A phase 2, randomized, double-blind, placebo- controlled study of chemo-immunotherapy combination using motolimod with pegylated liposomal doxorubicin in recurrent or persistent ovarian cancer: a Gynecologic Oncology Group partners study.

BACKGROUND: A phase 2, randomized, placebo-controlled trial was conducted in women with recurrent epithelial ovarian carcinoma to evaluate the efficacy and safety of motolimod-a Toll-like receptor 8 (TLR8) agonist that stimulates robust innate immune responses-combined with pegylated liposomal doxorubicin (PLD), a chemotherapeutic that induces immunogenic cell death. PATIENTS AND METHODS: Women with ovarian, fallopian tube, or primary peritoneal carcinoma were randomized 1 : 1 to receive PLD in combination with blinded motolimod or placebo. Randomization was stratified by platinum-free interval (≤6 versus >6-12 months) and Gynecologic Oncology Group (GOG) performance status (0 versus 1). Treatment cycles were repeated every 28 days until disease progression. RESULTS: The addition of motolimod to PLD did not significantly improve overall survival (OS; log rank one-sided P = 0.923, HR = 1.22) or progression-free survival (PFS; log rank one-sided P = 0.943, HR = 1.21). The combination was well tolerated, with no synergistic or unexpected serious toxicity. Most patients experienced adverse events of fatigue, anemia, nausea, decreased white blood cells, and constipation. In pre-specified subgroup analyses, motolimod-treated patients who experienced injection site reactions (ISR) had a lower risk of death compared with those who did not experience ISR. Additionally, pre-treatment in vitro responses of immune biomarkers to TLR8 stimulation predicted OS outcomes in patients receiving motolimod on study. Immune score (tumor infiltrating lymphocytes; TIL), TLR8 single-nucleotide polymorphisms, mutational status in BRCA and other DNA repair genes, and autoantibody biomarkers did not correlate with OS or PFS. CONCLUSIONS: The addition of motolimod to PLD did not improve clinical outcomes compared with placebo. However, subset analyses identified statistically significant differences in the OS of motolimod-treated patients on the basis of ISR and in vitro immune responses. Collectively, these data may provide important clues for identifying patients for treatment with immunomodulatory agents in novel combinations and/or delivery approaches. TRIAL REGISTRATION: Clinicaltrials.gov, NCT 01666444.

Intestinal epithelial cells secrete exosome-like vesicles.

BACKGROUND & AIMS: Given the observations that intestinal epithelial cells (IECs) can present antigens to CD4(+) T lymphocytes and that professional antigen-presenting cells secrete exosomes (antigen-presenting vesicles), we hypothesized that IECs may secrete exosomes carrying molecules implicated in antigen presentation, which may be able to cross the basement membrane and convey immune information to noncontiguous immune cells. METHODS: Human IEC lines HT29-19A and T84-DRB1*0401/CIITA were grown on microporous filters. Release of exosomes under basal or inflammatory conditions was evaluated in conditioned apical and basolateral media after differential ultracentrifugations. Morphologic and biochemical characterization of exosomes was performed using immunoelectron microscopy, Western blotting, and matrix-assisted laser desorption ionization-time of flight mass spectrometry. RESULTS: The intestinal cell lines released 30-90-nm-diameter vesicles from the apical and basolateral sides, and this release was significantly increased in the presence of interferon gamma. MHC class I, MHC class II, CD63, CD26/dipeptidyl-peptidase IV, and A33 antigen were present in epithelial-derived exosomes. CONCLUSIONS; Human IEC lines secrete exosomes bearing accessory molecules that may be involved in antigen presentation. These data are consistent with a model in which IECs may influence antigen presentation in the mucosal or systemic immune system independent of direct cellular contact with effector cells.

Helicobacter-induced inflammatory bowel disease in IL-10- and T cell-deficient mice.

Inflammatory bowel disease (IBD) is thought to result from a dysregulated mucosal immune response to luminal microbial antigens, with T lymphocytes mediating the colonic pathology. Infection with Helicobacter spp has been reported to cause IBD in immunodeficient mice, some of which lack T lymphocytes. To further understand the role of T cells and microbial antigens in triggering IBD, we infected interleukin (IL)-10(-/-), recombinase-activating gene (Rag)1(-/-), T-cell receptor (TCR)-alpha(-/-), TCR-beta(-/-), and wild-type mice with Helicobacter hepaticus or Helicobacter bilis and compared the histopathological IBD phenotype. IL-10(-/-) mice developed severe diffuse IBD with either H. bilis or H. hepaticus, whereas Rag1(-/-), TCR-alpha(-/-), TCR-beta(-/-), and wild-type mice showed different susceptibilities to Helicobacter spp infection. Proinflammatory cytokine mRNA expression was increased in the colons of Helicobacter-infected IL-10(-/-) and TCR-alpha(-/-) mice with IBD. These results confirm and extend the role of Helicobacter as a useful tool for investigating microbial-induced IBD and show the importance, but not strict dependence, of T cells in the development of bacterial-induced IBD.

Novel small RNA-encoding genes in the intergenic regions of Escherichia coli.

