T cells as antigen-presenting cells

Cytokine profile of anti-spike CD4+T cells predicts humoral and CD8+T cell responses after anti-SARS-CoV-2 mRNA vaccination

Coordinating immune responses - humoral and cellular - is vital for protection against severe Covid-19. Our study evaluates a multicytokine CD4+T cell signature's predictive for post-vaccinal serological and CD8+T cell responses. A cytokine signature composed of four cytokines (IL-2, TNF-α, IP10, IL-9) excluding IFN-γ, and generated through machine learning, effectively predicted the CD8+T cell response following mRNA-1273 or BNT162b2 vaccine administration. Its applicability extends to murine vaccination models, encompassing diverse immunization routes (such as intranasal) and vaccine platforms (including adjuvanted proteins). Notably, we found correlation between CD4+T lymphocyte-produced IL-21 and the humoral response. Consequently, we propose a test that offers a rapid overview of integrated immune responses. This approach holds particular relevance for scenarios involving immunocompromised patients because they often have low cell counts (lymphopenia) or pandemics. This study also underscores the pivotal role of CD4+T cells during a vaccine response and highlights their value in vaccine immunomonitoring.

Reactivity of HLADR antibody manifests expression of surface MHC II molecules on peripheral blood T lymphocytes in new world monkeys

BACKGROUND

Major histocompatibility complex (MHC) class II molecules expressed on B cells, monocytes and dendritic cells present processed peptides to CD4+ T cells as one of the mechanisms to combat infection and inflammation.

AIM

To study MHC II expression in a variety of nonhuman primate species, including New World (NWM) squirrel monkeys (Saimiri boliviensis boliviensis), owl monkeys (Aotus nancymae), common marmosets (Callithrix spp.), and Old World (OWM) rhesus (Macaca mulatta), baboons (Papio anubis).

METHODS

Two clones of cross-reactive mouse anti-human HLADR monoclonal antibodies (mAb) binding were analyzed by flow cytometry to evaluate MHC II expression on NHP immune cells, including T lymphocytes in whole blood (WB) and peripheral blood mononuclear cells (PBMC).

RESULTS

MHC class II antibody reactivity is seen with CD20+ B cells, CD14+ monocytes and CD3+ T lymphocytes. Specific reactivity with both clones was demonstrated in T lymphocytes: this reactivity was not inhibited by purified CD16 antibody but was completely inhibited when pre-blocked with purified unconjugated MHC II antibody. Freshly prepared PBMC also showed reactivity with T lymphocytes without any stimulation. Interestingly, peripheral blood from rhesus macaques and olive baboons (OWM) showed no such T lymphocyte associated MHCII antibody reactivity.

DISCUSSION & CONCLUSION

Our results from antibody (MHC II) reactivity clearly show the potential existence of constitutively expressed (with no stimulation) MHC II molecules on T lymphocytes in new world monkeys. These results suggest that additional study is warranted to evaluate the functional and evolutionary significance of these finding and to better understand MHC II expression on T lymphocytes in new world monkeys.

The Role of Lipids in the Regulation of Immune Responses

Lipid metabolism plays a major role in the regulation of the immune system. Exogenous (dietary and microbial-derived) and endogenous (non-microbial-derived) lipids play a direct role in regulating immune cell activation, differentiation and expansion, and inflammatory phenotypes. Understanding the complexities of lipid-immune interactions may have important implications for human health, as certain lipids or immune pathways may be beneficial in circumstances of acute infection yet detrimental in chronic inflammatory diseases. Further, there are key differences in the lipid effects between specific immune cell types and location (e.g., gut mucosal vs. systemic immune cells), suggesting that the immunomodulatory properties of lipids may be tissue-compartment-specific, although the direct effect of dietary lipids on the mucosal immune system warrants further investigation. Importantly, there is recent evidence to suggest that lipid-immune interactions are dependent on sex, metabolic status, and the gut microbiome in preclinical models. While the lipid-immune relationship has not been adequately established in/translated to humans, research is warranted to evaluate the differences in lipid-immune interactions across individuals and whether the optimization of lipid-immune interactions requires precision nutrition approaches to mitigate or manage disease. In this review, we discuss the mechanisms by which lipids regulate immune responses and the influence of dietary lipids on these processes, highlighting compelling areas for future research.

Single-cell and spatial transcriptome analyses revealed cell heterogeneity and immune environment alternations in metastatic axillary lymph nodes in breast cancer

BACKGROUND

Tumor heterogeneity plays essential roles in developing cancer therapies, including therapies for breast cancer (BC). In addition, it is also very important to understand the relationships between tumor microenvironments and the systematic immune environment.

METHODS

Here, we performed single-cell, VDJ sequencing and spatial transcriptome analyses on tumor and adjacent normal tissue as well as axillar lymph nodes (LNs) and peripheral blood mononuclear cells (PBMCs) from 8 BC patients.

RESULTS

We found that myeloid cells exhibited environment-dependent plasticity, where a group of macrophages with both M1 and M2 signatures possessed high tumor specificity spatially and was associated with worse patient survival. Cytotoxic T cells in tumor sites evolved in a separate path from those in the circulatory system. T cell receptor (TCR) repertoires in metastatic LNs showed significant higher consistency with TCRs in tumor than those in nonmetastatic LNs and PBMCs, suggesting the existence of common neo-antigens across metastatic LNs and primary tumor cites. In addition, the immune environment in metastatic LNs had transformed into a tumor-like status, where pro-inflammatory macrophages and exhausted T cells were upregulated, accompanied by a decrease in B cells and neutrophils. Finally, cell interactions showed that cancer-associated fibroblasts (CAFs) contributed most to shaping the immune-suppressive microenvironment, while CD8⁺ cells were the most signal-responsive cells.

CONCLUSIONS

This study revealed the cell structures of both micro- and macroenvironments, revealed how different cells diverged in related contexts as well as their prognostic capacities, and displayed a landscape of cell interactions with spatial information.

Peripheral Blood T-lymphocyte Phenotypes in Mother-Child Pairs Stratified by the Maternal HPV Status: Persistent HPV16 vs. HPV-Negative: A Case-Control Study

Only few studies exist on the phenotype distribution of peripheral blood lymphocytes concerning persistent oral HPV infection. T-lymphocyte subsets were phenotyped in women who had persistent genital or oral HPV16 infection, using HPV-negative women as a reference group. A subset of 42 mothers and their children (n = 28), were stratified into two groups according to the mothers' HPV status. PBMCs from previously cryopreserved venous samples were immunophenotyped by flow cytometry. Proportions of the CD4⁺ or CD8⁺ lymphocytes by their immunophenotype subsets were compared between HPV-positive and -negative mothers and their children. The mean rank distribution of CD8⁺ memory cells was significantly higher among mothers with persistent genital HPV16 infection. The median levels of both the antigen-presenting CD4⁺ cells and activated CD8⁺ cells were significantly lower in mothers with persistent oral HPV16 infection. When oral and genital HPV16-persistors were analyzed as a group, a marker of terminal effector cells was significantly increased as compared to HPV-negative women. Significantly higher levels of activated CD4⁺, CD8⁺ and circulating CD8⁺ memory cells were found among children whose mothers had persistent oral HPV16 infection. Persistent HPV16 infections are associated with changes in peripheral blood T-lymphocyte subsets. The mother's persistent oral HPV16 infection possibly results in immune alterations in her offspring.

