Analysis of mRNA for class I HLA on human gametogenic cells

Meiotic Genes and DNA Double Strand Break Repair in Cancer

Tumor cells show widespread genetic alterations that change the expression of genes driving tumor progression, including genes that maintain genomic integrity. In recent years, it has become clear that tumors frequently reactivate genes whose expression is typically restricted to germ cells. As germ cells have specialized pathways to facilitate the exchange of genetic information between homologous chromosomes, their aberrant regulation influences how cancer cells repair DNA double strand breaks (DSB). This drives genomic instability and affects the response of tumor cells to anticancer therapies. Since meiotic genes are usually transcriptionally repressed in somatic cells of healthy tissues, targeting aberrantly expressed meiotic genes may provide a unique opportunity to specifically kill cancer cells whilst sparing the non-transformed somatic cells. In this review, we highlight meiotic genes that have been reported to affect DSB repair in cancers derived from somatic cells. A better understanding of their mechanistic role in the context of homology-directed DNA repair in somatic cancers may provide useful insights to find novel vulnerabilities that can be targeted.

Proteogenomic Analysis Unveils the HLA Class I-Presented Immunopeptidome in Melanoma and EGFR-Mutant Lung Adenocarcinoma

Immune checkpoint inhibitors and adoptive lymphocyte transfer–based therapies have shown great therapeutic potential in cancers with high tumor mutational burden (TMB), such as melanoma, but not in cancers with low TMB, such as mutant epidermal growth factor receptor (EGFR)–driven lung adenocarcinoma. Precision immunotherapy is an unmet need for most cancers, particularly for cancers that respond inadequately to immune checkpoint inhibitors. Here, we employed large-scale MS-based proteogenomic profiling to identify potential immunogenic human leukocyte antigen (HLA) class I-presented peptides in melanoma and EGFR-mutant lung adenocarcinoma. Similar numbers of peptides were identified from both tumor types. Cell line and patient-specific databases (DBs) were constructed using variants identified from whole-exome sequencing. A de novo search algorithm was used to interrogate the HLA class I immunopeptidome MS data. We identified 12 variant peptides and several classes of tumor-associated antigen-derived peptides. We constructed a cancer germ line (CG) antigen DB with 285 antigens. This allowed us to identify 40 class I-presented CG antigen–derived peptides. The class I immunopeptidome comprised more than 1000 post-translationally modified (PTM) peptides representing 58 different PTMs, underscoring the critical role PTMs may play in HLA binding. Finally, leveraging de novo search algorithm and an annotated long noncoding RNA (lncRNA) DB, we developed a novel lncRNA-encoded peptide discovery pipeline to identify 44 lncRNA-derived peptides that are presented by class I. We validated tandem MS spectra of select variant, CG antigen, and lncRNA-derived peptides using synthetic peptides and performed HLA class I-binding assays to demonstrate binding to class I proteins. In summary, we provide direct evidence of HLA class I presentation of a large number of variant and tumor-associated peptides in both low and high TMB cancer. These results can potentially be useful for precision immunotherapies, such as vaccine or adoptive cell therapies in melanoma and EGFR-mutant lung cancers.

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Proteogenomics identified ∼35,000 class I-presented peptides.

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CG antigen and PTM peptides identified in melanoma and lung cancer.

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De novo search identified variant and lncRNA-derived peptides.

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A new strategy to identify class I-presented lncRNA-derived peptides developed.

Reverse Vaccinology Approach in Constructing a Multi-Epitope Vaccine Against Cancer-Testis Antigens Expressed in Non-Small Cell Lung Cancer

Background:

The 5-year survival rate of non-small cell lung cancer (NSCLC) patients has not significantly improved despite advancements in the currently applied treatments. Thus, efforts are put forth in developing novel immunotherapeutic agents targeting cancer-testis antigens (CTA) in NSCLC. This work utilized reverse vaccinology approach in designing a novel multi-epitope vaccine targeting melanoma-associated antigen 3 (MAGEA3), MAGEA4, New York esophageal squamous cell carcinoma-1 (NY-ESO-1), and Kita-Kyushu lung cancer antigen 1 (KK-LC1), being the most frequently expressed CTAs in NSCLC.

