Generation of tumor-reactive CTL against the tumor-associated antigen HER2 using retrovirally transduced dendritic cells derived from CD34+ hemopoietic progenitor cells

Ag-specific CD8+ CTL are crucial for effective tumor rejection. Attempts to treat human malignancies by adoptive transfer of tumor-reactive CTL have been limited due to the difficulty of generating and expanding autologous CTL with defined Ag specificity. The current study examined whether human CTL can be generated against the tumor-associated Ag HER2 using autologous dendritic cells (DC) that had been genetically engineered to express HER2. DC progenitors were expanded by culturing CD34+ hemopoietic progenitor cells in the presence of the designer cytokine HyperIL-6. Proliferating precursor cells were infected by a retroviral vector encoding the HER2 Ag and further differentiated into CD83+ DC expressing high levels of MHC, adhesion, and costimulatory molecules. Retroviral transduction of DC resulted in the expression of the HER2 molecule with a transduction efficiency of 15%. HER2-transduced DC correctly processed and presented the Ag, because HLA-A*0201-positive DC served as targets for CTL recognizing the HLA-A*0201-binding immunodominant peptide HER2(369-377). HER2-transduced DC were used as professional APCs for stimulating autologous T lymphocytes. Following repetitive stimulation, a HER2-specific, HLA-A*0201-restricted CTL line was generated that was capable of lysing HLA-A*0201-matched tumor cells overexpressing HER2. A CD8+ T cell clone could be generated that displayed the same specificity pattern as the parenteral CTL line. The ability to generate and expand HER2-specific, MHC class I-restricted CTL clones using HER2-transduced autologous DC in vitro facilitates the development of adoptive T cell transfer for patients with HER2-overexpressing tumors without the requirement of defining immunogenic peptides.     

Antigen-specific T cell repertoire modification of CD4+CD25+ regulatory T cells

T cell immune responses are regulated by the interplay between effector and suppressor T cells. Immunization with Ag leads to the selective expansion and survival of effector CD4(+) T cells with high affinity TCR against the Ag and MHC. However, it is not known if CD4(+)CD25(+) regulatory T cells (T(reg)) recognize the same Ag as effector T cells or whether Ag-specific TCR repertoire modification occurs in T(reg). In this study, we demonstrate that after a primary Ag challenge, T(reg) proliferate and TCR repertoire modification is observed although both of these responses were lower than those in conventional T cells. The repertoire modification of Ag-specific T(reg) after primary Ag challenge augmented the total suppressive function of T(reg) against TCR repertoire modification but not against the proliferation of memory CD4(+) T cells. These results reveal that T cell repertoire modification against a non-self Ag occurs in T(reg), which would be crucial for limiting excess primary and memory CD4(+) T cell responses. In addition, these studies provide evidence that manipulation of Ag-specific T(reg) is an ideal strategy for the clinical use of T(reg).     

Heterospecific CD4 help to rescue CD8 T cell killers

Help from CD4 T cells may be required for optimal generation and maintenance of memory CD8 T cells and also for optimal Ag reactivation. We examined whether the helper cell and the CD8 killer cell need to have the same Ag specificity for help to be effective during interactions of memory T cells with mature APC. This is important because virus and tumor Ag-specific CD4 T cell responses are selectively impaired in several chronic viral infections and malignancies. We performed studies in vitro and in vivo and found that functional memory CD4 T cells generated from a distinct antigenic source (heterospecific helpers) could provide direct and effective help to memory CD8 T cells. Functional heterospecific memory CD4 T cells could also rescue secondary CD8 T cell responses in an experimental tumor model in which homospecific CD4 help was impaired. This could provide a rationale for immunotherapy strategies designed to bypass impaired homospecific help.     

