Cellular and molecular characteristics of transformed T cells from an antigen-specific T-cell line

Natural immunity has significant impact on immune responses against cancer

The immune system defends the host against pathogenic attacks by micro-organisms and their products. It does not react against self-components due to the relatively efficient negative selection of developing T lymphocytes in the thymus. This process does permit T cells with low avidity against self to be present in the T cell repertoire. Such cells play an important physiological role as the host needs so-called autoimmune reactions in order to eliminate dying cells or transformed tumour cells. One of the mysteries in immunology is how the host maintains beneficial autoimmune reactions and avoids pathogenic autoimmune reactions. Activation of the adaptive T lymphocytes is mediated by the low avidity interaction between T-cell antigen receptors and antigenic peptides associated with major histocompatibility complex class I or class II molecules. This interaction is strengthened by T-cell co-receptors such as CD2, CD4, CD8, CD28 and CD154, which react with ligands expressed by cells of the innate immune system. In recent years, the importance of pre-activation of the innate immune system for initiation of adaptive T-cell immune responses has been appreciated. In the present review, I will summarize our work on how natural immunity plays an important role in determining the level of beneficial autoimmune reactions against cancer.

Self-Reactive T Cell Receptor-Reactive CD8+ T Cells Inhibit T Cell Lymphoma Growth In Vivo

Syngenic C57BL/6 mice (H-2(b)) vaccinated with mitomycin C-treated L12R4 T lymphoma cells develop protective immunity toward the MHC class II-negative tumor cells. In the present study, we characterize the nature, mode of function, and specificity of the effector cells in this immunity. These cells are TCR-specific CD8(+) T lymphocytes with effector function in vitro as well as in vivo upon transfer to naive mice. They produce high levels of IFN-gamma and TNF-alpha, but little or no IL-4. By means of TCRbeta-negative variant L12R4 cells, P3.3, and TCR-Vbeta2 cDNA-transfected and TCR-Vbeta2-expressing P3.3 lymphoma cells, we found that a significant part of the effector T cells are specific for the Vbeta12 region. The growth inhibition of L12R4 cells in vitro was inhibited by anti-H-2, anti-K(b), and anti-D(b) mAb. Furthermore, vaccination with Vbeta12 peptide p67-78, which binds to both K(b) and D(b) MHC class I molecules, induces partial protection against L12R4 T lymphoma cells. Thus, self-reactive TCR-Vbeta-specific, K(b)-, or D(b)-restricted CD8(+) T cells mediate inhibition of T cell lymphoma growth in vitro and in vivo.

Regulator T cells: specific for antigen and/or antigen receptors?

Adaptive immune responses are regulated by many different molecular and cellular effectors. Regulator T cells are coming to their rights again, and these T cells seem to have ordinary alpha/beta T-cell receptors (TCRs) and to develop in the thymus. Autoimmune responses are tightly regulated by such regulatory T cells, a phenomenon which is beneficial to the host in autoimmune situations. However, the regulation of autoimmune responses to tumour cells is harmful to the host, as this regulation delays the defence against the outgrowth of neoplastic cells. In the present review, we discuss whether regulatory T cells are specific for antigen and/or for antigen receptors. Our interest in these phenomena comes from the findings that T cells produce many more TCR-alpha and TCR-beta chains than are necessary for surface membrane expression of TCR-alphabeta heterodimers with CD3 complexes. Excess TCR chains are degraded by the proteasomes, and TCR peptides thus become available to the assembly pathway of major histocompatibility complex class I molecules. Consequently, do T cells express two different identification markers on the cell membrane, the TCR-alphabeta clonotype for recognition by B-cell receptors and clonotypic TCR-alphabeta peptides for recognition by T cells?

Molecular mechanisms in the TCR (TCR alpha beta-CD3 delta epsilon, gamma epsilon) interaction with zeta 2 homodimers: clues from a 'phenotypic revertant' clone

The association between the TCRalphabeta-CD3gammaepsilondeltaepsilon hexamers and zeta2 homodimers in the endoplasmic reticulum (ER) constitutes a key step in TCR assembly and export to the T cell surface. Incompletely assembled TCR-CD3 complexes are degraded in the ER or the lysosomes. A previously described Jurkat variant (J79) has a mutation at position 195 on the TCR Calpha domain causing a phenylalanine to valine exchange. This results in a lack of association between TCRalphabeta-CD3gammaepsilondeltaepsilon hexamers and zeta2 homodimers. Two main hypotheses could explain this phenomenon in J79 cells: TCR-CD3 hexamers may be incapable of interacting with zeta2 due to a structural change in the TCR Calpha region; alternatively, TCR-CD3 hexamers may be incapable of interacting with zeta2 due to factors unrelated to either molecular complex. In order to assess these two possibilities, the TCR-CD3 membrane-negative J79 cells were treated with ethylmethylsulfonate and clones positive for TCR membrane expression were isolated. The characterization of the J79r58 phenotypic revertant cell line is the subject of this study. The main question was to assess the reason for the TCR re-expression. The TCR on J79r58 cells appears qualitatively and functionally equivalent to wild-type TCR complexes. Nucleotide sequence analysis confirmed the presence of the original mutation in the TCR Calpha region but failed to detect compensatory mutations in alpha, beta, gamma, delta, epsilon or zeta chains. Thus, mutated J79-TCR-CD3 complexes can interact with zeta2 homodimers. Possible mechanisms for the unsuccessful TCR-CD3 interaction with zeta2 homodimers are presented and discussed.

