人类免疫缺陷病毒感染细胞毒性T细胞逃逸突变的研究进展

人类免疫缺陷病毒(HIV)-1感染者体内活化的细胞毒性T细胞(CTL)反应不足以清除病毒,这是由于HIV-1在HLA限制的CTL压力下经常发生逃逸突变.但是,部分CTL逃逸突变会造成HIV病毒适应性的下降.近年来,人们对HIV-1感染中CTL逃逸突变的特征以及不同位点的逃逸突变在疾病进程中的作用进行了比较深入的研究,因而探讨CTL压力下HIV逃逸突变的规律有助于了解HIV-1自然感染中的免疫保护机制,并为开发有效的HIV疫苗提供依据.     

人类免疫缺陷病毒感染细胞毒性T细胞逃逸突变的研究进展

人类免疫缺陷病毒(HIV)-1感染者体内活化的细胞毒性T细胞(CTL)反应不足以清除病毒,这是由于HIV-1在HLA限制的CTL压力下经常发生逃逸突变.但是,部分CTL逃逸突变会造成HIV病毒适应性的下降.近年来,人们对HIV-1感染中CTL逃逸突变的特征以及不同位点的逃逸突变在疾病进程中的作用进行了比较深入的研究,因而探讨CTL压力下HIV逃逸突变的规律有助于了解HIV-1自然感染中的免疫保护机制,并为开发有效的HIV疫苗提供依据.     

HLA多态性及HIV进化与疾病关联的研究进展

HIV-1的高度多样性除受病毒自身的复制特征影响外,HLA—I类分子介导CTL免疫反应的选择压力造成的突变对HIV-1多样性的产生有一定作用。近期许多研究显示HLA-I类等位基因、单体型和超型与HIV-1多样性及疾病进程的关系,HIV-1多样性和编码HLA—I类分子基因的多态性是平行的,本文就HLA多态性与HIV多样性及疾病关联的研究进展进行综述。     

HIV/AIDS患者特异性细胞毒性T细胞功能的研究

目的 了解中国HIV／AIDS患者HIV特异性细胞毒性T细胞(CTL)功能。方法 将覆盖HIV-1 P15、P17和P24 Gag全长的94个重叠多肽作为抗原，用IFN-γ ELISPOT方法检测HIV／AIDS患者HIV-1特异性CTL功能。结果 HIV-1抗原多肽P17-15、P17-16、P24-7、P17-8，P24-28最易被HIV／AIDS患者特异性CTL识别。HIV感染者识别HIV-1多肽的数量和强度均高于AIDS患者。结论 我国HTV／AIDS患者体内存在识别不同HIV-1 Gag多肽的特异性CTL，且HIV特异性CTL功能与疾病进展相关。     

HLA多态性及HIV进化与疾病关联的研究进展

HIV-1的高度多样性除受病毒自身的复制特征影响外,HLA-I类分子介导CTL免疫反应的选择压力造成的突变对HIV-1多样性的产生有一定作用。近期许多研究显示HLA-I类等位基因、单体型和超型与HIV-1多样性及疾病进程的关系,HIV-1多样性和编码HLA-I类分子基因的多态性是平行的,本文就HLA多态性与HIV多样性及疾病关联的研究进展进行综述。     

人类滤泡树突状细胞增强HIV的感染

目的：研究人类滤泡树突状细胞（follicular dendritic cell,FDC)能否增强艾滋病病毒的感染,并探讨其可能机制。方法：提取人扁桃体滤泡树突状细胞,与感染HIV－1ⅢB的外周血淋巴细胞或扁桃体T淋巴细胞共培养,测定HIV P24含量,HIV－1env DNA及HIV－1nef RNA。结果：FDC与感染HIV病毒的异体淋巴细胞共培养,P24抗原含量高于对照组6－7倍（P＜0．01）。PCR结果显示FDC组HIV－1 env基因扩增条带密度高于对照组。FDC与感染HIV病毒的自体T淋巴细胞共培养,P24抗原高于对照组10倍以上（P＜0．01）。FDC与感染HIV病毒的异体淋巴细胞共培养4或6h,可增加2－3倍的HIV－1 nef RNA的表达（P＜0．01）。结论：人类滤泡树突状细胞能够增强HIV在淋巴细胞中的感染,其相关机制为FDC可促进HIV在淋巴细胞内的复制。     

