MR1-restricted mucosal-associated invariant T (MAIT) cells respond to mycobacterial vaccination and infection in nonhuman primates.

Studies on mucosal-associated invariant T cells (MAITs) in nonhuman primates (NHP), a physiologically relevant model of human immunity, are handicapped due to a lack of macaque MAIT-specific reagents. Here we show that while MR1 ligand-contact residues are conserved between human and multiple NHP species, three T-cell receptor contact-residue mutations in NHP MR1 diminish binding of human MR1 tetramers to macaque MAITs. Construction of naturally loaded macaque MR1 tetramers facilitated identification and characterization of macaque MR1-binding ligands and MAITs, both of which mirrored their human counterparts. Using the macaque MR1 tetramer we show that NHP MAITs activated in vivo in response to both Bacillus Calmette-Guerin vaccination and Mycobacterium tuberculosis infection. These results demonstrate that NHP and human MR1 and MAITs function analogously, and establish a preclinical animal model to test MAIT-targeted vaccines and therapeutics for human infectious and autoimmune disease.

Human thymic MR1-restricted MAIT cells are innate pathogen-reactive effectors that adapt following thymic egress.

Human mucosal-associated invariant T (MAIT) cells express the semi-invariant T-cell receptor (TCR) Vα7.2 and are restricted by the major histocompatibility complex-Ib molecule MR1. While MAIT cells share similarities with other innate T cells, the extent to which MAIT cells are innate and their capacity to adapt is unknown. We evaluated the function of Vα7.2(+) T cells from the thymus, cord blood, and peripheral blood. Although antigen-inexperienced MAIT cells displayed a naïve phenotype, these had intrinsic effector capacity in response to Mycobacterium tuberculosis (Mtb)-infected cells. Vα7.2(+) effector thymocytes contained signal joint TCR gene excision circles (sjTRECs) suggesting limited replication and thymic origin. In evaluating the capacity of Mtb-reactive MAIT cells to adapt, we found that those from the peripheral blood demonstrated a memory phenotype and had undergone substantial expansion, suggesting that they responded to antigenic stimulation. MAIT cells, an evolutionarily conserved T-cell subset that detects a variety of intracellular infections, share features of innate and adaptive immunity.

Tuberculosis immunology in children: diagnostic and therapeutic challenges and opportunities.

Tuberculosis (TB) is one of the most important causes of infectious morbidity and mortality worldwide. Young children are more likely to develop severe disease from the causative agent Mycobacterium tuberculosis. These clinical observations likely reflect fundamental differences in the immune systems of young children and adults. Essential to effective TB immunity are functioning macrophages, dendritic cells, strong Th1-type T-cell immunity and a relative absence of Th2-type T-cell immunity. Critical differences between adults and children relevant to TB immunity include deficiencies in macrophage and dendritic cell function, deficiencies in the development of Th1-type T-cells in response to pathogens, and the propensity for infants and young children to develop Th2-type CD4+ T-cells in response to immunogens. In this article, knowledge about the requisite components of protective immunity, differences between the immune systems of children and adults relevant to pediatric tuberculosis, M. tuberculosis-specific T-cell immunity in children, and potential application to immunodiagnostics and vaccine development will be reviewed.

Rudimentary TCR signaling triggers default IL-10 secretion by human Th1 cells.

Understanding the process of inducing T cell activation has been hampered by the complex interactions between APC and inflammatory Th1 cells. To dissociate Ag-specific signaling through the TCR from costimulatory signaling, rTCR ligands (RTL) containing the alpha1 and beta1 domains of HLA-DR2b (DRA*0101:DRB1*1501) covalently linked with either the myelin basic protein peptide 85-99 (RTL303) or CABL-b3a2 (RTL311) peptides were constructed to provide a minimal ligand for peptide-specific TCRs. When incubated with peptide-specific Th1 cell clones in the absence of APC or costimulatory molecules, only the cognate RTL induced partial activation through the TCR. This partial activation included rapid TCR zeta-chain phosphorylation, calcium mobilization, and reduced extracellular signal-related kinase activity, as well as IL-10 production, but not proliferation or other obvious phenotypic changes. On restimulation with APC/peptide, the RTL-pretreated Th1 clones had reduced proliferation and secreted less IFN-gamma; IL-10 production persisted. These findings reveal for the first time the rudimentary signaling pattern delivered by initial engagement of the external TCR interface, which is further supplemented by coactivation molecules. Activation with RTLs provides a novel strategy for generating autoantigen-specific bystander suppression useful for treatment of complex autoimmune diseases.

Transfer of specificity for human immunodeficiency virus type 1 into primary human T lymphocytes by introduction of T-cell receptor genes.

