Requirement for cotolerogenic gene products in the clonal deletion of I-E reactive T cells

Genetic conflicts and the origin of self/nonself-discrimination in the vertebrate immune system

Genetic conflicts shape the genomes of prokaryotic and eukaryotic organisms. Here, we argue that some of the key evolutionary novelties of adaptive immune systems of vertebrates are descendants of prokaryotic toxin-antitoxin (TA) systems. Cytidine deaminases and RAG recombinase have evolved from genotoxic enzymes to programmable editors of host genomes, supporting the astounding discriminatory capability of variable lymphocyte receptors of jawless vertebrates, as well as immunoglobulins and T cell receptors of jawed vertebrates. The evolutionarily recent lymphoid lineage is uniquely sensitive to mutations of the DNA maintenance methylase, which is an orphaned distant relative of prokaryotic restriction-modification systems. We discuss how the emergence of adaptive immunity gave rise to higher order genetic conflicts between genetic parasites and their vertebrate host.

In Vitro Recapitulation of Murine Thymopoiesis from Single Hematopoietic Stem Cells

We report a serum-free, 3D murine artificial thymic organoid (M-ATO) system that mimics normal murine thymopoiesis with the production of all T cell stages, from early thymic progenitors to functional single-positive (CD8SP and CD4SP) TCRαβ and TCRγδ cells. RNA sequencing aligns M-ATO-derived populations with phenotypically identical primary thymocytes. M-ATOs initiated with Rag1-/- marrow produce the same differentiation block as seen in the endogenous thymus, and Notch signaling patterns in M-ATOs mirror primary thymopoiesis. M-ATOs initiated with defined hematopoietic stem cells (HSCs) and lymphoid progenitors from marrow and thymus generate each of the downstream differentiation stages, allowing the kinetics of T cell differentiation to be tracked. Remarkably, single HSCs deposited into each M-ATO generate the complete trajectory of T cell differentiation, producing diverse TCR repertoires across clones that largely match endogenous thymus. M-ATOs represent a highly reproducible and efficient experimental platform for the interrogation of clonal thymopoiesis from HSCs.

Ubiquitination of MHC Class II Is Required for Development of Regulatory but Not Conventional CD4+ T Cells

MHC class II (MHC II) displays peptides at the cell surface, a process critical for CD4⁺ T cell development and priming. Ubiquitination is a mechanism that dictates surface MHC II with the attachment of a polyubiquitin chain to peptide-loaded MHC II, promoting its traffic away from the plasma membrane. In this study, we have examined how MHC II ubiquitination impacts the composition and function of both conventional CD4⁺ T cell and regulatory T cell (T_reg) compartments. Responses were examined in two models of altered MHC II ubiquitination: MHCIIKR^{KI /KI} mice that express a mutant MHC II unable to be ubiquitinated or mice that lack membrane-associated RING-CH 8 (MARCH8), the E3 ubiquitin ligase responsible for MHC II ubiquitination specifically in thymic epithelial cells. Conventional CD4⁺ T cell populations in thymus, blood, and spleen of MHCIIKR^KI/KI and March8 ^-/- mice were largely unaltered. In MLRs, March8 ^-/-, but not MHCIIKR^KI/KI, CD4⁺ T cells had reduced reactivity to both self- and allogeneic MHC II. Thymic T_reg were significantly reduced in MHCIIKR^KI/KI mice, but not March8 ^-/- mice, whereas splenic T_reg were unaffected. Neither scenario provoked autoimmunity, with no evidence of immunohistopathology and normal levels of autoantibody. In summary, MHC II ubiquitination in specific APC types does not have a major impact on the conventional CD4⁺ T cell compartment but is important for T_reg development.

Quantitative Prediction of the Landscape of T Cell Epitope Immunogenicity in Sequence Space

Immunodominant T cell epitopes preferentially targeted in multiple individuals are the critical element of successful vaccines and targeted immunotherapies. However, the underlying principles of this “convergence” of adaptive immunity among different individuals remain poorly understood. To quantitatively describe epitope immunogenicity, here we propose a supervised machine learning framework generating probabilistic estimates of immunogenicity, termed “immunogenicity scores,” based on the numerical features computed through sequence-based simulation approximating the molecular scanning process of peptides presented onto major histocompatibility complex (MHC) by the human T cell receptor (TCR) repertoire. Notably, overlapping sets of intermolecular interaction parameters were commonly utilized in MHC-I and MHC-II prediction. Moreover, a similar simulation of individual TCR-peptide interaction using the same set of interaction parameters yielded correlates of TCR affinity. Pathogen-derived epitopes and tumor-associated epitopes with positive T cell reactivity generally had higher immunogenicity scores than non-immunogenic counterparts, whereas thymically expressed self-epitopes were assigned relatively low scores regardless of their immunogenicity annotation. Immunogenicity score dynamics among single amino acid mutants delineated the landscape of position- and residue-specific mutational impacts. Simulation of position-specific immunogenicity score dynamics detected residues with high escape potential in multiple epitopes, consistent with known escape mutations in the literature. This study indicates that targeting of epitopes by human adaptive immunity is to some extent directed by defined thermodynamic principles. The proposed framework also has a practical implication in that it may enable to more efficiently prioritize epitope candidates highly prone to T cell recognition in multiple individuals, warranting prospective validation across different cohorts.

CCR4 promotes medullary entry and thymocyte-dendritic cell interactions required for central tolerance

Hu et al. show that the chemokine receptor CCR4 is involved in thymocyte medullary entry, interactions with dendritic cells, and negative selection. In the absence of CCR4, central tolerance is not established, promoting autoimmunity.

Autoimmunity results from a breakdown in central or peripheral tolerance. To establish central tolerance, developing T cells must enter the thymic medulla, where they scan antigen-presenting cells (APCs) displaying a diverse array of autoantigens. If a thymocyte is activated by a self-antigen, the cell undergoes either deletion or diversion into the regulatory T cell (T reg) lineage, thus maintaining self-tolerance. Mechanisms promoting thymocyte medullary entry and interactions with APCs are incompletely understood. CCR4 is poised to contribute to central tolerance due to its expression by post-positive selection thymocytes, and expression of its ligands by medullary thymic dendritic cells (DCs). Here, we use two-photon time-lapse microscopy to demonstrate that CCR4 promotes medullary entry of the earliest post-positive selection thymocytes, as well as efficient interactions between medullary thymocytes and DCs. In keeping with the contribution of thymic DCs to central tolerance, CCR4 is involved in regulating negative selection of polyclonal and T cell receptor (TCR) transgenic thymocytes. In the absence of CCR4, autoreactive T cells accumulate in secondary lymphoid organs and autoimmunity ensues. These studies reveal a previously unappreciated role for CCR4 in the establishment of central tolerance.

The interleukin-15 system suppresses T cell-mediated autoimmunity by regulating negative selection and nT(H)17 cell homeostasis in the thymus

The interleukin-15 (IL-15) system is important for regulating both innate and adaptive immune responses, however, its role in autoimmune disease remained unclear. Here we found that Il15(-/-) and Il15ra(-/-) mice spontaneously developed late-onset autoimmune phenotypes. CD4(+) T cells of the knockout mice showed elevated autoreactivity as demonstrated by the induction of lymphocyte infiltration in the lacrimal and salivary glands when transferred into nude mice. The antigen-presenting cells in the thymic medullary regions expressed IL-15 and IL-15Rα, whose deficiency resulted in insufficient negative selection and elevated number of natural IL-17A-producing CD4(+) thymocytes. These findings reveal previously unknown functions of the IL-15 system in thymocyte development, and thus a new layer of regulation in T cell-mediated autoimmunity.

