Recognition by xenogeneic cytotoxic T lymphocytes of cells expressing HLA-A2 or HLA-B7 after DNA-mediated gene transfer

Genomics and psychological resilience: a research agenda

Although exposure to adversity increases risk for poor mental health outcomes, many people exposed to adversity do not develop such outcomes. Psychological resilience, defined broadly as positive emotional and/or behavioral adaptation to adversity, may be influenced by genetic factors that have remained largely unexplored in the era of large-scale genome-wide studies. In this perspective, we provide an integrative framework for studying human genome-wide variation underlying resilience. We first outline three complementary working definitions of psychological resilience-as a capacity, process, and outcome. For each definition, we review emerging empirical evidence, including findings from positive psychology, to illustrate how a resilience-based framework can guide novel and fruitful directions for the field of psychiatric genomics, distinct from the ongoing study of psychiatric risk and related traits. Finally, we provide practical recommendations for future genomic research on resilience, highlighting a need to augment cross-sectional findings with prospective designs that include detailed measurement of adversities and outcomes. A research framework that explicitly addresses resilience could help us to probe biological mechanisms of stress adaptation, identify individuals who may benefit the most from prevention and early intervention, and ascertain modifiable protective factors that mitigate negative outcomes even for those at high genetic risk.

Residue 67 in the DRbeta1*0101 and DRbeta1*0103 chains strongly influences antigen presentation and DR-peptide molecular complex conformation

Two closely-related molecules, DR(alpha,beta1*0101) and DR(alpha,beta1*0103), whose beta chains only differ by three amino acids at positions 67, 70, and 71, and six intermediate molecules obtained by site-directed mutagenesis were used to ascertain the respective roles of the three polymorphic residues. Substitutions at positions 70 (D-->Q), 71 (E-->R) and 67 (I or L-->F) strongly affected HA 306-318-specific T-cell recognition. The consequences of the substitution of residue 67 by a phenylalanine depended on the modified HLA-DR molecule. Although this substitution completely inhibited peptide-specific DR1-restricted T-cell recognition, its manifestations on the DR103-restricted T-cell response were variable (abolishing proliferation of some cell lines and not others), no matter what the peptide presented was (HA 306-319 or HIV P25 peptides). We also observed that inhibition of the proliferation of an alloreactive anti-DR103 T-cell clone, caused by a substitution at position 70, was completely cancelled by substitution of residue 67 by a phenylalanine. The observations based on functional experiments, thus, suggest that residue 67 plays an important role in determining conformation of the peptide presented to the T cells. Molecular modeling was used to predict changes induced by amino acid substitutions and highly supports functional data. Substitution of residue 67 by a phenylalanine could have repercussions on the structure of HLA-DR molecule/peptide complexes and affect T-cell recognition.

Use of gene therapy to suppress the antigen-specific immune responses in mice to an HLA antigen

Hematopoietic chimerism has been used in the laboratory to induce life-long immunologic tolerance to donor antigens. The present study demonstrates that mice transplanted with autologous bone marrow cells retrovirally transduced to express HLA-A2.1 develop a significantly depressed immune response to this antigen while retaining normal reactivity to HLA-B7. Retrovirus-mediated transduction was performed using whole bone marrow-producer cell coculture. This approach did not result in significant gene transfer into hematopoietic progenitor cells. Despite this, the antibody response to HLA-A2.1 in mice reconstituted with genetically modified BMC was completely suppressed three months following bone marrow transplantation. Cell-mediated immunity to HLA-A2.1 was partially suppressed in three-fourths of animals tested three months later, although one animal had a CTL profile similar to that an of HLA-A2.1 transgenic mouse. Complete suppression of the antibody-mediated immune response occurred when only one-third of mice had evidence of the introduced genes in their spleen and one-tenth had the introduced sequences in their circulating WBCs by PCR. In conclusion, engineering of BMC to express donor MHC genes may be an alternative to xenogeneic BMT to induce chimerism and tolerance. More efficient transduction of bone marrow progenitor cells may result in more persistent gene expression and long-lasting transplantation tolerance in recipients of genetically modified bone marrow. Successful application of this technology may also be useful in altering immune responses to other external and self antigens.