HIV-1Nef蛋白变异对艾滋病疾病进展影响机制的研究

人类免疫缺陷病毒（HIV-1、HIV-2）和猴免疫缺陷病毒（SIV）的Nef基因与病毒致病性有关，在疾病进展到AIDS期的过程中发挥重要作用。Nef可通过提高病毒颗粒感染性、激活CD4淋巴细胞及防止受感染细胞凋亡等多种途径促进HIV复制；Nef表位缺失可形成HIV免疫逃逸株，影响机体针对HIV病毒的免疫反应。Nef基因对HIV感染后AIDS疾病进展的影响机制至今仍无定论，本文就近年来此方面的研究，作一简要回顾。     

HIV-1高暴露持续血清阴性者对Nef、Gag肽段库的特异性CTL应答的研究

目的 研究中国HIV-1高暴露持续血清阴性（highly exposed persistently seronegative,HEPS）者的Nef、Gag特异性细胞毒性T淋巴细胞（cytotoxic T lymphocyte,CTL）应答特点,探讨HIV-1特异性CTL应答在这类特殊人群中抵抗感染的作用机制.方法 选取10例HIV-1高暴露持续血清阴性者,11例经性接触感染且从未接受抗病毒治疗的HIV/AIDS患者及4例未经暴露的健康志愿者.以覆盖HIV-1 gag全长和部分nef的14个肽段库为刺激原,应用IFN-γ ELISPOT法测定3组人群的特异性CTL应答,并对3组的应答强度、宽度以及对肽段库识别比例进行比较.结果 50%（5/10）的HEPS,100%（11/11）的HIV/AIDS患者均存在Nef及Gag特异性CTL应答,而4例健康对照均为阴性.存在应答的HEPS者对14个肽段库的平均应答强度和宽度分别是HIV/AIDS患者的4.3%和37.7%.在HEPS者中主要识别的肽段库均为HIV/AIDS患者中识别比例相对较低的肽段库.结论 与HIV/AIDS患者相比,HEPS者中的HIV-1特异性CTL应答存在着不同的特点和规律,可能在保护机体免于HIV-1感染中发挥着重要作用.     

CD8^＋T淋巴细胞非细胞毒性抗HIV作用研究进展

细胞免疫在抗病毒感染中发挥着至关重要的作用。人类免疫缺陷病毒(HIV)感染所引起的细胞免疫反应是由CD8^ T淋巴细胞的亚群细胞毒性T细胞(CTL)介导的先天免疫。CIIs一方面通过细胞毒性作用杀伤感染的细胞，另一方面分泌可溶性抗病毒因子(CAF)发挥直接的抗病毒作用，因此成为HIV感染中细胞免疫的重要组成部分。本就HIV感染这一疾病过程中CD8^ T淋巴细胞所发挥的非细胞毒性抗病毒效应作一概述。     

HIV-1B’/C重组病毒感染者Vif、Vpr和Vpu特异性细胞免疫应答研究

目的 探讨我国HIV-1 B'/C重组病毒感染者针对HIV-1调节蛋白的细胞免疫反应特征及其与病毒复制控制的关系.方法 以覆盖HIV-1 C亚型Vpr、Vpu和Vif蛋白全长的重叠肽段作为刺激抗原,利用ELISPOT方法检测新疆HIV-1 B'/C重组病毒感染者的特异性细胞免疫反应.使用SIGMAPLOT 10.0和SIGMASTAT 3.5进行统计分析,用双尾t检验比较组间差异,用Spearmam秩相关分析免疫反应与病毒载量及CD4细胞计数的关系.结果 在检测的60名HIV-1 B'/C重组病毒感染者中,能够识别Vif、Vpr和Vpu蛋白产生CIL应答者分别为68%、52%和8%,Vpr和Vif蛋白存在多个强CIL反应的免疫优势区域.研究中还发现针对Vpr、Vif和Vpu蛋白的CTL反应强度和广度与HIV感染者的病毒载量及CD4细胞数量无明显的相关性.结论 HIV-1 Vpr和Vif蛋白包含多个可被机体免疫系统特异性T细胞识别的免疫优势区域.对这些免疫优势区所包含的CIL表位进行鉴定并探讨其在自然感染过程中的作用,对新一代的HIV疫苗设计有重要的参考意义.     

Selective pressure exerted by immunodominant HIV-1-specific cytotoxic T lymphocyte responses during primary infection drives genetic variation restricted to the cognate epitope

HIV-specific cytotoxic T lymphocytes (CTL) play a central role in the control of HIV-1 replication during primary infection. It has been hypothesized that the appearance of CTL escape mutants represents an important mechanism by which HIV-1 escapes the host cell-mediated immune response. However, evidences for a direct relationship between CTL responses and emergence of CTL escape mutants are still limited. Here we report detailed longitudinal analysis of DNA sequence variation performed over the entire HIV-1 envelope in two subjects during primary HIV infection. Estimates of the frequencies of synonymous (ds) and non-synonymous (dN) nucleotide substitutions were used to identify regions of the HIV-1 envelope which were subjected to significant levels of selective pressure. These regions were shown to comprise defined epitopes recognized by CTL. Furthermore, dN mutation fixed within these epitopes effectively abolished recognition by the host CTL response. These results provide compelling evidence that the CTL epitope mutations directly resulted from the selective pressure exerted by the virus-specific cytotoxic response.     

