Specific suppression of T helper alloreactivity by allo-MHC class I-restricted CD8+CD28- T cells

Specific suppression of the host's immune response to donor HLA antigens remains the ultimate goal for clinical transplantation. In spite of considerable effort, however, allospecific human suppressor T cells (Ts) have been difficult to generate. Here we show that allospecific and xenospecific Ts can be raised by multiple priming of human T cells in mixed lymphocyte cultures. Ts derive from the CD8+CD28- subset and recognize specifically the MHC class I antigens expressed by antigen-presenting cells (APC) used for in vitro immunization. Allospecific Ts prevent the up-regulation of B7 molecules on target APC, interfering with the CD28-B7 interaction required for T helper (Th) activation. These findings provide a basis for the development of specific immunosuppressive therapy.     

Injection of detergent-denatured ovalbumin primes murine class I-restricted cytotoxic T cells in vivo

Complex adjuvant formulations have been used to introduce soluble protein antigens into the "endogenous" processing pathway and hence to elicit specific, major histocompatibility complex class I-restricted cytotoxic T lymphocyte (CTL) responses. We tested if simple modifications of a model protein antigen, i.e. ovalbumin (OVA), can render it immunogenic for murine class I-restricted CTL when injected into mice in soluble form. Injection of 1-100 micrograms native OVA into C57BL/6 (H-2b) mice did not stimulate a class I-restricted CTL response. In contrast, immunization of mice with 0.5 to 10 micrograms sodium dodecyl sulfate (SDS)- or deoxycholate (DOC)-denatured OVA efficiently primed CD8+ CTL specific for the well-characterized Kb-restricted OVA257-264 epitope. Gel-purified SDS-denatured OVA devoid of protein fragments and excess detergent efficiently stimulated a specific CTL response in vivo. OVA preparations denatured by heat or urea treatment were not immunogenic for murine CTL. Injection of non-treated or detergent-treated, antigenic OVA257-264 peptide into mice did not elicit a CTL response. Thus, denaturation of OVA by simple detergents such as SDS or DOC dramatically enhances its immunogenicity for class I-restricted CTL but not all modes of denaturation are equally effective.     

Perforin-deficient CD8+ T cells: in vivo priming and antigen-specific immunity against Listeria monocytogenes

CD8+ T cells require perforin to mediate immunity against some, but not all, intracellular pathogens. Previous studies with H-2b MHC perforin gene knockout (PO) mice revealed both perforin-dependent and perforin-independent pathways of CD8+ T cell-mediated immunity to Listeria monocytogenes (LM). In this study, we address two previously unresolved issues regarding the requirement for perforin in antilisterial immunity: 1) Is CD8+ T cell-mediated, perforin-independent immunity specific for a single Ag or generalizable to multiple Ags? 2) Is there a deficiency in the priming of the CD8+ T cell compartment of PO mice following an immunizing challenge with LM? We used H-2d MHC PO mice to generate CD8+ T cell lines individually specific for three known Ags expressed by a recombinant strain of virulent LM. Adoptive transfer experiments into BALB/c host mice revealed that immunity can be mediated by PO CD8+ T cells specific for all Ags examined, indicating that perforin-independent immunity is not limited to CD8+ T cells that recognize listeriolysin O. Analysis of epitope-specific CD8+ T cell expansion by MHC class I tetramer staining and ELISPOT revealed no deficiency in either the primary or secondary response to LM infection in PO mice. These results demonstrate that the perforin-independent pathway of antilisterial resistance mediated by CD8+ T cells is generalizable to multiple epitopes. Furthermore, the results show that reduced antilisterial resistance observed with polyclonal PO CD8+ T cells is a consequence of a deficiency in effector function and not a result of suboptimal CD8+ T cell priming.     

