Trans-acting element(s) operating across species barriers positively regulate expression of major histocompatibility complex class II genes

The influence of major histocompatibility complex class I antigens on tumor growth and metastasis

The work described here demonstrates the importance of major histocompatibility complex class I antigens for the control of tumor growth and metastasis by the host's immune system. In certain murine tumor cells which have lost expression of H-2 class I antigens, a de novo expression of H-2 can be achieved by transfection with syngeneic class I genes. In contrast to the parental cells the transfected tumors do not grow any more in syngeneic mice, or in other cases they do not form metastases. The studies suggest that the de novo expression of the H-2 antigens renders the tumors highly immunogenic and leads to effective recognition of a tumor-associated antigen in conjunction with the transfected H-2 antigen. These conclusions were confirmed in other tumor systems. For example, separation of a heterogeneous tumor into clones expressing high or low amounts of H-2 showed that only the tumor cell with low H-2 grew well in syngeneic mice, whereas the H-2 high tumor clones were rejected. In other studies in vitro induction by IFN-gamma of H-2 antigen on H-2 negative tumors led to reduced tumor growth in vivo which was due to the increased immunogenicity. About 10% of human tumors are also low or defective for HLA class I expression and often these tumors appear to be more malignant. The class I negative tumors could either have arisen from class I low or negative tissues or are HLA loss variants which escaped the attack of the immune system. Altogether, our studies and the data of other laboratories demonstrate the important role of class I antigens for anti-tumor immunity and they suggest that modulation of class I expression by gene transfection or by induction with soluble mediators could be a useful tool for the manipulation of tumor immunity.

A phenotypically dominant regulatory mechanism suppresses major histocompatibility complex class II gene expression in a murine plasmacytoma

The expression of major histocompatibility complex (MHC) class II antigens is down-regulated when B cells differentiate into plasma cells. We have studied the mechanism of down-regulation of MHC class II expression in a BALB/c strain-derived murine plasmacytoma cell line, NS1. NS1 cells express MHC class I antigens but not MHC class II antigens. We tested 20 uncloned hybrid cell lines obtained from the fusion of NS1 cells with MHC class II-expressing splenic B cells prepared from CBA, SJL or BALB/c mice. All the hybrid cell lines expressed MHC class I antigens of either or both parental haplotypes but did not express MHC class II. One NS1 X splenic B cell hybrid clone, K3, was used to further validate these results; K3 cells expressed MHC class I but not MHC class II antigens. K3 was fused to the MHC class II-expressing B lymphoma A20, and the seven resulting hybrid cell lines were again found to express MHC class I but not MHC class II antigens. Since NS1 is a subclone of the P3-X63Ag8 murine plasmacytoma, we also tested one P3-X63Ag8 x splenic B cell hybrid, Sp2/0, and two Sp2/0 x splenic B cell hybrids. All were found to express the appropriate MHC class I antigens but did not express MHC class II. Thus, our results suggest that the NS1 plasmacytoma suppresses MHC class II expression by a phenotypically dominant regulatory mechanism. We found that NS1 cells express correctly sized mRNA for the MHC class II genes A alpha, E alpha and the invariant chain. The co-expression of MHC class I protein and I-A and I-E region gene transcripts provides strong evidence that the MHC gene cluster is structurally intact, and that lack of class II expression is due to a genetic regulatory mechanism. The amounts of class II mRNA expressed by NS1 cells were at least equivalent to those found in splenic lymphocytes. Therefore, this regulation must operate post-transcriptionally.

Modulation of expression of class II histocompatibility antigens by secretion of a cellular inhibitor in K562 leukemic cells