Methods:

Epitopes were mapped from the sequences of CTAs. The population coverage (PC) of identified CD4+ and CD8+ epitopes were estimated. Candidate linear B cell (BL), CD4+, and CD8+ epitopes were adjoined in a multi-epitope construct (Mvax) with flagellin domain as an adjuvant. Antigenicity, and cross-reactivity of Mvax were examined. The tertiary structure of Mvax was modelled, and validated. All epitopes included in the vaccine were docked with their human leukocyte antigen (HLA) binders. The immunogenicity of epitopes in Mvax was validated through molecular dynamics analysis.

Results:

Mvax contains 22 epitopes from MAGEA3, MAGEA4, NY-ESO-1, and KK-LC1. It is classified as antigenic, non-allergen, non-toxic, and possesses physicochemical stability. Epitopes have no significant hits with other human proteins, except for 2 other CTAs frequently expressed in NSCLC. The stretch of BL epitopes in Mvax confers flexibility, and accessibility emphasizing its antigenicity. The tertiary structure analysis showed that Mvax model has good structural quality. All epitopes included in the vaccine are highly immunogenic as indicated by favorable binding affinity, low binding energy, and acceptable root-mean-square deviation (RMSD). CD4+ and CD8+ epitopes have global PC of 81.81%, and 84.15%, respectively.

Conclusion:

Overall, in silico evaluations show that Mvax is a potential immunotherapeutic agent against NSCLC.

Therapeutic applications of the cancer immunoediting hypothesis

Since the late 19th century, the immune system has increasingly garnered interest as a novel avenue for cancer therapy, particularly given scientific breakthroughs in recent decades delineating the fundamental role of the immune system in tumorigenesis. The immunoediting hypothesis has articulated this role, describing three phases of the tumor-immune system interaction: Elimination, Equilibrium, and Escape wherein tumors progress from active immunologic surveillance and destruction through dynamic immunologic stasis to unfettered growth. The primary goals of immunotherapy are to restrict and revert progression through these phases, thereby improving the immune system's ability to control tumor growth. In this review, we detail the development and foundation of the cancer immunoediting hypothesis and apply this hypothesis to the dynamic immunotherapy field that includes checkpoint blockade, vaccine therapy, and adoptive cell transfer.

Insights Into Mechanisms of Tumor and Immune System Interaction: Association With Wound Healing

A large number of studies have presented a great deal of information about tumor and immune system interaction. Nevertheless, the problem of tumor evasion from the immune reaction is still difficult to resolve. Understanding the ways in which immunosuppressive tumor microenvironment develops and maintains its potential is of utmost importance to ensure the best use of the suppressed immune functions. The study presents a review covering the data on tumor-associated antigens, mechanisms of tumor evasion from the immune reactions, and search for common immunosuppressive processes of tumor growth and normal wound healing. The study discusses the important role of monocytes/macrophages in the regulation of immune system reactions. We suggest that the simultaneous actions of growth factors and pro-inflammatory cytokines may result in the suppression of the immune system. The study describes intracellular signaling molecules that take part in the regulation of the myeloid cell functions. If the hypothesis is proved correct, the indicated interaction of cytokines could be regarded as a prospective target for antitumor therapy.

Novel TCR-based biologics: mobilising T cells to warm 'cold' tumours

Immunotherapeutic strategies have revolutionised cancer therapy in recent years, bringing meaningful improvements in outcomes for patients with previously intractable conditions. These successes have, however, been largely limited to certain types of liquid tumours and a small subset of solid tumours that are known to be particularly immunogenic. Broadening these advances across the majority of tumour indications, which are characterised by an immune-excluded, immune-deserted or immune-suppressed ('cold') phenotype, will require alternative approaches that are able to specifically address this unique biological environment. Several newer therapeutic modalities, including adoptive cell therapy and T cell redirecting bispecific molecules, are considered to hold particular promise and are being investigated in early phase clinical trials across various solid tumour indications. ImmTAC molecules are a novel class of T cell redirecting bispecific biologics that exploit TCR-based targeting of tumour cells; providing potent and highly specific access to the vast landscape of intracellular targets. The first of these reagents to reach the clinic, tebentafusp (IMCgp100), has generated demonstrable clinical efficacy in an immunologically cold solid tumour with a high unmet need. Here, we highlight the key elements of the ImmTAC platform that make it ideally positioned to overcome the cold tumour microenvironment in an off-the-shelf format.