Lenalidomide enhances antigen-specific activity and decreases CD45RA expression of T cells from patients with multiple myeloma

The aim of this study was to investigate whether the specific T cell response against the multiple myeloma Ag HM1.24 is enhanced by the immunomodulatory drug lenalidomide (Revlimid). Ag-specific CD3(+)CD8(+) T cells against the HM1.24 Ag were expanded in vitro by dendritic cells in 29 healthy donors and 26 patients with plasma cell dyscrasias. Ag-specific activation was analyzed by IFN-γ, granzyme B, and perforin secretion using ELISA, ELISPOT assay, and intracellular staining, and generation of Ag-specific T cells was analyzed by tetramer staining. Expression of T cell maturation markers (CD45RA, CD45R0, CCR7, and CD28) was investigated by flow cytometry. We found that activation of HM1.24-specific T cells from healthy donors and patients with plasma cell dyscrasias was enhanced significantly by lenalidomide and furthermore that the impact of lenalidomide on T cells depends on the duration of the exposure. Notably, lenalidomide supports the downregulation of CD45RA on T cells upon activation, observed in healthy donors and in patients in vitro and also in patients during lenalidomide therapy in vivo. We showed for the first time, to our knowledge, that lenalidomide enhances the Ag-specific activation of T cells and the subsequent downregulation of CD45RA expression of T cells in vitro and in vivo.     

Langerhans cells derived from genetically modified human CD34+ hemopoietic progenitors are more potent than peptide-pulsed Langerhans cells for inducing antigen-specific CD8+ cytolytic T lymphocyte responses

Sustained Ag expression by human dendritic cells (DCs) is an attractive means of optimizing Ag presentation for stimulating durable cellular immunity. To establish proof of principle, we used Langerhans cell (LC) progeny of retrovirally transduced CD34(+) hemopoietic progenitor cells to stimulate responses against the HLA-A*0201-restricted influenza matrix peptide (fluMP). Retroviral transduction of CD34(+) hemopoietic progenitor cells, during pre-expansion by thrombopoietin, c-kit ligand, and FLT-3 ligand, on recombinant fibronectin, but in the absence of FCS, resulted in gene expression by 20-30% of the LCs. Expression persisted at least 28 days, with little decline (<30%) over that time. Retroviral transduction did not alter the phenotype or potent immunogenicity of normal mature DCs. FluMP-transduced LCs stimulated a 130-fold expansion of T cells reactive with HLA-A*0201-fluMP tetramers, even at LC:T cell ratios of 1:100-150 and lower, whereas fluMP-pulsed LCs stimulated only a 30-fold expansion. FluMP-transduced LCs also stimulated higher IFN-gamma secretion (100-123 spot-forming cells/10(5) CD8(+) T cells) than did fluMP-pulsed LCs (10-91 spot-forming cells/10(5) CD8(+) T cells). CD8(+) T cells stimulated by transduced LCs did not react preferentially with retrovirally transduced targets, indicating that the responses targeted only the immunizing influenza and not the retroviral vector Ags, even though these could have provided nonspecific helper epitopes presented by the transduced LCs. These data demonstrate that gene-transduced LCs maintain the activated phenotype as well potent immunogenicity typical of mature DCs. LCs genetically modified to express fluMP are also more potent stimulators of Ag-specific CD8(+) T cell responses than are peptide-pulsed LCs.     

Peripheral deletion of mature CD8+ antigen-specific T cells after in vivo exposure to male antigen.

It has been well established that T cell tolerance to self Ag occurs primarily via clonal deletion of immature thymocytes in the thymus. Evidence also exists that there are additional mechanisms operative on mature T cells for establishing and maintaining tolerance in the periphery. To follow the fate of mature Ag-specific T cells in vivo, we used female transgenic mice, which contain a large population of male H-Y Ag-specific T cells that can be identified by immunostaining with mAb directed against CD8 and the transgenic TCR. H-Y Ag was introduced into these mice by injecting Ag-bearing male lymphocytes using conditions known to induce CTL precursor response reduction. The number of Ag-reactive CD8+ transgenic T cells in the periphery started to decrease after 2 days of in vivo exposure to male Ag. Decline was maximum (up to 80% of total) by 7 days, and stayed at this level for at least 6 wk. CD4+ cells and those CD8+ cells that did not carry the transgenic TCR were not affected. Most or all of the remaining Ag-reactive CD8+ cells in the periphery were fully responsive when stimulated by male Ag in vitro. Maturation of transgenic T cells in the thymus of injected mice remained the same as that of control animals. Our data provide direct evidence that mature Ag-reactive CD8+ cells are susceptible to clonal deletion in the periphery when exposed to the Ag in vivo. These findings suggest the presence of two types of APC in the periphery: stimulatory APC (e.g., macrophages and dendritic cells) required for initiating an active immune response; and functionally deleting APC (or veto cells) capable of deleting mature T lymphocytes that recognize Ag presented on their surface. Functionally deleting APC that present self Ag to peripheral T cells may provide a fail-safe mechanism against autoreactive cells that escaped deletion during differentiation in the thymus.     