Brain beta 2-microglobulin levels are elevated in the striatum in Parkinson's disease

beta 2-Microglobulin (B2-MG) content was measured for the first time in the brain (caudate nucleus, putamen, and cerebral cortex) from control and parkinsonian patients by a highly sensitive sandwich enzyme immunoassay. The concentrations of B2-MG in dopaminergic striatal regions were significantly higher in parkinsonian patients than those in controls, whereas those in the cerebral cortex showed no significant difference between parkinsonian and control subjects. Tumor necrosis factor-alpha (TNF-alpha) concentrations were also increased in the striatum, confirming our previous findings, but not in the cerebral cortex. Since TNF-alpha may induce B2-MG expression, these results suggest that an immunological response may occur in the nigrostriatal dopaminergic regions in Parkinson's disease.

Direct identification of an endogenous peptide recognized by multiple HLA-A2.1-specific cytotoxic T cells

An endogenous peptide recognized by a murine T-cell clone specific for the human class I major histocompatibility complex-encoded molecule HLA-A2.1 was identified through the use of microcapillary high-performance liquid chromatography coupled with electrospray-ionization tandem mass spectrometry. The peptide was associated with HLA-A2.1 on both normal cells and the antigen-processing-mutant cell line T2. This observation demonstrates that a processing mechanism other than that involving the transporter associated with antigen processing (TAP) proteins 1 and 2 can produce peptides that can be recognized by T cells. The peptide was also recognized by four other independently derived murine HLA-A2.1-specific murine T-cell clones. This suggests that xenogeneic responses are directed at a restricted subset of major histocompatibility complex product-associated peptides. Finally, quantitation of this peptide in cell extracts using mass spectrometry showed it to be among the most dominant HLA-A2.1 associated species on human lymphoid cells. The potential relevance of this observation to models of alloreactivity will be discussed. The methodology described should be generally useful for the identification of peptide epitopes recognized by alloreactive, tumor-specific, and autoimmune T cells.

Position 71 in the alpha helix of the DR beta domain is predicted to influence peptide binding and plays a central role in allorecognition

Despite all the structural and functional data that have been accumulated regarding major histocompatibility complex (MHC) class II molecules during recent years, the relative contribution of putative T cell receptor (TcR)-contacting residues and peptide-binding MHC polymorphisms to MHC-restricted and allospecific T cell responses remains a point of contention. Some authors emphasize the importance of direct interaction between the allospecific TcR and polymorphic MHC residues whereas other emphasize the role of naturally processed MHC-bound peptides. We have previously described a new HLA-DRB1 allele: DR BON (DRB1*0103). This gene differs from DRB1*0101 by six base pairs clustered in the third variable region of the second exon leading to three amino acid changes at positions 67, 70 and 71 of the beta chain of the HLA-DR molecule. To define the respective role of these residues in allorecognition, we have performed site-directed mutagenesis on the DRB1*0103 allele to create six mutants which are intermediary between the DR BON and the DR1 alleles. These mutant cDNA were expressed in mouse fibroblasts and the transfectants with the highest expression of class II molecules were used as stimulators for a panel of ten anti-DR BON and five anti-DR1 alloreactive T cell clones. We demonstrate that the residue at the peptide-binding position 71 is of paramount importance in the alloresponse of these clones. In addition some clones were sensitive to amino acid substitution at the TcR-contacting position 70, while substitution at position 67 affects very few clones. The dominance of residue 71 was also observed with an influenza hemagglutinin-specific HLA-DR BON-restricted T cell line.