Immune CD8+ T lymphocytes lyse Listeria monocytogenes-infected hepatocytes by a classical MHC class I-restricted mechanism

Hepatocytes constitute the principal site of listerial replication in the livers of mice infected i.v. CD8+ T lymphocytes play a predominant role in the host defenses to Listeria monocytogenes. In vitro experiments by others undertaken to delineate the functions of CD8+ T lymphocytes have focused primarily on their interaction with Listeria-infected macrophages. Such experiments do not address directly the role of CD8+ T lymphocytes in eliminating the bulk of Listeria replicating within the liver. Here, we report that immune CD8+ T cells at an E:T cell ratio > or = 10:1 lysed Listeria-infected hepatocytes as judged by the following two criteria. Aspartate aminotransferase activity in the culture supernatants, indicative of hepatocyte damage, increased significantly. Conversely, infected hepatocytes cocultured with immune CD8+ T cells exhibited a marked reduction in viable intracellular Listeria assessed by CFUs. Neither immune CD4+ T cells nor nonimmune CD8+ T cells caused a similar increase in aspartate aminotransferase activity released or a decrease in intracellular bacteria. Immune CD8+ T cell-mediated lysis of infected hepatocytes was restricted by classical MHC class I (H-2Kb) molecules and was inhibited by the presence of either brefeldin A or mAb specific for CD8. These results suggest that the predominant role of CD8+ T lymphocytes in host resistance to listerial infections of the liver may be due to their capacity to lyse infected hepatocytes.     

CD45RA(bright)/CD11a(bright) CD8+ T cells: effector T cells

An important aspect of peripheral T cell development is the differentiation from naive into memory cells. To distinguish naive from memory cells, CD45RA and CD11a are commonly used: CD45RA+ or CD11a(dim) T cells are regarded as naive, while CD45RA- or CD11a(bright) T cells are thought to be of memory type. There is, however, a CD8+ T cell subset which is CD45RA+ and at the same time CD11a(bright). It increases with age and in patients with systemic viral infections, though its functional role in the immune response is unknown. In the present study, we give evidence that this subset is related to memory-like T cells as it produces IFN-gamma and tumor necrosis factor-alpha, contains high levels of perforin, and expresses CD95 in the same way as memory-type CD45RA-/CD11a(bright) CD8+ T cells. Since it contains a high percentage of CD28- and CD57+ cells, is increased in size and granularity, and is transiently expressed following in vitro stimulation of naive CD8+ T cells, we speculate that this subset mainly represents recently activated effector T cells that are able to interact with CD80 and CD86 (B7-1 and B7-2 respectively) negative tissue cells.     

Retroviral-mediated expression of an MHC class I-restricted T cell receptor in the CD8 T cell compartment of bone marrow-reconstituted mice

The introduction of cloned T cell receptor (TCR) genes into bone marrow cells could provide a way to increase the frequency of tumor- or pathogen-specific cytotoxic T lymphocyte (CTL) precursors. We demonstrate here the ability of a retroviral vector to direct expression of a Valpha15/Vbeta13 MHC class I-restricted TCR in lethally irradiated mice reconstituted with transduced bone marrow cells. We have detected retroviral-mediated TCR expression by flow cytometry 6-19 weeks after transplantation in C57L (Vbeta13(-/-)) and Rag1(-/-) bone marrow-reconstituted mice, and in C57BL/6 hosts reconstituted with transduced C57BL/6-Rag1(-/-) bone marrow. Southern analysis confirmed the presence of integrated provirus and revealed that the frequency of transduction is greater than the frequency of cell surface TCR expression. Although TCR expression on Vbeta13+ transduced cells is lower than endogenous TCR levels, it is largely confined to CD4+CD8+ (thymus) and CD8+ (thymus and spleen) T cells. In Rag1(-/-) mice, which display a developmental arrest of thymocytes at the immature CD4-CD8- stage, retrovirus-mediated TCR expression selectively rescues CD4+CD8+ and CD8+ populations. These results indicate that the ectopically expressed TCR is functional during T cell development. Furthermore, we have observed Vbeta13+ TCR expression by up to 13% of peripheral CD8+ T cells in C57L and C57BL/6 hosts. This represents a substantial increase relative to total Vbeta13 frequency in normal C57BL/6 mice (3-5%), and an even greater increase over the estimated frequency of CTL precursors of a defined specificity (10(-5)-10(-4)). Our findings indicate that TCR gene transfer can be used to develop new approaches to immunotherapy, and provide the basis for further studies examining the contribution of retrovirus-mediated TCR expression to an antigen-specific CTL response.     