B cells expressing Ig transgenes respond to a T-dependent antigen only in the presence of Ia-compatible T cells

We sought a quicker and easier method for the isolation of B cells enriched for a given Ag specificity. Here, we report our results using transgenic mice bearing mu- and kappa-transgenes that encode an IgR against the hapten phosphorylcholine. Splenic B cells from such mice had a high percentage of phosphorylcholine-binding cells and differentiated in vitro in response to T cell hybridomas in an Ag-specific, Ia-restricted manner. Supernatants from such in vitro cultures could not transfer helper activity, nor could the T cell be replaced in other ways tried when using a classical T-dependent Ag. These results support the model of a cognate interaction between T and B cell, and we present evidence that the interaction may consist of two or more steps.     

Extensive replicative capacity of human central memory T cells

To characterize the replicative capacity of human central memory (T(CM)) CD4 T cells, we have developed a defined culture system optimized for the ex vivo expansion of Ag-specific CD4(+) T cells. Artificial APCs (aAPCs) consisting of magnetic beads coated with Abs to HLA class II and a costimulatory Ab to CD28 were prepared; peptide-charged HLA class II tetramers were then loaded on the beads to provide Ag specificity. Influenza-specific DR*0401 CD4 T(CM) were isolated from the peripheral blood of normal donors by flow cytometry. Peptide-loaded aAPC were not sufficient to induce resting CD4 T(CM) to proliferate. In contrast, we found that the beads efficiently promoted the growth of previously activated CD4 T(CM) cells, yielding cultures with >80% Ag-specific CD4 cells after two stimulations. Further stimulation with peptide-loaded aAPC increased purity to >99% Ag-specific T cells. After in vitro culture for 3-12 wk, the flu-specific CD4 T(CM) had surface markers that were generally consistent with an effector phenotype described for CD8 T cells, except for the maintenance of CD28 expression. The T(CM) were capable of 20-40 mean population doublings in vitro, and the expanded cells produced IFN-gamma, IL-2, and TNF-alpha in response to Ag, and a subset of cells also secreted IL-4 with PMA/ionomycin treatment. In conclusion, aAPCs expand T(CM) that have extensive replicative capacity, and have potential applications in adoptive immunotherapy as well as for studying the biology of human MHC class II-restricted T cells.     

Redox remodeling by dendritic cells protects antigen-specific T cells against oxidative stress

Microorganisms and microbial products induce the release of reactive oxygen species (ROS) from monocytes and other myeloid cells, which may trigger dysfunction and apoptosis of adjacent lymphocytes. Therefore, T cell-mediated immunity is likely to comprise mechanisms of T cell protection against ROS-inflicted toxicity. The present study aimed to clarify the dynamics of reduced sulfhydryl groups (thiols) in human T cells after presentation of viral and bacterial Ags by dendritic cells (DCs) or B cells. DCs, but not B cells, efficiently triggered intra- and extracellular thiol expression in T cells with corresponding Ag specificity. After interaction with DCs, the Ag-specific T cells acquired the capacity to neutralize exogenous oxygen radicals and resisted ROS-induced apoptosis. Our results imply that DCs provide Ag-specific T cells with antioxidative thiols during Ag presentation, which suggests a novel aspect of DC/T cell cross-talk of relevance to the maintenance of specific immunity in inflamed or infected tissue.     

