他克莫司与环孢菌素A对肝移植受者CD8+CD28-调节性T细胞的不同调节特性

目的 探讨他克莫司(FK506)与环孢菌素A(CsA)对肝移植受者CD8 GD28-调节性T细胞(Treg)及细胞因子IL-10的调节效应.方法 采用荧光标记单克隆抗体结合流式细胞技术分析接受FK506或CsA治疗的肝移植受者外周血CD8 T细胞及共刺激分子CD28的表达情况,采用流式细胞小球微阵列术(CBA)分析血浆中IL-10浓度.以健康志愿者和患终末期肝脏疾病拟进行肝移植者作为对照.结果 疾病对照组CD8 T细胞和CD8 CD28-T细胞/CD8 CD28 T细胞比值(Ratio值)显著低于健康对照组(P＜0.05).FKS06治疗组CD8 T细胞表达显著回升(P＜0.05),且增加的CD8 T细胞主要为CD8 CD28-Treg(P＜0.05).CaA治疗组CD8 T细胞和CD8 CD28-Treg未出现明显回升(P＞0.05).且FKS06治疗组CD8 CD28-Tteg表达显著高于CaA治疗组(P＜0.05).两治疗组血浆IL-10水平均显著高于健康对照组和疾病对照组(P＜0.05),但组间差别无显著性(P＞0.05).结论 FKS06可促进肝移植受者外周血CD8 CIY28-Treg表达并同时促进IL-10的产生从而加强T细胞的免疫耐受,而CaA虽不能有效促进CD8 CD28-Treg的表达但却能促进IL-10的产生.     

ABCB1基因多态性对肝移植后他克莫司用量的影响

背景：钙神经素抑制剂他克莫司被广泛用于移植后预防排斥反应的发生,但其治疗窗狭窄,且药代动力学个体差异较大。 目的：观察ABCB1基因多态性对肝移植患者移植后早期免疫抑制剂他克莫司的用量及C/D比值的影响。 方法：选择2008-01/2010-09-31在昆明市第一人民医院暨昆明医学院附属甘美医院肝胆外科接受原位肝移植患者67例,通过检测67例肝移植受者移植后不同时间他克莫司的血药浓度及其用量,并利用DNA直接测序检测受体ABCB1的基因多态性,分析肝移植后免疫抑制剂他克莫司的用量及其血药浓度与ABCB1基因多态性的关系。 结果与结论：肝移植后他克莫司的口服需药量在个体间存在很大差异,67例肝移植患者中,ABCB1不同位点的基因多态性分布不同,其中仅ABCB1 3435C>T基因多态性与他克莫司用量有关。提示ABCB1的基因多态性可能是患者肝移植后他克莫司药代动力学显著个体差异的重要因素,ABCB1 3435C>T野生型的患者需要更高剂量的他克莫司便可达到目标血药浓度水平,检测ABCB1的基因多态性可以优化肝移植后免疫抑制剂的个体化治疗方案。     

他克莫司用于治疗口腔扁平苔癣的疗效观察

目的：观察他克莫司用于治疗有症状的口腔扁平苔癣(OLP)的疗效。方法选取我院就诊OLP患者40例,局部应用他克莫司后了解用药后病损的症状,病变改善的时间,当前用药情况和副作用。结果40例患者中35例(87.5%)在局部应用他克莫司后症状有所改善,32(80%)例在使用后局部病变几近痊愈,3例(7.5%)认为病变没有变化,1(2.5%)人反应病变增多,1例(2.5%)反应症状加重,10(25%)人报告副作用与之前的报道一致(灼烧感,刺激疼,麻刺感等)。结论局部应用他克莫司对于OLP的治疗有效,大部分患者在用药1个月后感觉症状有所改善,但疗效不持久,停药后容易复发。     