CD8+ T cells in atopic disease

Refinements in radiographic techniques have resulted in increased use of radiographic studies in the evaluation of patients with head and neck cancer over the past 20 years. To assess the impact of such studies, we compared tumor clinical stages based solely on physical-examination findings with those obtained with the addition of CT findings. This study was accomplished through case review of 81 head and neck cancer patients who underwent CT after preliminary TNM-stage assignment as determined on the basis of physical examination alone. In this cohort, 44 patients (54%) had a change in assigned clinical stage. We reviewed individual anatomic sites to determine where CT was found to be most useful in modifying tumor stage. Changes in tumor and nodal stage were found across all major sites of the head and neck. Tumors of the hypopharynx were the most likely to change stage (90%) on the basis of CT findings, whereas tumors of the glottic larynx were least likely to undergo a change in stage (16%). The therapeutic implications of these findings are discussed in the context of the published literature.     

Human effector memory T cells express CD86: a functional role in naive T cell priming

The glycoprotein CD86 expressed on APCs provides a costimulatory signal necessary for an efficient activation of naive T cells. In contrast, there is controversy about the condition of expression and the function of CD86 on T cells. In this study, we have analyzed the phenotype and the biological activity of CD86+ T cells generated from human PBMC. Results show that CD86 expression on T cells is induced by long term stimulation via CD3 and IL-2R and is down-regulated as the cells become quiescent. The CD86-expressing cells are memory effector T cells: 1) they express CD45RO and high levels of the activation markers CD25, CD54, and HLA-Dr; 2) they selectively express CD30, CD40-ligand, and CD70; and 3) in response to stimulation, most of them produce IFN-gamma before dying by apoptosis. We then analyzed whether CD86 expressed on T cells is functional. Results show that paraformaldehyde-fixed CD86+ T cells enhance the proliferation and production of IFN-gamma by anti-CD3 mAb-stimulated naive T cells and induce proliferation of resting allogenic T cells. All these effects are prevented by neutralizing anti-CD86 mAbs. In contrast, we report no autocrine effect of CD86 in CD86+ T cell activation. In conclusion, these data show that human memory effector T cells express a functional form of CD86 that can costimulate naive T cell responses.     

Study of activation of murine T cells with bacterial superantigens. In vitro induction of enhanced responses in CD4+ T cells and of anergy in CD8+ T cells

Primary and secondary responses of murine CD4+ T cells and CD8+ T cells upon stimulation with staphylococcal enterotoxin E (SEE) bearing superantigenic properties were examined. Both isolated C57BL/6 splenic CD4+ T cells and CD8+ T cells proliferated and produced IL-2 and IFN-gamma upon stimulation with SEE in substantial levels. The amounts of IL-2 were greater in CD4+ T cells and those of IFN-gamma were somewhat greater in CD8+ T cells. SEE-induced CD4+ T lymphoblasts, larger parts of which bore the V beta 11 element in their TCR, proliferated, produced IL-2 and IFN-gamma, and showed toxin-dependent cytotoxicity in substantial levels upon restimulation with SEE. By contrast, SEE-induced CD8+ T lymphoblasts, the larger part of which bore the V beta 11 element, did not show the first two of the three responses at all upon restimulation with SEE, whereas these cells showed greater cytotoxicity. The CD8+ T lymphoblasts did not suppress the reactivity of the CD4+ T lymphoblasts. Both SEE-induced CD4+ T lymphoblasts and CD8+ T lymphoblasts proliferated and produced IL-2 and IFN-gamma in comparable levels upon stimulation with rIL-2 or mAb to CD3 or V beta 11.     