In this report we show that it is possible to induce the expression of HLA-DR antigens on K562 cells, previously reported to be unresponsive to interferon-gamma (IFN-gamma). However, only low cell concentrations and a high dose of IFN-gamma allowed the induction of HLA-DR antigens. Furthermore, the recombinant glycosylated IFN-gamma is 100-fold more efficient than the unglycosylated form. This induction of HLA-DR antigens on K562 was not related to a stage of differentiation or to the presence of cells subsets specifically sensitive to IFN-gamma, since repeated sorting of K562 HLA-DR-positive and negative cells did not lead to the selection of a cell subset with a different potential of induction for HLA-DR. The difficulty in obtaining induction is due to the production of a soluble endogenous inhibitor of proteic nature, whose action is not restricted to the K562 cell line since it operates also on both epithelial and fibroblastic cells. Treatment of normal human epithelial and fibroblastic cells with conditioned medium from K562 cultures caused a marked decrease in the expression of HLA class II antigens (DR and DP) induced by IFN-gamma (10,000 U/ml), but had no effect on cell growth; however, it also affected expression of HLA class I antigens. This inhibition is not mediated by prostaglandin or an IFN-alpha or IFN-beta-dependent mechanism. Production of this inhibitor by pluripotent human leukemic cells could cause an unbalance in the complex control exerted by the immunological system during hematopoietic differentiation or leukemic progression.

Selection and characterization of T-cell variants lacking molecules involved in T-cell activation (T3 T-cell receptor, T44, and T11): analysis of the functional relationship among different pathways of activation

A clone of the interleukin 2-producing Jurkat leukemia cell line termed JA3 (surface phenotype, T3+, Ti+, T44+, T11+, T40+) has been used to induce and select cell variants lacking surface molecules involved in T-cell activation. Following 200 rad of gamma-radiation (1 rad = 0.01 Gy), cells were treated with monoclonal antibodies (mAbs) directed to T3, Ti, T44, or T11 antigen and complement. After growth of the residual cells in culture, "negative" cells were cloned under limiting conditions. Depending on the specificity of the mAb used for the immunoselection, three groups of variants were obtained. (i) The use of mAbs directed to T3 or Ti resulted in cell variants that expressed the T3 Ti- T44+ Leu1+ T11+ T40+ 4F2+ HLA class I+ surface phenotype. (ii) Immunoselection with anti-T44 mAb resulted in 2 variants that shared the T3- Ti- T44- Leu1- T11+ T40+ 4F2+ HLA class I+ phenotype. (iii) Cell treatment with anti-T11 mAb resulted in 15 variants characterized by the lack of T11 antigen expression and of all the other T-cell-specific surface antigens. Therefore, it appears that the different sets of JA3 cell variants, like T cells at discrete stages of intrathymic differentiation, may follow a coordinated expression of surface differentiation antigens. Analysis of the functional responsiveness of the three distinct groups of JA3 cell variants to different stimuli showed that all produced interleukin 2 in response to A23187 calcium ionophore plus phorbol 12-myristate 13-acetate. The first group of variants (T3- Ti-) did not respond to stimulation with anti-T3, anti-Ti, or anti-T44 mAbs. Eight of 9 did not respond to phytohemagglutinin either; however, all responded to appropriate stimulatory combinations of anti-T11 mAbs (and to calcium ionophore). The second group of variants (T3-, Ti-, T44-, T11+), similar to the first group, did not respond to anti-T3, anti-Ti, anti-T44 mAbs, and phytohemagglutinin, but they were fully responsive to anti-T11 mAb. The last group of variants (lacking all the T-cell-specific surface antigens) only responded to calcium ionophore A23187.

Influence of the H-2u haplotype on immune function in F1 hybrid mice. II. F1 antiparent mixed lymphocyte reactivity

Recently we reported that antigen-primed T cells from (H-2u X H-2s) F1 and (H-2u X H-2q)F1 mice responded poorly in vitro to antigen in the context of antigen-presenting cells of the non-H-2u parent. It was suggested that this effect might be due to unbalanced expression of parental antigens in the F1 hybrid with the result that the non-H-2u A antigens were greatly reduced or absent in these mice. If this were the case, non-H-2u Ia-A cells might be expected to stimulate a mixed lymphocyte reaction (MLR) when cultured with F1 responder cells. When tested, (SJL X PL)F1 responder cells reacted strongly to SJL stimulator cells. There was no significant reaction to PL stimulator cells. The use of major histocompatibility complex (MHC) congenic mice showed the stimulatory antigens to be associated with the MHC. The MLR could be blocked significantly by monoclonal A-specific antibody of the appropriate specificity. When a monoclonal antibody reactive with a private epitope associated with As was used to probe for the presence of As on the surface of (SJL X PL)F1 spleen cells, no antigen could be detected, indicating loss or alteration of this antigen. These findings suggest that an alteration of the expression of the parental As molecule may be responsible for this phenomenon.