High-affinity TCRs generated by phage display provide CD4+ T cells with the ability to recognize and kill tumor cell lines

We examined the activity of human T cells engineered to express variants of a single TCR (1G4) specific for the cancer/testis Ag NY-ESO-1, generated by bacteriophage display with a wide range of affinities (from 4 microM to 26 pM). CD8(+) T cells expressing intermediate- and high-affinity 1G4 TCR variants bound NY-ESO-1/HLA-A2 tetramers with high avidity and Ag specificity, but increased affinity was associated with a loss of target cell specificity of the TCR gene-modified cells. T cells expressing the highest affinity TCR (K(D) value of 26 pM) completely lost Ag specificity. The TCRs with affinities in the midrange, K(D) 5 and 85 nM, showed specificity only when CD8 was absent or blocked, while the variant TCRs with affinities in the intermediate range-with K(D) values of 450 nM and 4 microM-demonstrated Ag-specific recognition. Although the biological activity of these two relatively low-affinity TCRs was comparable to wild-type reactivity in CD8(+) T cells, introduction of these TCR dramatically increased the reactivity of CD4(+) T cells to tumor cell lines.     

Dendritic cells generated either from CD34+ progenitor cells or from monocytes differ in their ability to activate antigen-specific CD8+ T cells.

Dendritic cells (DC) can be generated in vitro from monocytes (M-DC) or from CD34+ hemopoietic progenitor cells (CD34-DC) but their precursors are not equivalent cells, prompting a comparison of the functional capacities of these APC. Both types of DCs established from the same individuals using the same cytokines displayed a comparable phenotype of mature DC (CD1a+, CD83+, CD86+, CD4+, HLA-DR++, CD14-, CD15- ) and were equally potent stimulators of allogeneic T cell proliferation, being both more powerful than immature M-DCs. An autologous panel of APCs produced in HLA-A2+ individuals, including CD34-DC, M-DC, monocytes, and EBV-lymphoid cell line was comparatively evaluated for presentation of the Erb-B2 peptide E75 to a CTL line. After short exposures (5 h) to E75-loaded APCs, similar levels of intracellular IFN-gamma were induced in Ag-specific CD8+ T cells regardless of APC type. In sustained cultures (4-14 days), more Ag-specific T cells were obtained when peptide was presented on CD34-DC (p < 0.05) rather than on M-DC, EBV-lymphoid cell lines, or monocytes, and these effects were dose-dependent. Activated T cells expressed 4-1BB, and the presence of 4-1BB-Ig fusion protein partially blocked Ag-specific CD8+ cell activation after CD34-DC or M-DC presentation. Our results show that 34-DC have a preferential capacity to activate CD8+ T cells and that this property is not strictly correlated to their ability to induce allogeneic T cell proliferation but due to mechanisms that remain to be defined.     

Incomplete activation of CD4 T cells by antigen-presenting transitional immature B cells: implications for peripheral B and T cell responsiveness

B cells leave the bone marrow as transitional B cells. Transitional B cells represent a target of negative selection and peripheral tolerance, both of which are abrogated in vitro by mediators of T cell help. In vitro, transitional and mature B cells differ in their responses to B cell receptor ligation. Whereas mature B cells up-regulate the T cell costimulatory molecule CD86 (B7.2) and are activated, transitional B cells do not and undergo apoptosis. The ability of transitional B cells to process and present Ag to CD4 T cells and to elicit protective signals in the absence of CD86 up-regulation was investigated. We report that transitional B cells can process and present Ag as peptide:MHC class II complexes. However, their ability to activate T cells and elicit help signals from CD4-expressing Th cells was compromised compared with mature B cells, unless exogenous T cell costimulation was provided. A stringent requirement for CD28 costimulation was not evident in interactions between transitional B cells and preactivated CD4-expressing T cells, indicating that T cells involved in vivo in an ongoing immune response might rescue Ag-specific transitional B cells from negative selection. These data suggest that during an immune response, immature B cells may be able to sustain the responses of preactivated CD4(+) T cells, while being unable to initiate activation of naive T cells. Furthermore, the ability of preactivated, but not naive T cells to provide survival signals to B cell receptor-engaged transitional immature B cells argues that these B cells may be directed toward activation rather than negative selection when encountering Ag in the context of a pre-existing immune response.     

