated by an abrogation of concanavalin A(Con A)-induced colony-stimulating factor (CSF) release, while anti-CD8 treatment had no effect in these assays. Pre-existing S. mansoni-specific antibody levels were unaffected by anti-CD4 and anti-CD8 treatment. In vivo depletion of CD4+ T cells resulted in a dramatic reduction in immunity induced by one (up to 100%) and two (up to 70%) vaccinations with 20 krad-irradiated cercariae and also of resistance induced by Ro 11-attenuated infections (up to 100%). Depletion of CD8+ T cells had no effect on resistance induced by any of the vaccination protocols investigated. A correlation was observed between resistance and T cell-induced, macrophage-mediated killing of schistosomula in vitro, both of which were abrogated following anti-CD4 treatment but were unaffected by CD8+ T-cell depletion. The possible role of CD4+ T cells in vivo and the implications for vaccine development are discussed.     

Split peripheral tolerance: CD40 ligation blocks tolerance induction for CD8 T cells but not for CD4 T cells in response to intestinal antigens

The role of antigen-presenting cells in the balance between immunity and tolerance to intestinal antigens remains poorly understood. In this study, we examined whether CD40 ligation affects the induction of CD4 and CD8 T cell tolerance in response to intestinal antigens. We show that an agonistic anti-CD40 mAb treatment did not block the induction of OVA-specific CD4 T cell tolerance, whereas this approach enabled strong priming of OVA-specific cytotoxic T cells (CTL), preventing CTL tolerance to intestinal antigen. Such CTL priming was independent of CD4 T cell help but required B7 costimulation. Co-administration of anti-CD40 mAb increased the synthesis of IL-2 and the expression of CD25 by CD8 T cells, but neither IL-2 production nor CD25 expression by CD4 T cells was enhanced by anti-CD40 mAb. However, neutralization of TGF-beta together with addition of agonistic anti-CD40 mAb was able to reverse CD4 T cell tolerance. These findings suggest that the induction of tolerance versus immunity against intestinal antigens is determined by the status of the antigen-presenting cells and that signals via CD40 differently regulate the outcome of CD4 and CD8 T cells in vivo.     

A nonhuman primate model for the selective elimination of CD8+ lymphocytes using a mouse-human chimeric monoclonal antibody.

Nonhuman primates provide valuable animal models for human diseases. However, studies assessing the role of cell-mediated immune responses have been difficult to perform in nonhuman primates. We have shown that CD8+ lymphocyte-mediated immunity in rhesus monkeys can be selectively eliminated using the mouse-human chimeric anti-CD8 monoclonal antibody cM-T807. In vitro, this antibody completely blocked antigen-specific expansion of cytotoxic T cells and decreased major histocompatibility complex class I-restricted, antigen-specific lysis of target cells but did not mediate complement-dependent cell lysis. In vivo administration of cM-T807 in rhesus monkeys resulted in near total depletion of CD8+ T cells from the blood and lymph nodes for up to 6 weeks. This depletion was not solely complement-dependent and persisted longer in adults than in juveniles. Preservation of B cell and CD4+ T cell function in monkeys depleted of CD8+ lymphocytes was demonstrated by their ability to develop humoral immune responses to the administered chimeric monoclonal antibody. Furthermore, during CD8+ lymphocyte depletion, monkeys developed delayed-type hypersensitivity reactions comprised only of CD4+ T cells but not CD8+ T cells. This CD8+ lymphocyte depletion model should prove useful in defining the role of cell-mediated immune responses in controlling infectious diseases in nonhuman primates.