Regulation of a transfected human class II major histocompatibility complex gene in human fibroblasts

To investigate the cis-acting DNA elements that are involved in regulation of class II major histocompatibility complex genes, including gamma-interferon (gamma-IFN) induction, 5' flanking DNA deletions of a DQ beta "minigene" were analyzed in stable transfected cell lines. At least four elements 5' to the gene were found to be involved in DQ beta regulation. Deletion of sequences from -2500 to -159 base pairs (bp) resulted in increased transcription, suggesting that negative regulatory elements resided in the deleted region. These clones were all capable of responding to gamma-IFN. Further deletion of sequences from -159 to -128 bp resulted in constitutive high level transcription and the inability of these constructions to respond to gamma-IFN. A deletion to -107 bp resulted in a decrease in the basal level of expression that was restored by removal of the 5' DNA sequence to -82 bp, suggesting the presence of a second negative element. Finally, deletion to -64 bp caused a marked decrease in expression, suggesting the loss of an element necessary for high levels of transcription. The gamma-IFN control and the transcription control elements contain the conserved upstream sequences found in all class II genes, suggesting a role for these sequences.

MHC class II antigen and immunoglobulin expression in spontaneous phenotypic variants of the Burkitt's lymphoma cell line Namalwa

Phenotypic variant sublines of the Burkitt's lymphoma cell line Namalwa were examined with cDNA probes for the different MHC class II beta chain genes and with monoclonal antibodies specific for the corresponding cell surface antigens (DP, DQ and DR antigens). Expression of MHC class II antigens in the Namalwa sublines (known as CSN/70, IPN/45, PNT and KN2) was compared with that of the B-lymphoblastoid cell line DEW1, which is identical to Namalwa in DR allotype (DR 2,4). There were markedly different levels of expression of MHC class II antigens among the cell lines: in DEW1 and the Namalwa KN2 subline DP, DQ and DR antigens were expressed on almost all the cells. On the PNT and IPN/45 sublines, DR antigens were expressed on all the cells, and DP and DQ antigens were expressed at detectable levels on only a proportion of cells. On CSN/70, there was weak expression of DR antigens on a minority of cells and no detectable expression of DP and DQ antigens. When examined with MHC class II-specific cDNAs, restriction fragment patterns of DNA were identical for all the cell lines, suggesting that they had structurally identical MHC class II genes. In the Namalwa cell lines the synthesis of Ig and the expression of MHC class II antigens were coordinately regulated.

Extracellular matrix-modulated expression of human cell surface glycoproteins A42 and J143. Intrinsic and extrinsic signals determine antigenic phenotype

We have used serologic, biochemical, and genetic methods to characterize two stage-specific human differentiation antigens of neural and melanocytic cells: A42 (57,000 Mr glycoprotein) and J143 (140,000/30,000 Mr glycoprotein). The genes determining A42 and J143 cell surface expression in rodent-human hybrids were chromosomally mapped, and the respective human chromosomes were introduced into rodent cells derived from distinct differentiation lineages. Serologic analysis of the resulting hybrid clones has permitted the identification of two types of regulatory signals determining A42 and J143 expression. First, both antigens are expressed in hybrids constructed with antigen-positive human cells and also in certain hybrids constructed with antigen-negative human cells, indicating that intrinsic signals provided by the differentiation program of the rodent fusion partner induce antigen expression. Second, a series of human-mouse neuroblastoma hybrids, which are A42- or J143- when cultured on plastic surfaces, can be induced to express the antigens when cultured on substrates coated with extracellular matrix (ECM) produced by bovine corneal endothelial cells or fibronectin. This induction of antigen expression by extrinsic, ECM-derived signals is accompanied in the neuroblastoma hybrids by increased substrate adhesiveness and cell spreading and by characteristic changes in cell morphology. A similar program of phenotypic changes is also seen in spontaneous variants of human neuroblastoma and Ewing's sarcoma cells and in ECM-induced Ewing's sarcoma cells. These findings suggest that ECM-derived signals have a role analogous to mitogens and soluble differentiation factors in modulating differentiation phenotypes and tissue-specific patterns of cell surface antigen expression.

