MHC class I expression by developmental tumors: teratocarcinoma stem cells are TCA positive

Involvement of the Fas/FasL pathway in the pathogenesis of germ cell tumours of the adult testis

Induction of apoptosis by Fas ligand (FasL) of Fas-containing cells is a known mechanism involved in the eradication of inappropriate cells during normal development. Alterations of the Fas/FasL pathway have been found in various types of cancer, leading to circumvention of attack of the tumour by the immune system. An alternative way to circumvent eradication by induction of apoptosis is through changes in the downstream inhibitors. For example, Fas-associating phosphatase-1 (Fap-1) binds directly to the Fas receptor and results in a block of the downstream signalling. To shed more light on the role of the Fas/FasL pathway in the development of human testicular germ cell tumours of the adult testis, this study investigated the presence of Fas, FasL, Fap-1, HLA class I and II molecules, CD45 (lymphocyte marker), and CD57 [natural killer (NK) cell marker] by immunohistochemistry on frozen sections of 41 cases of seminomas, non-seminomas, and spermatocytic seminomas. Every germ cell tumour was positive for Fap-1 and negative for HLA classes I and II, like their non-malignant cells of origin. The infiltrating lymphocytes, predominantly present in seminomas, showed consistently positive staining for Fas and CD45, but not for Fap-1. No Fas was found on NK cells. All seminomas and non-seminomas (except teratomas), including their precursor stages, carcinoma in situ, intratubular seminoma and intratubular non-seminoma, showed positive staining for FasL, but not for Fas. Teratoma showed no staining for FasL and was positive for Fas. In contrast, both Fas and FasL were detectable on spermatocytic seminoma. These data indicate a different regulation of the Fas/FasL system in seminoma and spermatocytic seminoma, supporting a separate pathogenesis for these germ cell-derived tumours. The presence of Fap-1 in all histological variants of germ cell tumours might be related to the consistently positive staining in cells of the germ lineage. This study indicates that production of FasL by the germ cell tumour cells might be involved in the early development of these types of adult testicular cancer by inducting apoptosis of Fas-positive, Fap-1-negative tumour-infiltrating lymphocytes.

Effect of IFN-gamma and IFN-alpha on killing of human trophoblast by decidual LAK cells

Human decidual large granular lymphocytes are capable of killing both normal trophoblast and choriocarcinoma cells after stimulation with recombinant interleukin-2 (rIL-2) in vitro. We now show that pre-treatment of normal trophoblast and JEG-3 choriocarcinoma cells with interferon-gamma (IFN-gamma) protects these target cells from killing by decidual effectors, although pre-treatment with interferon-alpha (IFN-alpha) had no such effect. In contrast, JAR choriocarcinoma cells were readily killed before and after exposure to both IFN-gamma and IFN-alpha. This protective effect might be due to upregulation of non-classical trophoblast HLA Class I molecules, as IFN-gamma but not IFN-alpha enhances Class I surface expression in both normal trophoblast and JEG-3 choriocarcinoma cells. JAR cells, however, are constitutively and inductively negative for Class I expression.

Cellular immune recognition of HLA-G-expressing choriocarcinoma cell line Jeg-3

Jeg-3 choriocarcinoma cells express class-I MHC HLA-G and low levels of a novel HLA-C product. The functional significance of such novel MHC class-I expression in regard of the cellular immune response has been investigated. Jeg-3 cells are NK-insensitive, but susceptible to LAK cytotoxicity, some of which is mediated by T cells. No Jeg-3-specific CTL or proliferative responses could be generated in allogeneic responder PBMC from several different donors. There was no detectable xenogeneic recognition of Jeg-3 cells even when preceded by in vivo priming. Jeg-3 cells are able to suppress proliferative responses in humans and others species. This is not reproduced by conditioned medium from the Jeg-3 cells, but can be overridden by IL-2. The ability of the Jeg-3 choriocarcinoma (trophoblast) cells to suppress in the MLR may reflect the processes which are shared to enable the survival of the foetus in a semi-allogeneic mother or a tumour in its host. It is not clear whether there is any relationship between the unusual class-I-MHC expression by trophoblast and the putative regulatory properties of the latter.

