Allogeneic cell therapy in murine B-cell leukemia (BCL1): 1. Alloimmune-mediated graft-versus-leukemia (GVL) effects induced by unmodified and in vitro rIL-2-activated bone marrow and lymphocytes from different lymphoid compartments

We have investigated the efficacy of graft-versus-leukemia (GVL) effects induced by cells obtained from different syngeneic and allogeneic lymphoid compartments, by comparing the response to cell therapy with syngeneic (BALB/c x C57BL/6)F1 (H-2d/b) (F1) or allogeneic C57BL/6 (H-2b) (B6) lymphocytes in F1 recipients inoculated with B-cell leukemia (BCL1) of BALB/c (H-2d) origin. Eradication of BCL1 was confirmed in vivo by adoptive transfer of 10(5) spleen cells obtained from treated mice into syngeneic BALB/c recipients. Immunotherapy induced by allogeneic but not syngeneic spleen and lymph node lymphocytes was therapeutically more effective than thymocytes and bone marrow cells (BMC). Alloreactive cells could be further activated in vivo with recombinant human interleukin-2 (rIL-2). The GVL effect of allogeneic lymphocytes was cell-dose-dependent; a heavy leukemia load was more efficiently eradicated after three doses than after a single dose of allogeneic spleen cells (100% versus 23% disease-free survival rate of secondary adoptive recipients respectively). The GVL effect induced by allogeneic spleen cells was preserved after ex vivo exposure of cells to 250 cGy, but not 500 cGy or more. Interestingly, GVL was preserved following administration of ex vivo irradiated (500 cGy) spleen cells when rIL-2 was administered in vivo (p < 0.05). Syngeneic effector cells did not induce GVL, regardless of in vitro and in vivo activation with rIL-2. Our data suggest that allogeneic but not syngeneic (in analogy to autologous) cell therapy may be an effective tool to control residual leukemia following high-dose chemo-radiotherapy. The feasibility of augmenting GVL by successive doses of activated allogeneic donor lymphocytes, partly inactivated in vitro by low-dose ionizing irradiation to prevent severe graft-versus-host disease (GVHD), may lead to safer therapeutic approaches that can be used to reduce the incidence of relapse while avoiding the risk of uncontrolled GVHD.     

Genetic engineering of murine CD8+ and CD4+ T cells for preclinical adoptive immunotherapy studies

T-cell receptor (TCR) gene therapy enables for the rapid creation of antigen-specific T cells from mice of any strain and represents a valuable tool for preclinical immunotherapy studies. Here, we describe the superiority of γ-retroviral vectors compared with lentiviral vectors for transduction of murine T cells and surprisingly illustrate robust gene-transfer into phenotypically naive/memory-stem cell like (TN/TSCM; CD62L(hi)/CD44(low)) and central memory (TCM; CD62L(hi)/CD44(hi)) CD8+ T cells using murine stem cell-based γ-retroviral vectors (MSGV1). We created MSGV1 vectors for a major histocompatibility complex-class I-restricted TCR specific for the melanocyte-differentiation antigen, glycoprotein 100 (MSGV1-pmel-1), and a major histocompatibility complex-class II-restricted TCR specific for tyrosinase-related protein-1 (MSGV1-TRP-1), and found that robust gene expression required codon optimization of TCR sequences for the pmel-1 TCR. To test for functionality, we adoptively transferred TCR-engineered T cells into mice bearing B16 melanomas and observed delayed growth of established tumors with pmel-1 TCR engineered CD8+ T cells and significant tumor regression with TRP-1 TCR transduced CD4 T cells. We simultaneously created lentiviral vectors encoding the pmel-1 TCR, but found that these vectors mediated low TCR expression in murine T cells, but robust gene expression in other murine and human cell lines. These results indicate that preclinical murine models of adoptive immunotherapies are more practical using γ-retroviral rather than lentiviral vectors.     