The genes for tumor necrosis factor (TNF-alpha) and lymphotoxin (TNF-beta) are tandemly arranged on chromosome 17 of the mouse

We have isolated clones containing the gene for tumor necrosis factor (TNF-alpha) from a mouse genomic library. Four out of five clones containing the TNF-alpha gene also hybridized to a human lymphotoxin (TNF-beta) probe. We constructed a restriction enzyme cleavage map of a 6.4 kb region from one of the genomic clones. From partial sequencing data and hybridizations with exon-specific oligonucleotide probes, we conclude that this region contains the mouse TNF-alpha and TNF-beta genes in a tandem arrangement, that they are separated by only about 1100 bases, and that their intron-exon structure is very similar to that seen in man. We probed genomic blots of DNA from human/mouse hybrids containing single mouse chromosomes for the presence of the mouse TNF genes. The results show that the genes are located on mouse chromosome 17, which also contains the major histocompatibility complex. Therefore, both the mouse and the human TNF genes are tandemly arranged and located on the same chromosome as the MHC.

Stable integration of mouse DNA into Ia-negative human B-lymphoma cells causes reexpression of the human Ia-positive phenotype

RJ 2.2.5, a variant of the human B-lymphoma cell line Raji, does not express the HLA-DR, -DQ, and -DP class II (or Ia) histocompatibility antigens, as a result of a defect in the transcription of the corresponding genes. This defect is corrected after fusion of RJ 2.2.5 cells with mouse Ia-positive cells. Previous work showed that the trans-acting transcriptional activator supplied by the mouse cells is encoded by a locus on mouse chromosome 16. We show here that reexpression of human major histocompatibility complex class II genes by RJ 2.2.5 cells can also be achieved by stable integration of mouse genomic sequences into the RJ 2.2.5 genome after DNA-mediated gene transfer.

aIr-1, a newly found locus on mouse chromosome 16 encoding a trans-acting activator factor for MHC class II gene expression

RJ 2.2.5 is a human B cell line that has lost the capacity to express MHC class II genes. The human class II-positive phenotype is restored in somatic cell hybrids between RJ 2.2.5 and mouse spleen cells. By karyotype and molecular studies of an informative family of hybrids we have now shown that the reexpression of human class II gene products, as well as the maintenance of the mouse class II-positive phenotype, correlates with the presence of mouse chromosome 16. Thus, the existence on this mouse chromosome of a newly found locus, designated by us aIr-1, that determines a trans-acting activator function for class II gene expression, is established. Possible implications of this finding are discussed.

A Thy-1- mutant defining a gene acting in trans position to regulate cell-surface Thy-1 glycoprotein expression and Thy-1 messenger RNA content

The Thy-1 glycoprotein is a differentiation antigen which exhibits tissue-specific regulation. A mutant of a Thy-1.1+ T-cell lymphoma has been isolated which does not express Thy-1 glycoprotein on the cell surface and does not accumulate Thy-1 mRNA in the cytoplasm. Hybrids between the mutant and a Thy-1.2+ T-cell lymphoma express 20-30-fold lower levels of Thy-1 glycoprotein on their cell surface compared to wild-type T-cell lymphomas, and they have correspondingly low levels of cytoplasmic Thy-1 mRNA. A revertant of one hybrid was isolated which expressed wild-type levels of both Thy-1 alleles on its surface and contained correspondingly increased levels of Thy-1 mRNA. A Thy-1+ revertant of the Thy-1- mutant was isolated by cell sorting. A second generation Thy-1- mutant could be isolated from this revertant which also did not accumulate Thy-1 mRNA and which behaved in a way similar to the first generation mutant when hybridized to a Thy-1.2+ lymphoma. No changes in the structure or copy number of the Thy-1 structural gene could be detected in this series of mutants and revertants. These properties are consistent with a mutation in one (or more) gene(s) which acts in trans position to regulate Thy-1 glycoprotein expression.