环孢素A和他克莫司对肾移植受者外周血淋巴细胞活性影响的比较

目的：肾移植术后应用Calcineurin抑制剂需常规监测血清药物浓度,然而药物浓度并不能完全反应患者的免疫功能抑制状态,且药物的个体反应性差异较大,本研究旨在通过外周血单核细胞（PBMC）活性检测反应患者对Calcineurin抑制剂的敏感性。方法：采取40例肾移植受者术前抗凝血,Ficoll密度梯度离心法分离PBMC,置于RPMI1640培养基中培养,加入96孔培养板中予刀豆蛋白A刺激,并依次加入不同浓度的环孢素A（CsA）或他克莫司（TAC）,之后加入二苯基四氮唑溴盐（MTT）、二甲亚砜（DMSO）裂解后于波长570nm下测定吸光度。记录受试者肾移植后的急性排斥反应和巨细胞病毒感染等临床事件。结果：①受试者半数PBMC被抑制的药物浓度即为IC50。CsA和TAC的IC50均值分别为162.3ng/ml、0.289ng/ml,TAC对PBMC转化的抑制作用显著强于CsA;②Kendall相关系数分析示CsA的IC50与TAC的IC50之间有显著的相关关系（rk=0.3472,P=0.0082）;③CsA治疗组急性排斥反应发生率显著高于TAC组,而两组患者巨细胞病毒感染发生率差异不明显。结论：TAC抑制人PBMC母细胞转化能力约为CsA的589.1倍,因而TAC治疗的肾移植受者术后急性排斥反应发生率显著较低。将术前淋巴细胞的体外药敏试验与术后治疗性TDM合理结合,是改进个体化免疫抑制方案的举措之一。     

肾移植受者CYP3A5基因多态性对他克莫司血药浓度及疗效的影响*

背景：关于欧美人群中CYP3A5基因与他克莫司血药浓度之间关系已有报道,然而这些研究的数据多来自于移植后1个   月~1年,缺乏移植后早期的资料。 目的：探讨CYP3A 基因多态性与肾移植受者他克莫司血药浓度的关系,分析CYP3A5基因型对肾移植后排斥反应和毒性及不良反应的影响。 方法：按CYP3A5基因多态性将45例采用他克莫司+霉酚酸酯+泼尼松三联免疫抑制方案的肾移植患者分为*1/*1型组(11例)、*1/*3型组(15例)和*3/*3型组(19例),他克莫司初始剂量均为0.15 mg/(kg•d),1周后根据目标浓度调整他克莫司剂量。 结果与结论：术后7 d,1个月,3个月* 3/* 3型组他克莫司血药浓度/剂量比显著高于* 1/*3型组和*1/*1型组(P < 0.05) ;3个月内*1/*1型组急性排斥反应的比例显著高于*1/*3型组和*3/*3型组(P < 0.05)。3个月内*3/*3型组高血糖、神经及肾毒性等不良反应显著高于*1/*1型组。结果可见*1/*1基因型患者在肾移植早期难以达到有效目标血药浓度,使该组3个月内的急性排斥反应发生率明显升高,不合适采用目前他克莫司的初始剂量方案作为早期的抗排斥反应方案;*3/*3基因型患者他克莫司血药浓度明显升高,使3个月内毒性及不良反应发生率也明显升高。因此,根据CYP3A5 基因多态性作为他克莫司个体化用药的依据,既能使* 1 /* 1型患者早期急性排斥反应的发生率下降,又能使* 3 /*3型患者的药物不良反应减少,提高肾移植的临床效果。      