Expression and immunogenicity of HLA-B27 in high-transfection recipient P815: a new method to induce monoclonal antibodies directed against HLA-B27

The immunization of a (BALB/c x C57BL/6) FI mouse with murine transfectants expressing the HLA-B27 antigen resulted in a panel of polymorphic monoclonal antibodies with specificity for HLA-B27 and some additional HLA-antigens. Specificity of the antibodies was defined by cytofluorometric analysis on a panel of lymphoblastoid cell lines (LCL) derived from HLA typed individuals. Three of these antibodies are cytotoxic, and one of them inhibits B27-specific T cell cytotoxicity. Our results indicate that HLA-class I transfectants could be used to generate polymorphic antibodies, and that these antibodies may be helpful for HLA typing and for definition of epitopes recognized by T cells.

Cytotoxic T lymphocytes from HLA-A2 transgenic mice specific for HLA-A2 expressed on human cells

CTL clones were derived from HLA-A2.1 transgenic mice by immunization with a human cell expressing HLA-A2.1. None of these clones lysed murine transfectants, and only 3 of 23 lysed monkey transfectants expressing HLA-A2. In contrast, all of these clones lysed a wide variety of human cells expressing HLA-A2.1. These results demonstrate the existence of species-specific epitopes on the HLA-A2.1 molecule, and suggest that these epitopes are formed by the association of class I MHC products with one or more endogenous species-specific molecules. These results provide an explanation for the frequently observed failure of HLA class I-specific CTL to recognize these antigens on murine transfectants. These results also suggest that such endogenous proteins may also contribute to the formation of epitopes recognized by allospecific CTL.

Peripheral neuropathy in the acquired immunodeficiency syndrome

The histopathological and immunopathological features of peripheral neuropathy were investigated in 21 patients with the acquired immunopathological syndrome (AIDS) or AIDS-related complex (ARC). Clinical syndromes observed in the 11 (52%) symptomatic patients included distal symmetrical polyneuropathy (DSPN) and chronic inflammatory demyelinative polyneuropathy (CIDP). Specimens from 19 of 20 patients (95%), both symptomatic and asymptomatic, had histopathological evidence of moderate or severe demyelination (79%), axonal degeneration (36%), and mononuclear cell inflammation (37%). Nerves from patients with CIDP and DSPN showed similar degrees of demyelination and axonal degeneration, but inflammation was more intense in CIDP. Immunohistochemical staining identified the majority of inflammatory cells as T lymphocytes or macrophages, with a predominance of CD8+ cytotoxic/suppressor cells. Diffuse immunostaining for human leukocyte antigen (HLA)-DR was present on endothelial cells, mononuclear inflammatory cells, and Schwann cells, and variable patchy immunostaining for HLA-DR was present on nerve fibers. Control nerve specimens showed staining for HLA-DR limited to endothelial, and a few mononuclear cells. The patterns of immunostaining were similar for AIDS and ARC patients. Human immunodeficiency virus (HIV) was cultured from peripheral nerve in 3 patients, but HIV antigen was not detected by immunohistochemical staining of 8 specimens. The findings implicate HIV infection in nerve, with T cell- and macrophage-mediated tissue destruction as the pathogenetic mechanism of the AIDS/ARC neuropathy.

