The T Cell Receptor γ Chain Alternate Reading Frame Protein (TARP), a Prostate-specific Protein Localized in Mitochondria

A meta-analysis of epitopes in prostate-specific antigens identifies opportunities and knowledge gaps

BACKGROUND

The Cancer Epitope Database and Analysis Resource (CEDAR) is a newly developed repository of cancer epitope data from peer-reviewed publications, which includes epitope-specific T cell, antibody, and MHC ligand assays. Here we focus on prostate cancer as our first cancer category to demonstrate the capabilities of CEDAR, and to shed light on the advances of epitope-related prostate cancer research.

RESULTS

The meta-analysis focused on a subset of data describing epitopes from 8 prostate-specific (PS) antigens. A total of 460 epitopes were associated with these proteins, 187 T cell, 109B cell, and 271 MHC ligand epitopes. The number of epitopes was not correlated with the length of the protein; however, we found a significant positive correlation between the number of references per specific PS antigen and the number of reported epitopes. Forty-four different class I and 27 class II restrictions were found, with the most epitopes described for HLA-A*02:01 and HLA-DRB1*01:01. Cytokine assays were mostly limited to IFNg assays and a very limited number of tetramer assays were performed. Monoclonal and polyclonal B cell responses were balanced, with the highest number of epitopes studied in ELISA/Western blot assays. Additionally, epitopes were generically described as associated with prostate cancer, with little granularity specifying diseases state. We found that in vivo and tumor recognition assays were sparse, and the number of epitopes with annotated B/T cell receptor information were limited. Potential immunodominant regions were identified by the use of the ImmunomeBrowser tool.

CONCLUSION

CEDAR provides a comprehensive repository of epitopes related to prostate-specific antigens. This inventory of epitope data with its wealth of searchable T cell, B cell and MHC ligand information provides a useful tool for the scientific community. At the same time, we identify significant knowledge gaps that could be addressed by experimental analysis.

Sea Buckthorn Proanthocyanidins are the Protective Agent of Mitochondrial Function in Macrophages Under Oxidative Stress

Sea buckthorn proanthocyanidins (SBP) are the most important antioxidant components of sea buckthorn, which are widely used in functional foods and cosmetics. Studies have shown that SBP have significant protective effects on macrophages against oxidative stress induced by hydrogen peroxide (H₂O₂). However, the mechanism remains uncertain. In the present study, we explored the effects of SBP on mitochondrial function and the mechanism of their protective effects against oxidative stress in cells. Our results showed that SBP could increase mitochondrial membrane potential, inhibit mPTP opening, reduce mitochondrial swelling, and enhance mitochondrial synthesis and metabolism. Thus, they alleviated oxidative damage and protected the cells against mitochondrial function. Western blot analysis showed that SBP had a protective effect on RAW264.7 cells by activating the AMPK-PGC1α-Nrf2 pathway. These results showed that SBP alleviated mitochondrial damage and dysfunction caused by oxidative stress. This study revealed the mechanism of SBP in reducing oxidative damage and provided a theoretical basis for further research on natural bioactive compounds to exert antioxidant activity and prevent arteriosclerosis and other diseases.

TARP as antigen in cancer immunotherapy

In recent decades, immunotherapy has become a pivotal element in cancer treatment. A remaining challenge is the identification of cancer-associated antigens suitable as targets for immunotherapeutics with potent on-target and few off-tumor effects. The T-cell receptor gamma (TCRγ) chain alternate reading frame protein (TARP) was first discovered in the human prostate and androgen-sensitive prostate cancer. Thereafter, TARP was also identified in breast and endometrial cancers, salivary gland tumors, and pediatric and adult acute myeloid leukemia. Interestingly, TARP promotes tumor cell proliferation and migration, which is reflected in an association with worse survival. TARP expression in malignant cells, its role in oncogenesis, and its limited expression in normal tissues raised interest in its potential utility as a therapeutic target, and led to development of immunotherapeutic targeting strategies. In this review, we provide an overview of TARP expression, its role in different cancer types, and currently investigated TARP-directed immunotherapeutic options.