Gold-Nanostar-Chitosan-Mediated Delivery of SARS-CoV-2 DNA Vaccine for Respiratory Mucosal Immunization: Development and Proof-of-Principle

The COVID-19 pandemic is caused by the coronavirus SARS-CoV-2 (SC2). A variety of anti-SC2 vaccines have been approved for human applications, including those using messenger RNA (mRNA), adenoviruses expressing SC2 spike (S) protein, and inactivated virus. The protective periods of immunization afforded by these intramuscularly administered vaccines are currently unknown. An alternative self-administrable vaccine capable of mounting long-lasting immunity via sterilizing neutralizing antibodies would be hugely advantageous in tackling emerging mutant SC2 variants. This could also diminish the possibility of vaccinated individuals acting as passive carriers of COVID-19. Here, we investigate the potential of an intranasal (IN)-delivered DNA vaccine encoding the S protein of SC2 in BALB/c and C57BL/6J immunocompetent mouse models. The immune response to IN delivery of this SC2-spike DNA vaccine transported on a modified gold-chitosan nanocarrier shows a strong and consistent surge in antibodies (IgG, IgA, and IgM) and effective neutralization of pseudoviruses expressing S proteins of different SC2 variants (Wuhan, beta, and D614G). Immunophenotyping and histological analyses reveal chronological events involved in the recognition of SC2 S antigen by resident dendritic cells and alveolar macrophages, which prime the draining lymph nodes and spleen for peak SC2-specific cellular and humoral immune responses. The attainable high levels of anti-SC2 IgA in lung mucosa and tissue-resident memory T cells can efficiently inhibit SC2 and its variants at the site of entry and also provide long-lasting immunity.

Cytokines regulate the antigen-presenting characteristics of human circulating and tissue-resident intestinal ILCs

ILCs and T helper cells have been shown to exert bi-directional regulation in mice. However, how crosstalk between ILCs and CD4⁺ T cells influences immune function in humans is unknown. Here we show that human intestinal ILCs co-localize with T cells in healthy and colorectal cancer tissue and display elevated HLA-DR expression in tumor and tumor-adjacent areas. Although mostly lacking co-stimulatory molecules ex vivo, intestinal and peripheral blood (PB) ILCs acquire antigen-presenting characteristics triggered by inflammasome-associated cytokines IL-1β and IL-18. IL-1β drives the expression of HLA-DR and co-stimulatory molecules on PB ILCs in an NF-κB-dependent manner, priming them as efficient inducers of cytomegalovirus-specific memory CD4⁺ T-cell responses. This effect is strongly inhibited by the anti-inflammatory cytokine TGF-β. Our results suggest that circulating and tissue-resident ILCs have the intrinsic capacity to respond to the immediate cytokine milieu and regulate local CD4⁺ T-cell responses, with potential implications for anti-tumor immunity and inflammation.

Murine ILCs can modulate T cell responses in MHCII-dependent manner. Here the authors show that human ILCs process and present antigens and induce T-cell responses upon exposure to IL-1-family cytokines; along with the article by Lehmann et al, this work elucidates how cytokines set context specificity of ILC-T cell crosstalk by regulating ILC antigen presentation.

T Cell Dysregulation in Non-silicotic Silica Exposed Workers: A Step Toward Immune Tolerance Breakdown

Background: Chronic silica exposure can lead to silicosis, complicated or not by autoimmune diseases (AID). The pathophysiology of silica-induced AID remains not fully understood, especially immune mechanisms that may develop in patients without yet established silicosis. We conducted a prospective clinical study to analyze the impact of crystalline silica (CS) on T cell phenotype and regulatory T cells (Tregs) frequency, as well as on auto-antibodies development in non-silicotic workers exposed to CS.

Methods: Workers with moderate to high exposure level to CS and aged between 30 and 60 years-old were considered for inclusion. Peripheral blood mononuclear cells were analyzed by flow cytometry. Auto-antibodies were screened in serum by immunofluorescence. Blood from 42 and 45 healthy subjects (HC) was used as control for T cell phenotype and serum analyses, respectively.

Results: Among the 63 included workers exposed to CS, 55 had full data available and were analyzed. Ten were exposed to CS for <5 years, 18 for 5–10 years and 27 for more than 10 years. The frequency of Tregs (CD4⁺CD25⁺CD127⁻FoxP3⁺) was significantly lower in CS exposed workers as compared to HC. We found an increased expression of the activation marker HLA-DR on T cells (CD3⁺, CD4⁺, and CD8⁺) of CS exposed workers as compared to HC. Tregs to activated T cells ratio was also lower in exposed subjects. In the latter, HLA-DR expression level and Tregs frequency were significantly associated with CS exposure duration. Serum autoantibody detection was significantly higher in CS exposed workers as compared to HC. Especially, among workers exposed more than 10 years, antinuclear antibodies and ANCA were detected in 44 and 22% among them, as compared to 5 and 2.5% in HC, respectively.

Conclusion: This work shows that CS exposure is associated with a decrease of Tregs frequency, an increase of T cell activation status, and a tolerance breakdown against auto-antigens. These results show that alterations of the T cell compartment can be detected early over the course of CS exposure, preceding silicosis development or AID onset.

Characterization of the immune response following in vitro mayaro and chikungunya viruses (Alphavirus, Togaviridae) infection of mononuclear cells

Two Alphaviruses stand out for their clinical importance in Brazil: chikungunya (CHIKV) and mayaro (MAYV) viruses. Few studies exist on the mechanisms of the immune response after infection by these viruses and neither a treatment nor a vaccine for these pathogens are available. Although their infection does not have a high mortality rate, they can lead to a joint involvement that can persist for months. The aims of this work were the study of the mechanisms of antiviral immune response following in vitro (U937 cells) infection with these viruses; to investigate the characteristics of the infection by these viruses; and to determine possible molecular targets that could serve as antiviral therapies against these pathogens. Several genes were modulated after infection by these viruses, and the three antiviral detection and response pathways were activated (Toll-like, RIG-I and NOD-like). Eotaxin and IL-6 were induced in all experiments. The cellular immune response profile found for each virus was different, with CHIKV activating primarily an inflammatory response (Th1 and Th17) and MAYV inducing a regulatory/suppressive response, an important feature to contain the inflammation resulting from infection. The data acquired by this study could provide an explanation why CHIKV infections, due to activation of the inflammatory response, are more clinically relevant than MAYV infections, which generates mostly an anti-inflammatory response after infection.

Congenital Cytomegalovirus Infection: Maternal-Child HLA-C, HLA-E, and HLA-G Affect Clinical Outcome

Congenital CMV infection (cCMV) is the most common congenital infection causing permanent long-term impairments (LTI). cCMV immunopathogenesis is largely unknown due to the complex interplay between viral, maternal, placental, and child factors. In this study, a large retrospective nationwide cohort of children with cCMV and their mothers was used. HLA-C, HLA-E, and HLA-G were assessed in 96 mother–child pairs in relation to symptoms at birth and LTI at 6 years of age. The mothers were additionally typed for killer cell immunoglobulin-like receptors. The maternal HLA-G 14 bp deletion/deletion polymorphism was associated with a worse outcome, as the immunomodulation effect of higher protein levels may induce less CMV control, with a direct impact on placenta and fetus. The absence of maternal HLA-C belonging to the C2 group was associated with symptoms at birth, as activating signals on decidual NK may override inhibitory signals, contributing to a placental pro-inflammatory environment. Here, the increased HLA-E*0101 and HLA-C mismatches, which were associated with symptoms at birth, may enhance maternal allo-reactivity to fetal Ags, and cause suboptimal viral clearance. Finally, HLA-C non-inherited maternal antigens (NIMAs) were associated with LTI. The tolerance induced in the fetus toward NIMAs may indirectly induce a suboptimal CMV antiviral response throughout childhood. In light of our findings, the potential role of maternal–child HLA in controlling CMV infection and cCMV-related disease, and the clinical value as predictor for long-term outcome certainly deserve further evaluation.