HLA-restricted recognition of viral antigens in HLA transgenic mice

Cytotoxic T lymphocytes (CTL) recognize antigen in the context of the class-I products of the major histocompatibility complex (MHC). The extensive polymorphism of class-I molecules is thought to be linked to their capacity to present a large variety of foreign antigens. Whether a single T-cell receptor (TCR) recognizes two separate epitopes (the foreign antigen and an epitope on MHC molecules), or a single epitope resulting from the combination of a foreign antigen and an MHC molecule, has not yet been resolved. In view of the differences between species in primary structure of histocompatibility antigens, it might be predicted that the TCR repertoire would evolve in concert with the diversity of MHC antigens. The mouse and human TCR repertoire would be optimally adapted to engage in productive interactions only with mouse (H-2) and human (HLA) MHC antigens respectively, especially if the more conserved features of histocompatibility antigens, in addition to foreign antigen, were seen by the TCR. Alternatively, only the most variable segments of MHC antigens might be engaged in antigen presentation and thus in interaction with the TCR. In that case, interaction between MHC plus antigen and the TCR might not necessarily be limited by species-specific features. By analysis of the T-cell response against virus-infected cells in HLA-B27/human beta 2-microglobulin double transgenic mice, we report here that the mouse T-cell repertoire is perfectly capable of using the human HLA-B27 antigen as a restriction element.

Cytotoxic T lymphocyte recognition of a xenogeneic major histocompatibility complex antigen expressed in transgenic mice

Introduction of a porcine major histocompatability complex (MHC) class I gene (PD1) into the genome of a C57BL/10 (B10) mouse has been shown to lead to cell surface expression of the porcine MHC antigen, SLAPD1 in a transgenic mouse. The PD1 product expressed on spleen cells from the transgenic mice stimulated B10 spleen cells in a mixed lymphocyte culture to generate PD1-specific cytotoxic T lymphocytes (CTL). The CTL were PD1 specific since they lysed transgenic splenic blast cells and PD1-transfected L cells, but not B10 blasts or control L cells. The CTL were L3T4-, Lyt-2+ and their activity was partially inhibited by either anti-Lyt-2 antibody or by anti-swine MHC alloantibodies. The repertoire of responding B10 anti-transgenic CTL was assessed by examining their cross-reactivity on a series of murine allogeneic targets. The B10 anti-transgenic CTL showed some cross-reactivity on conventional allogeneic targets, but reacted strongly on a series of mutant H-2Kbm blast cells. In addition, B10 anti-B6.cH-2bm6 CTL cross-reacted extensively on the transgenic target cells. These results demonstrated that normal B10 CTL possess a repertoire specific for the products of the xenogeneic class I gene PD1, that this repertoire is cross-reactive with the conventional alloreactive CTL repertoire, and that there exists an unanticipated relationship between PD1-specific CTL and CTL specific for Kb mutant determinants.

Transfer of cloned human class I major histocompatibility complex genes into HLA mutant human lymphoblastoid cells

Three new kinds of recombinant DNA constructs were used to transfer cloned human class I HLA genes (A2 and B8) into unique HLA mutant lymphoblastoid cells: pHeBo(x): a class I gene, "x," in plasmid vector pHeBo, which contains a hygromycin resistance gene and Epstein-Barr virus oriP element that sustains extrachromosomal replication; pHPT(x): gene x in a vector with a hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene; pHPTe(x): gene x in a vector with the HPRT gene and oriP element. Cell surface class I antigen expression was strong in transferents made with class I-deficient lymphoblastoid cell line mutants .144 (A-null), .53 (B-null), and .184 (A-null, B-null). Transferents expressing HLA-A2 were recognized specifically by HLA-A2-specific cytotoxic T lymphocytes. When introduced on either of the vectors with the Epstein-Barr virus oriP element, the class I gene replicated extrachromosomally and was lost at rates of 0.2 to 0.3 per cell division. When introduced with vector pHPT (lacking Epstein-Barr virus oriP), the B8 gene was inserted at different chromosomal locations. Introduction of the HLA-B8 gene failed to restore antigen expression by HLA-B-null mutant .174, providing evidence that, unlike mutants exemplified by .53, .144, and .184, some HLA antigen loss mutants are deficient in a trans-acting function needed for class I antigen expression. Of more general interest, the results obtained with HLA class I genes in vectors that replicate extrachromosomally suggest ways of relating genic expression to chromatin structure and function and of attempting to clone functional human centromeres.