他克莫司和环孢素A对肾移植后患者炎性细胞因子和血脂的影响

背景：环孢素A与他克莫司是肾移植后临床广泛应用的免疫抑制剂。 目的：观察他克莫司和环孢素A对肾移植后炎性细胞因子和血脂的影响。 方法：选择首次接受同种异体肾移植后患者112例,随机分为环孢素A组和他克莫司组,移植后分别给予环孢素A+吗替麦考酚酯+糖皮质激素三联疗法与他克莫司+吗替麦考酚酯+糖皮质激素三联疗法。 结果与结论：他克莫司组的1年人/肾存活率、治疗逆转率高于环孢素A组(P < 0.05),急性排斥反应发生率低于环孢素A组(P < 0.05);移植后1个月及1年的血清白细胞介素2,6,8和血糖水平高于移植前(P < 0.05),低于环孢素A组(P < 0.05),血清白细胞介素4,10低于移植前(P < 0.05),高于环孢素A组(P< 0.05);移植后1个月的血清总胆固醇、三酰甘油和低密度脂蛋白胆固醇高于移植前(P < 0.05),但低于环孢素A组(P < 0.05);移植后1年的血清总胆固醇和低密度脂蛋白胆固醇低于环孢素A组(P < 0.05)。说明他克莫司可通过抑制肾移植后炎性细胞因子释放,改善糖脂代谢等途径降低患者的排斥反应,提高肾移植的存活率。     

他克莫司对肾移植受者外周血NK和NKT细胞比例的影响及临床意义

他克莫司(Tacrolimus)是一种强效免疫抑制剂,现已广泛应用于肾脏、肝脏及心脏移植,有效减低了排异反应的发生,提高了移植受者的存活率.但是他克莫司个体药代动力学差异大,不同个体对其血药浓度的敏感性及耐受性有差异,故单纯依靠血药浓度监测不能有效反映移植受者的免疫状态.因此如何了解移植受者的免疫状态,指导免疫抑制剂的个体化应用,在免疫抑制不足及免疫过度之间寻找平衡,成为困扰移植医生的问题.NK细胞(natrural killer cell)是天然免疫系统的主要效应细胞.     

急性腹泻期间肾移植受者他克莫司血药浓度的变化

背景：长期以来器官移植工作者比较重视吗替麦考酚酯的肠道不良作用,而对他克莫司与腹泻的关系则未引起足够的关注。 目的：观察肾移植受者急性腹泻期间他克莫司的谷浓度变化及对腹泻的治疗效果。 方法：观察90例出现急性腹泻的肾移植受者,免疫抑制方案均为他克莫司+吗替麦考酚酯+泼尼松,检测围腹泻期间内他克莫司血药谷浓度及相关病原学指标,将浓度升高的72例患者中病原学检查阴性的48例患者分为2组,每组24例,一组在治疗过程中只减少他克莫司剂量,另一组同时减少他克莫司及吗替麦考酚酯剂量,观察对腹泻的治疗效果及他克莫司谷浓度升高持续时间。 结果与结论：两种方案对腹泻的治疗效果及他克莫司谷浓度升高持续时间差异均无显著性意义。腹泻是他克莫司浓度异常升高的重要因素,腹泻期间应适当减少他克莫司剂量及增加其血药浓度监测频率,以免增加他克莫司的不良反应;在治疗过程中没有必要同时减少吗替麦考酚酯剂量,以免增加排斥发应发生率。     

他克莫司血药浓度的方法学评价

评价德灵公司均相酶法他克莫司（Tacrolimus）试剂盒检测他克莫司血药浓度的可靠性。用本方法在日立7600分析仪上对其检测他克莫司血药浓度的精密度、线性、回收率、相关性等指标进行评价。本方法的评价表明,在他克莫司质控浓度为5.0ng/mL和15.0ng/mL时,批内变异系数分别为14.17%、10.66%,批间变异系数分别为12.56%、9.92%。平均回收率95.98%,在1.5~30ng/mL范围内,线性良好。与微粒子酶联免疫吸附法测定相关性良好（r=0.93）。结论：该方法操作简便、快速、准确,多通道检测,适用于临床上对肝肾移植患者他克莫司药物谷值浓度的监测。     