CD8+ T cell tolerance and cancer immunotherapy

To provide protection against all foreign pathogens one can possibly encounter during their lifetime, the T cell repertoire has to be as diverse as possible. At the same time, it is desirable that the T cell repertoire remains unresponsive towards healthy tissues. To realize this self/nonself discriminatory property, T cells undergo tightly controlled selection processes during maturation in the thymus. The key parameter determining the outcome of these selection processes is the avidity of the T cells for self-MHC/self-peptide complexes expressed in the thymus; low avidity interactions result in positive selection, whereas high avidity interactions lead to negative selection. Despite the selection processes, self-tolerance is far from absolute. In many cases, this is due to the presence of self-antigen in the thymus at a level that is too low to induce thymic deletion. In addition, T cells with a low avidity for ubiquitously expressed self-antigens can escape clonal deletion and enter the periphery. A thorough understanding of the self-specific T cell repertoire is important because many potential targets for cancer immunotherapy are self-proteins. In this review, the authors discuss the impact of self-antigen expression on the CD8+ T cell repertoire. An overview of the fate and functional capacities of self-specific T cells with specificity for tissue-restricted self-antigens and for ubiquitously expressed self-antigens is provided. Furthermore, the authors discuss the influence of negative selection on the antitumor reactivity of the mature T cell repertoire.     

Differentiation of Ia-reactive CD8+ murine T cells does not require Ia engagement. Implications for the role of CD4 and CD8 accessory molecules in T cell differentiation

The present study was undertaken to assess the Ia differentiation requirements of CD8+ class II-allospecific CTL, whose CD8+ phenotype is apparently "discordant" with their MHC class II reactivity. To do so, we compared the effect of in vivo anti-Ia blockade on the differentiation of Ia-reactive CD8+ CTL with its effect on the differentiation of CD4+ T cells. We found that anti-Ia blockade did not detectably interfere with the differentiation of CD8+ Ia-reactive CTL, even though it arrested the differentiation of CD4+ T cells. Thus, the differentiation of CD4+ T cells is strictly dependent upon Ia engagement, whereas the differentiation of CD8+ T cells, even those with reactivity against MHC class II alloantigens, does not require Ia engagement. These results support the concept that Ia-reactive CD8+ T cells are conventional CD8+ CTL, probably selected by self-class I MHC molecules during differentiation, whose receptors fortuitously crossreact on MHC class II alloantigens. Taken together, the present data indicate an intimate relationship between CD4/CD8 expression with MHC class specificity during T cell differentiation and selection. We suggest that an active triggering role for CD4 and CD8 accessory molecules in T cell differentiation is best able to explain these observations.     

Regulatory CD4+CD25+ T cells restrict memory CD8+ T cell responses

CD4+ T cell help is important for the generation of CD8+ T cell responses. We used depleting anti-CD4 mAb to analyze the role of CD4+ T cells for memory CD8+ T cell responses after secondary infection of mice with the intracellular bacterium Listeria monocytogenes, or after boost immunization by specific peptide or DNA vaccination. Surprisingly, anti-CD4 mAb treatment during secondary CD8+ T cell responses markedly enlarged the population size of antigen-specific CD8+ T cells. After boost immunization with peptide or DNA, this effect was particularly profound, and antigen-specific CD8+ T cell populations were enlarged at least 10-fold. In terms of cytokine production and cytotoxicity, the enlarged CD8+ T cell population consisted of functional effector T cells. In depletion and transfer experiments, the suppressive function could be ascribed to CD4+CD25+ T cells. Our results demonstrate that CD4+ T cells control the CD8+ T cell response in two directions. Initially, they promote the generation of a CD8+ T cell responses and later they restrain the strength of the CD8+ T cell memory response. Down-modulation of CD8+ T cell responses during infection could prevent harmful consequences after eradication of the pathogen.     