Sendai virus recombinant vaccine expressing a secreted, unconstrained respiratory syncytial virus fusion protein protects against RSV in cotton rats

The respiratory syncytial virus (RSV) is responsible for as many as 199000 annual deaths worldwide. Currently, there is no standard treatment for RSV disease and no vaccine. Sendai virus (SeV) is an attractive pediatric vaccine candidate because it elicits robust and long-lasting virus-specific B cell and T cell activities in systemic and mucosal tissues. The virus serves as a gene delivery system as well as a Jennerian vaccine against its close cousin, human parainfluenza virus type 1. Here we describe the testing of a recombinant SeV (SeVRSV-Fs) that expresses an unconstrained, secreted RSV-F protein as a vaccine against RSV in cotton rats. After a single intranasal immunization of cotton rats with SeVRSV-Fs, RSV-specific binding and neutralizing antibodies were generated. These antibodies exhibited cross-reactivity with both RSV A and B isolates. RSV-F-specific IFN-γ-producing T cells were also activated. The SeVRSV-Fs vaccine conferred protection against RSV challenge without enhanced immunopathology. In total, results showed that an SeV recombinant that expresses RSV F in an unconstrained, soluble form can induce humoral and cellular immunity that protects against infection with RSV.

Non-random lymphocyte distribution among virus-infected cells of the respiratory tract

The rules of T cell positioning within virus-infected respiratory tract tissues are poorly understood. We therefore marked cervical lymph node or spleen cells from Sendai virus (SeV) primed mice and transferred lymphocytes to animals infected with SeV expressing an enhanced green fluorescent protein (SeV-eGFP). Confocal imaging showed that when T cells entered a field of infected respiratory tract epithelium, they assumed a spatial distribution that maximized distances between each donor cell and its nearest neighbor. We therefore hypothesized that lymphocytes repelled one another by altering their chemokine/cytokine microenvironment. Subsequent in vitro tests confirmed that when SeV-primed lymphocytes were co-cultured with infected respiratory tract stroma, there was a profound upregulation of chemokines including RANTES, CXCL9, CXCL10, and CCL2. Based on these data, we propose that newly resident lymphocytes within virus-infected respiratory tract tissues may create halos of chemokines/cytokines to mark their territories; lymphocyte cross-talk may then inhibit cell overlap and redundancy to expedite virus clearance.

The phenotype and activation status of regulatory T cells during Friend retrovirus infection

The suppressive capacity of regulatory T cells (Tregs) has been extensively studied and is well established for many diseases. The expansion, accumulation, and activation of Tregs in viral infections are of major interest in order to find ways to alter Treg functions for therapeutic benefit. Tregs are able to dampen effector T cell responses to viral infections and thereby contribute to the establishment of a chronic infection. In the Friend retrovirus (FV) mouse model, Tregs are known to expand in all infected organs. To better understand the characteristics of these Treg populations, their phenotype was analyzed in detail. During acute FV-infection, Tregs became activated in the spleen and bone marrow, as indicated by various T cell activation markers, such as CD43 and CD103. Interestingly, Tregs in the bone marrow, which contains the highest viral loads during acute infection, displayed greater levels of activation than Tregs from the spleen. Treg expansion was driven by proliferation but no FV-specific Tregs could be detected. Activated Tregs in FV-infection did not produce Granzyme B (GzmB) or tumor necrosis factor α (TNFα), which are thought to be a potential mechanism for their suppressive activity. Furthermore, Tregs expressed inhibitory markers, such as TIM3, PD-1 and PD-L1. Blocking TIM3 and PD-L1 with antibodies during chronic FV-infection increased the numbers of activated Tregs. These data may have important implications for the understanding of Treg functions during chronic viral infections.

Endogenous mouse mammary tumor viruses (mtv): new roles for an old virus in cancer, infection, and immunity

Mouse Mammary Tumor Viruses are beta-retroviruses that exist in both exogenous (MMTV) and endogenous (Mtv) forms. Exogenous MMTV is transmitted via the milk of lactating animals and is capable of inducing mammary gland tumors later in life. MMTV has provided a number of critical models for studying both viral infection as well as human breast cancer. In addition to the horizontally transmitted MMTV, most inbred mouse strains contain permanently integrated Mtv proviruses within their genome that are remnants of MMTV infection and vertically transmitted. Historically, Mtv have been appreciated for their role in shaping the T cell repertoire during thymic development via negative selection. In addition, more recent work has demonstrated a larger role for Mtv in modulating host immune responses due to its peripheral expression. The influence of Mtv on host response has been observed during experimental murine models of Polyomavirus- and ESb-induced lymphoma as well as Leishmania major and Plasmodium berghei ANKA infection. Decreased susceptibility to bacterial pathogens and virus-induced tumors has been observed among mice lacking all Mtv. We have also demonstrated a role for Mtv Sag in the expansion of regulatory T cells following chronic viral infection. The aim of this review is to summarize the latest research in the field regarding peripheral expression of Mtv with a particular focus on their role and influence on the immune system, infectious disease outcome, and potential involvement in tumor formation.

Challenging the Tritope Model of T cell receptor structure-function relationships with classical data on 'super' and 'allo-MHC' antigens

The response of the immune system to allo-MHC-encoded antigens and Mls 'superantigens' has been experimentally analysed in detail, but the data have not been coupled to a theoretical framework. It should therefore be instructive to see how well the newly proposed Tritope Model of TCR structure-function relationships deals with the signalling interactions between the TCR and the above antigens. We will pay heed to William Bateson's admonition, 'treasure the exceptions', by showing how a meaningful theory interrogates the data with the same validity that the data interrogate the theory. The concordances, as well as the contradictions, with the Tritope Model are a test of its heuristic value.

Human invariant chain isoform p35 restores thymic selection and antigen presentation in CD74-deficient mice

The invariant chain (Ii) has pleiotropic functions and is a key factor in antigen presentation. Ii associates with major histocompatibility complex class II molecules in the endoplasmic reticulum (ER) and targets the complex in the endocytic pathway to allow antigenic peptide loading. The human Iip35 isoform includes a cytoplasmic extension containing a di-arginine motif causing ER retention. This minor isoform does not exist in mice and its function in humans has not been thoroughly investigated. We have recently generated transgenic mice expressing Iip35 and these were crossed with Ii-deficient mice to generate animals (Tgp35/mIiKO) expressing exclusively the human isoform. In these mice, we show that Iip35 is expressed in antigen presenting cells and is inducible by interferon gamma (IFN-γ). Despite the low constitutive expression of the protein and some minor differences in the Vβ repertoire of Tgp35/mIiKO mice, Iip35 restored thymic selection of CD4(+) T cells and of invariant natural killer T cells. In vitro functional assays using purified primary macrophages treated with IFN-γ showed that Iip35 allows presentation of an Ii-dependent ovalbumin T-cell epitope. Altogether, our results suggest that Iip35 is functional and does not require co-expression of other isoforms for antigen presentation.