Intracellular cytokine expression in the CD4+ and CD8+ T cells from intestinal mucosa of simian immunodeficiency virus infected macaques

7H-Dibenzo[c,g]carbazole (DBC) is an environmental pollutant that produces DNA adducts and tumors in mouse liver and skin following subcutaneous injection and topical application. The two synthetic derivatives 5,9-dimethyl-DBC (DMDBC) and N7-methyl-DBC (NMDBC) induce tissue-specific lesions. DNA adducts and tumors are observed only in liver following exposure to DMDBC and only in skin following exposure to NMDBC. We used the positive selection MutaMouse model to measure the induction of mutations in the two target organs, 28 days after a single subcutaneous injection or topical application of DBC, DMDBC and NMDBC. In liver, DBC and DMDBC induced 30- to 50-fold increases in mutant frequency (MF), while NMDBC had only a weak effect, regardless of the route of administration. After topical application, DBC and NMDBC produced 3.4- to 7.9-fold increases in MF in skin, while DMDBC had a weak effect. After subcutaneous injection, the three compounds had no or weak effect in skin. This study shows gene mutations arise in the respective target organs in which primary DNA damage and tumors are observed. These results illustrate the relevance of the MutaMouse model for testing organ-specific mutagens.     

Elevation of CD8+ CD11b+ Leu-8- T cells is associated with the humoral immunodeficiency in myeloma patients

Batten disease (juvenile-onset neuronal ceroid lipofuscinosis [JNCL]) is an autosomal recessive condition characterized by accumulation of lipopigments (lipofuscin and ceroid) in neurons and other cell types. The Batten disease gene, CLN3, was recently isolated, and four disease-causing mutations were identified, including a 1.02-kb deletion that is present in the majority of patients (The International Batten Disease Consortium 1995). One hundred eighty-eight unrelated patients with JNCL were screened in this study to determine how many disease chromosomes carried the 1.02-kb deletion and how many carried other mutations in CLN3. One hundred thirty-nine patients (74%) were found to have the 1.02-kb deletion on both chromosomes, whereas 49 patients (41 heterozygous for the 1.02-kb deletion) had mutations other than the 1.02-kb deletion. SSCP analysis and direct sequencing were used to screen for new mutations in these individuals. Nineteen novel mutations were found: six missense mutations, five nonsense mutations, three small deletions, three small insertions, one intronic mutation, and one splice-site mutation. This report brings the total number of disease-associated mutations in CLN3 to 23. All patients homozygous for mutations predicted to give rise to truncated proteins were found to have classical JNCL. However, a proportion of the patients (n = 4) who were compound heterozygotes for a missense mutation and the 1.02-kb deletion were found to display an atypical phenotype that was dominated by visual failure rather than by severe neurodegeneration. All missense mutations were found to affect residues conserved between the human protein and homologues in diverse species.     

Xenospecific CD8+ cytotoxic T lymphocyte generation: accessory function for CD4+ T cells and natural killer 1.1+ cells

BACKGROUND: Controversy exists as to whether natural killer (NK)1.1+ cells additionally support cytotoxic T lymphocyte (CTL) generation. We have previously demonstrated that mice generate a strong in vitro xenospecific CTL response in local popliteal lymph nodes (LN) to footpad immunizations with large numbers of human tumor cells. METHODS: In vivo depletion of various LN subsets using cytotoxic monoclonal antibodies was used to determine their relative importance in stimulating xenospecific CD8+ CTL responses to human Jurkat tumor cells. Depletion of functional NK cells in vivo was evidenced by the relative lack of NK1.1+ cells and NK activity in the spleens and LN of anti-NK1.1 monoclonal antibody-treated mice. CONCLUSION: Depletion of LN subsets indicated that CD4+ T cells were critical in generating an effective xenospecific CD8+ CTL response, but also suggested that NK1.1+ cells play a significant additional accessory role in the development of mouse anti-human xenospecific CTL.     