CD4+CD25+ T cells regulate virus-specific primary and memory CD8+ T cell responses

Naturally occurring CD4+CD25+ regulatory T cells appear important to prevent activation of autoreactive T cells. This article demonstrates that the magnitude of a CD8+ T cell-mediated immune response to an acute viral infection is also subject to control by CD4+CD25+ T regulatory cells (Treg). Accordingly, if natural Treg were depleted with specific anti-CD25 antibody before infection with HSV, the resultant CD8+ T cell response to the immunodominant peptide SSIEFARL was significantly enhanced. This was shown by several in vitro measures of CD8+ T cell reactivity and by assays that directly determine CD8+ T cell function, such as proliferation and cytotoxicity in vivo. The enhanced responsiveness in CD25-depleted animals was between three- and fourfold with the effect evident both in the acute and memory phases of the immune response. Surprisingly, HSV infection resulted in enhanced Treg function with such cells able to suppress CD8+ T cell responses to both viral and unrelated antigens. Our results are discussed both in term of how viral infection might temporarily diminish immunity to other infectious agents and their application to vaccines. Thus, controlling suppressor effects at the time of vaccination could result in more effective immunity.     

Complementary dendritic cell-activating function of CD8+ and CD4+ T cells: helper role of CD8+ T cells in the development of T helper type 1 responses

Dendritic cells (DCs) activated by CD40L-expressing CD4+ T cells act as mediators of "T helper (Th)" signals for CD8+ T lymphocytes, inducing their cytotoxic function and supporting their long-term activity. Here, we show that the optimal activation of DCs, their ability to produce high levels of bioactive interleukin (IL)-12p70 and to induce Th1-type CD4+ T cells, is supported by the complementary DC-activating signals from both CD4+ and CD8+ T cells. Cord blood- or peripheral blood-isolated naive CD8+ T cells do not express CD40L, but, in contrast to naive CD4+ T cells, they are efficient producers of IFN-gamma at the earliest stages of the interaction with DCs. Naive CD8+ T cells cooperate with CD40L-expressing naive CD4+ T cells in the induction of IL-12p70 in DCs, promoting the development of primary Th1-type CD4+ T cell responses. Moreover, the recognition of major histocompatibility complex class I-presented epitopes by antigen-specific CD8+ T cells results in the TNF-alpha- and IFN-gamma-dependent increase in the activation level of DCs and in the induction of type-1 polarized mature DCs capable of producing high levels of IL-12p70 upon a subsequent CD40 ligation. The ability of class I-restricted CD8+ T cells to coactivate and polarize DCs may support the induction of Th1-type responses against class I-presented epitopes of intracellular pathogens and contact allergens, and may have therapeutical implications in cancer and chronic infections.     

FBL-reactive CD8+ cytotoxic and CD4+ helper T lymphocytes recognize distinct Friend murine leukemia virus-encoded antigens

Immunization of C57BL/6 (B6) mice with FBL, a Friend murine leukemia virus (F-MuLV), induces both tumor-specific cytolytic CD8+ (CTL) and lymphokine-producing CD4+ Th that are effective in adoptive therapy of B6 mice bearing disseminated FBL leukemia. The current study evaluated the F-MuLV antigenic determinants expressed on FBL that are recognized by FBL-reactive CD8+ and CD4+ T cells. To identify the specificity of the FBL-reactive CD8+ CTL, Fisher rat embryo fibroblast (FRE) cells transfected with plasmids encoding F-MuLV gag or envelope (env) gene products plus the class I-restricting element Db were utilized. FBL-reactive CTL recognized FRE target cells transfected with the F-MuLV gag-encoded gene products, but failed to recognize targets expressing F-MuLV env. Attempts to generate env-specific CD8+ CTL by immunization with a recombinant vaccinia virus containing an inserted F-MuLV env gene were unsuccessful, despite the generation of a cytolytic response to vaccinia epitopes, implying that B6 mice fail to generate CD8+ CTL to env determinants. By contrast, CD4+ Th clones recognized FRE target cells transfected with env and not gag genes, and immunization with the recombinant vaccinia virus induced an env-specific CD4+ T cell response. These data show that in a Friend retrovirus-induced tumor model in which tumor rejection can be mediated by either CTL or Th, antigens derived from discrete retroviral proteins are predominantly responsible for activation of each T cell subset.     