Reduced frequencies and heightened CD103 expression among virus-induced CD8(+) T cells in the respiratory tract airways of vitamin A-deficient mice

Vitamin A deficiency (VAD) has profound effects on immune responses in the gut, but its effect on other mucosal responses is less well understood. Sendai virus (SeV) is a candidate human parainfluenza virus type 1 (hPIV-1) vaccine and a candidate vaccine vector for other respiratory viruses. A single intranasal dose of SeV elicits a protective immune response against hPIV-1 within days after vaccination. To define the effect of VAD on acute responses toward SeV, we monitored both antibodies and CD8(+) T cells in mice. On day 10 following SeV infection, there was a trend toward lower antibody activities in the nasal washes of VAD mice than in those of controls, while bronchoalveolar lavage (BAL) fluid and serum antibodies were not reduced. In contrast, there was a dramatic reduction of immunodominant CD8(+) T cell frequencies in the lower respiratory tract (LRT) airways of VAD animals. These T cells also showed unusually high CD103 (the αE subunit of αEβ7) expression patterns. In both VAD and control mice, E-cadherin (the ligand for αEβ7) was better expressed among epithelial cells lining the upper respiratory tract (URT) than in LRT airways. The results support a working hypothesis that the high CD103 expression among T cell populations in VAD mice alters mechanisms of T cell cross talk with URT and LRT epithelial cells, thereby inhibiting T cell migration and egress into the lower airway. Our data emphasize that the consequences of VAD are not limited to gut-resident cells and characterize VAD influences on an immune response to a respiratory virus vaccine.

T cell protein tyrosine phosphatase attenuates T cell signaling to maintain tolerance in mice

Many autoimmune diseases exhibit familial aggregation, indicating that they have genetic determinants. Single nucleotide polymorphisms in PTPN2, which encodes T cell protein tyrosine phosphatase (TCPTP), have been linked with the development of several autoimmune diseases, including type 1 diabetes and Crohn's disease. In this study, we have identified TCPTP as a key negative regulator of TCR signaling, which might explain the association of PTPN2 SNPs with autoimmune disease. We found that TCPTP dephosphorylates and inactivates Src family kinases to regulate T cell responses. Using T cell-specific TCPTP-deficient mice, we established that TCPTP attenuates T cell activation and proliferation in vitro and blunts antigen-induced responses in vivo. TCPTP deficiency lowered the in vivo threshold for TCR-dependent CD8(+) T cell proliferation. Consistent with this, T cell-specific TCPTP-deficient mice developed widespread inflammation and autoimmunity that was transferable to wild-type recipient mice by CD8(+) T cells alone. This autoimmunity was associated with increased serum levels of proinflammatory cytokines and anti-nuclear antibodies, T cell infiltrates in non-lymphoid tissues, and liver disease. These data indicate that TCPTP is a critical negative regulator of TCR signaling that sets the threshold for TCR-induced naive T cell responses to prevent autoimmune and inflammatory disorders arising.

Phenotypes and functions of persistent Sendai virus-induced antibody forming cells and CD8+ T cells in diffuse nasal-associated lymphoid tissue typify lymphocyte responses of the gut

Lymphocytes of the diffuse nasal-associated lymphoid tissue (d-NALT) are uniquely positioned to tackle respiratory pathogens at their point-of-entry, yet are rarely examined after intranasal (i.n.) vaccinations or infections. Here we evaluate an i.n. inoculation with Sendai virus (SeV) for elicitation of virus-specific antibody forming cells (AFCs) and CD8(+) T cells in the d-NALT. Virus-specific AFCs and CD8(+) T cells each appeared by day 7 after SeV inoculation and persisted for 8 months, explaining the long-sustained protection against respiratory virus challenge conferred by this vaccine. AFCs produced IgM, IgG1, IgG2a, IgG2b and IgA, while CD8+ T cells were cytolytic and produced low levels of cytokines. Phenotypic analyses of virus-specific T cells revealed striking similarities with pathogen-specific immune responses in the intestine, highlighting some key features of adaptive immunity at a mucosal site.

Themis is a member of a new metazoan gene family and is required for the completion of thymocyte positive selection

T cell antigen receptor (TCR) signaling in CD4(+)CD8(+) double-positive thymocytes determines cell survival and lineage commitment, but the genetic and molecular basis of this process is poorly defined. To address this issue, we used ethylnitrosourea mutagenesis to identify a previously unknown T lineage-specific gene, Themis, which is critical for the completion of positive selection. Themis contains a tandem repeat of a unique globular domain (called 'CABIT' here) that includes a cysteine motif that defines a family of five uncharacterized vertebrate proteins with orthologs in most animal species. Themis-deficient thymocytes showed no substantial impairment in early TCR signaling but did show altered expression of genes involved in the cell cycle and survival before and during positive selection. Our data suggest a unique function for Themis in sustaining positive selection.

Mls: A Link Between Immunology and Retrovirology

The nature of the mysterious minor lymphocyte stimulating (Mls) antigens has recently been clarified. These molecules which were key elements for our current understanding of immune tolerance, have a strong influence on the mouse immune system and are encoded by the open reading frame (orf) of endogenous and exogenous mouse mammary tumor viruses (MMTV's). The knowledge that these antigens are encoded by cancerogenic retroviruses opens an interdisciplinary approach for understanding the mechanisms of immune responses and immune tolerance, retroviral carcinogenesis, and retroviral strategies for infection.

Analysis of nondegradative protein ubiquitylation with a monoclonal antibody specific for lysine-63-linked polyubiquitin

Modification of proteins by the addition of lysine (K)-63-linked polyubiquitin (polyUb) chains is suggested to play important roles in a variety of cellular events, including DNA repair, signal transduction, and receptor endocytosis. However, identifying such modifications in living cells is complex and cumbersome. We have generated a monoclonal antibody (mAb) that specifically recognizes K63-linked polyUb, but not any other isopeptide-linked (K6, K11, K27, K29, K33, or K48) polyUb or monoubiquitin. We demonstrate the sensitivity and specificity of this K63Ub-specific mAb to detect K63Ub-modified proteins in cell lysates by Western blotting and in cells by immunofluorescence, and K63Ub-modified TRAF6 and MEKK1 in vitro and ex vivo. This unique mAb will facilitate the analysis of K63-linked polyubiquitylation ex vivo and presents a strategy for the generation of similar reagents against other forms of polyUb.

Mouse endogenous superantigens: Ms and Mls-like determinants encoded by mouse retroviruses

Commonly used inbred mouse strains express different combinations of integrated mouse mammary tumor proviruses (MMTV). This appendix summarizes the proviruses that have been detected. The reported functional properties of those MMTV proviral products which have been identified as superantigens are also summarized, including the ability to elicit primary or secondary T cell responses and to induce Vb-specific clonal deletion during T cell differentiation. In addition, the amino acid sequences of putative ORF gene products of different MMTV are compared.