Differential expression of the HLA-B7 and the HLA-A2 gene in transfected mouse L(tk-) cells after stimulation by mouse interferon

Mouse L(tk-) cells were transfected with recombinant genomic clones encoding the human major histocompatibility antigens HLA-A2 or HLA-B7. The exposure of 15 different transfected cell clones to mouse interferon resulted in an up to 2.9-fold enhancement of the HLA-A2 antigen at the cell surface but in an up to 5.5-fold enhancement of the HLA-B7 antigen as shown by quantitative radioimmunoassay with monoclonal antibodies directed against different HLA epitopes. Using the HLA-Bw6 specific monoclonal antibody 2BC4, an even higher increase of the HLA-B7 antigen (up to 12-fold) could be observed. This higher inducibility of an HLA-B versus HLA-A locus gene may reflect distinct regulatory mechanism controlling the expression of HLA class I subregion antigens.

HLA antigens expressed on murine cells are preferentially recognized by murine cytotoxic T cells in the context of the H-2 major histocompatibility complex

The frequency of murine cytotoxic T lymphocytes (CTL) capable of responding to HLA antigens expressed on human or murine cells was determined by limiting dilution analysis. HLA antigens expressed on human cells stimulated CTL with a precursor frequency of about 1 in 2 X 10(5) spleen cells in primed mice, over two orders of magnitude weaker than a primary allogeneic response. There was a 10-fold increase in the frequency of precursors responding to HLA antigens when they were expressed on murine cells. It was determined that the increased frequency of responders was due to CTL that could only recognize HLA antigens on the syngeneic murine line to which they had been stimulated and that these CTL could not lyse any other HLA expressing murine cells of different H-2 haplotypes. The lytic activity of these CTL was inhibited by H-2b-specific antibodies. These results indicate that such CTL recognize HLA antigens in the context of the H-2 major histocompatibility complex. The magnitude and specificity of CTL responses to xenoantigens are discussed in the context of a model for T-cell interactions with major histocompatibility antigens.

Transfer of cloned human class I major histocompatibility complex genes into HLA mutant human lymphoblastoid cells

Three new kinds of recombinant DNA constructs were used to transfer cloned human class I HLA genes (A2 and B8) into unique HLA mutant lymphoblastoid cells: pHeBo(x): a class I gene, "x," in plasmid vector pHeBo, which contains a hygromycin resistance gene and Epstein-Barr virus oriP element that sustains extrachromosomal replication; pHPT(x): gene x in a vector with a hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene; pHPTe(x): gene x in a vector with the HPRT gene and oriP element. Cell surface class I antigen expression was strong in transferents made with class I-deficient lymphoblastoid cell line mutants .144 (A-null), .53 (B-null), and .184 (A-null, B-null). Transferents expressing HLA-A2 were recognized specifically by HLA-A2-specific cytotoxic T lymphocytes. When introduced on either of the vectors with the Epstein-Barr virus oriP element, the class I gene replicated extrachromosomally and was lost at rates of 0.2 to 0.3 per cell division. When introduced with vector pHPT (lacking Epstein-Barr virus oriP), the B8 gene was inserted at different chromosomal locations. Introduction of the HLA-B8 gene failed to restore antigen expression by HLA-B-null mutant .174, providing evidence that, unlike mutants exemplified by .53, .144, and .184, some HLA antigen loss mutants are deficient in a trans-acting function needed for class I antigen expression. Of more general interest, the results obtained with HLA class I genes in vectors that replicate extrachromosomally suggest ways of relating genic expression to chromatin structure and function and of attempting to clone functional human centromeres.