TARP is an immunotherapeutic target in acute myeloid leukemia expressed in the leukemic stem cell compartment

Immunotherapeutic strategies targeting the rare leukemic stem cell compartment might provide salvage to the high relapse rates currently observed in acute myeloid leukemia (AML). We applied gene expression profiling for comparison of leukemic blasts and leukemic stem cells with their normal counterparts. Here, we show that the T-cell receptor γ chain alternate reading frame protein (TARP) is over-expressed in de novo pediatric (n=13) and adult (n=17) AML sorted leukemic stem cells and blasts compared to hematopoietic stem cells and normal myeloblasts (15 healthy controls). Moreover, TARP expression was significantly associated with a fms-like tyrosine kinase receptor-3 internal tandem duplication in pediatric AML. TARP overexpression was confirmed in AML cell lines (n=9), and was found to be absent in B-cell acute lymphocytic leukemia (n=5) and chronic myeloid leukemia (n=1). Sequencing revealed that both a classical TARP transcript, as described in breast and prostate adenocarcinoma, and an AML-specific alternative TARP transcript, were present. Protein expression levels mostly matched transcript levels. TARP was shown to reside in the cytoplasmic compartment and showed sporadic endoplasmic reticulum co-localization. TARP-T-cell receptor engineered cytotoxic T-cells in vitro killed AML cell lines and patient leukemic cells co-expressing TARP and HLA-A*0201. In conclusion, TARP qualifies as a relevant target for immunotherapeutic T-cell therapy in AML.

Elevated TARP promotes proliferation and metastasis of salivary adenoid cystic carcinoma

OBJECTIVE

This study aims to analyze the expression of T-cell receptor γ chain alternate reading frame protein (TARP) in salivary adenoid cystic carcinoma (SACC) and its distant metastases and to investigate its influences on the development and progression of SACC.

STUDY DESIGN

TARP expression was analyzed in 50 primary SACCs, 13 specimens of metastatic adenoid cystic carcinoma of salivary gland origin, and 20 noncancerous tissues around SACC via immunohistochemistry. Cell Counting Kit-8 tests, wound healing assay, and Transwell experiments were performed to evaluate the effects of lentivirus-mediated TARP overexpression on the proliferation, migration, and invasion of SACC cells.

RESULTS

TARP expression was significantly increased in primary SACCs compared with adjacent noncancerous tissues, and this increase was further enhanced in metastases compared with primary SACCs. The expression level of TARP correlated significantly with tumor size, tumor-node-metastasis stage, perineural invasion, histologic type, and distant metastasis. Furthermore, TARP overexpression promoted the growth, migration, and invasion of SACC cells.

CONCLUSIONS

TARP plays an important role in and may be used as a marker to indicate the development and progression of SACC.

Molecular characterization of the feline T-cell receptor γ alternate reading frame protein (TARP) ortholog

T-cell receptor γ alternate reading frame protein (TARP) is expressed by human prostate epithelial, prostate cancer, and mammary cancer cells, but is not found in normal mammary tissue. To date, this protein has only been described in humans. Additionally, no animal model has been established to investigate the potential merits of TARP as tumor marker or a target for adoptive tumor immunotherapy. In this study conducted to characterize feline T-cell receptor γ sequences, constructs very similar to human TARP transcripts were obtained by RACE from the spleen and prostate gland of cats. Transcription of TARP in normal, hyperplastic, and neoplastic feline mammary tissues was evaluated by conventional RT-PCR. In felines similarly to the situation reported in humans, a C-region encoding two open reading frames is spliced to a J-region gene. In contrast to humans, the feline J-region gene was found to be a pseudogene containing a deletion within its recombination signal sequence. Our findings demonstrated that the feline TARP ortholog is transcribed in the prostate gland and mammary tumors but not normal mammary tissues as is the case with human TARP.

Detecting cancer outlier genes with potential rearrangement using gene expression data and biological networks

Gene alterations are a major component of the landscape of tumor genomes. To assess the significance of these alterations in the development of prostate cancer, it is necessary to identify these alterations and analyze them from systems biology perspective. Here, we present a new method (EigFusion) for predicting outlier genes with potential gene rearrangement. EigFusion demonstrated excellent performance in identifying outlier genes with potential rearrangement by testing it to synthetic and real data to evaluate performance. EigFusion was able to identify previously unrecognized genes such as FABP5 and KCNH8 and confirmed their association with primary and metastatic prostate samples while confirmed the metastatic specificity for other genes such as PAH, TOP2A, and SPINK1. We performed protein network based approaches to analyze the network context of potential rearranged genes. Functional gene rearrangement Modules are constructed by integrating functional protein networks. Rearranged genes showed to be highly connected to well-known altered genes in cancer such as AR, RB1, MYC, and BRCA1. Finally, using clinical outcome data of prostate cancer patients, potential rearranged genes demonstrated significant association with prostate cancer specific death.