The CD4+ T lymphocyte is a site of steroid resistance in asthma

Phytohaemagglutinin (PHA)-induced T-cell proliferation is suppressed completely in steroid-sensitive asthma (SSA) by fluticasone propionate (FP). By contrast, in patients with steroid-resistant asthma (SRA), this proliferative response is only partially attenuated by steroids, which suggests that the T lymphocyte may harbour a key molecular defect in these patients. Both CD4+ and CD8+ T cells may be involved in orchestrating the inflammation underlying asthma. We examined whether CD4+ or CD8+ T cells isolated from SRA and SSA patients are equally susceptible to steroid suppression of PHA-induced proliferation. Complete suppression of CD4+ T-lymphocyte proliferation was seen in both SSA and control subjects at concentrations of 10(-9) M FP. In contrast, proliferation of CD4+ T cells from SRA patients was only partially inhibited, even at 10(-6) M FP. CD8+ responses from SRA, SSA and controls were all similar, with only a partial suppression of proliferation at 10(-6) M FP. Differential suppression by FP of CD4+ T cells has thus been demonstrated between SRA and SSA patients.     

Potent and selective stimulation of memory-phenotype CD8+ T cells in vivo by IL-15

Proliferation of memory-phenotype (CD44hi) CD8+ cells induced by infectious agents can be mimicked by injection of type I interferon (IFN I) and by IFN I-inducing agents such as lipopolysaccharide and Poly I:C; such proliferation does not affect naive T cells and appears to be TCR independent. Since IFN I inhibits proliferation in vitro, IFN I-induced proliferation of CD8+ cells in vivo presumably occurs indirectly through production of secondary cytokines, e.g., interleukin-2 (IL-2) or IL-15. We show here that, unlike IL-2, IL-15 closely mimics the effects of IFN I in causing strong and selective stimulation of memory-phenotype CD44hi CD8+ (but not CD4+) cells in vivo; similar specificity applies to purified T cells in vitro and correlates with much higher expression of IL-2Rbeta on CD8+ cells than on CD4+ cells.     

Processing and release of IL-16 from CD4+ but not CD8+ T cells is activation dependent

IL-16 is synthesized as a precursor molecule of 68 kDa (pro-IL-16) that is processed by caspase-3, a member of the IL-1 converting enzyme (ICE) family. This cleavage results in a 13-kDa carboxy terminal peptide, which constitutes the bioactive secreted form of IL-16. We have previously reported constitutive IL-16 mRNA expression and pro-IL-16 protein in CD4+ and CD8+ T cells. Although bioactive IL-16 protein is present in unstimulated CD8+ T cells, there is no bioactive IL-16 present in CD4+ T cells. Along these lines, unstimulated CD8+ T cells contain active caspase-3. In the current studies we investigated the regulation of IL-16 protein and mRNA expression in CD4+ T cells and determined the kinetics of secretion following stimulation of the TCR. CD4+ T cells release IL-16 protein following antigenic stimulation, and this release is accelerated in time by costimulation via CD28. However, CD3/CD28 costimulation did not alter IL-16 mRNA appearance or stability in either CD4+ or CD8+ T cells. The secretion of bioactive IL-16 from CD4+ T cells correlated with the appearance of cleavage of pro-caspase-3 into its 20-kDa active form. Thus, resting CD8+ T cells contain active caspase-3 that is capable of cleaving pro-IL-16, whereas CD4+ T cells require activation for the appearance of active caspase-3. The mechanism of release or secretion of bioactive IL-16 is currently unknown, but does not correlate with cellular apoptosis.     