Induction of a Regulatory Phenotype in CD3+ CD4+ HLA-DR+ T Cells after Allogeneic Mixed Lymphocyte Culture; Indications of Both Contact-Dependent and -Independent Activation

Although the observation of major histocompatibility complex II (MHCII) receptors on T cells is longstanding, the explanation for this occurrence remains enigmatic. Reports of an inducible, endogenous expression exist, as do studies demonstrating a protein acquisition from other cells by mechanisms including vesicle transfer. Irrespective of origin, the presence of the human MHCII isotype, human leukocyte antigen DR (HLA-DR), potentially identifies a regulatory T cell population. Using an allogeneic mixed lymphocyte culture (MLC) to induce an antigen-specific immune response, the role of antigen-presenting cells (APCs) for the presence of HLA-DR on cluster of differentiation 3(CD3)+ CD4+ T cells was evaluated. Moreover, a functional phenotype was established for these T cells. It was demonstrated that APCs were essential for HLA-DR on CD3+ CD4+ T cells. Additionally, a regulatory T cell phenotype was induced in CD3+ CD4+ HLA-DR+ responder T cells with an expression of CD25, CTLA-4, CD62L, PD-1, and TNFRII. This phenotype was induced both with and without physical T cell:APC contact, which could reveal novel indications about its functionality. To further investigate contact-independent communication, a phenotype of the small cell-derived vesicles from the MLCs was determined. Yet heterogeneous, this vesicle phenotype displayed contact-dependent differences, providing clues about their intended function in cellular communication.

DNA methylation patterns in naïve CD4+ T cells identify epigenetic susceptibility loci for malar rash and discoid rash in systemic lupus erythematosus

Objective

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterised by heterogeneous clinical manifestations, autoantibody production and epigenetic dysregulation in T cells. We sought to investigate the epigenetic contribution to the development of cutaneous manifestations in SLE.

Methods

We performed genome-wide DNA methylation analyses in patients with SLE stratified by a history of malar rash, discoid rash or neither cutaneous manifestation, and age, sex and ethnicity matched healthy controls. We characterised differentially methylated regions (DMRs) in naïve CD4+ T cells unique to each disease subset, and assessed functional relationships between DMRs using bioinformatic approaches.

Results

We identified 36 and 37 unique DMRs that contribute to the epigenetic susceptibility to malar rash and discoid rash, respectively. These DMRs were primarily localised to genes mediating cell proliferation and apoptosis. Hypomethylation of MIR886 and TRIM69, and hypermethylation of RNF39 were specific to patients with SLE with a history of malar rash. Hypomethylation of the cytoskeleton-related gene RHOJ was specific to patients with SLE with a history of discoid rash. In addition, discoid rash-specific hypomethylated DMRs were found in genes involved in antigen-processing and presentation such as TAP1 and PSMB8. Network analyses showed that DMRs in patients with SLE with but not without a history of cutaneous manifestations are associated with TAP-dependent processing and major histocompatibility-class I antigen cross-presentation (p=3.66×10⁻¹⁸ in malar rash, and 3.67×10⁻¹³ in discoid rash).

Conclusions

We characterised DNA methylation changes in naïve CD4+ T cells specific to malar rash and discoid rash in patients with SLE. These data suggest unique epigenetic susceptibility loci that predispose to or are associated with the development of cutaneous manifestations in SLE.

Immunisation with an allogeneic peptide promotes the induction of antigen-specific MHC II(pos) CD4+ rat T cells demonstrating immunostimulatory properties

BACKGROUND

The phenomenon of T cell stimulation by MHC class II expressing (MHC II(pos)) CD4+ T cells has been intensively investigated for T cell clones but, so far, not for native T cells. The extensive use of T cell clones may explain the inconsistent outcomes of T cell-mediated antigen-presentation. Therefore, we used freshly isolated primed rat CD4+ T cells induced by immunisation with an allogeneic peptide P1, which is involved in allograft rejection.

METHODS

MHC II(pos) and MHC II(neg) CD4+ T cells were isolated from popliteal lymph nodes of P1-immunised Lewis rats and were purified by combining depletion and positive selection steps. Purified MHC II(pos) CD4+ T cells and MHC II(neg) CD4+ T cells (10⁵ cells per well each) were autostimulated or restimulated with P1-loaded (33 μg/ml peptide P1) and subsequently irradiated (with 20 Gy) autologous DC.

RESULTS

Seven days after immunisation, a small population of MHC II(pos) CD4+ T cells was detectable (approximately 8.0% of total lymph node cells), as well as a large population of MHC II(neg) CD4+ T cells (up to 45%). Antigen-specific proliferation was observed for both T cell populations but only P1-loaded MHC II(pos) CD4+ T cells presented antigen presenting cell (APC) function for P1-primed T cells. Their inability to activate unprimed T cells may be due to impaired surface expression of costimulatory molecules (CD80 and CD86).

CONCLUSION

Immunisation with the allogeneic peptide antigen P1 induced antigen-specific MHC II(pos) CD4+ rat T cells demonstrating perfect APC function for primed T cells in vitro.

Unraveling features of the natural MHC class II peptidome of skin-migrated dendritic cells

Dendritic cells (DCs) migrating from peripheral tissues at steady state are considered the most efficient antigen-presenting cells (APCs) involved in the induction of peripheral T-cell tolerance via self-antigen presentation on MHC class II molecules. However, difficulties in obtaining sufficient numbers of such DCs have precluded previous analyses of their natural MHC class II peptidome in laboratory animals or humans. Here, we overcome this difficulty by collecting the large quantities of sheep DCs that migrate from the skin via the afferent lymphatics at steady state to the draining lymph node. We compared the repertoire of MHC class II-bound peptides from afferent lymph DCs with autologous APCs derived from peripheral blood. A large fraction of the MHC class II peptidome from skin DCs was derived from membrane-recycling proteins (59%) and from proteins of the antigen presentation machinery (50%), whereas these types of peptides constituted a more limited fraction in blood APCs (21 and 11%, respectively). One sheep cytokeratin peptide was identified in the skin DC peptidome indicating active processing of epithelium-derived antigens. Conversely, peptides derived from cytosolic and soluble antigens of the extracellular milieu were more represented in blood APCs than skin DCs. The biased peptidome of skin-migrated DCs indicates that these cells express a peptide repertoire for the generation of self-reactive and/or regulatory T cells mainly directed toward DC molecules from internal and external membranes and to a lesser extent toward antigens of the extracellular milieu, including some tissue-specific peptides.

The lymph node revisited: development, morphology, functioning, and role in triggering primary immune responses

Scenarios have been proposed to explain how lymphoid components of a lymph node favor the encounter of a drained antigen with a circulating competent naïve lymphocyte to trigger a primary immune response. However, these scenarios rest on incorrect concepts about the organ. This situation resulted from a loss of interest for studies on in vivo lymphoid organs due to a widespread switch, decades ago, to work on suspended lymphoid cells. However, an in vivo holistic study of the organ continued in our laboratory. The present review synthesizes resulting knowledge on lymph node morphology and global functioning. We show that the opening of an afferent lymphatic vessel into the subcapsular sinus is the focal point from which the related portion of a lymph node-a node compartment-is developed. As to the formation of a compartment's lymphoid components, it is neonatally orchestrated by the dichotomic nature and distribution of antigens in this subcapsular sinus, which determines a dichotomic recruitment of circulating cells and the compartment's architectural complexity. The transport process of an antigen from a given tissue territory into restricted sites of the draining compartment further defines its local morphological features and activities, while providing the possibility to reduce the wandering of a short-lived naïve cell through innumerable target-devoid sites. We also explain that the nodal lymphoid components are not implicated in the triggering of primary responses, but are rather products of such responses. Scenarios for the triggering of primary responses, consistent with real node morphology and functioning, are proposed.