Tumor-associated antigens for specific immunotherapy of prostate cancer

Prostate cancer (PCa) is the most common noncutaneous cancer diagnosis and the second leading cause of cancer-related deaths among men in the United States. Effective treatment modalities for advanced metastatic PCa are limited. Immunotherapeutic strategies based on T cells and antibodies represent interesting approaches to prevent progression from localized to advanced PCa and to improve survival outcomes for patients with advanced disease. CD8⁺ cytotoxic T lymphocytes (CTLs) efficiently recognize and destroy tumor cells. CD4⁺ T cells augment the antigen-presenting capacity of dendritic cells and promote the expansion of tumor-reactive CTLs. Antibodies mediate their antitumor effects via antibody-dependent cellular cytotoxicity, activation of the complement system, improving the uptake of coated tumor cells by phagocytes, and the functional interference of biological pathways essential for tumor growth. Consequently, several tumor-associated antigens (TAAs) have been identified that represent promising targets for T cell- or antibody-based immunotherapy. These TAAs comprise proteins preferentially expressed in normal and malignant prostate tissues and molecules which are not predominantly restricted to the prostate, but are overexpressed in various tumor entities including PCa. Clinical trials provide evidence that specific immunotherapeutic strategies using such TAAs represent safe and feasible concepts for the induction of immunological and clinical responses in PCa patients. However, further improvement of the current approaches is required which may be achieved by combining T cell- and/or antibody-based strategies with radio-, hormone-, chemo- or antiangiogenic therapy.

A gene expression signature from peripheral whole blood for stage I lung adenocarcinoma

Affordable early screening in subjects with high risk of lung cancer has great potential to improve survival from this deadly disease. We measured gene expression from lung tissue and peripheral whole blood (PWB) from adenocarcinoma cases and controls to identify dysregulated lung cancer genes that could be tested in blood to improve identification of at-risk patients in the future. Genome-wide mRNA expression analysis was conducted in 153 subjects (73 adenocarcinoma cases, 80 controls) from the Environment And Genetics in Lung cancer Etiology study using PWB and paired snap-frozen tumor and noninvolved lung tissue samples. Analyses were conducted using unpaired t tests, linear mixed effects, and ANOVA models. The area under the receiver operating characteristic curve (AUC) was computed to assess the predictive accuracy of the identified biomarkers. We identified 50 dysregulated genes in stage I adenocarcinoma versus control PWB samples (false discovery rate ≤0.1, fold change ≥1.5 or ≤0.66). Among them, eight (TGFBR3, RUNX3, TRGC2, TRGV9, TARP, ACP1, VCAN, and TSTA3) differentiated paired tumor versus noninvolved lung tissue samples in stage I cases, suggesting a similar pattern of lung cancer-related changes in PWB and lung tissue. These results were confirmed in two independent gene expression analyses in a blood-based case-control study (n = 212) and a tumor-nontumor paired tissue study (n = 54). The eight genes discriminated patients with lung cancer from healthy controls with high accuracy (AUC = 0.81, 95% CI = 0.74-0.87). Our finding suggests the use of gene expression from PWB for the identification of early detection markers of lung cancer in the future.

Mitochondria as a sequestration site for incomplete TCRβ peptides: the TCRβ transmembrane domain is a sufficient mitochondrial targeting signal

The existence of incomplete T cell receptor (TCR) mRNA forms, including germline transcripts and products of unfruitful TCR rearrangements, has long been known. However, it is unclear whether these molecules are functional. We have previously shown that T cells also contain truncated TCRβ peptides that lack the N-terminal part and contain C-terminus sequences. These partial forms of TCRβ, target the mitochondrion and induce apoptosis, exhibiting a novel mode of TCR mediated cell death. Here we aimed at analyzing the minimal TCR sequences that direct the peptide to the mitochondrion. It is shown that truncated TCRβ, targets mitochondria and induces mitochondrial perinuclear clustering, in both monkey COS-7 and human 293 cells. These phenomena are mediated by the C-terminus of the molecule. Whereas the positively charged amino acids flanking the transmembrane domain (TMD) of TCRβ are beneficial for this process, they are not essential. Indeed, the isolated TMD of TCRβ serves as a sufficient mitochondrial targeting sequence. These results indicate that any given partial form of TCRβ, that contains the TMD, is bound to be sequestered by the mitochondrion. This may assure that incomplete TCR forms would not interfere with correct TCR complex formation.