Massive expression of germ cell-specific genes is a hallmark of cancer and a potential target for novel treatment development

Cancer cells have been found to frequently express genes that are normally restricted to the testis, often referred to as cancer/testis (CT) antigens or genes. Because germ cell-specific antigens are not recognized as “self” by the innate immune system, CT-genes have previously been suggested as ideal candidate targets for cancer therapy. The use of CT-genes in cancer therapy has thus far been unsuccessful, most likely because their identification has relied on gene expression in whole testis, including the testicular somatic cells, precluding the detection of true germ cell-specific genes. By comparing the transcriptomes of micro-dissected germ cell subtypes, representing the main developmental stages of human spermatogenesis, with the publicly accessible transcriptomes of 2617 samples from 49 different healthy somatic tissues and 9232 samples from 33 tumor types, we here discover hundreds of true germ cell-specific cancer expressed genes. Strikingly, we found these germ cell cancer genes (GC-genes) to be widely expressed in all analyzed tumors. Many GC-genes appeared to be involved in processes that are likely to actively promote tumor viability, proliferation and metastasis. Targeting these true GC-genes thus has the potential to inhibit tumor growth with infertility being the only possible side effect. Moreover, we identified a subset of GC-genes that are not expressed in spermatogonial stem cells. Targeting of this GC-gene subset is predicted to only lead to temporary infertility, as untargeted spermatogonial stem cells can recover spermatogenesis after treatment. Our GC-gene dataset enables improved understanding of tumor biology and provides multiple novel targets for cancer treatment.

Targeting Head and Neck Cancer by Vaccination

Head and neck cancer (HNC) is a heterogeneous group of squamous cell cancers that affect the oral cavity, pharynx, and larynx. Worldwide, it is the sixth most common cancer but in parts of Southern and South-East Asia, HNC is one of the most common cancers. A significant proportion of HNC is driven by human papillomavirus (HPV) infection, whereas HPV-independent HNC is associated with alcohol, smoking, and smokeless tobacco consumption. Here, we review the past and present experience of targeting HNC with vaccination focusing on HPV-derived antigens as well as non-viral antigens for HPV-negative HNC. Novel therapeutic approaches for HNC will focus not only on effective vaccine platforms but will also target the stroma-rich immunosuppressive microenvironment found in those tumours.

KIF-2C expression is correlated with poor prognosis of operable esophageal squamous cell carcinoma male patients

To determine the prognostic significance of Kinesin family member 2C (KIF-2C) expression in patients with operable esophageal squamous cell carcinoma (ESCC), we conducted an immunohistochemical analysis of KIF-2C expression in 415 surgically resected primary tumor tissues and 40 adjacent non-cancerous tissues from patients with operable ESCC. The median duration of postoperative follow-up was 76.0 months. Higher KIF-2C expression was associated with significantly increased risks of higher pathologic tumor (pT) status (P=0.038) and poorer tumor differentiation (P=0.022). For the entire cohort, KIF-2C expression was not an independent factor significantly associated with overall survival (OS) (P=0.097) or disease-free survival (DFS) (P=0.152). In female patients, KIF-2C expression had no effect on OS (P=0.880) and DFS (P=0.864). However, OS (hazard ratio (HR)=1.480, P=0.013) and DFS (HR=1.418, P=0.024) were worse for male patients with high KIF-2C expression compared with male patients with low KIF-2C expression. Moreover, the OS and DFS of male patients with high KIF-2C expression were also significantly shorter compared with female patients with low KIF-2C expression (P=0.022, P=0.029) and female patients with high KIF-2C expression (P=0.014, P=0.018). Based on these findings, KIF-2C expression in tumor tissues promises to serve as an independent prognostic marker for male, but not female, patients with operable ESCC. Prognosis was worse for male patients with high KIF-2C expression compared with patients with the same pathologic tumor-node-metastasis (pTNM) stage.