IL-2/neuroantigen fusion proteins as antigen-specific tolerogens in experimental autoimmune encephalomyelitis (EAE): correlation of T cell-mediated antigen presentation and tolerance induction

The purpose of this study was to assess whether the Ag-targeting activity of cytokine/neuroantigen (NAg) fusion proteins may be associated with mechanisms of tolerance induction. To assess this question, we expressed fusion proteins comprised of a N-terminal cytokine domain and a C-terminal NAg domain. The cytokine domain comprised either rat IL-2 or IL-4, and the NAg domain comprised the dominant encephalitogenic determinant of the guinea pig myelin basic protein. Subcutaneous administration of IL2NAg (IL-2/NAg fusion protein) into Lewis rats either before or after an encephalitogenic challenge resulted in an attenuated course of experimental autoimmune encephalomyelitis. In contrast, parallel treatment of rats with IL4NAg (IL-4/NAg fusion protein) or NAg lacked tolerogenic activity. In the presence of IL-2R(+) MHC class II(+) T cells, IL2NAg fusion proteins were at least 1,000 times more potent as an Ag than NAg alone. The tolerogenic activity of IL2NAg in vivo and the enhanced potency in vitro were both dependent upon covalent linkage of IL-2 and NAg. IL4NAg also exhibited enhanced antigenic potency. IL4NAg was approximately 100-fold more active than NAg alone in the presence of splenic APC. The enhanced potency of IL4NAg also required covalent linkage of cytokine and NAg and was blocked by soluble IL-4 or by a mAb specific for IL-4. Other control cytokine/NAg fusion proteins did not exhibit a similar enhancement of Ag potency compared with NAg alone. Thus, the IL2NAg and IL4NAg fusion proteins targeted NAg for enhanced presentation by particular subsets of APC. The activities of IL2NAg revealed a potential relationship between NAg targeting to activated T cells, T cell-mediated Ag presentation, and tolerance induction.

Role of MHC class II expressing CD4+ T cells in proteolipid protein(91-110)-induced EAE in HLA-DR3 transgenic mice

MHC class II molecules play a central role in the control of adaptive immune responses through selection of the CD4(+) T cell repertoire in the thymus and antigen presentation in the periphery. Inherited susceptibility to autoimmune disorders such as multiple sclerosis, rheumatoid arthritis and IDDM are associated with particular MHC class II alleles. Advent of HLA transgenic mice has helped us in deciphering the role of particular HLA DR and DQ class II molecules in human autoimmune diseases. In mice, the expression of class II is restricted to professional antigen-presenting cells (APC). However, in humans, class II is also expressed on T cells, unlike murine T cells. We have developed new humanized HLA class II transgenic mice expressing class II molecules not only on APC but also on a subset of CD4(+) T cells. The expression of class II on CD4(+) T cells is inducible, and class II(+) CD4(+) T cells can present antigen in the absence of APC. Further, using EAE, a well-established animal model of MS, we tested the functional significance of these class II(+) CD4(+) T cells. DR3.AEo transgenic mice were susceptible to proteolipid protein(91-110)-induced EAE and showed CNS pathology accompanied by widespread inflammation and demyelination seen in human MS patients, suggesting a role for class II(+) CD4(+) T cells in the pathogenesis.

Vaccination with Theratope (STn-KLH) as treatment for breast cancer

Cancer vaccines have demonstrated that they can stimulate antibody and cell-mediated immune responses against tumor-associated antigens in the laboratory. However, few clinical studies with cancer vaccines have demonstrated convincing clinical responses. Sialyl-Tn is a carbohydrate associated with MUC1. It is a unique tumor-associated antigen, present on many adenocarcinomas including breast, ovarian, colorectal, gastric and pancreatic. Consequently, Sialyl-TN is an ideal candidate for boosting the patient's immune system specifically against a unique tumor-associated antigen. The cancer vaccine Theratope was developed by Biomira, Inc. using a synthetic Sialyl-Tn antigen that emulates the unique carbohydrate on human cancer. Clinical trials have predominantly been carried out in breast cancer patients and these trials are outlined in this profile.

Mycobacterial immune reconstitution inflammatory syndrome in HIV-1 infection after antiretroviral therapy is associated with deregulated specific T-cell responses: beneficial effect of IL-2 and GM-CSF immunotherapy

BACKGROUND

With the advent of antiretroviral therapy (ART) cases of immune reconstitution inflammatory syndrome (IRIS) have increasingly been reported. IRIS usually occurs in individuals with a rapidly rising CD4 T-cell count or percentage upon initiation of ART, who develop a deregulated immune response to infection with or without reactivation of opportunistic organisms. Here, we evaluated rises in absolute CD4 T-cells, and specific CD4 T-cell responses in 4 HIV-1+ individuals presenting with mycobacterial associated IRIS who received in conjunction with ART, IL-2 plus GM-CSF immunotherapy.

METHODS

We assessed CD4 T-cell counts, HIV-1 RNA loads, phenotype for naïve and activation markers, and in vitro proliferative responses. Results were compared with those observed in 11 matched, successfully treated asymptomatic clinical progressors (CP) with no evidence of opportunistic infections, and uninfected controls.

RESULTS

Median CD4 T-cell counts in IRIS patients rose from 22 cells/microl before initiation of ART, to 70 cells/microl after 8 months of therapy (median 6.5 fold increase). This coincided with IRIS diagnosis, lower levels of naïve CD4 T-cells, increased expression of immune activation markers, and weak CD4 T-cell responses. In contrast, CP had a median CD4 T-cell counts of 76 cells/microl at baseline, which rose to 249 cells/microl 6 months post ART, when strong T-cell responses were seen in > 80% of patients. Higher levels of expression of immune activation markers were seen in IRIS patients compared to CP and UC (IRIS > CP > UC). Immunotherapy with IL-2 and GM-CSF paralleled clinical recovery.

CONCLUSION

These data suggest that mycobacterial IRIS is associated with inadequate immune reconstitution rather than vigorous specific T-cell responses, and concomitant administration of IL-2 and GM-CSF immunotherapy with effective ART may correct/augment T-cell immunity in such setting resulting in clinical benefit.

Human leukocyte antigen-class II-negative long-term cultured human T-cell leukemia virus type-I-infected T-cell lines with progressed cytological properties significantly induce superantigen-dependent normal T-cell proliferation

While most human T-cell leukemia virus type-I (HTLV-I)-infected T cells express abundant class II antigens, some aggressive-type adult T-cell leukemia (ATL) cells lose their expression. To investigate the significance of the class II antigen of HTLV-I infected cells, the progressiveness of HTLV-I-infected long-term cultured T-cell lines was evaluated, and then their antigen-presenting capacity was examined using a superantigen, staphylococcus enterotoxin B (SEB). Among the cell lines derived from peripheral blood, HPB-ATL-T (ATL-T), HPB-ATL-2 (ATL-2) and HPB-ATL-O were more progressed than Tax exclusively expressing HPB-CTL-I (CTL-I), because the former deleted p16 gene (polymerase chain reaction (PCR)) and strongly transcribed survivin (reverse transcriptase-PCR). Notably, interferon gamma-independent loss of class II expression of ATL-T and ATL-2 was found. In antigen-presenting experiments, however, both cell lines induced SEB-dependent significant T-cell proliferation estimated by [(3)H] thymidine uptake. No class II-re-expressed ATL-2 cells were observed in the SEB-presenting cultures by indirect immunofluorescence, and only minimum inhibition of SEB-dependent T-cell response by anti-human leukocyte antigen (HLA)-DR monoclonal antibody was observed. These findings suggest that both ATL-T and ATL-2 very effectively present SEB to T cells less dependently on class II molecules. These less immunogenic leukemic cells of aggressive ATL may contribute to disease aggression.

MHC class II biosynthesis by activated rat CD4+ T cells: development of repression in vitro and modulation by APC-derived signals

This study focused on synthesis of MHC class II glycoproteins (MHCII) by rat CD4(+) T-helper cells. During activation in Con A and IL-2, purified rat splenic CD4(+) T cells expressed abundant surface MHCII together with transcripts for I-A alpha/beta, invariant chain, and the type III and type IV MHC class II transactivator (CIITA). Activated thymic CD8(+)CD4(-) and CD8(+)CD4(+) T cells exhibited essentially the same phenotype. MHCII synthesis by CD4(+) T cells enabled presentation of myelin basic protein (MBP) to antigen-specific responders. T cell expression of MHCII was due to direct biosynthesis rather than adsorption from professional APC; indeed, T cell-mediated expression of MHCII was optimal in the absence of professional APC. Despite periodic reactivation with Con A during 3-4 weeks of culture, CD4(+) T cells repressed MHCII synthesis and reverted to a MHCII(-) phenotype. These short-term lines resembled established lines of MBP-specific T cells in that mitogenic activation elicited extensive blastogenesis without MHCII synthesis. Activation-dependent synthesis of MHCII however was partially restored in lines of mitogen-stimulated T cells when the cultures were reconstituted with irradiated splenic APC. These data indicate that most naive rat CD4(+) T cells exhibit activation-dependent synthesis of MHCII whereas continuously propagated T cells require an APC-derived signal to support MHCII synthesis.