Sendai virus recombinant vaccine expressing hPIV-3 HN or F elicits protective immunity and combines with a second recombinant to prevent hPIV-1, hPIV-3 and RSV infections

The human parainfluenza viruses (hPIVs) and respiratory syncytial virus (RSV) are the leading causes of serious respiratory illness in the human pediatric population. Despite decades of research, there are currently no licensed vaccines for either the hPIV or RSV pathogens. Here we describe the testing of hPIV-3 and RSV candidate vaccines using Sendai virus (SeV, murine PIV-1) as a vector. SeV was selected as the vaccine backbone, because it has been shown to elicit robust and durable immune activities in animal studies, and has already advanced to human safety trials as a xenogenic vaccine for hPIV-1. Two new SeV-based hPIV-3 vaccine candidates were first generated by inserting either the fusion (F) gene or hemagglutinin-neuraminidase (HN) gene from hPIV-3 into SeV. The resultant rSeV-hPIV3-F and rSeV-hPIV3-HN vaccines expressed their inserted hPIV-3 genes upon infection. The inoculation of either vaccine into cotton rats elicited binding and neutralizing antibody activities, as well as interferon-gamma-producing T cells. Vaccination of cotton rats resulted in protection against subsequent challenges with either homologous or heterologous hPIV-3. Furthermore, vaccination of cotton rats with a mixture of rSeV-hPIV3-HN and a previously described recombinant SeV expressing the F protein of RSV resulted in protection against three different challenge viruses: hPIV-3, hPIV-1 and RSV. Results encourage the continued development of the candidate recombinant SeV vaccines to combat serious respiratory infections of children.

Tumor immunotherapy across MHC barriers using allogeneic T-cell precursors

We present a strategy for adoptive immunotherapy using T-lineage committed lymphoid precursor cells generated by Notch1-based culture. We found that allogeneic T-cell precursors can be transferred to irradiated individuals irrespective of major histocompatibility complex (MHC) disparities and give rise to host-MHC restricted and host-tolerant functional allogeneic T cells, improving survival in irradiated recipients as well as enhancing anti-tumor responses. T-cell precursors transduced to express a chimeric receptor targeting hCD19 resulted in significant additional anti-tumor activity, demonstrating the feasibility of genetic engineering of these cells. We conclude that ex vivo generated MHC-disparate T-cell precursors from any donor can be used universally for 'off-the-shelf' immunotherapy, and can be further enhanced by genetic engineering for targeted immunotherapy.

What do we know about the mechanisms of elimination of autoreactive T and B cells and what challenges remain

Tolerance to self-antigens within the adaptive immune system is safeguarded, at least in part, through deletion of autoreactive T and B lymphocytes. This deletion can occur during the development of these cells in primary lymphoid organs, the thymus or bone marrow, respectively, or at the mature stage in peripheral lymphoid tissues. Deletion of autoreactive lymphocytes is achieved to a large extent through apoptotic cell death. This review describes current understanding of the mechanisms that mediate apoptosis of autoreactive lymphocytes during their development in primary lymphoid organs and during their activation in the periphery. In particular, we discuss the roles of the proapoptotic Bcl-2 family member Bim and the small family of Nur77-related transcriptional regulators in lymphocyte negative selection. Finally, we speculate on the processes that may lead to the activation of Bim when antigen receptors are activated on autoreactive T or B cells.

Respiratory syncytial virus (RSV) fusion protein expressed by recombinant Sendai virus elicits B-cell and T-cell responses in cotton rats and confers protection against RSV subtypes A and B

The respiratory syncytial virus (RSV) is a serious pediatric pathogen for which there is currently no clinically approved vaccine. This report describes the design and testing of a new RSV vaccine construct (rSV-RSV-F), created by the recombination of an RSV F sequence with the murine parainfluenza virus-type 1 (Sendai virus, SV) genome. SV was selected as the vaccine backbone for this study, because it has previously been shown to elicit high-magnitude, durable immune activities in animal studies and has advanced to human safety trials as a xenogenic vaccine for human parainfluenza virus-type 1 (hPIV-1). Cells infected with the recombinant SV expressed RSV F protein, but F was not incorporated into progeny SV virions. When cotton rats were inoculated with the vaccine, high-titer RSV-binding and neutralizing antibodies as well as interferon-gamma-producing T-cells were induced. Most striking was the protection against intra-nasal RSV challenge conferred by the vaccine. The rSV-RSV-F construct was also tested as a mixture with a second SV construct expressing the RSV G protein, but no clear advantage was demonstrated by combining the two vaccines. As a final analysis, the efficacy of the rSV-RSV-F vaccine was tested against an array of RSV isolates. Results showed that neutralizing and protective responses were effective against RSV isolates of both A and B subtypes. Together, experimental results encourage promotion of this recombinant SV construct as a vaccine candidate for the prevention of RSV in humans.

A recombinant Sendai virus is controlled by CD4+ effector T cells responding to a secreted human immunodeficiency virus type 1 envelope glycoprotein

The importance of antigen-specific CD4(+) helper T cells in virus infections is well recognized, but their possible role as direct mediators of virus clearance is less well characterized. Here we describe a recombinant Sendai virus strategy for probing the effector role(s) of CD4(+) T cells. Mice were vaccinated with DNA and vaccinia virus recombinant vectors encoding a secreted human immunodeficiency virus type 1 (HIV-1) envelope protein and then challenged with a Sendai virus carrying a homologous HIV-1 envelope gene. The primed mice showed (i) prompt homing of numerous envelope-primed CD4(+) T cell populations to the virus-infected lung, (ii) substantial production of gamma interferon, and interleukin-2 (IL-2), IL-4, and IL-5 in that site, and (iii) significantly reduced pulmonary viral load. The challenge experiments were repeated with immunoglobulin(-/-) microMT mice in the presence or absence of CD8(+) and/or CD4(+) T cells. These selectively immunodeficient mice were protected by primed CD4(+) T cells in the absence of antibody or CD8(+) T cells. Together, these results highlight the role of CD4(+) T cells as direct effectors in vivo and, because this protocol gives such a potent response, identify an outstanding experimental model for further dissecting CD4(+) T-cell-mediated immunity in the lung.

Alteration of T-cell receptor repertoires during thymic T-cell development

The majority of thymocytes die in the thymus, whereas small populations of T cells that are able to specifically recognize an antigen are considered to survive. Although the thymic selection is thought to have a profound effect on T-cell receptor (TCR) repertoire, little is known how TCR repertoire is formed during the thymocyte developmental process. We examined TCRalpha- and beta-chain variable regions (TCRAV and TCRBV) repertoire in thymic T-cell subpopulations from mice bearing different major histocompatibility (MHC) haplotypes. In Balb/c mice, but not C57BL/6, remarkable alterations of the TCR repertoire were observed in mature T-cell subpopulations as previously reported. In contrast, there were no significant differences of TCRBV repertoire between DN3 (CD25(+)CD44(-)) and DN4 (CD25(-)CD44(-)), and between DN4 and DP. These results suggest that (1) TCR repertoire of mature T cells was formed mainly under the influence of endogenous superantigens, while MHC haplotypes played the least role; (2) the 'beta-selection' process during immature stages had little impact on TCRBV repertoire formation; and (3) TCR repertoire in immature T-cell subpopulations was extremely similar between different strains of mice. We thus consider that pre-selection TCR repertoire in immature T cells could be determined by some genetic factors conserved among different strains.