NOD鼠体内CD_4~+NKG2D~+T细胞与CD_8~+T细胞间关系

目的探讨NOD鼠体内CD_4~+NKG2D~+T细胞与CD_8~+T细胞间关系。方法动态监测NOD鼠外周血中CD_4~+NKG2D~+T及CD8+NKG2D~+T细胞在不同周龄频率。利用IGRP206-214特异性CTL清除的NOD鼠,对其外周血中CD_4~+NKG2D+/CD_4~+T及CD8+NKG2D+/CD_8~+T细胞频率进行分析。将磁珠分选所得CD_4~+NKG2D~+T细胞分别与经CFSE标记的纯CD_4~+NKG2D-T细胞、CD_8~+T细胞共培养4 d,检测体系中CD_4~+NKG2D-T细胞、CD_8~+T细胞CFSE的荧光强度变化。结果 NOD鼠外周血CD_4~+NKG2D+/CD_4~+T及CD8+NKG2D+/CD_8~+T细胞频率均随其1型糖尿病疾病进程发展逐渐升高,且二者之间呈正相关。IGRP206-214特异性CTL清除的NOD鼠,外周血中CD_4~+NKG2D+/CD_4~+T细胞频率随CD8+NKG2D+/CD_8~+T细胞频率降低显著下降。与单独培养的CD_4~+NKG2D-T细胞相比,加入CD_4~+NKG2D~+T细胞的培养体系中,CD_4~+NKG2D-T细胞增殖加快。但CD_4~+NKG2D~+T细胞对CD_8~+T增殖作用不明显。结论 NOD鼠体内存在着一群与1型糖尿病疾病进程正相关的CD_4~+NKG2D~+T细胞,且该群细胞极有可能是通过直接作用于CD_4~+NKG2D-T细胞而间接对CD_8~+T细胞产生作用。     

CD4+CD25+ T regulatory cells, immunotherapy of cancer, and interleukin-2

CD4+CD25+ T regulatory (Treg) cells control immunologic tolerance to self-antigens and play a role in suppressing antitumor immune responses, but the mechanism of suppression in vivo remains uncertain. Recently, signaling through the high-affinity interleukin-2 (IL-2) receptor has been shown to be critical for Treg cell differentiation and survival in vivo. Mice deficient in IL-2 or its receptor (CD25 or CD122) or deficient in downstream signaling molecules, including JAK-3 and STAT-5, do not develop a stable population of Treg cells and subsequently acquire lymphoproliferative disease and autoimmunity. in vitro, IL-2 is required to expand Treg cells and to induce their suppressive characteristics. Conversely, IL-2-based regimens can activate cellular antitumor immunity and are the mainstay of immunotherapies directed against melanoma and kidney cancers. Given the seemingly disparate effects of IL-2, the authors discuss the possibility that IL-2 may not be the optimal T-cell growth factor in vivo, but rather an inducer of self-tolerance. The authors propose that other gamma c-signaling cytokines, including IL-15, may be alternative choices for the immunotherapy of cancer.     

Robust expansion of viral antigen-specific CD4+ and CD8+ T cells for adoptive T cell therapy using gene-modified activated T cells as antigen presenting cells

Cytomegalovirus (CMV) reactivation after stem cell transplantation can be treated with CMV-specific T cells, but current in vitro techniques using dendritic cells as antigen-presenting cells are time-consuming and expensive. To simplify the production of clinical grade CMV-specific T cells, we evaluated gene-modified activated T cells [antigen presenting T cells (T-APCs)] as a reliable and easily produced source of APCs to boost CD4+ and CD8+ T-cell responses against the immunodominant CMV antigen pp65. T-APCs expressing the full-length immunodominant CMV pp65 gene were used to stimulate the expansion of autologous T cells. After 10 to 14 days, the T cell lines were tested for antigen specificity by using the flow cytometric intracellular detection of interferon-gamma after stimulation for 6 hours with a pp65 peptide library of 15-mers, overlapping by 11 amino acids. Under optimal conditions, this technique induced a median 766-fold and a 652-fold expansion of pp65-specific CD4+ and CD8+ responder cells, respectively, in 15 T cell lines. In 13 of 15 T cell lines, over 10 antigen-specific CD4+ plus CD8+ T cells were generated starting with only 5x10 peripheral blood mononuclear cells, representing an over 3-log increase. These data indicate that T-APCs efficiently boost pp65-specific CD4+ and CD8+ T cell numbers to clinically useful levels. The approach has the advantage of using a single leukocyte collection from the donor to generate large numbers of CMV-specific T cells within a total 3-week culture period using only one stimulation of antigen.     