Involvement of X-chromosome Reactivation in Augmenting Cancer Testis Antigens Expression: A Hypothesis

Cancer testis antigens (CTAs) are attractive targets for tumor immunotherapy because of their tumor-specific expression. Since more than half of confirmed CTAs are located on the X-chromosome, we asked whether there is a link between CTA expression and X-chromosomes. Recent reports have shown that reactivation of the inactive X-chromosome, known as X-chromosome reactivation (XCR), a unique phenomenon that exists in many high-risk tumors in women, can transform the expression of many X-linked genes from monoallelic to biallelic. In this review, we discuss the link between CTA and XCR with the hopes of providing some novel insights into tumor biology.

Profiling cancer testis antigens in non-small-cell lung cancer

Cancer testis antigens (CTAs) are of clinical interest as biomarkers and present valuable targets for immunotherapy. To comprehensively characterize the CTA landscape of non-small-cell lung cancer (NSCLC), we compared RNAseq data from 199 NSCLC tissues to the normal transcriptome of 142 samples from 32 different normal organs. Of 232 CTAs currently annotated in the Caner Testis Database (CTdatabase), 96 were confirmed in NSCLC. To obtain an unbiased CTA profile of NSCLC, we applied stringent criteria on our RNAseq data set and defined 90 genes as CTAs, of which 55 genes were not annotated in the CTdatabase, thus representing potential new CTAs. Cluster analysis revealed that CTA expression is histology dependent and concurrent expression is common. IHC confirmed tissue-specific protein expression of selected new CTAs (TKTL1, TGIF2LX, VCX, and CXORF67). Furthermore, methylation was identified as a regulatory mechanism of CTA expression based on independent data from The Cancer Genome Atlas. The proposed prognostic impact of CTAs in lung cancer was not confirmed, neither in our RNAseq cohort nor in an independent meta-analysis of 1,117 NSCLC cases. In summary, we defined a set of 90 reliable CTAs, including information on protein expression, methylation, and survival association. The detailed RNAseq catalog can guide biomarker studies and efforts to identify targets for immunotherapeutic strategies.

Oncogenic cancer/testis antigens: prime candidates for immunotherapy

Recent developments have set the stage for immunotherapy as a supplement to conventional cancer treatment. Consequently, a significant effort is required to further improve efficacy and specificity, particularly the identification of optimal therapeutic targets for clinical testing. Cancer/testis antigens are immunogenic, highly cancer-specific, and frequently expressed in various types of cancer, which make them promising candidate targets for cancer immunotherapy, including cancer vaccination and adoptive T-cell transfer with chimeric T-cell receptors. Our current understanding of tumor immunology and immune escape suggests that targeting oncogenic antigens may be beneficial, meaning that identification of cancer/testis antigens with oncogenic properties is of high priority. Recent work from our lab and others provide evidence that many cancer/testis antigens, in fact, have oncogenic functions, including support of growth, survival and metastasis. This novel insight into the function of cancer/testis antigens has the potential to deliver more effective cancer vaccines. Moreover, immune targeting of oncogenic cancer/testis antigens in combination with conventional cytotoxic therapies or novel immunotherapies such as checkpoint blockade or adoptive transfer, represents a highly synergistic approach with the potential to improve patient survival.

Investigation of FOXM1 as a Potential New Target for Melanoma

Recent studies have shown that immunotherapies and molecular targeted therapies are effective for advanced melanoma. Non-antigen-specific immunotherapies such as immunocheckpoint blockades have been shown to be effective in the treatment of advanced melanoma. However, the response rates remain low. To improve their efficacy, they should be combined with antigen-specific immunotherapy. Elevated expression of the transcription factor, Forkhead box M1 (FOXM1), has been reported in various human cancers, and it has been shown to have potential as a target for immunotherapy. The purpose of this study was to investigate the FOXM1 expression in human melanoma samples and cell lines, to evaluate the relationship between the FOXM1 expression and the clinical features of melanoma patients and to investigate the association between the FOXM1 and MAPK and PI3K/AKT pathways in melanoma cell lines. We conducted the quantitative reverse transcription PCR (qRT-PCR) and Western blotting analyses of melanoma cell lines, and investigated melanoma and nevus tissue samples by qRT-PCR and immunohistochemistry. We performed MEK siRNA and PI3K/AKT inhibitor studies and FOXM1 siRNA studies in melanoma cell lines. We found that FOXM1 was expressed in all of the melanoma cell lines, and was expressed in 49% of primary melanomas, 67% of metastatic melanomas and 10% of nevi by performing immunohistochemical staining. Metastatic melanoma samples exhibited significantly higher mRNA levels of FOXM1 (p = 0.004). Primary melanomas thicker than 2 mm were also more likely to express FOXM1. Patients whose primary melanoma expressed FOXM1 had a significantly poorer overall survival compared to patients without FOXM1 expression (p = 0.024). Downregulation of FOXM1 by siRNA significantly inhibited the proliferation of melanoma cells, and blockade of the MAPK and PI3K/AKT pathways decreased the FOXM1 expression in melanoma cell lines. In conclusion, FOXM1 is considered to be a new therapeutic target for melanoma.