IL-21 influences the frequency, phenotype, and affinity of the antigen-specific CD8 T cell response

IL-21, a newly described cytokine belonging to the IL-2 gamma-chain receptor cytokine family (that includes IL-2, IL-7, and IL-15), has been described as an important regulator of the cellular immune response. In this study, the role of IL-21 in the generation of a human Ag-specific CD8+ T cell response is characterized by tracking a rare, but measurable population of self-Ag-specific T cells in vitro. Autologous dendritic cells pulsed with the melanoma antigen recognized T cells 1 self-peptide were used to stimulate CD8+ T cells from HLA-A2+ healthy donors and melanoma patients. We demonstrate that exposure to IL-21 increased the total number of MART-1-specific CD8+ T cells that could be elicited by >20-fold and, at the clonal level, enriched for a population of high-affinity CD8+ T cells with a peptide dose requirement more than 1 log(10)-fold less than their untreated counterparts. Phenotypic analysis of T cells from IL-21-treated cultures revealed a unique population of CD45RO+ CD28(high) CD8+ T cells, a phenotype that was stable for at least 4 wk after IL-21 exposure. These CD28(high) CD8+ T cells produced IL-2 upon Ag stimulation and represent potential helper-independent CTLs. Our studies demonstrate a significant role for IL-21 in the primary Ag-specific human CTL response and support the use of IL-21 in the ex vivo generation of potent Ag-specific CTLs for adoptive therapy or as an adjuvant cytokine during in vivo immunization against tumor Ags.     

Transfer of regulatory properties from tolerogenic to proinflammatory dendritic cells via induced autoreactive regulatory T cells

Infectious tolerance is a term generally assigned to the process through which regulatory T cells (Tregs) transfer immunoregulatory properties to other T cells. In this study, we demonstrated that a similar process applies to human dendritic cells (DCs), albeit through a different mechanism. We induced and cloned proinsulin-specific Tregs using tolerogenic DCs and investigated mechanisms by which induced Ag-specific regulatory T cells (iaTregs) endorse the suppressive effects. iaTregs expressed FOXP3, programmed death-1, and membrane-bound TGF-β and upregulated IL-10 and CTLA-4 after stimulation with the cognate Ag. The iaTregs suppressed effector T cells only when both encountered the cognate Ags on the same APCs (linked suppression). This occurred independently of IL-10, TGF-β, programmed death-1, or CTLA-4. Instead, iaTregs used a granzyme B-mediated mechanism to kill B cells and monocytes, whereas proinflammatory DCs that resisted being killed were induced to upregulate the inhibitory receptors B7 (family) homolog 3 and ICOS ligand. These re-educated mature monocyte-derived dendritic cells (mDCs) suppressed effector T cells and induced IL-10-producing cells from the naive T cell pool. Our data indicated that human tolerogenic DCs confer infectious tolerance by inducing Ag-specific Tregs, which, in turn, re-educate proinflammatory mature DCs into DCs with regulatory properties.     

Relationships between antigen-specific helper and inducer suppressor T cell hybridomas

Ts1, or inducer suppressor T cells, share many phenotypic and functional characteristics with helper/inducer subset of T cells. In order to evaluate the relationship between these cell types, we made a series of new Ts1 hybridomas by the fusion of Ts1 cells with the functionally TCR alpha/beta-negative BW thymoma (BW 1100). Three Ts1 hybridomas (CKB-Ts1-38, CKB-Ts1-53, and CKB-Ts1-81) were established that express TCR and produce Ag-specific suppressor factors constitutively, thus making it possible to study the nature and specificity of Ag receptors, MHC restriction, and lymphokine production by the Ts1 hybridomas. Results presented in this report demonstrate that all the Ts1 hybridomas described here express CD3-associated TCR-alpha beta. These three Ts1 hybridomas recognize Ag (NP-KLH) specifically in a growth inhibition assay and this recognition is restricted by IE molecules. Two of the hybridomas also produce IL-2 or IL-2 and IL-4 upon Ag-specific activation. Thus, by these three criteria the Ts1 hybridomas appear indistinguishable from Th cells. These three Ts1 hybridomas, however, release suppressor factors (TsF1) in the supernatant that suppress both in vivo DTH and in vitro PFC responses in an Ag-specific manner. Like the TsF1 factors characterized previously, the suppression mediated by these factors are Igh restricted and lack H-2 restriction. These factors mediate suppression when given in the induction phase but not during the effector phase of the immune response. The TsF1 factors are absorbed by Ag (NP-BSA), and anti-TCR affinity columns and the suppressor activity can be recovered by elution. The data are consistent with the interpretation that Ts1 inducer-suppressor T cells are related to Th cells; the feature that distinguishes these cells is the ability to produce Ag-binding factors that specifically suppress immune responses.     