Immunotherapy in prostate cancer: emerging strategies against a formidable foe

Recent clinical trials have shown therapeutic vaccines to be promising treatment modalities against prostate cancer. Unlike preventive vaccines that teach the immune system to fight off specific microorganisms, therapeutic vaccines stimulate the immune system to recognize and attack certain cancer-associated proteins. Additional strategies are being investigated that combine vaccines and standard therapeutics, including radiation, chemotherapy, targeted therapies, and hormonal therapy, to optimize the vaccines' effects. Recent vaccine late-phase clinical trials have reported evidence of clinical benefit while maintaining excellent quality of life. One such vaccine, sipuleucel-T, was recently FDA-approved for the treatment of metastatic prostate cancer. Another vaccine, PSA-TRICOM, is also showing promise in completed and ongoing randomized multicenter clinical trials in both early- and late-stage prostate cancer. Clinical results available to date indicate that immune-based therapies could play a significant role in the treatment of prostate and other malignancies.

Antibody responses to galectin-8, TARP and TRAP1 in prostate cancer patients treated with a GM-CSF-secreting cellular immunotherapy

A critical factor in clinical development of cancer immunotherapies is the identification of tumor-associated antigens that may be related to immunotherapy potency. In this study, protein microarrays containing >8,000 human proteins were screened with serum from prostate cancer patients (N = 13) before and after treatment with a granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting whole cell immunotherapy. Thirty-three proteins were identified that displayed significantly elevated (P Collapse

Key Words

• immunotherapy
• tumor antigen
• autoantibody
• protein microarray
• prostate cancer
• biomarker

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MESH Headings

• Antibodies/blood
• Antibodies/immunology
• Biomarkers, Pharmacological
• Biomarkers, Tumor/immunology
• Clinical Trials as Topic
• Disease Progression
• Galectins/immunology
• Granulocyte-Macrophage Colony-Stimulating Factor/therapeutic use
• HSP90 Heat-Shock Proteins/biosynthesis
• HSP90 Heat-Shock Proteins/genetics
• HSP90 Heat-Shock Proteins/immunology
• High-Throughput Screening Assays
• Humans
• Immunotherapy, Adoptive
• Male
• Neoplasm Metastasis
• Nuclear Proteins/biosynthesis
• Nuclear Proteins/genetics
• Nuclear Proteins/immunology
• Prognosis
• Prostatic Neoplasms/diagnosis
• Prostatic Neoplasms/immunology
• Prostatic Neoplasms/mortality
• Prostatic Neoplasms/pathology
• Prostatic Neoplasms/therapy
• Protein Array Analysis
• Retrospective Studies
• Survival Analysis
• Treatment Outcome

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Affiliation(s)

Minh C. Nguyen Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Guang Huan Tu Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Kathryn E. Koprivnikar Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Melissa Gonzalez-Edick Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Karin U. Jooss Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Thomas C. Harding Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA Five Prime Therapeutics, Inc., 1650 Owens Street Suite 200, San Francisco, CA 94158 USA

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Novel methods to identify biologically relevant genes for leukemia and prostate cancer from gene expression profiles

Background

High-throughput microarray experiments now permit researchers to screen thousands of genes simultaneously and determine the different expression levels of genes in normal or cancerous tissues. In this paper, we address the challenge of selecting a relevant and manageable subset of genes from a large microarray dataset. Currently, most gene selection methods focus on identifying a set of genes that can further improve classification accuracy. Few or none of these small sets of genes, however, are biologically relevant (i.e. supported by medical evidence). To deal with this critical issue, we propose two novel methods that can identify biologically relevant genes concerning cancers.