Murine cells expressing an HLA molecule are specifically lysed by HLA-restricted antiviral human T cells

Class I HLA (histocompatibility locus antigen) molecules are the targets of allospecific cytolytic T lymphocytes (CTL) in graft rejection, and constitute the restricting elements necessary for the interaction between antiviral CTL and virus-infected cells. Cells expressing only one HLA in the absence of other human molecules would provide a remarkable model for studying the function of these molecules. However, HLA+ murine cells transfected with human genes are generally not lysed by allospecific human CTL, and this is ascribed to insufficient HLA expression, lack of human beta 2-microglobulin, alteration of HLA molecules or absence of receptors for human T8 or LFA1 molecules in murine cells. Here we report, for the first time, the specific lysis of virus-infected HLA+ murine cells by HLA-restricted antiviral human CTL. Therefore, these murine cells constitute an excellent model for studying the role of HLA molecules.

Recombinant human tumor necrosis factor increases mRNA levels and surface expression of HLA-A,B antigens in vascular endothelial cells and dermal fibroblasts in vitro

Recombinant human tumor necrosis factor (TNF), purified to greater than 99% homogeneity, increases surface expression of class I major histocompatibility complex (MHC) antigens to a maximum of 9-fold on cultured human endothelial cells (HEC) and human dermal fibroblasts (HDF). The increase is concentration dependent (peak 20-100 units/ml) and time dependent (nearly maximal by 4 days); expression remains elevated in the continued presence of TNF and requires greater than 7 days to return to basal levels upon TNF withdrawal. The increase in surface expression appears to result from increases in steady-state mRNA levels for the class I antigens, although the increase in mRNA is proportionately greater than for surface expression. No surface expression of or mRNA for class II MHC antigens is detectable in either control or TNF-treated HEC or HDF. These effects are similar to those produced by leukocyte or fibroblast (type I) interferons (IFNs). The protein synthesis inhibitor cycloheximide (CHX), when added coincidentally with type I IFNs, leads to superinduction of mRNA for class I MHC antigens and, unexpectedly, leads to the appearance of mRNA for class II MHC antigens. CHX has no effect by itself upon mRNA levels for class I or class II MHC antigens, nor does it modulate the increases in mRNA produced by immune (type II) IFN. Most interesting, CHX blocks the increase in mRNA for class I MHC antigens induced by TNF. Thus TNF appears to act on MHC gene expression through a newly synthesized protein intermediate. Our results provide direct evidence that TNF can modulate gene expression in normal (untransformed) cell types and contribute to understanding the complex nature of MHC gene regulation. Finally, they suggest that TNF may act in vivo as an immunoregulatory molecule.

HLA-B locus polymorphism: studies with a specific hybridization probe

The large number of class I histocompatibility genes (HLA) and their extensive homology has made it difficult to assign bands on genomic Southern blots to known genes. Therefore, we have tried to obtain nucleic acid probes for class I genes that are locus specific or have restricted locus specificity. Computer sequence-homology analysis was used to compare the nucleic acid sequences of two genomic clones, one coding for the HLA-B7 antigen (JY150) and one containing a class I pseudogene (pHLA12.4). A sequence in the 3' untranslated region with very low homology was identified. This sequence from the HLA-B7 gene was subcloned into M13 phage. This fragment, JY150/C5, hybridized with two genomic bands in DNA from human HLA homozygotes--presumably the HLA-B locus gene and a closely related gene. The probe was used to assess restriction fragment polymorphism at the HLA-B locus in homozygous consanguineous cell lines. This analysis permitted the association of certain polymorphic restriction enzyme fragments with some alleles of this locus. However, many HLA-B alleles have identical restriction fragments produced by a number of restriction endonucleases.