他克莫司和西罗莫司对行肝癌肝移植患者Foxp3+调节性T细胞产生及肝癌复发的影响

背景：通过促进调节性T细胞的产生及增强其功能的发挥已成为维持移植物免疫耐受的有效手段。 目的：探讨他克莫司和西罗莫司对行肝移植的肝癌患者Foxp3⁺调节性T细胞产生及肝癌复发的影响。 方法：纳入符合米兰标准的肝癌肝移植患者40例,随机分为西罗莫司组和他克莫司组,每组20例,移植后第2~12个月间每月抽取受试者外周血检测Foxp3⁺调节性T细胞,并行彩超和外周血检测甲胎蛋白,必要时肝穿刺活检观察排斥反应及肿瘤的复发情况。 结果与结论：流式细胞仪检测结果显示,西罗莫司组外周血Foxp3⁺调节性T细胞阳性率明显高于他克莫司组(P < 0.05),移植肝穿刺活检证实西罗莫司组排斥反应与他克莫司组差异无显著性意义(P > 0.05),而移植肝彩超、外周血甲胎蛋白检测及移植肝穿刺活检或手术亦证实在肝癌复发率方面西罗莫司组明显低于他克莫司组(P < 0.05)。说明西罗莫司在肝癌肝移植中对肿瘤复发的抑制作用方面优于他克莫司,且排斥反应较他克莫司并未增加,甚至有更好的免疫耐受效果。     

共刺激信号分子表达异常与自身免疫性疾病的关系

目的 分析类风湿性关节炎（RA）和系统性红斑狼疮（SLE）细胞免疫异常中共刺激活化信号途径的异同点,探讨细胞活化的共刺激信号途径对于RA和SLE发病的意义。方法 采用流式细胞术分析SLE和RA患者T细胞表面共刺激分子CD28、CD152／CTLA-4、CD154／CD40L和ICOS表达情况。结果 ①RA患者CD4^＋T细胞比例明显增加,SLE患者以CD8^＋T细胞增加显著。②SLE患者CD4^＋和CD8^＋T细胞上CD28和CD152的表达增加;RA患者T细胞亚群上CD28分子的表达减少,CD152分子的表达增加。③RA患者CD4^＋T细胞上CD154分子表达增加,CD8^＋T细胞上CD154分子表达减少,T细胞亚群上可诱导共刺激分子（ICOS）的表达无明显变化;SLE患者CD4^＋和CD8^＋T细胞上CD1254或ICOS分子的表达均减少。结论 RA和SLE患者机体的免疫异常中存在着明显的分子信号途径差异。     

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.     

HIV/AIDS患者CD28在外周血CD4+、CD8+ T细胞上的表达变化

目的　研究国内HIV AIDS患者CD2 8在外周血CD4 + 、CD8+ T淋巴细胞上表达的变化 ,并探讨这些变化的临床意义。方法　用流式细胞仪检测 5 1例正常对照、14例HIV感染者和 36例AIDS患者的外周血CD4 + 、CD8+ T淋巴细胞表面的CD2 8分子的表达 ,用bDNA法检测 11例HIV感染者和 18例AIDS患者的血浆病毒载量。结果　CD4 + CD2 8+ T细胞的绝对计数与百分比、CD8+ CD2 8+T细胞的百分比均显示为正常对照组 >HIV感染组 >AIDS组 ;而CD8+ CD2 8+ T细胞的绝对计数显示HIV感染组和对照组显著大于AIDS组 ,HIV感染组与对照组间差异无显著性。CD4 + 、CD2 8+ CD4 + T淋巴细胞计数与血浆病毒载量显著负相关。结论　HIV AIDS患者外周血CD2 8在CD4 + 、CD8+ T淋巴细胞上表达随着病情进展而降低 ,反映了细胞免疫功能随着疾病进展损害逐渐加重 ,是判断病情进展的指标。     