Vaccination with CTL epitopes that escape: an alternative approach to HIV vaccine development?

This article describes a novel approach to HIV vaccine design that is, as yet, unproven and still in preliminary development. In rhesus macaques infected with simian immunodeficiency virus (SIV), we have identified particular cellular immune responses that select for viral variants during primary infection. We speculate that the detection of viral variants with altered amino acids in CTL epitopes implies the successful clearance of cells harboring wild-type virus. Here, we present our rationale suggesting why such potent early CTL responses that exert an antiviral effect may be particularly attractive targets for induction by candidate vaccines. Conventional wisdom suggests that regions of the virus that are structurally and functionally important will generally be well-conserved both among clades and within an infected host. Amino acid replacements within these well-conserved regions should be difficult for the virus to accommodate. Therefore, these regions are traditionally considered ideal targets for vaccine induced immune responses because they are refractory to CTL escape mutations. Many examples of these regions have been identified in both HIV-1 and SIV(mac) (J. Immunol. 162 (1999) 3727; J. Virol. 67 (1993) 438) and have been included in candidate vaccine formulations. Human clinical trials testing these vaccines are currently underway. Our proposed method of vaccination with CTL epitopes that escape explores an alternative hypothesis. Rather than engendering responses to regions of the virus that do not escape, we reason that vaccination needs to accelerate the development of the initial immune responses that effectively select for amino acid variants during acute infection. By examining CTL escape during the acute phase, we will identify CTL responses that the virus cannot tolerate and incorporate these responses into vaccines.     

Dendritic cells transfected with the nef genes of HIV-1 primary isolates specifically activate cytotoxic T lymphocytes from seropositive subjects

The HIV-1 Nef protein down-modulates surface expression of MHC class I proteins. Primary infected T lymphocytes thus escape lysis by cytotoxic T lymphocytes (CTL). In contrast, during HIV-1 infection there are strong CTL responses to several HIV proteins, and there is mounting evidence that CTL are critical for controlling the virus. The present study was carried out to assess Nef protein-cell interaction as it occurs in naturally infected antigen-presenting cells. To evaluate the presentation of peptides derived from viral antigen to CTL, we transfected nef genes obtained from peripheral blood mononuclear cells of HIV-1-seropositive subjects into dendritic cells isolated from monocytes of healthy donors. We demonstrate that expression and subsequent processing of Nef by transfected dendritic cells did not alter the presentation of an immunodominant epitope of Nef to CTL of HIV ⁺ subjects. However, mutations in nef gene sequences from primary isolates may abolish this presentation by a mechanism that probably interferes with protein processing.     

Structural constraints on viral escape from HIV- and SIV-specific cytotoxic T-lymphocytes

Cytotoxic T lymphocytes (CTL) play a central role in controlling lentiviral infections in both humans and monkeys. While they contain the spread of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV), CTL are not capable of fully eradicating virus following infection. Ongoing viral replication can therefore lead to the accumulation of viral mutations within CTL epitopes that can undermine cellular immune control of virus. Here we review the importance of CTL in controlling HIV/SIV infection and how immunologic pressure exerted by effector T cells selects for viral variants that escape CTL recognition. We review two examples of viral escape from CTL at highly conserved epitopes that illustrate the extraordinary capacity of lentiviruses to adapt to their immunologic environment despite structural constraints on the ability of the virus to accommodate mutations.     

Broadly cross-reactive HIV-specific cytotoxic T-lymphocytes in highly-exposed persistently seronegative donors

HIV-specific cytotoxic T-lymphocytes (CTL) are believed to play a key part in the control of virus levels throughout HIV infection. An important goal of a potential prophylactic vaccine against HIV is therefore to elicit a strong CTL response which is broadly cross-reactive against a diverse range of HIV strains. We have detected HIV-specific CTL in two groups of highly-exposed but persistently seronegative female sex workers in Africa which show extensive cross-reactivity between different viral sequences. In a small group of women exposed to both HIV-1 and HIV-2 in Gambia, studied over 4 years, we have repeatedly detected HLA-B35-restricted CTL which exhibit cross-reactivity between the HIV-1 and HIV-2 sequences of the CTL epitopes. In women with particularly intense exposure to what are likely to be multiple clades of HIV-1 in Nairobi Kenya, we have detected CTL directed towards epitopes conserved between HIV-1 clades. In neither group is there any evidence that variation in CCR5 sequence or expression is responsible for their apparent resistance to HIV infection. However, in seropositive donors from Oxford infected with African strains of HIV-1, we have defined CTL responses which are specific for particular clades and have mapped some unique A clade CTL epitopes, together with others to highly-conserved regions of the virus. Further information about the extent of cross-reactive CTL immunity will be important for future vaccine design and evaluation.     