B7-CD28 costimulation unveils the hierarchy of tumor epitopes recognized by major histocompatibility complex class I-restricted CD8+ cytolytic T lymphocytes

Immunization of mice with tumors genetically engineered to express the B7 costimulatory molecules amplifies the antitumor immune response mediated by CD8+ cytolytic T lymphocytes (CTL). In this report, we examined the effect of B7-CD28 costimulation on the hierarchy of tumor epitopes. Using a combination of affinity chromatography/reversed-phase high performance liquid chromatography and CTL cloning, we show that major histocompatibility complex (MHC) class I molecules from EL4 lymphoma cells can present at least six distinct CTL epitopes presented by MHC class I molecules. Nevertheless, mice immunized with wild-type B7-negative EL4 cells develop CTL only to one immunodominant epitope. In contrast, immunization with B7-transduced EL4 cells led to not only the amplification of the CTL response to this immunodominant epitope, but also to the recognition of five otherwise silent subdominant epitopes. The adoptive transfer of a CTL clone against such a subdominant epitope cured mice bearing EL4 lymphoma growing as an ascites tumor. The fact that CTL response can be spread to normally silent epitopes as a result of B7-CD28 costimulation suggests a novel approach to manipulate the hierarchy of CTL epitopes and offers an opportunity to explore novel targets for T cell-mediated cancer therapy.     

Migration and activation of antigen-specific CD8+ T cells upon in vivo stimulation with allogeneic tumor

The response of CD8+ T cells to allogeneic tumor was studied by adoptive transfer of cells from TCR transgenic 2C mice specific for Ld alloantigen. Transferred cells were monitored during the course of a response to i.p. challenge with live P815 (H-2d) using the 1B2 mAb specific for the 2C TCR. Tumor was present in the draining LN and spleen within 3 to 4 days of challenge. The first changes in 1B2+ cells occurred in the spleen on day 4; VLA-4 expression increased in an Ag-specific manner and L-selectin expression decreased in an Ag-nonspecific manner. The number of 1B2+ cells in the spleen declined over days 4 to 6. The first detectable increase in CD25 expression and blast transformation was in the peritoneal cavity beginning days 5 and 6. Clonal expansion was largely limited to this site and was maximal on day 8. As expansion occurred in the peritoneal cavity; the number of 1B2+ cells in the draining LN and spleen also increased. These cells had an activated phenotype (CD44(high), VLA-4(high)) but most did not express CD25 and were not blasts. These results suggest that initial Ag recognition in the spleen results in altered expression of adhesion receptors so that cells gain access to the peritoneal cavity where they undergo clonal expansion and differentiation. Following the response, 1B2+ cells decline in number but a memory population (CD44(high), L-selectin(high and low)) persists for long times in the spleen and LN.     

CD30-regulated apoptosis in murine CD8 T cells after cessation of TCR signals

This work constitutes the first attempt to characterize the wettability of poly(alpha-hydroxy acid) (PAHA) microspheres in situ, prepared according to a complex process involving emulsification, solvent evaporation, washing and freeze-drying. The analysis of the flotation profile of the microspheres has allowed us to determine both advancing and receding contact angles at the microsphere/air/water interface and furnished information on the organization of poly(vinyl alcohol) (PVA) and bovine serum albumin (BSA) at the surface of the PAHA coating. By the comparison of contact angles measured from model surfaces obtained by sampling pure PAHA, PVA, BSA and mixed PVA/PAHA monolayers on glass and poly(methyl methacrylate) (PMMA) substrates, it was concluded that the emulsifier (PVA or BSA) was strongly anchored to the surfaces of the microspheres. The use of BSA to formulate the microspheres from a single oil-in-water emulsion led to dry particles having a hydrophobic surface. The unfolding of the hydrophilic segments of the BSA embedded at the surface of the microspheres, following immersion in water, increased the wettability of the microspheres by water. The same qualitative results were obtained when PVA was used to stabilize single emulsions. On the other hand, microspheres formulated from a double water-in-oil-in-water emulsion displayed no modifications of their wettability when immersed in water. This can be explained by the absence of mobility of the hydrophilic segments of the emulsifier which are blocked in the surface or at the subsurface of the polymer matrix.