Results

In this paper, we propose two novel techniques, entitled random forest gene selection (RFGS) and support vector sampling technique (SVST). Compared with results from six other methods developed in this paper, we demonstrate experimentally that RFGS and SVST can identify more biologically relevant genes in patients with leukemia or prostate cancer. Among the top 25 genes selected using SVST method, 15 genes were biologically relevant genes in patients with leukemia and 13 genes were biologically relevant genes in patients with prostate cancer. Meanwhile, the RFGS method, while less effective than SVST, still identified an average of 9 biologically relevant genes in both leukemia and prostate cancers. In contrast to traditional statistical methods, which only identify less than 8 genes in patients with leukemia and less than 8 genes in patients with prostate cancer, our methods yield significantly better results.

Conclusions

Our proposed SVST and RFGS methods are novel approaches that can identify a greater number of biologically relevant genes. These methods have been successfully applied to both leukemia and prostate cancers. Research in the fields of biology and medicine should benefit from the identification of biologically relevant genes by confirming recent discoveries in cancer research or suggesting new avenues for exploration.

Incomplete T-cell receptor-beta peptides target the mitochondrion and induce apoptosis

The default pathway of cell-surface T-cell receptor (TCR) complex formation, and the subsequent transport to the membrane, is thought to entail endoplasmic reticulum (ER) localization followed by proteasome degradation of the unassembled chains. We show herein an alternative pathway: short, incomplete peptide versions of TCRbeta naturally occur in the thymus. Such peptides, which have minimally lost the leader sequence or have been massively truncated, leaving only the very C terminus intact, are sorted preferentially to the mitochondrion. As a consequence of the mitochondrial localization, apoptotic cell death is induced. Structure function analysis showed that both the specific localization and induction of apoptosis depend on the transmembrane domain (TMD) and associated residues at the COOH-terminus of TCR. Truncated forms of TCR, such as the short peptides that we detected in the thymus, may be products of protein degradation within thymocytes. Alternatively, they may occur through the translation of truncated mRNAs resulting from unfruitful rearrangement or from germline transcription. It is proposed that mitochondria serve as a subcellular sequestration site for incomplete TCR molecules.

Expression of POTE protein in human testis detected by novel monoclonal antibodies

The POTE gene family is composed of 13 highly homologous paralogs preferentially expressed in prostate, ovary, testis, and placenta. We produced 10 monoclonal antibodies (MAbs) against three representative POTE paralogs: POTE-21, POTE-2gammaC, and POTE-22. One reacted with all three paralogs, six MAbs reacted with POTE-2gammaC and POTE-22, and three MAbs were specific to POTE-21. Epitopes of all 10 MAbs were located in the cysteine-rich repeats (CRRs) motifs located at the N-terminus of each POTE paralog. Testing the reactivity of each MAb with 12 different CRRs revealed slight differences among the antigenic determinants, which accounts for differences in cross-reactivity. Using MAbs HP8 and PG5 we were able to detect a POTE-actin fusion protein in human testis by immunoprecipitation followed by Western blotting. By immunohistochemistry we demonstrated that the POTE protein is expressed in primary spermatocytes, implying a role in spermatogenesis.

Gene expression profiling of the human prostate zones

OBJECTIVE

To investigate differences in gene expression in different zones of the prostate by microarray analyses, to better understand why aggressive tumours predominantly occur in the peripheral zone (PZ), whereas benign prostatic hyperplasia (BPH) occurs almost exclusively in the transition zone (TZ).

MATERIALS AND METHODS

Expression profiling of both prostate zones was done by microarray analysis. Reverse transcription-polymerase chain reaction (RT-PCR) of the top 18 genes confirmed the microarray analyses. RT-PCR with common cell-type markers indicated that the differential expression between the zones was not caused by an unequal distribution of different cell types. Primary stromal and epithelial prostate cells were used to study cell type expression in the 12 highest differentially expressed zonal-specific genes.

RESULTS

In all, 346 genes were identified as preferentially expressed in the TZ or PZ. A few of the TZ-specific genes, including ASPA, FLJ10970 and COCH, were also stroma-specific. Comparisons with other microarray studies showed that gene expression profiles of prostate cancer and BPH correlate with the expression profiles of the PZ and TZ, respectively.