Function and regulation of MHC class II molecules in T-lymphocytes: of mice and men

The main function of major histocompatibility complex (MHC) class II molecules is to present processed antigens, which are derived primarily from exogenous sources, to CD4(+) T-lymphocytes. MHC class II molecules thereby are critical for the initiation of the antigen-specific immune response. Besides antigen presentation, growing evidence is showing that ligation of MHC class II molecules also activates intracellular signaling pathways, frequently leading to apoptosis. Constitutive expression of MHC class II molecules is confined to professional antigen-presenting cells (APC) of the immune system, and in nonprofessional APCs MHC class II molecules can be induced by a variety of immune regulators. Interestingly, activated T cells from many species, with the exception of mice, synthesize and express MHC class II molecules at their cell surface. In this review, we discuss our current knowledge on the transcriptional regulation of MHC class II expression in activated human and mouse T cells, and the contribution of DNA methylation of the T-cell employed class II transactivator promoter III to the MHC class II deficiency of mouse T cells. We also discuss the proposed functions of the activated T cell synthesized and expressed MHC class II molecules, including antigen presentation, T-T cell interactions, and MHC class II-mediated intracellular signaling.

Regulation of MHC class II expression in human T-cell malignancies

Expression of major histocompatibility complex (MHC) class II molecules in human activated T cells is under normal circumstances regulated exclusively by the CIITA-PIII subtype of the class II transactivator (CIITA). In this study, we show that the absence of MHC class II expression in leukemic T cells was due to a lack of expression of CIITA, whereas in T-lymphoma cells, expression of CIITA correlated with expression of MHC class II. Interestingly, activation of a CIITA-promoter (P)III-reporter construct was not affected in leukemic T cells. This revealed that the absence of endogenous CIITA expression was not caused by a lack of transcription factors critical for CIITA-PIII activation but suggests the involvement of an epigenetic silencing mechanism. Subsequent analysis showed that the lack of human leukocyte antigen-DR (HLA-DR) expression correlated with hypermethylation of CIITA-PIII in leukemic T-cell lines and in primary T-cell acute lymphoblastic leukemia (T-ALL) and a T-cell prolymphocytic leukemia (T-PLL). Treatment of leukemic T-cell lines with a demethylation agent showed re-expression of CIITA-PIII and HLA-DRA. Furthermore, in vitro methylation of CIITA-PIII and subsequent assessment of CIITA-PIII activity in Jurkat leukemic T cells resulted in reduction of constitutive and CREB-1 (cyclic adenosine monophosphate [cAMP]-response element binding protein 1)-induced promoter activity. Together, these results argue for an important role of DNA hyper-methylation in the control of CIITA expression in leukemic T cells.

Cytotoxic T cells with reciprocal antigenic peptide presentation function are not generally resistant to mutual lysis

Cytotoxic T cells normally express major histocompatibility complex class I molecules, to which their T cell antigen receptors are restricted. Therefore, a single cytotoxic T cell can not only act as a cytolytic effector cell, but also as an antigen-presenting cell for other cytotoxic T cells of the same or a different clone. In the present paper, we used a murine cytotoxic T cell clone, 10BK.1, recognizing the ovalbumin-derived peptide OVA257-264 in combination with H-2Kb to investigate the consequences of reciprocal antigen presentation by these cytotoxic T cells. These cells proliferate after incubation with the relevant peptide in the absence of added accessory cells, indicating reciprocal antigenic peptide presentation by the cytotoxic T cell. We found that reciprocal lysis of these cells was dependent on the time point of incubation with antigen. We did not observe reciprocal lysis of cytotoxic T cells used 30 days after the last restimulation with antigen. In contrast, 10BK.1 cells used two days after the last restimulation showed an increased capacity for reciprocal lysis. The lytic capacity decreased with time after restimulation. Reciprocal lysis of 10BK.1 cells depended on reciprocal peptide presentation by at least two 10BK.1 cells. Recognition of the antigenic peptide, together with class I molecules on the surface of classical syngeneic target cells did not induce lysis of freshly stimulated 10BK.1 cells, suggesting that reciprocal lysis was not just a consequence of re-activation of the cytotoxic T cells. Reciprocal destruction of freshly activated 10BK.1 cells proceeded independent of CD95/CD95 ligand. Despite an increased secretion of tumour necrosis factor-alpha by 10BK.1 cells on day 2 after antigen stimulation, compared with cells on day 30 after stimulation, tumour necrosis factor-alpha was not responsible for the reciprocal destruction of freshly stimulated 10BK.1 cells. Lysis of preactivated 10BK.1 cells was independent of autocrine interleukin-2 production by the cytotoxic T cells, but interleukin-2 was required for optimal priming of cytotoxic T cells for reciprocal lysis.

Monitoring CD4+ T cell responses against viral and tumor antigens using T cells as novel target APC

CD4+ T cells play an important role in the induction and maintenance of an effective antiviral and antitumor immune response. However, standardized monitoring of antigen-specific CD4+ T cells has not been established at the single-cell level. We now present a sensitive, specific, and simple methodology in which purified memory CD4+ T cells are expanded from PBMC in a single cycle of antigen-driven stimulation and quantitatively assayed by interferon-gamma ELISPOT. Issues of nonspecific background in assays were resolved with the use of innovative target cells, autologous PHA-expanded CD4+ T cells (T-APC). Remarkably, T-APC could not only present peptide epitopes from model antigens NY-ESO-1 and influenza nucleoprotein, but could also process full-length antigen endogenously expressed from recombinant fowlpox vector. This approach makes it possible to monitor CD4+ T cells in large series of patients, regardless of HLA haplotype, against the full peptide repertoire of a given antigen.

Acquisition of CD80 by human T cells at early stages of activation: functional involvement of CD80 acquisition in T cell to T cell interaction

The interaction between CD28 on T cells and CD80 on APCs intensifies the linkage between TCR and MHC at the site of contact between T cells and APCs. In this study, we demonstrate that during human T cell/human APC interaction, the autologous or allogeneic human CD4(+) T cells become positive for the detection of CD80 at an early stage of activation (24 h). This detection of CD80 is attributable to the acquisition of CD80 from APCs, as opposed to the up-regulation of endogenous CD80, as demonstrated by CD4(+) T cells treated with cyclohexamide. Furthermore, no CD80 mRNA could be detected at 24 h in T cells that had acquired CD80 from APCs. CD80 acquisition by T cells from APCs was enhanced upon TCR engagement. The amount of CD80 acquisition by CD4(+) T cells was shown to be related to the expression of CD80 on APCs. Using soluble fusion proteins (soluble CTLA-4, CD28, and CD80) to block either CD28 on the surface of T cells or CD80 on the surface of APCs, it was demonstrated that CD80 acquisition by T cells is mediated through its receptors, possibly CD28 interaction. Moreover, we demonstrate that T cells that have acquired CD80 have the ability to stimulate other T cells. These data thus suggest that CD80 acquisition by human T cells might play a role in the immunoregulation of T cell responses.

Regulatory functions of human CD4(+) T cells recognizing allopeptides in the context of self-HLA class II

Pretransplant blood transfusions sharing one human leukocyte antigen DR (HLA-DR) with the recipient have been shown to enhance graft survival, whereas HLA-DR mismatched blood transfusions will lead to immunization of the patient. The involvement of self HLA-DR suggests a role for CD4(+) regulatory T cells recognizing allopeptides in the context of self HLA class II molecules. Specific immunoregulation may be due to recognition of these allopeptides in the DR molecules of autologous T cells or dendritic cells. We tested this hypothesis on the basis of the reactivity of cell line ThoU6 which recognizes a peptide derived from an allo DR3 molecule, in the context of self DPB1*0301, and EL26, a CD4(+) T-cell clone recognizing HLA-A2 peptide in the presence of DRB1*1501. Addition of the line and clone to an assay in which the alloreactive cytotoxic T cell response (in a limiting dilution analysis) of PBLs sharing the restriction element was measured, resulted in a suppression of the anti-donor response but only when the proper peptide was added. These regulatory CD4(+) T cells were cytotoxic for targets presenting the proper peptide in the context of self MHC class II. Furthermore, these cells produced IL-10 after stimulation with the specific MHC/peptide combinations. Despite the similarity in function, EL26 and ThoU6 showed some differences in their phenotypic characteristics. Although both were CD25(+), EL26 expressed surface TGF-beta and CTLA-4, while ThoU6 did not. Similar regulatory T cells may explain the enhanced graft survival after HLA-DR shared blood transfusions either by their interaction with autologous alloreactive T cells or by modulation of autologous dendritic cells presenting the peptide involved.