RA患者外周血CD8＋CD28-和CD4＋CD25＋调节性T细胞的表达及疾病活动性指标相关性分析

目的：检测类风湿性关节炎（RA）患者外周血CD8＋CD28-、CD4＋CD25＋调节性T细胞亚群,探讨其与临床活动性指标的关系。方法：采用流式细胞术检测台州医院RA患者外周血CD8＋CD28-、CD4＋CD25＋ T细胞亚群比例,探讨调节性T细胞与RA活动性、类风湿因子（RF）、免疫球蛋白（Ig）、C反应蛋白（CRP）、补体C3、抗CCP抗体、抗核抗体（ANA）、血小板（PLT）及血沉（ESR）的关系。结果：活动期RA患者外周血CD4＋CD25＋调节性T细胞亚群比例显著低于正常对照组（P〈0.01）,但稳定期RA患者与正常对照组结果差异无统计学意义（P〉0.05）。活动期和稳定期RA患者CD8＋CD28-与正常对照组相比较,结果无统计学意义（P〉0.05）;CD4＋CD25＋与CRP密切相关（r=-0.593,P〈0.05）,CD8＋CD28-与ESR相关系数呈弱相关。CD4＋CD25＋和CD8＋CD28-细胞与RF、IGG、C3、ANA、anti-CCP和PLT未见明显相关性。结论：活动期RA患者外周血CD4＋CD25＋ T细胞亚群比例减少,CD4＋CD25＋ T细胞可能与类风湿性关节炎疾病进展有关。     

慢性乙型肝炎患者CD4~+和CD8~+T细胞亚群的研究

目的:比较不同感染状态慢性乙型肝炎(CHB)患者外周血CD4+和CD8+T细胞亚群的差异。方法:收集CHB患者78例,根据感染状态分为乙型肝炎e抗原(HBeAg)阳性且肝功能正常、HBeAg阳性且肝功能异常和HBeAg阴性3组。13例健康志愿者(正常对照组)来自曙光医院体检中心。应用流式细胞术(FCM)检测不同感染状态CHB患者外周血中CD4+CD25+、CD8+CD28-、CD4+CD95+、CD8+CD95+细胞亚群的分布情况,并对各亚群分布情况与HBeAg和HBVD-NA水平的相关性进行分析。结果:与正常对照组相比,HBeAg(+)肝功能正常组的CD4+CD25+/CD4+和CD4+CD95+/CD4+明显升高(P<0.01,P<0.05),3个感染组CD8+CD28-/CD8+值均明显升高(P<0.01);与HBeAg(+)肝功能正常组相比,HBeAg(+)肝功能异常组和HBeAg(-)组的CD4+CD25+/CD4+明显降低(P<0.01),HBeAg(-)组CD8+CD95+/CD8+明显降低(P<0.05),HBeAg(+)肝功能异常组的CD8+CD95+/CD8+明显降低(P<0.01)。CD4+CD25+/CD4+,CD4+CD95+/CD4+与HBVDNA呈正相关(P<0.01,P<0.05),CD8+CD28-/CD8+与HBVDNA和HBeAg均呈正相关(P<0.01)。结论:CHB患者外周血中CD4+CD25+、CD8+CD28-T、CD4+CD95+细胞表达频率增加,可能对慢性乙肝病毒感染过程中的免疫耐受起一定作用。     

Increased cytolytic T lymphocyte activity and decreased B7 responsiveness are associated with CD28 down-regulation on CD8+ T cells from HIV-infected subjects.

The CD28 receptor on CD4+ and CD8+ T cells interacts with B7 molecules on antigen-presenting cells (APC) to generate essential costimulatory signals. The cytolytic potential of CD8+ T cells could be linked to CD28 expression. Since HIV induces dysfunction of both CD4+ and CD8+ T cells, we evaluated CD28 expression and function in both subsets during HIV infection. CD28 expression on CD8+ T cells from HIV+ subjects was strongly reduced in a disease stage-related fashion. CD28- CD8+ T cells preferentially expressed CD57 and CD11b, but lacked CD26 and IL-2R alpha. The CD8+ T cells from the patients showed a significantly reduced proliferative response to co-stimulation with cell-bound anti-CD3 and B7. Nevertheless, when stimulated with plate-fixed anti-CD3, CD8+ T cells from HIV-infected subjects proliferated normally, and normal levels of IL-2R alpha and transferrin-receptor could be induced on CD28- CD8+ T cells from the patients. In addition, stimulation with plate-fixed anti-CD3 induced proliferative responses in highly purified CD28- CD8+ T cells from both HIV- and HIV+ persons. Furthermore, the increased cytotoxic activity of peripheral blood mononuclear cells (PBMC) from HIV+ subjects, measured in an anti-CD3 redirected assay, was predominantly exerted by CD28- CD57+ T cells. CD4+ T cells from the patients showed a slight but significant CD28 down-regulation and were slightly hyporesponsive to B7 co-stimulation. Decrease of CD28 on CD8+ T cells from HIV+ subjects is associated with an impaired response to co-stimulation via B7. CD28- CD8+ T cells from seropositives, however, are not completely inert, since they contain in vivo activated CTL and they can be additionally activated through a B7-independent stimulation.     