Recognition of interspecies hybrid class I histocompatibility antigens by antigen-specific cytolytic T lymphocytes

Two reciprocal interspecies hybrid class I histocompatibility genes have been constructed between genomic clones of human HLA-A2 and murine H-2Kb. The proteins encoded by these genes have been designated A21+2/Kb, where the polymorphic domains, alpha 1 and alpha 2, of HLA-A2 are linked to the carboxyl-terminal domains (alpha 3, transmembrane, and intracytoplasmic domains) of H-2Kb, and Kb1+2/A2, where the alpha 1 and alpha 2 domains of the H-2Kb antigen are linked to the carboxyl-terminal domains of HLA-A2. These genes have been transfected and expressed in recipient mouse L cells and human RD (rhabdomyosarcoma) cells. Both hybrid antigens were found to be serologically intact when tested with a panel of antigen-specific monoclonal antibodies. The monoclonal antibody W6/32, which recognizes a monomorphic determinant on all HLA-A, -B, and -C antigens, recognizes the alpha 1 and/or the alpha 2 domain, rather than the more conserved alpha 3 domain. Human cytolytic T lymphocytes (CTL) specific for the HLA-A2 antigen recognized the A2 and A21+2/Kb proteins only when expressed in human cells and not when expressed in mouse cells, even when surface antigen levels were 10-fold greater on the mouse cells than on the human cells. In contrast, a long-term, murine anti-H-2b CTL line not only lysed mouse L-cell lines that expressed the parental Kb and hybrid Kb1+2/A2 antigens but also lysed the Kb and Kb1+2/A2 human cell RD transformants as well. In both cases, the level of CTL recognition and lysis of the transformants that expressed the native antigen Kb was greater than of those transformants that expressed the hybrid antigen Kb1+2/A2. These data suggest that the carboxyl-terminal domains play some role in CTL allorecognition. The lack of human CTL recognition of HLA molecules expressed in mouse L cells, however, cannot be explained by the presence of a xenogeneic carboxyl terminus. Since murine CTL can recognize their target antigen when expressed on the surface of human cells, the possibility remains either that a ligand necessary for other molecular interactions of human CTL may be absent on mouse target cells or that murine and human CTL differ in affinity of binding to target antigens in the absence of accessory-molecule interactions.

Structural analysis of the functional sites of class I HLA antigens

Considerable knowledge of the molecular organization of class I HLA antigens has been attained through extensive structural analysis of these proteins and their genes. Particularly, the nature and location of the polymorphic regions has been established, as well as the basic patterns of structural variability. This work has not unveiled the functionally relevant sites of the HLA molecules but has provided the basis to develop new strategies to do so. The molecular analysis of the determinants recognized by specific antibodies and cytolytic T lymphocytes is being approached through the biochemical characterization of mutants induced in vitro and population variants that are selected by their loss of specific serological or CTL allodeterminants. Other approaches include the immunological analysis of sera raised against synthetic peptides whose structure mimics highly variable segments of class I HLA molecules. These studies have already revealed the participation of several regions in specific allorecognition by antibodies or CTLs and their potential is becoming increasingly evident. A new and possibly powerful approach is currently being used for the dissection of functional sites. It makes use of the structural information derived from sequence analysis and involves expression of cloned HLA genes in transfected mouse or human cells in conjunction with site-directed mutagenesis techniques. Although some difficulties still lie ahead in developing a system suitable for functional assays, the possibility of tailoring HLA mutants and studying the modulation of their recognition determinants by predetermined structural alterations open new pathways to the molecular analysis of HLA function.

Serological expression after sequential double transfection with purified HLA-A11 gene of mouse fibroblasts carrying human beta-2 microglobulin

A genomic cosmid library constructed from DNA from a genotyped individual (JF = HLA-A11, Cw-, B38/A26, Cw7, B51) was screened for clones containing class I histocompatibility genes. Among these clones, one was found to carry a 4.8 kb Hind III fragment which is highly correlated with HLA-A11. This clone was used to transfect LMTK+ cultured mouse fibroblast transformants expressing human beta-2 microglobulin. The human beta-2 microglobulin heavy chain-associated determinant was positively detected by the M18 monoclonal antibody. HLA-A11 expression on these doubly transformed cells was specifically demonstrated by complement-dependent cytotoxicity with HLA-A11 + A3-specific but not with HLA-A3-specific monoclonal antibodies. Absorption studies with human alloantisera confirmed the presence on these cells of HLA-A11 determinants and of cross-reacting determinants which absorbed anti-HLA-A1 and -A3 alloantisera. The JF5-J27 transfected cell expressed both heavy and light chains of human class I histocompatibility genes.