Role of cytotoxic T-lymphocyte-mediated immune selection in a dominant human leukocyte antigen-B8-restricted cytotoxic T-lymphocyte epitope in Nef

OBJECTIVES: To study the role of cytotoxic T-lymphocyte (CTL) escape for disease progression in HIV-1 infection, we analyzed the CTL response to the dominant human leukocyte antigen (HLA)-B8-restricted CTL epitope FLKEKGGL (FL8) in HIV-1 Nef. METHODS: HIV-1 nef genes derived from 56 patients were analyzed by polymerase chain reaction (PCR)-based sequencing. T-cell responses against FL8 and mutated FL8 variants were detected by gamma-interferon (gamma-IFN) enzyme linked immunospot (ELISPOT) assay. RESULTS: The longitudinal analysis of an HIV-1-infected patient with good control of HIV-1 viremia for several years demonstrated an association of rising viremia with the emergence of CTL escape mutations within the HLA-B8-restricted Nef-specific CTL epitopes FLKEKGGL and WPAIRERM. Analysis of nef genes in 56 HIV-1-infected patients demonstrated a significant correlation between the occurrence of mutations in the FL8 epitope and the presence of HLA-B8. The mutations within the FL8 epitope could decrease CTL recognition; however, there was strong variation regarding the recognition of viral variants between individual donors. The presence of FL8 mutations was associated with lower CD4 cell counts and higher viral loads. CONCLUSIONS: Our data demonstrate a strong CTL selection pressure on the immunodominant HLA-B8-restricted CTL epitope FL8 in HIV-1 Nef. The association of FL8 mutations with lower CD4 cell counts indicates an important role of CTL escape mutations for disease progression.     

Natural analogue peptides of an HIV-1 GP120 T-helper epitope antagonize response of GP120-specific human CD4 T-cell clones

Neutralizing antibodies and specific cytotoxic T lymphocytes (CTL) may contribute to controlling viral spread, and ideally, to virus clearance in HIV infection. Both effector mechanisms depend on specific CD4 T-helper (Th) cells. Nevertheless, HIV hypervariability facilitates appearance of escape mutants for antibodies and for CTL responses. Here we also show that natural mutations (i.e., from sequences of different HIV strains) in an immunodominant Th epitope recognized by human CD4 clones specific for the envelope glycoprotein gp120 escape CD4 T-cell recognition. Furthermore, several natural analogue peptides exert an antagonistic function by inhibiting proliferative response of T cells specific to gp120 with a wild-type sequence. If similar events occur in vivo, they may represent an additional escape mechanism for HIV. In fact, antagonism for CD4 Th response may occur during superinfection with a different strain, or with the appearance of a variant carrying a mutated antagonistic sequence. In both cases, impaired Th cell function could lead to reduced immune control of HIV infection by interfering with CTL and antibody response.     

Co-evolution of human immunodeficiency virus and cytotoxic T-lymphocyte responses

After more than a decade of intensive research, the precise of human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) in determining the course of the infection remains open to argument. It is established that HIV-specific CTL appear early in the infection and are temporally associated with the clearance of culturable virus from the blood; that CTL are generally detectable at very high levels throughout the asymptomatic phase and decline at the time of progression to AIDS; and that CTL-mediated killing is sufficiently fast to prevent production of new virus by HIV-infected cells. However, viral turnover is throughout the course of the infection, and –infected individuals progress inexorably to disease in spite of the CTL response. In order Co address the question of whether CTL play an active part in influencing the course of HIV infection, one approach has been to seek evidence for CTL-mediated selection pressure on the virus. Several clear examples of CTL epitope-specific mutations selected to fixation are described. We argue that CTL escape is a common event which occurs at all stages of the Infection. Detailed longitudinal studies are required to detect CTL escape and to nd the complexities contributed by factors SUC h as a polyvalent CTL response and the presence of epitope variants which antagonise the CTL response. In conclusion, there is strong evidence of a dynamic process in which CTL impose important selection constraints upon HIV fro m which the virus attempts to escape; ultimately, at the time of disease progression, the tenuous control of CTL over the virus is lost.