Integration of CD28 and CTLA-4 function results in differential responses of T cells to CD80 and CD86

CD80 and CD86 have the capacity to either stimulate or inhibit T cell responses through their receptors CD28 and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4). Blockade of CD80 and CD86 in autoimmune disease settings has revealed distinct outcomes, yet the differential functions of CD80 and CD86 are still unclear. We have studied the ability of individual ligands to stimulate primary responses in human CD4(+) T cells. Our data reveal both quantitative and qualitative differences between the ligands. Both CD80 and CD86 demonstrated the capacity to costimulate T cell proliferation. However, CD80 committed a greater number of T cells to divide with faster kinetics, consistent with it being a superior ligand for CD28. Once cell division had been initiated, all T cells undergoing cell division expressed CTLA-4, irrespective of whether CD80 or CD86 costimulation was used. However, only in the presence of CD80 was evidence of CTLA-4 engagement and inhibitory function observed. Finally, differences between CD80 and CD86 costimulation extended to the T cell phenotype, in particular the levels of CD40 ligand expression.     

The CD28/HLA-DR expressions on CD4+T but not CD8+T cells are significant predictors for progression to AIDS

To investigate the changes of CD28 and HLA-DR molecules on CD4+ and CD8+ T cells during HIV infection, we classified 130 HIV-infected Koreans into four groups by the CD4 level as follows: group I (> or = 500 cells/mm3), group II (201-499 cells/mm3), group III (51-200 cells/mm3), and group IV (< or = 50 cells/mm3). In CD4+ T cells, the proportion of CD28 expression decreased significantly with the CD4 level while the proportion of HLA-DR expression increased gradually. In particular, the changes of HLA-DR expressions on CD4+ T cells were parallel to the loss of CD28 molecules from stage III to IV. However, the CD28 expression on CD8+ T cells decreased dramatically in the early stage of HIV infection, and the sum and pattern of CD28 and HLA-DR expressions on CD8+ T cells was stable after the first stage. Even though CD28 down-regulation on CD8+ T cells was very severe from the early stage of HIV infection, it might not influence the survival time of HIV-infected Koreans. The sum of the CD28+ subsets and HLA-DR subsets in each T cell was stable in all stages of disease progression. The sums of the CD28+ subsets and HLA-DR+ subsets in CD4+ T and CD8+ T cells were constant as approximately 100% and 55-60% of each T cell. These results suggested that the changes of CD28/HLA-DR expressions on CD4+ T cells were more predictable than those on CD8+ T cells in the evaluation of the disease progression during HIV-infected periods. However, we need further studies to understand why the sum of two molecules in each T cell are constant.     

Secondary but not primary T cell responses are enhanced in CTLA-4-deficient CD8+ T cells

Negative as well as positive co-stimulation appears to play an important role in controlling T cell activation. CTLA-4 has been proposed to negatively regulate T cell responses. CTLA-4-deficient mice develop a lymphoproliferative disorder, initiated by the activation and expansion of CD4⁺ T cells. To assess the function of CTLA-4 on CD8⁺ T cells, CTLA-4^−/- animals were crossed to an MHC class I-restricted 2C TCR transgenic mouse line. We demonstrate that although the primary T cell responses were similar, the CTLA-4-deficient 2C TCR⁺ CD8⁺ T cells displayed a greater proliferative response upon secondary stimulation than the 2C TCR⁺ CD8⁺ T cells from CTLA-4 wild-type mice. These results suggest that CTLA-4 regulates antigen-specific memory CD8⁺ T cell responses.