Crem activator isoforms in normal and impaired human spermatogenesis analyzed by real time RT-PCR

cAMP responsive element modulator (CREM) activator isoforms are involved in mammalian spermatogenesis and spermiogenesis. CREM proteins are highly expressed in postmeiotic germ cells of rodents and primates. Homozygous CREM inactivated mice exhibit round spermatid maturation arrest. The lack of CREM expression at both the mRNA and protein levels is associated with spermatid maturation arrest in infertile patients. Using real-time RT-PCR, we have examined the levels of CREM activator isoform mRNAs: CREMtheta1, CREMtheta2 and CREMt2 + Ex-gamma in gametogenic and interstitial cell fractions from normal human testis, in homogenized tissue samples from spermatogenic arrest and from testicular tumors. We have shown for the first time the presence of CREM activator isoform containing exon gamma (CREMtau2 + Exgamma) in normal human spermatogenesis. Among the three CREM isoforms, CREMtheta1 was expressed in its highest level in the male gonads. In comparison, CREMtheta2 mRNA was significantly less suggesting that the P3 promoter is much more active in human testis than the P4 promoter. Minimal-nill levels of mRNA for either of the CREM activator isoforms were detected in lymphocytes or in gonadal tissues from patients with SCOS (Sertoli Cell Only Syndrome). This data underlines the significance of CREMtheta1 isoform in the regulation of transcription during post-meiotic germ cell differentiation.

Interleukin-1 superfamily genes expression in normal or impaired human spermatogenesis

Interleukin-1 (IL-1) is a pleiotropic cytokine that may play a role in contributing to the specific immune environment of mammalian testis and in regulating cell differentiation. We have determined the transcription activity of the IL-1 gene family (using real-time polymerase chain reaction (PCR)) in two main functional testicular compartments (interstitial and intratubular ones), and in tissue homogenates obtained from patients with fertility disorders (spermatogenic arrest and testicular tumors). We observed the prominent expression of gene coding for IL-1 receptor antagonist (IL-1RA) in a purified fraction of gametogenic cells (normal gonad). Caspase-1 (ICE - IL-1beta-converting enzyme) was highly expressed (on mRNA level) in interstitial compartments as well in testicular tumors (immune enhancement?). In addition we found, that the activity of IL-1RA gene decreased along spermatogenic alteration in an inversely related manner with IL-1alpha (from normal gonad through spermatogenic arrest to Sertoli cell only syndrome). Therefore, the quotient value of IL-1alpha/IL-1RA could potentially serve as the diagnostic molecular probe for spermatogenesis assessment. The precise level of mRNA for IL-1-IL-18 cytokines and their receptors, and specifically of the receptor antagonist in immune privileged gonad, could be one of the main factors responsible for maintaining testicular homeostasis, thus enabling generation of the mature spermatozoa.

Quantitative mRNA Analysis of IL-1 Gene System in Human Testis

PROBLEM

There is a growing body of evidence that interleukins exhibit modulatory activity on development of reproductive cells. In this context, there appears to be a role for IL-1, which is also produced in human testis. We have analysed transcripts of IL-1 gene system (IL-1alpha, IL-1beta, IL-1RI, IL-1RII and IL-1RA) to evaluate the possible link between the level of gene(s) transcription and their function.

METHOD OF STUDY

To determine the activity of gene transcription, a quantitative PCR with isotopic and/or nonisotopic detection was applied.