In vitro expansion of Ag-specific T cells by HLA-A*0201-transfected K562 cells for immune monitoring

BACKGROUND: Development of a practical and sensitive assay for evaluating immune responses against cancer Ag has been a challenge for immune monitoring of patients. We have established a reproducible method using peptide-pulsed K562-A*0201 cells as APC to expand Ag-specific T cells in vitro. This method may be applied for monitoring T-cell responses in cancer immunotherapy clinical trials. METHODS: Autologous PBMC from HLA-A*0201+ healthy donors and patients with melanoma were stimulated with peptide-pulsed K562-A*0201 cells under varying conditions. We investigated (1) different culture conditions, including the requirements for serum and cytokines for expansion of CD8+ T lymphocytes; (2) a range of peptide concentrations for Ag loading; (3) phenotypic characterization of responding T cells; and (4) APC:responder ratios and their effects on T-cell expansion. We validated these conditions by ELISPOT and intracellular cytokine staining (ICS) assays using peptides from influenza, Epslein-Barr Virus (EBV) and tyrosinase. RESULTS: Conditions for optimal T-cell expansion using K562-A*0201 APC included input of 2 x 10(6) PBMC, a 10 microg/mL peptide concentration to pulse K562-A*0201 cells, a 1:30 APC:responder T-cell ratio and culture in 10% autologous plasma supplemented with IL-2 and IL-15. In these conditions, Ag-specific T cells expanded >100-fold over a 10-day culture period (peak at day 12). DISCUSSION: This bulk culture method is simple and reliable for expanding human Ag-specific T cells using peptide-pulsed K562-A*0201 cells. This HLA-matched APC line can be adapted to other HLA haplotypes, and has advantages for monitoring clinical trials of immunotherapy with limited availability of autologous APC and PBMC from patients.     

Inverse Rap1 and phospho-ERK expression discriminate the maintenance phase of tolerance and priming of antigen-specific CD4+ T cells in vitro and in vivo

T cell recognition of Ag can result in priming or tolerance depending on the context in which Ag is recognized. Previously, we have reported that these distinct functional outcomes are associated with marked differences in the amplitude, kinetics, and cellular localization of activated, pERK signals at the level of individual Ag-specific T cells in vitro. Here, we show that the GTPase Rap1, which can antagonize the generation of such pERK signals and has been reported to accumulate in tolerant cells, exhibits an inverse pattern of expression to pERK in individual Ag-specific primed and tolerized T cells. Although pERK is expressed by more primed than tolerized T cells when rechallenged with Ag in vitro, Rap1 is expressed by higher percentages of tolerant compared with primed Ag-specific T cells. Moreover, whereas pERK localizes to the TCR and lipid rafts in primed cells, but exhibits a diffuse cellular distribution in tolerized cells, Rap1 colocalizes with the TCR and lipid raft structures under conditions of tolerance, but not priming, in vitro. This inverse relationship between Rap1 and pERK expression is physiologically relevant, given that we observed the same patterns in Ag-specific T cells in situ, following induction of priming and tolerance in vivo. Together, these data suggest that the maintenance of tolerance of individual Ag-specific T cells may reflect the recruitment of up-regulated Rap1 to the immune synapse, potentially resulting in sequestration of Raf-1 and uncoupling of the TCR from the Ras-ERK-MAPK cascade.     

Tissue distribution of human minor histocompatibility antigens. Ubiquitous versus restricted tissue distribution indicates heterogeneity among human cytotoxic T lymphocyte-defined non-MHC antigens.