HLA class I homologous transcripts in the human embryonal carcinoma cell line Tera-2

We have used the human teratocarcinoma-derived embryonal carcinoma cell line Tera-2 cl. 13 to explore the putative expression of novel HLA class I(-like) genes. Serological analyses revealed that Tera-2 cells do not express polymorphic HLA class I (-A, -B, -C) specificities, but do express HLA class I-like antigens. These phenotypic properties parallel those of certain mouse embryonal carcinoma cells. To study the expression of HLA class I(-like) genes in the Tera-2 cells two different approaches were used. Screening of a Tera-2 cDNA library with a full-length HLA class I cDNA probe under conditions that would allow for the identification of relatively distinct HLA class I-like sequences yielded 27 positive clones, all of which were of the regular HLA-A, -B, -C type. Reverse northern hybridizations of the restriction enzyme-digested Tlab region comprising cosmids with Tera-2 cDNA as the probe resulted in the identification of several putative human genes whose equivalents map within the mouse Tla region. However, none of these genes appeared to be structurally related to HLA class I. A putative H3.3 histone gene was identified in the proximal Tla region of the C57BL/10 mouse. It is concluded that no structural homologues of mouse Qa/Tla genes are expressed in the human developmental cell line Tera-2.

Northern blot analysis of HLA-G expression by BeWo human choriocarcinoma cells

The BeWo human choriocarcinoma cell line expresses an unusual 41 kDa beta 2-microglobulin-associated class I MHC antigen. HLA-E, -F and -G are known to encode antigens of lower Mr than HLA-A, -B or -C proteins. Using locus-specific probes, we now show that RNA isolated from BeWo cells contains markedly more HLA-G transcripts than peripheral blood lymphocytes (PBL), whilst the converse was noted for HLA-B. These results support recent cloning and sequencing data showing the presence of HLA-G transcripts in BeWo cells.

Evolution of the MHC class I genes of a New World primate from ancestral homologues of human non-classical genes

The products of the classical human major histocompatibility complex (MHC) class I genes (HLA-A, -B, -C) are highly polymorphic molecules that bind peptides and present them to T lymphocytes. The non-polymorphic, non-classical MHC class I gene products (HLA-E, -F, -G) are not restricting elements for the majority of T lymphocytes. The evolutionary relationship of the non-classical and classical MHC class I genes is unclear. Here we present the cloning and sequencing of the MHC class I genes of a New World primate, the cotton-top tamarin (Saguinus oedipus). The expressed MHC class I genes of this species are more closely related to the human non-classical HLA-G gene than they are to genes of the human classical HLA-A, -B, and -C loci. These observations imply that classical and non-classical genes do not necessarily constitute mutually exclusive groups over evolutionary time.

Human trophoblast cells in culture express an unusual major histocompatibility complex class I-like antigen

We present evidence that the trophoblast cells obtained from first trimester placentae by a culture method developed in our laboratory express a class I-like HLA antigen that is only sparsely distributed on the cell surface, lacks classical polymorphic determinants, and consists of heavy chains of lower molecular weight than those of classical HLA in association with beta 2-microglobulin (beta 2M). The latter two features are in general agreement with a previous report describing the nature of the HLA molecule on trophoblast disaggregated from term amniochorion. These cultured trophoblast cells could be useful for molecular studies of the unusual class I antigen, as well as for other in vitro experiments designed to mimic the in vivo local trophoblast-uterine interactions.

Novel human MHC class I genes are expressed by tumour cell lines representing embryonic and extraembryonic tissues

The expression of HLA class I(-like) genes was studied in two human developmental tumour cell lines representing embryonic (Tera-2) and extraembryonic (Jeg-3) origins. Neither cell line expresses polymorphic HLA-A, -B, -C antigens as determined by standard serological typing. Tera-2 cells express the HLA class I-like T cell system A (TCA) determinants; Jeg-3 cells are TCA negative. Northern blot analysis using an HLA class I alpha 3 domain specific probe revealed markedly reduced levels of HLA class I(-like) transcripts in both cell lines, which can be upregulated in Tera-2 cells by incubation with gamma interferon (gamma IFN). Immunoprecipitation studies with a large panel of HLA class I/beta-2 microglobulin (beta 2m) monoclonal antibodies (mAbs), detect low quantities of regular HLA class I heavy chains that are not associated with beta 2m on the surface of Tera-2 cells. In contrast, Jeg-3 cells express significant amounts of cell membrane beta 2m associated molecules of 41 and 45 kilodalton (kD). Screening of a Tera-2 cDNA library, yielded 30 clones that hybridize to a full length HLA class I cDNA probe. Sixteen have been characterized and represent HLA class I sequences, consistent with the haplotype of Tera-2. A similar screening of a Jeg-3 cDNA library isolated clones representing a single novel HLA-C-like sequence; this probably codes for the 45 kD cell surface molecules of Jeg-3. The 41 kD molecule may be encoded by the HLA-6.0 gene since this is constitutively expressed in Jeg-3 cells.