MHC Alloantigens Elicit Secondary, But Not Primary, Indirect In Vitro Proliferative Responses

The relative contributions of direct and indirect pathways of allorecognition to graft rejection remain controversial. Recent reports suggest that the indirect pathway may play a prominent role in both acute and chronic allograft rejection. Such studies suggest that MHC-derived allopeptides are more immunogenic than those derived from minor histocompatibility or other nominal Ags. The aim of this study was to characterize the immunogenicity of MHC alloantigens in MHC-defined miniature swine via primary and secondary MLR culture assays. APCs were selectively depleted from either responder or stimulator cell populations to specifically analyze direct and indirect proliferative responses, respectively. Radio-resistant cytokine secretion and subsequent backstimulation of responder cells was eliminated by using stimulators that were either lysed or unresponsive to the responder MHC haplotypes. When the effect of backstimulation was eliminated from MLR culture assays, indirect proliferative responses were not observed among naive responders. Only after in vivo priming of responder animals could indirect proliferation be detected. These data do not refute the potential importance of indirect allorecognition in graft rejection. However, they suggest that MHC-derived alloantigens behave similarly in vitro to minor histocompatibility Ags, with comparable immunogenicity. These data also suggest that the MLR culture assay does not accurately reflect the importance of indirect mechanisms that have previously been reported in experimental models of graft rejection. A greater understanding of the indirect pathway and the associated immunogenicity of MHC allopeptides has the potential benefit of enabling the development of therapeutic interventions to prevent or halt allograft rejection.

Regulation and specificity of MHC2TA promoter usage in human primary T lymphocytes and cell line

Although activated human T cells express MHC class II antigens, the regulation of these antigens in T cells is poorly understood. This study focuses on the control of the MHC2TA gene in these cells. MHC2TA encodes the transcriptional master regulator of MHC class II, the class II trans-activator (CIITA). It has at least three distinct promoters (PI, PIII, and PIV), each active in an overlapping subset of cell types and directing a slightly different product. This report used highly purified blood T cells prepared by negative immunoselection to analyze CIITA. Real-time PCR analysis indicates that resting T cells do not express detectable CIITA transcript, while activated T cells express the PIII CIITA form. Transient transfection of activated blood T cells using wild-type and mutant PIII promoter-reporter constructs shows that two promoter elements, activation response element-1 (ARE-1) and ARE-2, are important for PIII function. cAMP response element binding protein, a known activator of gene expression in activated T cells, activates PIII in primary T cells. However, an intact ARE-2 site is not required for this activation, indicating that cAMP response element binding protein does not activate via this site. EMSAs indicate that an activating transcription factor/cAMP response element binding protein/cAMP response element modulator family member, but not phosphorylated cAMP response element binding protein-1, binds to ARE-2. ARE-2 also forms a complex with an unidentified protein. The ARE-2 binding protein is constitutively expressed in a DR(+) T cell line, reflecting differences between the DR(+) cell line and primary blood lymphocytes. These results show that MHC2TA PIII is induced in activated T lymphocytes, and that the induced binding of ARE-2 is a crucial step in this process.

Cytotoxic HIV-1 p55gag-specific CD4+ T cells produce HIV-inhibitory cytokines and chemokines

CD4+ T-helper cells appear to be essential in sustaining immune responses in chronic viral infections, as the maintenance of CD8+ cytotoxic T-lymphocyte responses and the control of viremia were demonstrated to depend on CD4+ T cell help. In order to investigate the function of HIV-specific CD4+ T cells in chronic HIV-1-infection, 49 chronically HIV-infected patients were analyzed before and 3 and 6 months after initiation of antiviral treatment. Ten patients showed a substantial, although weak, proliferative response to HIV-1-p55gag protein for which no improvement was observed upon initiation of HAART. From one individual, HIV-1-p55gag-specific CD4-positive T-cell clones were generated that were heterogeneous in their TCR Vbeta gene usage and HLA-DRB1*13 and DRB1*03 restricted, respectively. In addition, some CD4+ TCC produced substantial amounts of IFN-gamma and MIP-1alpha/beta were perforin-positive, and showed cytotoxic activity. These diverse functional features of HIV-specific CD4+ T cells suggest that they may exert direct antiviral activity.

Acquisition of functional MHC class II/peptide complexes by T cells during thymic development and CNS-directed pathogenesis

This study provides evidence that both rat and mouse thymic and splenic T cells express significant levels of MHC class II glycoproteins (MHCII) in vivo. Derivation of rat and mouse chimeras revealed that a major source of MHCII on thymic T cells was acquired from radioresistant host APC. Expression of MHC on thymic T cells appeared physiologically relevant because presentation of rat myelin basic protein (RMBP) by nonadherent, radiosensitive thymic T cells was associated with the adoptive transfer of tolerance. Mature MBP-specific effector T cells isolated from the CNS in both rat and mouse models of EAE also expressed significant levels of MHCII. Adoptive transfer of activated B10.PL MBP/I-A(u)-restricted TCR transgenic T cells into F1(C57BL/6 x B10.PL) mice revealed acquisition of allogeneic I-A(b) on encephalitogenic CNS-derived T cells. Overall, this study indicates that immature and mature T cells in rats and mice acquire functional MHCII in vivo during thymic development and pathogenic inflammation.

Activated human T cells accomplish MHC class II expression through T cell-specific occupation of class II transactivator promoter III

Activated human T cells express HLA-DR, HLA-DQ, and HLA-DP on their surface, but the regulation and functioning of MHC class II molecules in T lymphocytes are poorly understood. Because the MHC class II transactivator (CIITA) is essential for MHC class II expression, we have investigated transcriptional activation of CIITA in activated T cells. In this study, we show that in human activated CD4(+) T cells, CIITA promoter III (CIITA-PIII) drives the expression of CIITA. The in vivo genomic footprint analysis revealed activated T cell-specific occupation of CIITA-PIII. Subsequent EMSA analysis of several promoter regions showed differences in banding pattern among activated T cells, naive T cells, primary B cells, and Raji B cells. Activating response element (ARE)-1 is shown to interact with the acute myeloid leukemia 2 transcription factor in nuclear extracts derived from both T and B cells. Interestingly, the acute myeloid leukemia 3 transcription factor was bound in nuclear extracts of T cells only. The ARE-2 sequence is able to bind CREB/activating transcription factor family members in both T and B cells. In addition, a yet unidentified Ets family member was found to interact with site C in activated T cells, whereas in B cells site C was bound by PU.1 and Pip/IFN regulatory factor 4/IFN consensus sequence binding protein for activated T cells. In Jurkat T cells, both ARE-1 and ARE-2 are crucial for CIITA-PIII activity, similar to Raji B cells. The differential banding pattern in in vivo genomic footprinting and transcription factor binding at the ARE-1 and site C between T cells and B cells probably reflects differences in CIITA-PIII activation pathways employed by these cell types.