An MHC Class Ib-Restricted TCR That Cross-Reacts with an MHC Class Ia Molecule

TCR transgenic 6C5 T cells recognize an insulin B chain epitope presented by the nonclassical class I MHC molecule, Qa-1(b). Positive selection of these T cells was shown previously to require Qa-1(b). Despite dedicated specificity for Qa-1(b), evidence presented in the current study indicates that 6C5 T cells can cross-recognize a classical class I molecule. Clonal deletion was observed unexpectedly in 6C5.H-2(bxq) mice, which do not express I-E MHC class II molecules and thus should not be subject to superantigen-mediated negative selection. 6C5 T cells were observed to respond in vivo and in vitro to spleen cells from allogeneic H-2(q) mice, and specificity was mapped to D(q). Evidence was obtained for direct recognition of D(q), rather than indirect presentation of a D(q)-derived peptide presented by Qa-1(b). Polyclonal CD8(+) T cells from class Ia-deficient K(b)D(b-/-) mice reacted in vitro to allogeneic spleen cells with an apparent frequency comparable to conventional class Ia-restricted T cells. Our results provide a clear example of a Qa-1-specific TCR that can cross-react with a class Ia molecule and evidence supporting the idea that this may be a common property of T cells selected by class Ib molecules.

Long lived multi-isotype anti-HIV antibody responses following a prime-double boost immunization strategy

Despite decades of work, an effective HIV vaccine remains elusive. In an effort to elicit protective immunity, investigators have sought to define vaccines able to elicit durable HIV-specific B-cell and T-cell activities. Additionally, vaccines are sought which can induce antibodies of a variety of isotypes, as each isotype possesses unique attributes in terms of opsonization, Fc receptor binding capacity, complement fixation and location. One prominent new vaccine strategy, applied to numerous distinct antigenic systems is the prime boost-regimen, with DNA, vaccinia virus (VV), and/or purified recombinant protein. To examine the durability, location and isotype distribution of responses induced by prime-boost regimens, we tested successive immunizations with DNA, VV and protein (D-V-P), comparing three forms of protein inoculations: (i) purified protein administered intramuscularly with complete Freunds adjuvant, (ii) purified protein administered intranasally, and (iii) purified protein conjugated to oxidized mannan, administered intranasally. We found that all three protocols elicited serum antibodies of multiple isotypes, with serum IgA being most prominent among mice immunized with mannan-conjugated protein. All D-V-P protocols, regardless of protein form or route, also elicited antibody responses at mucosal surfaces. In bronchoalveolar lavage, a tendency toward IgA production was again most prominent in mice boosted with the protein-mannan conjugate. Both B-cell and T-cell responses were sustained for more than 1 year post-immunization following each form of vaccination. Contemporaneous with long-lasting serum and mucosal antibodies were antibody forming cells in the bone marrow of primed animals. Results highlight the D-V-P vaccination strategy as a promising approach for attaining durable, multi-isotype B-cell and T-cell activities toward HIV.

Minor components of a multi-envelope HIV vaccine are recognized by type-specific T-helper cells

HIV has thus far evaded control by vaccines, in part due to the high diversity among viral isolates. To effectively target HIV diversity, we propose that multi-envelope HIV vaccines should be designed. We hypothesize that minor components of complex envelope cocktail vaccines can be immunogenic and can thus elicit unique T-cell responses. To test our hypothesis, we first defined unique T-helper cell determinants on 1007 (clade B) and UG92005 (UG, clade D) gp140 envelope proteins delivered by DNA vaccination. Peptide-specific T-helper cell responses were then used as markers for type-specific immune activity. Results showed that type-specific responses could indeed be generated when an envelope protein was represented as only 1 part per 100 of the total vaccine. We also found that type-specific T-helper cell responses were elicited and sustained toward an envelope that appeared only once within a sequential prime/boost/boost regimen. Our results illustrate the flexibility and durability of immune responses toward individual components of mixed envelope vaccines and encourage the continued development of vaccine cocktails for the control of HIV.

Clustering of Th cell epitopes on exposed regions of HIV envelope despite defects in antibody activity

A long-standing question in the field of immunology concerns the factors that contribute to Th cell epitope immunodominance. For a number of viral membrane proteins, Th cell epitopes are localized to exposed protein surfaces, often overlapping with Ab binding sites. It has therefore been proposed that Abs on B cell surfaces selectively bind and protect exposed protein fragments during Ag processing, and that this interaction helps to shape the Th cell repertoire. While attractive in concept, this hypothesis has not been thoroughly tested. To test this hypothesis, we have compared Th cell peptide immunodominance in normal C57BL/6 mice with that in C57BL/6( micro MT/ micro MT) mice (lacking normal B cell activity). Animals were first vaccinated with DNA constructs expressing one of three different HIV envelope proteins, after which the CD4(+) T cell response profiles were characterized toward overlapping peptides using an IFN-gamma ELISPOT assay. We found a striking similarity between the peptide response profiles in the two mouse strains. Profiles also matched those of previous experiments in which different envelope vaccination regimens were used. Our results clearly demonstrate that normal Ab activity is not required for the establishment or maintenance of Th peptide immunodominance in the HIV envelope response. To explain the clustering of Th cell epitopes, we propose that localization of peptide on exposed envelope surfaces facilitates proteolytic activity and preferential peptide shuttling through the Ag processing pathway.

Limited breadth of a T-helper cell response to a human immunodeficiency virus envelope protein

Single-envelope human immunodeficiency virus (HIV) vaccines have been studied for more than a decade, with some successes in homologous challenge experiments in nonhuman primates but with no clear successes in clinical trials. To gain insight into the breadth of the immunity elicited by such vaccines, we have dissected the T-helper cell response of C57BL/6 mice to an individual, molecularly cloned envelope protein. Here, we report that T-helper cells responsive to HIV type 1 1035 envelope are very highly restricted in C57BL/6 animals: seven different hybridomas recovered from five separate mice recognized the same peptide, PKVSFEPIPIHYCAP, located in the C2 region of gp120. Three of these hybridomas were tested on a natural variant of the peptide but failed to respond. A more extensive analysis of whole splenic populations from other C57BL/6 mice immunized with the 1035 envelope reproducibly confirmed that the gp120-specific T-helper response was almost exclusively focused on a single epitope. We conclude that single-envelope vaccines may frequently fail to provoke an immune response sufficiently diverse to recognize variant sequences among circulating HIV. The results encourage the inclusion of more than one envelope in future vaccines to enhance the potential diversity and respective surveillance capacities of responding T-helper cell populations.

Integrated src kinase and costimulatory activity enhances signal transduction through single-chain chimeric receptors in T lymphocytes

Adoptive immunotherapy using receptor-modified T lymphocytes has shown promise in preclinical studies for the treatment of infectious and malignant diseases. These modified T cells express chimeric receptors that link ligand recognition and signal transduction domains in a single gene product. Typically, a single chain Fv fragment is genetically attached to the cytoplasmic domain of the T-cell receptor (TCR) zeta chain. Modulating the signaling characteristics of chimeric receptors will be important for their application to human immunotherapy. It was hypothesized that linking coreceptor and costimulatory signaling motifs together with the zeta signaling domain will enhance receptor function. The present study compares signaling characteristics of 9 single-chain receptors consisting of the H-2K(b) extracellular and transmembrane domains and various combinations of T cell signal transduction domains. Signal transduction regions studied include the TCR zeta chain, the CD4 coreceptor, the lck protein tyrosine kinase, and the CD28 costimulatory receptor. Biochemical characteristics of the receptors, analyzed using calcium flux, receptor, and ZAP-70 phosphorylation, and lck association may be predicted from the known functions of receptor constituents. The combination of zeta together with coreceptor and costimulatory function in a single receptor maximizes chimeric receptor sensitivity and potency. Combining zeta with either the costimulatory or coreceptor function independently also enhances receptor function, though to a lesser extent. It is therefore possible to link TCR, coreceptor, and costimulatory activities in a single functional entity using modular domains. Such receptors demonstrate distinct signaling properties and should prove useful in the development of chimeric receptors for therapeutic purposes.