动脉粥样硬化患者单个核细胞Siglec-1在促进CD4+和CD8+T淋巴细胞增殖和分泌细胞因子中的作用

目的 探讨动脉粥样硬化(AS)患者单个核细胞(PBMC)唾液酸黏附素(Siglec-1)在刺激白细胞分化抗原(CD)4+和CD8+T淋巴细胞活化增殖中的作用.方法 实验研究.用磁珠分离长征医院18例急性冠状动脉综合征(ACS)和41例稳定型心绞痛(SA)患者及32名健康对照者CD14阳性PBMC后,用不同浓度α-干扰素(IFN-α,0、2、5、10 ng/ml)刺激Siglec-1高表达,或用小干扰RNA或抗Siglec-1单抗靶向抑制Siglec-1表达,再与1名第三方健康献血者CD4 +/CD8+T淋巴细胞共培养5d.然后,将实验分为11组:健康人CD14(1组),健康人CD14+ IFN-α5 ng/ml(2组),健康人CD14+ IFN-Ω 5 ng/ml+ anti-Siglec-1 2 μg/ml(3组),ACS CD14(4组),ACS CD14+ siRNA干扰对照组(Mock,5组),ACS CD14+ siRNA 679 40 nmol/L(6组),ACS CD14+ anti-Siglec-1 2μg/ml(7组),SACD14(8组),SA CD14+ Mock(9组),SA CD14+ siRNA 679 40 nmol/L(10组),SA CD14+ anti-Siglec-12 μg/ml(11组);每组测定10份标本.用CCK-8活细胞计数试剂盒检测共培养T淋巴细胞增殖,用ELISA检测共培养T淋巴细胞分泌白细胞介素(IL)-2、IL-10、IL-12、γ干扰素(IFN-γ).测定各组PBMC刺激T淋巴细胞分泌细胞因子的计量数据用中位数(四分位数)表示,采用非参数秩和检验.结果 靶向阻断Siglec-1后(6组),PBMC刺激CD4+T淋巴细胞及CD8+T淋巴细胞的增殖能力减弱,PBMC刺激CD4+T淋巴细胞分泌IL-2、IL-12、IFN-γ分别为67.00(62.50～ 87.30)、0.86(0 ～1.63)、47.82(37.60 ～ 56.67) pg/ml,且分泌能力减弱;IL-10为56.00(46.25 ～67.40) pg/ml,且分泌能力增强;未处理组(4组)上述细胞因子分别为213.70(187.50 ～ 275.30)、6.87 (4.90 ～8.93)、114.90(89.50～167.40)、21.08(15.70～33.20) pg/ml,二者差异有统计学意义(U值分别为8.50、17.00、8.50、87.50,P均＜0.05).当健康对照组单核细胞经IFN-α刺激上调Siglec-1表达后(2组),刺激CD4+T淋巴细胞分泌IL-2、IL-12、IFN-γ分别为220.44(174.30 ～ 312.30)、7.90 (6.540 ～10.40)、143.75(78.20～210.00) pg/ml,且能力增强;IL-10为21.95(16.30 ～25.00) pg/ml,而能力减弱,与1组比较,差异有统计学意义(U值分别为89.50、98.00、100.00、0,P均＜0.05).抑制或增强Siglec-1对CD8+T淋巴细胞分泌的上述细胞因子无影响(P均＞0.05).结论 IFN-α可刺激Siglec-1表达增加,Siglec-1可通过促进CD4+/CD8+T淋巴细胞增殖或CD4+T淋巴细胞分泌Th1型细胞因子参与AS发病过程.     