The introduction of genes encoding T-cell receptor (TCR) chains specific for human immunodeficiency virus into T cells of infected patients represents a means to quantitatively and qualitatively improve immunity to the virus. Our results demonstrate that the high level of TCR expression required for physiologic functioning can be reproducibly achieved with retroviral vectors encoding full-length unmodified TCR chains under the control of a strong internal constitutive phosphoglycerate kinase promoter.

HIV-specific cytotoxic T lymphocytes traffic to lymph nodes and localize at sites of HIV replication and cell death.

We have tracked the in vivo migration and have identified in vivo correlates of cytotoxic T-lymphocyte (CTL) activity in HIV-seropositive subjects infused with autologous gene-marked CD8(+) HIV-specific CTL. The number of circulating gene-marked CTL ranged from 1.6 to 3.5% shortly after infusion to less than 0.5% 2 weeks later. Gene-marked CTL were present in the lymph node at 4.5- to 11-fold excess and colocalized within parafollicular regions of the lymph node adjacent to cells expressing HIV tat fusion transcripts, a correlate of virus replication. The CTL clones expressed the CCR5 receptor and localized among HIV-infected cells expressing the ligands MIP-1alpha and MIP-1beta, CC-chemokines produced at sites of virus replication. Aggregates of apoptotic cells and cells expressing granzyme-B localized within these same sites. In contrast, lymph node sections from untreated HIV-seropositive subjects, all with significant viral burden (> 50,000 HIV RNA copies/mL plasma), showed no CC-chemokine expression and exhibited only sporadic and randomly distributed cells expressing granzymes and/or apoptotic cells. These studies show that the infused CTL specifically migrate to sites of HIV replication and retain their antigen-specific cytolytic potential. Moreover, these studies provide a methodology that will facilitate studies of both the magnitude and functional phenotype of Ag-specific CD8(+) T cells in vivo.

The antiviral activity of HIV-specific CD8+ CTL clones is limited by elimination due to encounter with HIV-infected targets.

Adoptive immunotherapy of virus infection with viral-specific CTL has shown promise in animal models and human virus infections and is being evaluated as a therapy for established HIV-1 infection. Defining the individual obstacles for success is difficult in human trials. We have therefore examined the localization, persistence, and antiviral activity of HIV-1 gag-specific CTL clones in both HIV-1-infected and uninfected haplotype-matched human (hu)-PBL-SCID mice. Injection of gag-specific clones but not control CTL into HIV-1-infected hosts reduced plasma viremia by >10-fold but failed to eliminate the virus infection from most treated animals. The failure to eradicate virus did not reflect selection of escape variants because the gag epitope remained unmutated in virus isolates obtained after CTL therapy. Injection of carboxyfluorescein diacetate succinimide ester-labeled CTL demonstrated markedly different fates for gag-specific CTL in the presence or absence of HIV-1 infection. HIV-1-specific CTL rapidly disappeared in infected recipients, whereas they were maintained at high numbers in uninfected mice. By contrast, control CTL were long lived in both infected and uninfected recipients. Thus, interaction of CTL with virus-infected target cells in vivo leads not only to target destruction but also to the rapid disappearance of the infused CTL, and it limits the capacity of CTL therapy to eliminate HIV-1 infection.

In vivo migration and function of transferred HIV-1-specific cytotoxic T cells.

The persistence of HIV replication in infected individuals may reflect an inadequate host HIV-specific CD8+ cytotoxic T lymphocyte (CTL) response. The functional activity of HIV-specific CTLs and the ability of these effector cells to migrate in vivo to sites of infection was directly assessed by expanding autologous HIV-1 Gag-specific CD8+ CTL clones in vitro and adoptively transferring these CTLs to HIV-infected individuals. The transferred CTLs retained lytic function in vivo, accumulated adjacent to HIV-infected cells in lymph nodes and transiently reduced the levels of circulating productively infected CD4+ T cells. These results provide direct evidence that HIV-specific CTLs target sites of HIV replication and mediate antiviral activity, and indicate that the development of immunotherapeutic approaches to sustain a strong CTL response to HIV may be a useful adjunct to treatment of HIV infection.

T-cell mediated rejection of gene-modified HIV-specific cytotoxic T lymphocytes in HIV-infected patients.

The introduction and expression of genes in somatic cells is an innovative therapy for correcting genetic deficiency diseases and augmenting immune function. A potential obstacle to gene therapy is the elimination of such gene-modified cells by an immune response to novel protein products of the introduced genes. We are conducting an immunotherapy trial in which individuals seropositive for human immunodeficiency virus (HIV) receive CD8+ HIV-specific cytotoxic T cells modified by retroviral transduction to express a gene permitting positive and negative selection. However, five of six subjects developed cytotoxic T-lymphocyte responses specific for the novel protein and eliminated the transduced cytotoxic T cells. The rejection of genetically modified cells by these immunocompromised hosts suggests that strategies to render gene-modified cells less susceptible to host immune surveillance will be required for successful gene therapy of immunocompetent hosts.