Both B and gammadelta TCR(+) lymphocytes regulate alphabeta TCR(+) lymphocytes involved in superantigen specific responses

Endogenous superantigens (SAg) presented by MHC class II IA molecules induce slow-evolving negative selection of alpha beta T cells. The role of both B and gamma delta T cells on the regulation of these SAg-specific alpha beta T cell responses was addressed in IA(b+)IE(b-) C57BL/6 mice bearing genetically induced B cell and gamma delta T cell deficiencies. B lymphocytes were required in the negative selection of Vbeta5(+)/Vbeta12(+) CD4(+) T cells. In contrast, gamma delta T cells positively stimulated the utilization of the same SAg-responsive alpha beta T cell subsets. These differences started in mature CD4(+) thymocytes and extended to naive T cell pools for B cell negative selection, and up to memory T cells for gamma deltaT cell influences. The levels of SAg-responsive T cells did not vary between C57BL/6 and double deficient (B cell and gamma delta T cell-deficient) congenic mice, implying that both B and gamma delta T cells acted through independent mechanisms.

Identification of MHC class II-associated peptides that promote the presentation of toxic shock syndrome toxin-1 to T cells

Previous studies have shown that the DM-deficient cell line, T2-I-A(b), is very inefficient at presenting toxic shock syndrome toxin 1 (TSST-1) to T cells, suggesting that I-A(b)-associated peptides play an essential role in the presentation of this superantigen. Consistent with this, the loading of an I-A(b)-binding peptide, staphylococcal enterotoxin B 121-136, onto T2-I-A(b) cells enhanced TSST-1 presentation >1000-fold. However, despite extensive screening, no other peptides have been identified that significantly promote TSST-1 presentation. In addition, the peptide effect on TSST-1 presentation has been demonstrated only in the context of the tumor cell line T2-I-A(b). Here we show that peptides that do not promote TSST-1 presentation can be converted into "promoting" peptides by the progressive truncation of C-terminal residues. These studies result in the identification of two peptides derived from IgGV heavy chain and I-Ealpha proteins that are extremely strong promoters of TSST-1 presentation (47,500- and 12,000-fold, respectively). We have also developed a system to examine the role of MHC class II-associated peptides in superantigen presentation using splenic APC taken directly ex vivo. The data confirmed that the length of the MHC class II-bound peptide plays a critical role in the presentation of TSST-1 by splenic APC and showed that different subpopulations of APC are equally peptide dependent in TSST-1 presentation. Finally, we demonstrated that the presentation of staphylococcal enterotoxin A, like TSST-1, is peptide dependent, whereas staphylococcal enterotoxin B presentation is peptide independent.

Analysis of virus-specific CD4(+) t cells during long-term gammaherpesvirus infection

Major histocompatibility complex class II-mediated antigen presentation after intranasal infection with murine gammaherpesvirus 68 differs in mediastinal lymph nodes and spleen. Evidence that virus-specific CD4(+) T cells were being stimulated was found as late as 6 to 8 months after infection, and cells specific for the viral gp150(67-83) and ORF11(168-180) peptides were maintained as a fairly stable proportion of the total response.

Requirement for a complex array of costimulators in the negative selection of autoreactive thymocytes in vivo

Autoreactive thymocytes can be deleted at an immature stage of their development by Ag-induced apoptosis or negative selection. In addition to Ag, negative selection also requires costimulatory signals from APC. We recently used a fetal thymus organ culture system to show that CD5, CD28, and TNF cooperatively regulate deletion of autoreactive thymocytes. Although these experiments provided strong evidence for the action of several costimulators in negative selection, we wished to demonstrate a role for these molecules in a physiologically natural model where thymocytes are deleted in vivo by endogenously expressed AGS: Accordingly, we examined thymocyte deletion in costimulator-null mice in three models of autoantigen-induced negative selection. We compared CD5(-/-) CD28(-/-) mice to CD40L(-/-) mice, which exhibited a profound block in negative selection in all three systems. Surprisingly, only one of the three models revealed a requirement for the CD5 and CD28 costimulators in autoantigen-induced deletion. These results suggest that an extraordinarily complex array of costimulators is involved in negative selection. We predict that different sets of costimulators will be required depending on the timing of negative selection, the Ag, the signal strength, the APC, and whether Ag presentation occurs on class I or class II MHC molecules.

Localization of CD4+ T cell epitope hotspots to exposed strands of HIV envelope glycoprotein suggests structural influences on antigen processing

The spectrum of immunogenic epitopes presented by the H2-IA(b) MHC class II molecule to CD4(+) T cells has been defined for two different (clade B and clade D) HIV envelope (gp140) glycoproteins. Hybridoma T cell lines were generated from mice immunized by a sequential prime and boost regime with DNA, recombinant vaccinia viruses, and protein. The epitopes recognized by reactive T cell hybridomas then were characterized with overlapping peptides synthesized to span the entire gp140 sequence. Evidence of clonality also was assessed with antibodies to T cell receptor Valpha and Vbeta chains. A total of 80 unique clonotypes were characterized from six individual mice. Immunogenic peptides were identified within only four regions of the HIV envelope. These epitope hotspots comprised relatively short sequences ( approximately 20-80 aa in length) that were generally bordered by regions of heavy glycosylation. Analysis in the context of the gp120 crystal structure showed a pattern of uniform distribution to exposed, nonhelical strands of the protein. A likely explanation is that the physical location of the peptide within the native protein leads to differential antigen processing and consequent epitope selection.