Altered structure of HLA class I heavy chains associated with mouse beta-2 microglobulin

The serological reactivities of HLA-A3, -B7, and -CW3 heavy chains associated with either mouse, bovine, or human beta-2-microglobulin (beta 2m) and expressed on the surface of transfected mouse fibroblasts were analyzed. All reactivities associated with one cluster (defined by monoclonal antibody W6/32) of antigenic determinants expressed by these HLA class I molecules were lost, or profoundly reduced, after each heavy chain associated with mouse beta 2-m. Expression by the transfected fibroblasts of the HLA-A3, -B7, and -CW3 heavy chains in association with human beta 2m restores these reactivities. Since most of the amino acid differences between mouse and human beta 2m probably correspond to externally oriented hydrophilic residues, these results suggest that critical interactions in the three-dimensional structure of HLA class I molecules occur between the light chain and the first two external domains of the class I heavy chains, to which some of the altered reactivities have been mapped.

Recognition of HLA-A2 and -B7 antigens by cloned cytotoxic T lymphocytes after gene transfer into human and monkey, but not mouse, cells

The genes that code for the human major histocompatibility class I antigens, HLA-A2 and HLA-B7, were introduced into human, monkey, and mouse cell lines by cotransfection with suitable biochemical markers and the fluorescence-activated cell sorter was used to identify and/or select stable cell populations expressing high surface levels of these antigens. Levels of expression obtained were similar to those observed for endogenous HLA antigens on various human cell lines and were 25-80% of those observed on the human B-lymphoblastoid cell line JY. Serologically defined HLA-A2 and HLA-B7 polymorphic determinants remained intact on all transfected recipient cells analyzed. Cloned human allospecific cytotoxic T lymphocytes (CTL) specific for HLA-A2 or HLA-B7 were capable of lysing appropriate HLA-transfected human cells with comparable efficiency to JY cell lysis. Two of 10 CTL clones lysed appropriate monkey cell transfectants with approximately equal to 20% the efficiency of human cell transfectants. No specific lysis of any HLA-transfected mouse cell lines, including a B cell lymphoma, was observed despite comparable levels of surface antigen expression or after induction of higher levels by mouse gamma-interferon. Furthermore, L cells expressing human beta 2-microglobulin in addition to HLA-A2 or -B7 were not lysed by these CTL. Thus, an additional species-specific component may be involved in lysis by allogeneic CTL--possibly related to the function(s) of other surface proteins on target cells.

Xenogeneic cytotoxic T-cell clones recognize alloantigenic determinants on HLA-A2

Long-term murine cytotoxic T-cell clones arising in response to stimulation with human lymphoblastoid cells and reactive with the HLA-A2 antigen are characterized. These clones distinguish between HLA-A2 and 21 other serologically defined HLA-A and -B antigens. In addition, most clones discriminate between prototypical HLA-A2 antigens, expressed by the majority of HLA-A2-positive individuals, and variant HLA-A2 antigens, which are serologically identical with the prototype, but distinguishable by human cytotoxic T cells and by biochemical analysis. This discrimination is reflected as an inability to cause any significant lysis of variant HLA-A2-expressing target cells at effector-to-target ratios 10- to 100-fold greater than those giving 50% lysis of prototype HLA-A2-expressing cells. By screening a panel of serologically HLA-A2-positive cells, a new variant HLA-A2-expressing cell line has been defined. The recognition patterns of these xenogeneic clones are suggested to reflect recognition of alloantigenic polymorphic determinants. Based on the strong bias in the xenogeneic T-cell repertoire for such determinants, we propose a model for T-cell recognition of class I products of the major histocompatibility complex.