Complementary role of CD4+ T cells and secondary lymphoid tissues for cross-presentation of tumor antigen to CD8+ T cells

MHC class I-restricted tumor antigens can be presented to CD8+ T cells by two distinct pathways: via direct and indirect presentation. The relative contribution of these two pathways toward the initial activation of tumor antigen-specific CD8+ T cells and their subsequent tumor rejection is still vigorously debated. Using a tumor model able to dissect the relative contributions of direct and indirect presentation, we show unequivocally the inefficiency of direct presentation and the essential requirement of indirect presentation for the priming of naive tumor antigen-specific T cells leading to tumor rejection. Moreover, we characterize the essential environment under which indirect presentation occurs, and find efficient cross-priming of tumor-specific CD8+ T cells in the complete absence of secondary lymphoid tissues. The independence of this process from local lymph nodes is compromised, however, in the absence of CD4+ T cell help. Therefore, our paper demonstrates that effective immune protection against tumors requires the cross-priming of CD8+ T cells under conditions that require either CD4+ T cell help, or draining lymph nodes.     

On the role of CD4+ T cells in the CD8+ T-cell response elicited by recombinant adenovirus vaccines.

We have investigated the role of CD4(+) T cells in the development of the CD8(+) T-cell response after immunization with recombinant adenovirus (rAd). In the absence of CD4(+) T cells, the "unhelped" CD8(+) T-cell population exhibited a reduction in primary expansion and long-term survival that appeared to be due to inadequate priming of na?ve T cells. There were few functional or phenotypic differences between the helped and unhelped CD8(+) T-cell populations with the exception of O-glycosylated CD43, a marker of effector cells, which was augmented on the unhelped CD8(+) T-cell population. In some cases, the unhelped CD8(+) T-cell population exhibited reduced ability to control virus infection; however, this appeared to be a function of the reduced frequency of antigen-specific CD8(+) T cells. Most notably, the unhelped CD8(+) T-cell population exhibited no defect in secondary expansion. These results provide insight into the role of CD4(+) T cells during the primary CD8(+) T-cell response generated by rAd vaccines and identify potential benefits and issues that must be considered when using adenovirus vaccines under conditions where CD4(+) T-cell function may be limiting, such as vaccination of human immunodeficiency virus patients.     

Loss of HIV-1-specific CD8+ T cell proliferation after acute HIV-1 infection and restoration by vaccine-induced HIV-1-specific CD4+ T cells

Virus-specific CD8(+) T cells are associated with declining viremia in acute human immunodeficiency virus (HIV)1 infection, but do not correlate with control of viremia in chronic infection, suggesting a progressive functional defect not measured by interferon gamma assays presently used. Here, we demonstrate that HIV-1-specific CD8(+) T cells proliferate rapidly upon encounter with cognate antigen in acute infection, but lose this capacity with ongoing viral replication. This functional defect can be induced in vitro by depletion of CD4(+) T cells or addition of interleukin 2-neutralizing antibodies, and can be corrected in chronic infection in vitro by addition of autologous CD4(+) T cells isolated during acute infection and in vivo by vaccine-mediated induction of HIV-1-specific CD4(+) T helper cell responses. These data demonstrate a loss of HIV-1-specific CD8(+) T cell function that not only correlates with progressive infection, but also can be restored in chronic infection by augmentation of HIV-1-specific T helper cell function. This identification of a reversible defect in cell-mediated immunity in chronic HIV-1 infection has important implications for immunotherapeutic interventions.     