We determined the tissue distribution of 7 human minor histocompatibility (H) Ag. Each of these Ag is defined by one or more MHC class I-restricted CTL clones, previously generated from PBL primed against minor H Ag by HLA-identical bone marrow transplantation (BMT). CTL-mediated lysis of tissue-derived cells and cultured cell lines was used as an in vitro assay for minor H Ag expression of several human tissues. The Ag HA-3 (HLA-A1-restricted), HA-4 (HLA-A2 restricted), HA-6 and HA-7 (HLA-B7 restricted), and the male-specific Ag H-Y (HLA-A2 and B7 restricted) were found to be expressed on cells of all tissues tested. In contrast, the HLA-A2-restricted Ag HA-1 and HA-2 were demonstrated on PHA-blasts, EBV-BLCL, purified T cells, B cells, monocytes, and immature thymocytes, but could not be demonstrated on skin-derived cultured fibroblasts, keratinocytes, melanocytes, cultured epithelial cells of kidney proximal tubili, and umbilical cord vein-derived endothelial cells. Incubation of the latter cell lines with rIFN-gamma, rTNF-alpha, and/or rIL-1 alpha, in concentrations shown to maximally increase their susceptibility to lysis by allo-MHC class I CTL, did not induce recognition by HA-1- and HA-2-specific CTL in vitro. These results indicate an ubiquitous tissue expression of the minor H Ag HA-3, -4, -6, -7 and H-Y in contrast to a to the hemopoietic cell lineage-restricted expression for HA-1 and HA-2. The heterogeneity in tissue expression of T cell-defined, class I-restricted non-MHC Ag implies that they might be derived from intracellular proteins with either an ubiquitous or a more specialized cell type-specific function.     

Antigen-specific CD8+ T cells switch the immune response induced by antigen from an IgG to a cell-mediated mode.

We have developed an in vivo/in vitro immunization procedure with xenogeneic RBC as Ag that results in the generation of a lymphoid population that expresses potent delayed-type hypersensitivity (DTH) and produces little, if any, antibody. This lymphoid population contains Ag-specific CD8+ T cells that can inhibit the induction of a strong IgG response. These CD8+ T cells are shown to not only inhibit the antibody response in an Ag-specific manner but allow the Ag to induce cells of the target population to express DTH. Furthermore, the Ag-specific inhibition of the antibody response and the Ag-specific enhancement of the induction of DTH appear to be coordinately regulated, as the same number of CD8+ T cells cells is required to achieve both effects. Thus these CD8+ T cells are shown to switch the response induced by Ag from a humoral to a cell-mediated mode. These regulatory characteristics are consistent with a physiologic role for these cells of ensuring the absence of antibody production during a strong, cell-mediated response.     

Functional analysis of a T cell line specific for antiidiotypic antibodies to a Schistosoma mansoni protective epitope. I. Role in the anti-S. mansoni antibody response.

Previous data have shown that from an antiparasitic IgE mAb (mAb1), antianti-Id IgG and IgE antibodies (Ab3) could be prepared. These Ab3 demonstrated the same functional properties as the Ab1, such as in vitro cytotoxic activity toward schistosomula and in vivo a protective effect against Schistosoma mansoni infection. To study the possible interactions between the idiotypic network and the regulation of isotypic expression, we focused on Id-specific T cells obtained by immunization with Ab2. Both Ab2 idiotopes and native schistosomula Ag were able to stimulate the proliferation of anti-Ab2 T cells in vitro. The activation of anti-Ab2 T cells by Ab2 shared the classic characteristics of Th cells, namely, it was MHC-restricted and required APC. A T cell line could be maintained in long term culture by stimulation with schistosomula Ag. The adoptive transfer of cells from this line to 26-kDa Ag-immunized or S. mansoni-infected rats led to a dramatic increase in the specific humoral response. This effect was restricted to antibodies specific for 26- and 56-kDa Ag (the targets of the mAb1) and was observed for the two isotypes tested, i.e., IgG and IgE. Finally, the helper effect on the antibody response could be further amplified by cooperation of anti-Ab2 T cells with Id-specific cells of the first generation (anti-Ab1 cells). Together with Ag-specific Th cells, the Id-specific T cells may, due to their specificity and their functional properties, play a major role in the induction and more importantly, in the maintenance of the immune response.