Mouse xenoantigens contribute to rat T-cell Vbeta repertoire generation in mixed xenogeneic bone marrow chimeras

We previously demonstrated that rat bone-marrow-derived cells in mixed xenogeneic chimeras (rat + mouse --> mouse) contribute to peripheral selection of mouse T-cell receptor (TCR) variable betas (Vbetas) repertoire. In this study, we analysed rat T cells that developed in the chimeras to assess the contribution of mouse xenoantigens to the development of rat TCR repertoire. The expression of rat Vbetas was analysed using flow cytometry and a reverse transcription-polymerase chain reaction (RT-PCR) method that allows for both semiquantitative analysis of rat Vbeta gene expression and size heterogeneity of the complementarity determining region 3 (CDR3) domain. Three distinct patterns of Vbeta expression were detected. Partial deletion was observed for Vbeta5, 7, 12, 14, 16, 17 and 20 that exhibited reduced levels of peripheral expression by 3.4-, 1.8-, 8.7-, 2.0-, 7.8-, 9.5- and 1.8-fold, respectively, compared with the levels of Vbetas in naYve rats. Higher levels of peripheral expression were detected for three rat Vbeta genes; Vbeta6 (2.2-fold), Vbeta8.2 (3.2-fold), and Vbeta9 (1.7-fold). The relative expression of the other 10 known rat Vbeta families in chimeras was unchanged as compared with that of normal rats. We did not observe detectable changes in the pattern of CDR3 expression in chimeras, suggesting that the mouse xenogeneic environment exerted its influence on the development of rat T cells via the Vbeta-encoded CDR1/2 domains. Our data demonstrate that the rat T-cell repertoire in chimeras is shaped by both contractions as well as expansions of selected Vbetas and suggest that mouse xenoantigens and/or superantigens of endogenous mouse retroviruses may contribute as ligands for these selection processes

Functional comparison of thymic B cells and dendritic cells in vivo

In this report we present a transgenic mouse model in which we targeted gene expression specifically to B-lymphocytes. Using the human CD19 promoter, we expressed major histocompatibility complex class II I-E molecules specifically on B cells of all tissues, but not on other cell types. If only B cells expressed I-E in a class II-deficient background, positive selection of CD4+ T cells could not be observed. A comparison of the frequencies of I-E reactive Vβ5+ and Vβ11+ T cells shows that I-E expression on thymic B cells is sufficient to negatively select I-E reactive CD4+ T cells partially, but not CD8+ T cells. Thus partial negative but no positive selection events can be induced by B-lymphocytes in vivo.

Functional comparison of thymic B cells and dendritic cells in vivo

In this report we present a transgenic mouse model in which we targeted gene expression specifically to B-lymphocytes. Using the human CD19 promoter, we expressed major histocompatibility complex class II I-E molecules specifically on B cells of all tissues, but not on other cell types. If only B cells expressed I-E in a class II-deficient background, positive selection of CD4+ T cells could not be observed. A comparison of the frequencies of I-E reactive Vβ5+ and Vβ11+ T cells shows that I-E expression on thymic B cells is sufficient to negatively select I-E reactive CD4+ T cells partially, but not CD8+ T cells. Thus partial negative but no positive selection events can be induced by B-lymphocytes in vivo.

T-cell vaccination alters the course of murine herpesvirus 68 infection and the establishment of viral latency in mice

Diseases caused by gammaherpesviruses such as Epstein-Barr virus are a major health concern, and there is significant interest in developing vaccines against this class of viral infections. However, the requirements for effective control of gammaherpesvirus infection are only poorly understood. The recent development of the murine herpesvirus MHV-68 model provides an experimental tool to dissect the immune response to gammaherpesvirus infections. In this study, we investigated the impact of priming T cells specific for class I- and class II-restricted epitopes on the acute phase of the infection and the subsequent establishment of latency and infectious mononucleosis. The data show that vaccination with either major histocompatibility complex class I- or class II-restricted T-cell epitopes derived from lytic cycle proteins significantly reduced lung viral titers during the acute infection. Moreover, the peak level of latently infected spleen cells was significantly reduced following vaccination with immunodominant CD8(+) T-cell epitopes. However, this vaccination approach did not prevent the long-term establishment of latency or the development of the infectious mononucleosis-like syndrome in infected mice. Thus, the virus is able to establish latency efficiently despite strong immunological control of the lytic infection.

Chronic deletion, escape from deletion and activation of mouse mammary tumor virus superantigen-reactive T cells in C57BL/10 mice

Though C57BL/10 mice express the mouse mammary tumor virus superantigens (sag) encoded by Mtv-8 and Mtv-9, it has been thought that these sag do not bind to the MHC class II molecule H2-Ab and consequently do not affect the T cell repertoire. However, we show that cells bearing TCR Vbeta chains specific for Mtv-8 and -9 sag are chronically deleted in C57BL/10 mice. Thymocytes and peripheral T cells escaping deletion by Mtv sag display a small reduction in the level of cell surface CD4. T cells escaping thymic deletion respond variably to endogenous Mtv sag with some, but not all, reactive populations appearing overrepresented in the activated/memory subset. The data suggest that in normal mice fine modulation of coreceptor expression levels may be a common way by which thymocytes escape elimination, that systems utilizing potentially Mtv sag-reactive TCR on a C57BL background may be inappropriate for the measurement of the affinity of TCR/MHC/peptide interactions required in thymic selection, and that detection of the activity of human sag may be aided by analysis of CD4 levels and activation markers on T cells in conjunction with studies of the frequency of cells bearing specific TCRVbeta chains.

Chronic Modulation of the TCR Repertoire in the Lymphoid Periphery

Using TCR Vβ5 transgenic mice as a model system, we demonstrate that the induction of peripheral tolerance can mold the TCR repertoire throughout adult life. In these mice, three distinct populations of peripheral T cells are affected by chronic selective events in the lymphoid periphery. First, CD4+Vβ5+ T cells are deleted in the lymphoid periphery by superantigens encoded by mouse mammary tumor viruses-8 and -9 in an MHC class II-dependent manner. Second, mature CD8+Vβ5+ T cells transit through a CD8lowVβ5low deletional intermediate during tolerance induction by a process that depends upon neither mouse mammary tumor virus-encoded superantigens nor MHC class II expression. Third, a population of CD4−CD8−Vβ5+ T cells arises in the lymphoid periphery in an age-dependent manner. We analyzed the TCR Vα repertoire of each of these cellular compartments in both Vβ5 transgenic and nontransgenic C57BL/6 mice as a function of age. This analysis revealed age-related changes in the expression of Vα families among different cellular compartments, highlighting the dynamic state of the peripheral immune repertoire. Our work indicates that the chronic processes maintaining peripheral T cell tolerance can dramatically shape the available TCR repertoire.

Idiosyncratic alterations of TCR size distributions affecting both CD4 and CD8 T cell subsets in aging mice

We have used a spectratyping method, which displays the size distribution for the complementarity-determining region 3 (CDR3) for T cells utilizing a specific TCR-Vbeta gene, to examine the effects of aging on the TCR repertoire of (BALB/c x C57BL/6)F1 hybrid mice. Although the size distributions from T cells of 8-month-old mice were typically symmetrically shaped around one or two bands of intermediate size, spectratypes from mice 16 or 24 months of age were frequently distorted, with specific size classes either over- or underrepresented compared to normal young controls. Each of 12 mice tested at 16 or 24 months of age had a skewed spectratype for at least one of the 24 Vbeta families examined, and some mice had more than 50% of their spectratypes skewed significantly, as judged by a chi2 test. Comparable age-associated skewing of the T cell repertoire occurred in the CD4 and CD8 subsets, and every mouse over 16 months of age exhibited at least one skewed Vbeta family in both the CD4 and CD8 populations. Although the mice were genetically identical and raised in common facilities, their spectratype patterns were nonetheless idiosyncratic: i.e., the specific set of abnormalities was distinct for each individual old mouse. Whether these distortions of the TCR repertoire in middle-aged and older mice lead to alterations in immune function remains to be determined.