mTORC1 and mTORC2 selectively regulate CD8+ T cell differentiation

Activation of mTOR-dependent pathways regulates the specification and differentiation of CD4⁺ T effector cell subsets. Herein, we show that mTOR complex 1 (mTORC1) and mTORC2 have distinct roles in the generation of CD8⁺ T cell effector and memory populations. Evaluation of mice with a T cell–specific deletion of the gene encoding the negative regulator of mTORC1, tuberous sclerosis complex 2 (TSC2), resulted in the generation of highly glycolytic and potent effector CD8⁺ T cells; however, due to constitutive mTORC1 activation, these cells retained a terminally differentiated effector phenotype and were incapable of transitioning into a memory state. In contrast, CD8⁺ T cells deficient in mTORC1 activity due to loss of RAS homolog enriched in brain (RHEB) failed to differentiate into effector cells but retained memory characteristics, such as surface marker expression, a lower metabolic rate, and increased longevity. However, these RHEB-deficient memory-like T cells failed to generate recall responses as the result of metabolic defects. While mTORC1 influenced CD8⁺ T cell effector responses, mTORC2 activity regulated CD8⁺ T cell memory. mTORC2 inhibition resulted in metabolic reprogramming, which enhanced the generation of CD8⁺ memory cells. Overall, these results define specific roles for mTORC1 and mTORC2 that link metabolism and CD8⁺ T cell effector and memory generation and suggest that these functions have the potential to be targeted for enhancing vaccine efficacy and antitumor immunity.     

Blockade of T cell costimulation reveals interrelated actions of CD4+ and CD8+ T cells in control of SIV replication

In vivo blockade of CD28 and CD40 T cell costimulation pathways during acute simian immunodeficiency virus (SIV) infection of rhesus macaques was performed to assess the relative contributions of CD4+ T cells, CD8+ T cells, and Ab responses in modulating SIV replication and disease progression. Transient administration of CTLA4-Ig and anti-CD40L mAb to SIV-infected rhesus macaques resulted in dramatic inhibition of the generation of both SIV-specific cellular and humoral immune responses. Acute levels of proliferating CD8+ T cells were associated with early control of SIV viremia but did not predict ensuing set point viremia or survival. The level of in vivo CD4+ T cell proliferation during acute SIV infection correlated with concomitant peak levels of SIV plasma viremia, whereas measures of in vivo CD4+ T cell proliferation that extended into chronic infection correlated with lower SIV viral load and increased survival. These results suggest that proliferating CD4+ T cells function both as sources of virus production and as antiviral effectors and that increased levels of CD4+ T cell proliferation during SIV infections reflect antigen-driven antiviral responses rather than a compensatory homeostatic response. These results highlight the interrelated actions of CD4+ and CD8+ T cell responses in vivo that modulate SIV replication and pathogenesis.     

CD4+ T cells in atherosclerosis.

Atherosclerosis is an inflammatory disease. T lymphocytes, occurring concomitantly with macrophages, are found in atherosclerotic lesions with substantial numbers in all stages. Most of the T cells in the lesions are CD4(+) T cells. The finding of activated T cells and macrophages in lesions and cloning of T cells specific for modified low-density lipoproteins from lesions suggest that a cell-mediated immune reaction is taking place in atherosclerosis. This review provides an overview of our current understanding of the roles of CD4(+) T cell subpopulations in atherosclerosis.     

Apoptotic depletion of CD4+ T cells in idiopathic CD4+ T lymphocytopenia.

Progressive loss of CD4+ T lymphocytes, accompanied by opportunistic infections characteristic of the acquired immune deficiency syndrome, ahs been reported in the absence of any known etiology. The pathogenesis of this syndrome, a subset of idiopathic CD4+ T lymphocytopenia (ICL), is uncertain. We report that CD4+ T cells from seven of eight ICL patients underwent accelerated programmed cell death, a process facilitated by T cell receptor cross-linking. Apoptosis was associated with enhanced expression of Fas and Fas ligand in unstimulated cell populations, and partially inhibited by soluble anti-Fas mAb. In addition, apoptosis was suppressed by aurintricarboxylic acid, an inhibitor of calcium-dependent endonucleases and proteases, in cells from four of seven patients, The in vivo significance of these findings was supported by three factors: the absence of accelerated apoptosis in persons with stable, physiologic CD4 lymphopenia without clinical immune deficiency; detection of serum antihistone H2B autoantibodies, one consequence of DNA fragmentation, in some patients; and its selectivity, with apoptosis limited to the CD4 population in some, and occurring among CD8+ T cells predominantly in those individuals with marked depletion of both CD4+ T lymphocytes linked to clinical immune suppression have evidence for accelerated T cell apoptosis in vitro that may be pathophysiologic and amenable to therapy with apoptosis inhibitors.