RESULTS AND CONCLUSIONS

We have detected differential expression of IL-1alpha and IL-1beta genes in separate functional compartments of a male gonad. A strong expression of IL-1alpha gene in an intratubular cell fraction was shown, while the IL-1beta expression seemed to be dominant in extratubular compartment of the male gonad. Abundant amounts of IL-1RA mRNA in gametogenic cells fraction slightly higher than in interstitium have also been found. IL-1RA is the most important regulatory molecule in IL-1 system, which down-regulates activity of both interleukins. Looking more closely at gene(s) differential expression it appears that IL-1alpha can be preferentially down-regulated by IL-1RA gene in intratubular fraction while the IL-1beta, through the "false" IL-1RII receptor in the interstitium. Genes coding for both receptors (IL-1RI and IL-1RII) showed, however, relatively low levels of transcription in both studied compartments. IL-1 genes system creates a complex intragonadal environment and the function of these genes is reflected by their respective distribution in the two main functional compartments of the testis.

The human SPANX multigene family: genomic organization, alignment and expression in male germ cells and tumor cell lines

Multigenicity is one of the features of cancer/testis-associated genes. In the present study we analyzed the number and expression of genes of the SPANX(CTp11) family of cancer/testis-associated genes. Genomic database analysis, next to the four previously described SPANX genes, revealed the presence of a novel gene: SPANXE. Moreover, we detected an allelic variant of SPANXB resulting in one amino acid substitution in the encoded protein: SPANXB'. Most SPANX genes are present on contig NT_011574 located at Xq26.3-Xq27.1. Based on expressed sequence tag databases and RT-PCR analysis three additional novel SPANX sequences were identified, though not represented so far in the human genome sequence. Sequence alignments justify a subdivision of this gene family based on the absence (SPANXA-likes) or presence (SPANXB) of an 18 base pair sequence stretch in the open reading frame. The alignments also reveal an unusually high level (99%) of intron homology. Furthermore, the nucleotide variations in the open reading frame almost all lead to amino acid substitutions. Southern blot and database analyses indicate that SPANX sequences are exclusively present in primates. With RT-PCR analysis on human sperm cell precursors and tumor cell lines most family members could be detected. SPANXB was only found in sperm cell precursors and could not be detected in the tumor cell lines tested. Overall SPANXA was the most frequently expressed SPANX variant in melanoma and glioblastoma cell lines.

Human leucocyte antigen I expression in spermatozoa from infertile men

The expression of class I human leucocyte antigen (HLA) has been investigated by reverse transcription polymerase chain reaction (RT-PCR) and flow cytometry on human purified ejaculated spermatozoa from an infertile population. Similar investigation in a control fertile population has been performed. Among 22 fertile and 20 infertile men, 17 were selected for the study because they showed no contamination with non-sperm cells. HLA I molecules were expressed in four of nine fertile subjects (44.4%) and three of eight infertile subjects (37.5%), with no significant difference between groups. These data demonstrate for the first time the presence of class I HLA antigens on spermatozoa of infertile subjects. In addition, considering that similar results have been obtained in both fertile and infertile populations, the hypothesis that the fertilizing capacity of the spermatozoon is independent of class I HLA-antigen expression on their surface may be advanced.

cDNA and protein characterization of human MAGE-10

MAGE genes are frequently expressed in several types of human malignancy and code for antigens recognized by cytotoxic T lymphocytes. We have previously described a monoclonal antibody (MAb), named 6C1, that recognizes the MAGE-1 protein and cross-reacts with a 72-kDa protein present in lysates of melanoma cells such as MZ2-MEL. To identify this protein, we have screened an expression library prepared from MZ2-MEL cells. Several clones that encoded a protein recognized by antibody 6C1 contained a sequence identical to that of MAGE-10, another member of the MAGE-A gene family. Full-length MAGE-10 cDNA clones, obtained after screening additional cDNA melanoma libraries, were found to be approximately 2.5 kb in length. In vitro translation and transient transfection experiments indicated that MAGE-10 codes for a protein of approximately 72 kDa. This product was recognized by MAb 6C1 as well as by a polyclonal serum raised against a MAGE-10 peptide, thus demonstrating its identity with MAGE-10. Analysis of MAGE-10 mRNA by RT-PCR confirmed its presence in testis and placenta but not in other normal tissues. Expression of MAGE-10 in melanoma tumors was found to parallel that of MAGE-1. Western blot analysis with the polyclonal anti-MAGE-10 antibody showed the presence of MAGE-10 in lysates of purified trophoblast cells. Immuno-cytochemistry of cultured melanoma cells indicated that MAGE-10 is a nuclear protein.