Induction of endogenous mammary tumor virus in lymphocytes infected with murine acquired immunodeficiency syndrome virus

Mice infected with murine acquired immunodeficiency syndrome (MAIDS) virus developed lymphoadenopathy and profound immunodeficiency. Concomitantly the expression of endogenous mammary tumor virus (MTV) mRNA increased significantly, especially for the 1.7-kb 3' open reading frame (ORF) mRNA encoding MTV superantigen. B cell lines that are established from MAIDS mice and exhibit superantigen activity also express a high level of 1.7-kb endogenous MTV and mRNA. Infection of a B cell tumor line in vitro with retrovirus containing the cloned MAIDS virus gene induced superantigen activity and this cell line also expressed the 1.7-kb superantigen coding MTV 3' ORF mRNA. These results strongly suggest a link between MAIDS virus infection and the induction of endogenous superantigen activity. This may play an important role in the pathogenesis of the MAIDS virus.

Loss of Endogenous Mouse Mammary Tumor Virus Superantigen Increases Tumor Resistance

From a cross between a tumor-susceptible mouse strain (DBA/2; D) and a tumor-resistant MHC-identical strain (B10.D2; D2) new recombinant inbred mouse strains were established over many generations of inbreeding and tumor resistance selection. Since resistance to the highly metastatic DBA/2 lymphoma variant ESb had an immunologic basis, and the two parental strains differed in endogenous viral superantigens (vSAGs), DNA of three D2×D recombinant inbred mouse lines was typed for endogenous mouse mammary tumor viruses using mouse mammary tumor virus long terminal repeat- and env gene-specific probes. The resistant D2×D mice were very similar to the susceptible parental strain D in their Mtv Southern blots, except for the lack of a single band corresponding to Mtv-7, the provirus coding for the strong DBA/2 superantigen Mls-1a. A backcross analysis revealed that Mtv-7-negative F2 mice were significantly more resistant than Mtv-7-positive F2 mice. When Mtv-7 was reintroduced into the resistant lines by crossing them with either CBA/J or BALB/D2.Mls-1a, the mice became again more tumor susceptible. Finally, we demonstrate the ability to transfer immunoresistance and graft-vs-leukemia reactivity from tumor-resistant to tumor-susceptible mice.

CD4+ T Cells Mature in the Absence of MHC Class I and Class II Expression in Ly-6A.2 Transgenic Mice

The TCRs expressed on T lymphocytes recognize foreign peptides bound to MHC molecules. This reactivity is the basis of specific immune response to the foreign Ag. How such specificities are generated in the thymus is still being debated. Signals generated through TCR upon interaction with self MHC-peptide complexes are critical for maturation of the CD4+ helper and CD8+ cytotoxic subsets. We have observed maturation of CD4+ but not CD8+ T cells in Ly-6A.2 transgenic MHC null mice. Since there can be no interactions with MHC molecules in these mice, these CD4+ cells must express the T cell repertoire that exists before positive and negative selection. Interestingly, despite an absence of selection by MHC molecules, the CD4+ cells that mature recognize MHC molecules at a frequency as high as in CD4+ cells in normal mice. These results demonstrate that: 1) the germline sequences encoding TCRs are biased toward reactivity to MHC molecules; and 2) CD4+ cells as opposed to CD8+ cells have distinct lineage commitment signals. These results also suggest that signals originating from Ly-6 can promote or substitute for signals generated from TCR that are required for positive selection. Moreover, this animal model offers a system to study T cell development in the thymus that can provide insights into mechanisms of lineage commitment in developing T cells.

Defective TCR expression in transgenic mice constructed using cDNA-based alpha- and beta-chain genes under the control of heterologous regulatory elements

We describe the generation of ovalbumin (OVA)-specific, MHC class II-restricted alpha beta T cell receptor (TCR) transgenic mice. Initial attempts at generating these transgenic mice utilized heterologous regulatory elements to drive the expression of cDNA genes encoding the separate alpha- and beta-chains of the TCR. Unexpectedly, T cells bearing the transgenic alpha beta TCR failed to emerge from the thymus in these mice, although the transgenes did modify endogenous TCR expression. However, subsequent modification of the approach which enabled expression of the TCR beta-chain under the control of its natural regulatory elements generated mice whose peripheral T cells expressed the transgenic TCR and were capable of antigen-dependent proliferation. These results show that successful generation of MHC class II-restricted, OVA-specific alpha beta TCR transgenic mice was dependent upon combining cDNA- and genomic DNA-based constructs for expression of the respective alpha- and beta-chains of the TCR.

Thymocyte glucocorticoid resistance alters positive selection and inhibits autoimmunity and lymphoproliferative disease in MRL-lpr/lpr mice

Thymus-derived glucocorticoids antagonize T cell receptor (TCR)-induced thymocyte apoptosis, allowing the survival (positive selection) of cells bearing TCRs that recognize self antigens with low-to-moderate avidity. Here we demonstrate that expression of an antisense glucocorticoid receptor transgene in thymocytes of spontaneously autoimmune MRL-lpr/lpr mice causes the loss of specific TCR Vbeta-bearing T cells that are normally positively selected in this strain. These transgenic mice had lower autoantibody production and milder symptoms of autoimmune disease than MRL-lpr/lpr controls and had markedly reduced accumulation of the TCR+Thy-1+CD4-CD8-B220+ T cells that are the hallmark of the lpr mutation. Thus, decreased glucocorticoid signaling in thymocytes alters the T cell repertoire and greatly diminishes autoimmunity in MRL-lpr/lpr autoimmune mice.

In vivo the environmental pollutants lead and mercury induce oligoclonal T cell responses skewed toward type-2 reactivities

An oligoclonal utilization of Vbetas has been reported for pathogenesis of several autoimmune diseases, anti-tumorigenic activity, and superantigen-regulation of thymic T cell development. Altered ratios of Th1 and Th2 cells also are observed in immunodysregulations, leading to impaired cell-mediated immunity with an increased incidence of infectious disease or cancer and/or aberrant immunity that could culminate with an autoimmune disease. Lead (Pb) and mercury (Hg) are known pollutants with immunodisrupting activities; Hg is known to cause autoimmune glomerulonephritis. Both metals are known to suppress host resistance to pathogens. To further evaluate the manner by which these metals cause in vivo immunomodulation, their in vivo effects on Vbeta expression were evaluated along with the Th1 and Th2 frequency. Exposure of BALB/c mice to PbCl2 or HgCl2 induced an oligoclonal response with increases of Vbeta 5+, Vbeta 7+, and Vbeta 13+ CD4+ splenic, but not thymic, T cells. A significantly skewed frequency of Pb-induced splenic Th2 cells expressing Vbeta 7 or Vbeta 13 over Th1 cells was determined by limiting dilution analysis, but this Th2 predominance was not observed with CD4+ T cells expressing Vbeta 8. DO11.10 transgenic mouse exposed to Pb and antigen also demonstrated a skewed type-2 response evidenced by significantly increased IgE levels, lowered IFN-gamma levels, and increased IgG1 and lowered IgG2a anti-OVA levels. Even in the absence of specific T cell responses to a Pb-induced antigen, due to the restricted T cell specificity in the transgenic mouse model, Pb still was able to skew the response toward type-2 reactivity. However, this skewing occurred only in the presence of antigen. Therefore, the Pb-induced oligoclonal T cell response in BALB/c mice which must be initiated by self-antigens and was predominately type-2 may be responsible for autoantibody production and the detrimental health effects associated with Pb exposure.