Theratope vaccine (STn-KLH)

Active specific immunotherapy (ASI) is a promising approach to treating cancer. Numerous studies in the laboratory have demonstrated that various cancer vaccines can stimulate antibody and cell mediated immune responses against tumour-associated antigens [1-9]. Yet few studies have demonstrated convincing clinical responses. Sialyl-Tn (STn) is a carbohydrate associated with the MUC1 mucin on a number of human cancer cells and is associated with more aggressive disease. Consequently, STn is an ideal candidate for ASI therapy. Theratope vaccine is a cancer vaccine that was designed by Biomira, Inc. (Edmonton, Alberta, Canada) by incorporating a synthetic STn antigen that emulates the carbohydrate seen on human tumours. The clinical trials conducted to date with Theratope vaccine are outlined in this report. Overall, Theratope vaccine has been well-tolerated with minimal toxicity. The most common side effects have been in duration and erythema at the site of injections. Both in a non-transplant setting following low dose iv. cyclophosphamide and high dose autologous transplant setting, there has been a trend toward Theratope vaccine decreasing the risk for relapse, prolonging the time to relapse and thus impacting on overall survival. The definitive Phase III trial comparing the outcome of patients with metastatic breast cancer receiving vaccinations with Theratope vaccine versus vaccination with the nonspecific immune stimulants Keyhole Limpet Hemocyanin (KLH) and Detox -B stable emulsion (Detox-B) (now called Enhanzyn Immunostimulant) was closed to enrolment on March 30, 2001. Over 1000 women with distant metastatic breast cancer were enrolled into the program.

MHC class-II-restricted antigen presentation by myelin basic protein-specific CD4+ T cells causes prolonged desensitization and outgrowth of CD4- responders

T cells express MHC class II glycoproteins under various conditions of activation or inflammation. To assess whether T cell APC (T-APC) activity had long-term tolerogenic consequences, myelin basic protein (MBP)-specific rat T cells were induced to acquire MBP-derived I-A complexes to promote reciprocal antigen presentation. T-T antigen presentation caused extensive cell death among T-APC and MBP-specific T responders and caused long-term desensitization of surviving responders. Addition of the anti-I-A mAb OX6 to activated I-A+ responders inhibited T-APC activity, accelerated recovery from postactivation refractoriness, and prevented long-term loss of reactivity in responder T cells. Antigenic activation of responder T cells with irradiated T-APC induced profound losses in reactivity that lasted for over 1 month of propagation in IL-2 and was associated with preferential outgrowth of CD4- T cells. Antigen-activated CD4- T cells exhibited more rapid IL-2-dependent growth that eventually normalized compared to CD4+ T cells 1-2 months after antigen exposure. In conclusion, expression of T-APC activity by activated T cells represents an important negative feedback pathway that depletes antigen-reactive T cells and causes long-term desensitization of surviving T cells. Hence, T cell APC may be an important mechanism of self-tolerance.

Acquisition of CD80 (B7-1) by T cells

Activation of T cells usually requires two signals. Signal 1 is mediated via a peptide-MHC on the APC; signal 2 is mediated via a costimulatory molecule on the APC surface. We demonstrate here that naive CD4(+) T cells actually acquire the costimulatory molecule CD80 (B7-1) from syngeneic APCs after activation. This phenomenon was demonstrated showing acquisition of CD80 by T cells from CD80/CD86 (B7-2) knockout mice, and by treating T cells with cyclohexamide to further rule out endogenous expression of CD80 by T cells. Moreover, no CD80 mRNA could be detected in T cells that had acquired CD80. The amount of acquisition of CD80 by T cells was shown to be directly related to both the strength of signal 1 and the amount of CD80 on the APC. Specificity of this acquisition was also shown by the lack of acquisition by T cells from CD28 knockout mice (implicating CD28 in this process), the lack of acquisition of CD40 (another molecule on the APC surface) by T cells, and confocal microscopy studies. We demonstrate for the first time that 1) naive T cells, following acquisition of CD80 from APCs, were themselves shown to be capable of acting as APCs; and 2) memory T cells that have acquired CD80 from APCs undergo apoptosis in the presence of increased levels of signal 1. Thus we demonstrate both immunostimulatory and immunoregulatory functions as a result of CD80 acquisition by different T cell populations.

Localization of soluble major histocompatibility class II-peptide complexes on T cell surface

Affinity purified major histocompatibility (MHC)-peptide complexes are heterodimeric cell surface glycoproteins and are known to recognize antigen-specific CD4(+) T cell receptors (TCRs). In general, the affinity of MHC-peptide complexes to TCRs are considered very low with a K(D) of 5 x 10(-5) M and, therefore, stabilization of these complexes on T cell surface was not reported earlier. This could be due to (1) incomplete occupancy of MHC molecules with antigenic peptides, (2) variability of the binding constant of peptides to MHC molecules, (3) presence of endogenously bound peptides in MHC preparations, or (4) a combination of these. Using well-characterized HLA-DR2 complex loaded with a high affinity immunodominant epitope analog from human myelin basic protein (MBP), which shows release of gamma-IFN by specific stimulation of transformed human T cell clone (SS8T). The present report demonstrates a method for the localization of bound MHC class II-peptide complexes on T cell surface by backscatter electron imaging using in-lens Field Emission Scanning Electron Microscopy (FESEM). The localization is specific to the complex recognized by the TCR on MHC class II (DR2) and MBP peptide restricted human T cells.

Recipient elimination of allogeneic lymphoid cells: donor CD4+ cells are effective alloantigen-presenting cells

The encounter with allogeneic major histocompatibility complex (MHC) molecules expressed on donor leukocytes during transfusion of blood products has been shown to impact the recipient's immune responses in a number of settings. To better understand the responses induced by the transfer of allogeneic cells, a murine model was used to characterize the recipient responses that control the fate of the allogeneic lymphoid cells. Recipient CD8+ cells could rapidly eliminate a large number of donor cells within 3 days after injection. When elimination responses were studied in the absence of CD8+ cells, it was found that alloantibody production was the secondary elimination mechanism. Optimal recipient CD8+ and B cell responses in this model required help from CD4+ cells that could be provided by 3 different pathways. Although recipient CD4+ cells could provide help when activated by direct recognition of allogeneic MHC class II molecules expressed on donor cells or by indirect recognition of processed alloantigen presented on recipient antigen-presenting cells (APCs), the most rapid recipient responses were generated by help provided by donor CD4+ cells. Purified donor CD4+ cells were also able to induce these rapid responses, indicating that activated donor CD4+cells expressing allogeneic MHC molecules were able to effectively stimulate responses by both recipient CD8+ and B cells.

Recipient elimination of allogeneic lymphoid cells: donor CD4+ cells are effective alloantigen-presenting cells

The encounter with allogeneic major histocompatibility complex (MHC) molecules expressed on donor leukocytes during transfusion of blood products has been shown to impact the recipient's immune responses in a number of settings. To better understand the responses induced by the transfer of allogeneic cells, a murine model was used to characterize the recipient responses that control the fate of the allogeneic lymphoid cells. Recipient CD8+ cells could rapidly eliminate a large number of donor cells within 3 days after injection. When elimination responses were studied in the absence of CD8+ cells, it was found that alloantibody production was the secondary elimination mechanism. Optimal recipient CD8+ and B cell responses in this model required help from CD4+ cells that could be provided by 3 different pathways. Although recipient CD4+ cells could provide help when activated by direct recognition of allogeneic MHC class II molecules expressed on donor cells or by indirect recognition of processed alloantigen presented on recipient antigen-presenting cells (APCs), the most rapid recipient responses were generated by help provided by donor CD4+ cells. Purified donor CD4+ cells were also able to induce these rapid responses, indicating that activated donor CD4+cells expressing allogeneic MHC molecules were able to effectively stimulate responses by both recipient CD8+ and B cells.