CONCLUSION

Gene expression differs between the PZ and TZ of the prostate, and stromal-epithelial interactions might be responsible for the distinct zonal localization of prostate diseases.

Recognition of prostate and breast tumor cells by helper T lymphocytes specific for a prostate and breast tumor-associated antigen, TARP

PURPOSE

T cell-based immunotherapy via the in vitro or in vivo expansion of prostate tumor-associated antigen (TAA)-specific T lymphocytes is one of the most promising therapeutic approaches to treat prostate cancer. T-cell alternate reading frame protein (TARP) is a mitochondrial protein that is specifically expressed in prostate epithelial cells. We have done experiments aimed at identifying helper T lymphocyte (HTL) epitopes for TARP for the design of T cell-based immunotherapy for prostate cancer.

EXPERIMENTAL DESIGN

Dendritic cells from normal donors were pulsed with synthetic peptides derived from TARP, which were predicted to serve as HTL epitopes. These dendritic cells were used to stimulate CD4(+) T cells in vitro to trigger HTL responses against TARP. T-cell responses to these peptides were also studied with lymphocytes from prostate cancer patients.

RESULTS

The two peptides, TARP(1-14) and TARP(14-27), were shown to elicit effective in vitro HTL responses using lymphocytes from both normal volunteers and prostate cancer patients. Peptide TARP(1-14)-reactive HTLs were found restricted by HLA-DR53 and could recognize naturally processed protein antigen derived from tumor cells, which was presented by autologous dendritic cells. Most significantly, stimulation with peptide TARP(14-27) generated four HTL lines restricted by HLA-DR1, HLA-DR9, HLA-DR13, and HLA-DR15, some of which capable of recognizing naturally processed antigens presented by dendritic cell or directly by TARP-positive tumor cells.

CONCLUSIONS

Our results show that TARP constitutes a TAA that can be recognized by tumor-reactive HTL. The newly described TARP epitopes could be used to optimize and improve T-cell epitope-based immunotherapy against prostate and other tumors expressing TARP.

Expression of T cell receptor alpha gene (TCRA) in human rhabdomyosarcoma and other musculo-skeletal sarcomas

Expression of the T cell receptor (TCR) genes is not restricted to T lymphocytes. Human prostate and breast express a truncated TCR gamma transcript. In the mouse, TCR alpha (TCRA) and beta partial transcripts are expressed by mesenchymal cells and TCRA transcripts by epithelial cells of the kidney. We show now that TCRA constant region expression is common in normal and neoplastic human cells of mesenchymal and neuroectodermal origin. TCR transcripts are derived from an unrearranged TCRA locus. Moreover, rhabdomyosarcoma cells highly expressed a specific J49-C splicing product deriving from the assembly of J49 segment and constant region. TCRA ectopic transcripts/proteins negatively regulate rhabdomyosarcoma cell growth as suggested by TCRA gene expression downmodulation effects using a specific duplex small interfering RNA.

Mesenchymal stem cells: harnessing cell plasticity to tissue and organ repair

Plastic behavior of cells is a hallmark of embryonic development. The emergence of primary mesenchyme from within the inner cell mass entails the first epithelial-mesenchymal transition step that is then followed by sequential transitions; the formation of new tissues and organs requires transitions from mesenchyme into epithelium and vice versa. Although it is currently believed that in the adult such transitions do not persist, the frequent occurrence of mesenchymal stem cells (MSCs) in various tissues of the adult organisms, and the reported plasticity of such adult mesenchymal cells, raises the question as to whether the frequency of mesenchymal epithelial transitions in the adult have been underestimated. Indeed, adult mesenchymal stem cells have been reported to differentiate in culture into a multitude of mature cell types including epithelial cells. This opens the way to the use of these stem cells for the construction of new tissues and organs for therapeutic purposes, but the question is still open as to whether mesenchymal stem cells transdifferentiate also in vivo. The molecular mechanism that underlies the plasticity of mesenchymal stem cells and their capacity to transdifferentiate is unresolved. We found that these cells have a promiscuous gene expression pattern; mesenchymal cells, whether primary or cloned cell lines, express T cell receptor (TCR) beta and alpha genes, along with other components of the TCR complex. These cells may therefore be in a standby state, in which many gene families are expressed at a low level thereby making the cell readily capable of shifting fates.