Lack of restricted T-cell receptor beta-chain variable region (V beta) usage of reactive T-lymphocytes in Hodgkin's disease

T-cell response against tumour-associated antigens is mediated by the TCR complex. To determine a possibly restricted TCR-V beta repertoire in reactive T-lymphocytes in Hodgkin's disease (HD), 20 cases (of which 10 were EBV-positive cases) were investigated using 14 monoclonal antibodies (MoAbs) recognizing 11 different TCR-V beta region family products and Northern blot analysis with cDNA probes specific for mRNA transcripts of 11 V beta families that were not detectable by MoAbs. Four V beta families (V beta 5, V beta 6, V beta 8, V beta 19) were investigated using both immunohistochemistry (IHC) with anti-V beta MoAbs and Northern blot analysis. Immunohistochemical and Northern blot findings were correlated with the detection of the Epstein-Barr virus (EBV) genome in Hodgkin's and Reed-Sternberg cells (H-RS). The non-neoplastic lymphocytes in HD were predominantly of T-phenotype (CD3+). Most of these cells were TCR-alpha beta+ (beta F1+) and only a few T-cells were reactive for TCR-delta 1 antibody (TCR-gamma delta+). In the majority of cases helper/inducer T-cells (CD4+) outnumbered suppressor/cytotoxic T-cells (CD8+). Labelling of these samples with the panel of 14 anti-V beta MoAbs showed that only a small percentage (0.2-5.5%) of beta F1+ lymphocytes were positive with each of these MoAbs. The proportion of these cells was comparable to that seen in normal tissues. Most TCR V beta+ cells were randomly distributed, but in virtually all cases occasional V beta+ cells pertaining to the various V beta families were seen in close contact to H-RS cells. Using total RNA extracted from malignant and normal tissues, no visible band was detected with the various V beta probes. As determined in the present study, the percentage of T-cells expressing a given V beta family must be > or = 10% to be detected with Northern blot. Thus, the percentage of V beta+ cells expressing V beta families which were explored only with Northern blot were within the same range as those of the 11 different TCR-V beta region families assessed with IHC, i.e. 1-10% of lymphoid cells. The results of the present study show that in HD there is no restricted T-cell V beta repertoire usage regardless of the detection of EBV. In addition, since the various V beta families are represented in T-cell subpopulations forming rosettes around H-RS cells, we conclude that the T-cells attracted by H-RS cells constitute a polyclonal population.

The IE allogeneic response of T cells from C57Bl/6 mice is associated with genes in the TCRa locus

It has been demonstrated that induction of immune responses, infectious diseases and autoimmune manifestations can be associated with at least four gene loci: the major histocompatibility complex (MHC) locus; the immunoglobulin (Ig) heavy chain (Hc) locus; and the T-cell receptor (TCR) TCR-alpha or TCR-beta chain loci. In the present study, we have analysed whether T-cell responses of IE-negative C57Bl/6 (B6) mice to IE alloantigen (IE alpha transgenic B6 mice = B6.E alpha 16) or to trinitrophenylated (TNP) syngeneic spleen cells were influenced by changes in the Ig-Hc locus or the TCRa locus. Whereas the fine specificity of T-cell responses to IE alloantigen was the same in B6 mice and in Ig-Hc congenic B6.26a or TCRa congenic B6.10TCa mice, the latter strain of mice demonstrated much higher IE-specific T-cell responses against B6.E alpha 16 spleen cells than B6 or B6.26a mice. This high responsiveness was a dominant feature and associated with the TCRa locus. In addition, the TCRV alpha or V beta repertoire of the congenic strains of mice was polyclonal and very similar. The TNP-specific T-cell responses of B6 and B6.10TCa mice showed the same restricted TCRV alpha and V beta repertoire. It is concluded that in both an oligoclonal T-cell response (anti-TNP) and a polyclonal T-cell response (anti-IE), exchange of Ig-Hc or TCRa loci does not significantly influence the TCRV alpha or V beta repertoire in IE-negative C57Bl/6 mice.

Characterization of T cell receptor assembly and expression in a Ti gamma delta-positive cell line

T cell antigen receptor (TcR) heterodimers of both the Ti-alpha beta and Ti-gamma delta types are expressed at the surface of T cells noncovalently associated with the CD3 complex composed of the monomorphic chains gamma, delta, epsilon and zeta. The structural relationship and assembly of the various components of this multimeric protein complex is still not fully understood. In this report, the human leukemic T cell line Lyon which expresses a Ti-gamma delta/CD3 complex, was characterized and compared to another human leukemic T cell line Jurkat (Ti-alpha beta/CD3). Membrane TCR-/CD3- variants of the T cell Lyon were induced and found to produce all of the Ti/CD3 components, with the exception of Ti-delta. Biochemical analysis indicated that: (1) Ti-gamma/CD3 gamma, delta, epsilon complexes were formed in the endoplasmic reticulum in the absence of Ti-delta; (2) the CD3-zeta chain did not associate with the Ti-gamma/CD3 gamma delta epsilon complex and (3) the Ti-delta chain was required for cell surface expression of the Ti-gamma delta/CD3 complex. Introduction of Jurkat wild-type Ti-alpha cDNA into Lyon T cells resulted in Ti-alpha beta/CD3 expression and abrogated Ti-gamma delta/CD3 expression. In contrast, the expression of the Ti-gamma delta/CD3 complex was not affected by transfection of a mutated Ti-alpha cDNA into Lyon cells. The mutated Ti-alpha chain formed complexes with Ti-beta and CD3 gamma delta epsilon, but the CD3-zeta chain did not associate with these complexes. Taken together analysis of Lyon cells transfected with either wild-type or mutated Ti-alpha suggested that the CD3-zeta chain may have higher affinity for Ti-alpha beta/CD3 complexes than for Ti-gamma delta/CD3 complexes.