Major histocompatibility complex expression on human, male germ cells: a review

PROBLEM

The male reproductive compartment is an immunologically privileged site. The expression pattern of human leukocyte antigens (HLAs) may play an important role in the maintenance of immune tolerance toward differentiating gametogenic cells. This review presents current knowledge about HLA gene expression on human, male germ cells, on mRNA and protein levels, and on their methylation status.

METHOD OF STUDY

Different techniques were applied to study HLA gene expression in human testis: (a) protein: e.g., cytotoxicity test, fluorescent labeling techniques, enzyme-linked immunosorbent assay, and confocal microscopy; (b) mRNA: reverse transcriptase-polymerase chain reaction, Northern blot hybridization, and in situ hybridization; and (c) methylation status.

RESULTS

In normal testicular tissue we observe a lack of HLA-class I (classical) antigens expression and inversely related expression pattern of HLA class I classical and nonclassical genes. HLA-A, -B, -C, and -E loci are likewise methylated in somatic and germ cells, whereas -F and -G genes are less methylated in sperm precursors.

CONCLUSIONS

Immunologic tolerance in human testis is actively maintained by the specific expression pattern of HLA genes regulated by hormones and growth factors.

HLA expression on immature and mature human germ cells

Human leukocyte antigens (HLA) are membrane-bound glycoproteins encoded by the human major histocompatibility complex located on chromosome 6. They are known to function in immnunologic recognition and, with regard to reproduction, a number of non-immune functions have been proposed. Although the expression patterns of the major histocompatibility antigens have been extensively studied at the maternal fetal interface, there are still controversial reports on the expression of these molecules by human gametes and preimplantation stages. This brief review focuses on recent studies where the expression and distribution of HLA on human spermatogenic cells (spermatogonia, primary and secondary spermatocytes, spermatids, spermatozoa), primary and secondary oocytes, and preimplantation embryos have been investigated. These results, and their possible implications for the fertilization process and further embryonic development, will be presented.

Analysis of HLA class Ib gene expression in male gametogenic cells

We have investigated mRNA expression for nonclassical MHC class I genes (HLA-E,-F,-G) in human gametogenic cells. Testicular tissue was treated by collagenase and the resulting cell suspension was further purified by fractionation on Percoll gradients in a two-step procedure. Three gametogenic cell fractions were analyzed: purified heterogenous suspension of gametogenic cells, fraction of round spermatids and fraction of elongated spermatids. Total RNA isolated from each cell population was subjected to both reverse transcriptase/polymerase chain reaction and Northern blot analysis using oligonucleotides specific for HLA-E, -F and -G. Both method gave similar results. We have found a considerable level of HLA-E mRNA, very low amounts of reamplified cDNA for HLA-F and both a complete lack of mRNA and reamplified cDNA for the HLA-G gene in the analyzed gametogenic cell fractions. Additionally, we have localized HLA-E molecules on the cells of the adluminal compartment within seminiferous tubules using immunostaining with monoclonal antibodies specific for HLA-E heavy chain followed by confocal microscopy analysis. The unique expression pattern of HLA class I antigens in the male gonad could play an important role in an efficient protection against an autoimmunological attack toward germ cells.

Analysis of mRNA expression for interleukin-1 genes on human testicular cells

We have investigated mRNA expression for IL-1 alpha and IL-1 beta gene on fractionated human testicular cells. Using RT-PCR and Northern blot hybridization technique we detected the presence of IL-1 alpha transcripts, predominantly in the intratubular compartment of the testis, comprising gametogenic and Sertoli cells. We were also able to detect mRNA for IL-1 alpha on the testicular interstitium, but at significantly lower levels. The intertubular compartment of the testis, mainly consisting of macrophages and Leydig cells, appeared however, to be a site for IL-1 beta gene expression. Our experimental data confirm previous results obtained in animal models indicating that the testis is capable of producing interleukin-1 under physiological conditions. Testicular IL-1 may function as a tissue-specific factor modulating both spermato- and steroidogenic activity of human testis.