Regulation of human cell engraftment and development of EBV-related lymphoproliferative disorders in Hu-PBL-scid mice

Human PBMC engraft in mice homozygous for the severe combined immunodeficiency (Prkdcscid) mutation (Hu-PBL-scid mice). Hu-PBL-NOD-scid mice generate 5- to 10-fold higher levels of human cells than do Hu-PBL-C.B-17-scid mice, and Hu-PBL-NOD-scid beta2-microglobulin-null (NOD-scid-B2mnull) mice support even higher levels of engraftment, particularly CD4+ T cells. The basis for increased engraftment of human PBMC and the functional capabilities of these cells in NOD-scid and NOD-scid-B2mnull mice are unknown. We now report that human cell proliferation in NOD-scid mice increased after in vivo depletion of NK cells. Human cell engraftment depended on CD4+ cells and required CD40-CD154 interaction, but engrafted CD4+ cells rapidly became nonresponsive to anti-CD3 Ab stimulation. Depletion of human CD8+ cells led to increased human CD4+ and CD20+ cell engraftment and increased levels of human Ig. We further document that Hu-PBL-NOD-scid mice are resistant to development of human EBV-related lymphoproliferative disorders. These disorders, however, develop rapidly following depletion of human CD8+ cells and are prevented by re-engraftment of CD8+ T cells. These data demonstrate that 1) murine NK cells regulate human cell engraftment in scid recipients; 2) human CD4+ cells are required for human CD8+ cell engraftment; and 3) once engrafted, human CD8+ cells regulate human CD4+ and CD20+ cell expansion, Ig levels, and outgrowth of EBV-related lymphoproliferative disorders. We propose that the Hu-PBL-NOD-scid model is suitable for the in vivo analysis of immunoregulatory interactions between human CD4+ and CD8+ cells.

Anergic T cells as active regulators of the immune response

T cell anergy is one of the mechanisms leading to the establishment and maintenance of peripheral tolerance. Recent data from our and other laboratories indicate that anergic T cells are not functionally inert but in fact are capable of regulating the immune response in an active manner. In this review, we describe our viewpoint on how anergic self-reactive T cells could contribute to regulation of the immune response.

Strategies to evaluate metabolic stress and catabolism by means of immunological variables

In this article, we outline how metabolic stress and catabolism are set off and influenced by the neuroendocrine network that interacts intensely with the immune system. When evaluating metabolic stress in individuals, the vast ocean of mediators, cell-surface markers and intracellular components that participate in metabolism and catabolic or anabolic changes make it necessary to focus on specific entities that may best mirror all these events. T cell responsiveness and factors that orchestrate the T helper type 1 and type 2 balance form an immunological mirror that can competently reflect catabolism and metabolic stress.

Activation of alloreactive T cells by allogeneic nonprofessional antigen-presenting cells and interleukin-12 from bystander autologous professional antigen-presenting cells

BACKGROUND

After solid organ transplantation most alloantigens are presented to the recipient's immune system by normal tissue cells, which can be considered to act as nonprofessional antigen-presenting cells (APC). It is well accepted that such nonprofessional APC fail to activate recipient resting T cells due to their inability to deliver costimulatory activity. In our study, we tested a hypothesis that such costimulatory activity may be provided by "bystander" recipient professional APC.

METHODS

We set up mixed lymphocyte cultures (MLC) of purified T cell responders and T cell stimulator cells, the latter as nonprofessional APC carrying allogeneic MHC class I and II, and tested if responder-type autologous APC could facilitate responder T cell proliferation. In this assay also the effects of anti-CD28 antibody and interleukin- (IL) 1beta, IL-6, or IL-12 mediated costimulation on responder T cell proliferation and IL-2 production were investigated.

RESULTS

Autologous APC, i.e., monocytes, were found to facilitate the proliferative response of resting T cells stimulated by allogeneic nonprofessional APC. IL-12 was identified as the most important costimulatory factor for induction of proliferation. IL-1beta enhanced IL-2 production and proliferation of allostimulated resting T cells but its presence was not essential. Although CD28 triggering alone was ineffective, this costimulatory pathway enhanced IL-2 production and proliferation when combined with IL-12 or IL-1beta.

CONCLUSIONS

We conclude that costimulatory activity for activation of resting human T cells by nonprofessional donor APC can be delivered through activity of bystander recipient-type autologous APC. This mechanism of allostimulation may contribute to the induction and perpetuation of alloreactivity "in vivo" in a time frame when intragraft professional donor-type APC have been replaced with professional recipient-type APC.

Class II MHC/Peptide Complexes Are Released from APC and Are Acquired by T Cell Responders During Specific Antigen Recognition

T cell expression of class II MHC/peptide complexes may be important for maintenance of peripheral self-tolerance, but mechanisms underlying the genesis of class II MHC glycoproteins on T cells are not well resolved. T cell APC (T-APC) used herein were transformed IL-2-dependent clones that constitutively synthesized class II MHC glycoproteins. When pulsed with myelin basic protein (MBP) and injected into Lewis rats, these T-APC reduced the severity of experimental autoimmune encephalomyelitis, whereas unpulsed T-APC were without activity. Normal MBP-reactive clones cultured without APC did not express class II MHC even when activated with mitogens and exposed to IFN-γ. However, during a 4-h culture with T-APC or macrophage APC, recognition of MBP or mitogenic activation of responder T cells elicited high levels of I-A and I-E expression on responders. Acquisition of class II MHC glycoproteins by responders was resistant to the protein synthesis inhibitor cycloheximide, coincided with transfer of a PKH26 lipophilic dye from APC to responders, and resulted in the expression of syngeneic and allogeneic MHC glycoproteins on responders. Unlike rested I-A− T cell clones, rat thymic and splenic T cells expressed readily detectable levels of class II MHC glycoproteins. When preactivated with mitogens, naive T cells acquired APC-derived MHC class II molecules and other membrane-associated proteins when cultured with xenogeneic APC in the absence of Ag. In conclusion, this study provides evidence that APC donate membrane-bound peptide/MHC complexes to Ag-specific T cell responders by a mechanism associated with the induction of tolerance.

Immunological self/nonself discrimination: integration of self vs nonself during cognate T cell interactions with antigen-presenting cells

The hypothesis is presented that immunological integration of nonefficacious vs efficacious T cell antigen receptor (TCR) signals are foundational for self/nonself discrimination and that multiple integrative mechanisms are intrinsic to the molecular to molar organization of an adaptive immune response. These integrative mechanisms are proposed to adaptively regulate expression of costimulatory signals, such that foreign proteins are associated with the expression of costimulatory signals, whereas self-proteins are associated with the lack of costimulatory signaling. Overall, this model offers several unique contributions to the study of immunology. First, this model postulates that cognate TCR/major histocompatibility complex (MHC) interactions are sufficient to adaptively mediate immunological self/nonself discrimination. This model thereby offers a unique alternative to models that largely rely on innate immunity to prime immune discrimination. Second, the integrative model argues that the immune system can simultaneously reinforce self-tolerance and promote immunity to foreign organisms at the same time and in the same location. Many alternative models presume that pathogenic self-reactive T cells do not exist at the outset of an immune response against foreign agents. Third, the integrative model uniquely predicts relationships between immunodeficiency and autoimmune pathogenesis. Fourth, this model illustrates the regulatory advantages of cognate antigen presenting cell (APC) systems (i.e., T cell or B cell APC) compared to nonspecific APC. Cognate APC systems together with the respective clonotypic responders may comprise a fundamental "network" of lymphoid cells. Such networks would have clone-specific regulatory capabilities and may be central for immunological self/nonself discrimination. Fifth, this model provides an explanation for "infectious" tolerance without creating specialized subsets of "suppressor" or "regulatory" T cells. Each mature T cell retains the potential to reinforce tolerance or mediate immunity, depending on the specific antigenic cues present in the immediate environment.

Functional characteristics of human peripheral blood alpha/betaTCR+, CD4- and CD8- double-negative (DN) T cells

The function of human peripheral blood alpha/betaTCR positive, CD4- and CD8- double-negative T lymphocytes (DN cells) in vivo is not completely understood. The response of immunomagnetically isolated DN cells to PHA and anti-CD3 was compared to the response of single-positive (SP) CD4 and CD8 subsets. Proliferation of DN cells in response to PHA was largely independent of APC. This suggests activation requirements for DN cells that are different from SP cells. Upon activation, HLA-DR was found to be upregulated early on DN cells, and IL-4 and IL-10 were detected in the supernatants of DN cells. These observations in vitro could correspond with an immunoregulatory role of human DN cells in vivo.