BACKGROUND: Small, untranslated RNA molecules were identified initially in bacteria, but examples can be found in all kingdoms of life. These RNAs carry out diverse functions, and many of them are regulators of gene expression. Genes encoding small, untranslated RNAs are difficult to detect experimentally or to predict by traditional sequence analysis approaches. Thus, in spite of the rising recognition that such RNAs may play key roles in bacterial physiology, many of the small RNAs known to date were discovered fortuitously. RESULTS: To search the Escherichia coli genome sequence for genes encoding small RNAs, we developed a computational strategy employing transcription signals and genomic features of the known small RNA-encoding genes. The search, for which we used rather restrictive criteria, has led to the prediction of 24 putative sRNA-encoding genes, of which 23 were tested experimentally. Here we report on the discovery of 14 genes encoding novel small RNAs in E. coli and their expression patterns under a variety of physiological conditions. Most of the newly discovered RNAs are abundant. Interestingly, the expression level of a significant number of these RNAs increases upon entry into stationary phase. CONCLUSIONS: Based on our results, we conclude that small RNAs are much more widespread than previously imagined and that these versatile molecules may play important roles in the fine-tuning of cell responses to changing environments.

Hypoxia-inducible factor 1-dependent induction of intestinal trefoil factor protects barrier function during hypoxia.

Mucosal organs such as the intestine are supported by a rich and complex underlying vasculature. For this reason, the intestine, and particularly barrier-protective epithelial cells, are susceptible to damage related to diminished blood flow and concomitant tissue hypoxia. We sought to identify compensatory mechanisms that protect epithelial barrier during episodes of intestinal hypoxia. Initial studies examining T84 colonic epithelial cells revealed that barrier function is uniquely resistant to changes elicited by hypoxia. A search for intestinal-specific, barrier-protective factors revealed that the human intestinal trefoil factor (ITF) gene promoter bears a previously unappreciated binding site for hypoxia-inducible factor (HIF)-1. Hypoxia resulted in parallel induction of ITF mRNA and protein. Electrophoretic mobility shift assay analysis using ITF-specific, HIF-1 consensus motifs resulted in a hypoxia-inducible DNA binding activity, and loading cells with antisense oligonucleotides directed against the alpha chain of HIF-1 resulted in a loss of ITF hypoxia inducibility. Moreover, addition of anti-ITF antibody resulted in a loss of barrier function in epithelial cells exposed to hypoxia, and the addition of recombinant human ITF to vascular endothelial cells partially protected endothelial cells from hypoxia-elicited barrier disruption. Extensions of these studies in vivo revealed prominent hypoxia-elicited increases in intestinal permeability in ITF null mice. HIF-1-dependent induction of ITF may provide an adaptive link for maintenance of barrier function during hypoxia.

PromEC: An updated database of Escherichia coli mRNA promoters with experimentally identified transcriptional start sites.

PromEC is an updated compilation of Escherichia coli mRNA promoter sequences. It includes documentation on the location of experimentally identified mRNA transcriptional start sites on the E. coli chromosome, as well as the actual sequences in the promoter region. The database was updated as of July 2000 and includes 472 entries. PromEC is accessible at http://bioinfo.md.huji.ac. il/marg/promec

Antigen processing and presentation by intestinal epithelial cells - polarity and complexity.

The mechanisms by which gut-associated lymphoid tissue (GALT) maintains a balance between oral tolerance and active immune response in the face of exposure to high antigen concentrations remains a central question in mucosal immunity. Here, Robert Hershberg and colleagues discuss the evidence that human intestinal epithelial cells function as antigen-presenting cells (APCs) capable of regulating T-cell responses in the intestinal mucosa

Human CD1d associates with prolyl-4-hydroxylase during its biosynthesis.

Recent studies have shown that the CD1 family of proteins present various glycolipid antigens to subsets of T cells. CD1d is expressed on human intestinal epithelial cells (IEC) and exists in two biochemical forms: 37-kDa, beta2-microglobulin (beta2m) independent, nonglycosylated, and 47-kDa, beta2m dependent, glycosylated forms. The biosynthetic pathways and the mechanisms of generation of these two biochemically distinct forms of CD1d in human IEC are unknown. Using a human colonic cell line, T84, transfected with CD1d, the biosynthesis of CD1d was investigated. Pulse-chase metabolic labeling studies of T84 transfected with wild type CD1d demonstrated that CD1d was a stable protein over a 4-day chase period. During the first 24 h of the chase, a novel 65-kDa glycoprotein was co-immunoprecipitated with CD1d. Microsequencing of this protein identified the glycoprotein as the alpha and beta subunits of the resident endoplasmic reticulum protein, prolyl-4-hydroxylase (P4H), an enzyme responsible for hydroxyl modification of proline residues. To study if either one or both biochemical forms of CD1d contained hydroxyproline residues, amino acid composition analysis of the 37 and 48 kDa was performed, and demonstrated that only the 37-kDa, but not the 48-kDa form of CD1d, contained hydroxyproline residues. These studies demonstrate that CD1d exhibits a prolonged association with P4H and that the 37-kDa form contains hydroxyproline residues. This suggests that P4H association with CD1d during its biosynthesis results in a novel post-translational modification of CD1d.

Ligation of intestinal epithelial CD1d induces bioactive IL-10: critical role of the cytoplasmic tail in autocrine signaling.

The intestinal epithelium is anatomically positioned to serve as the critical interface between the lumen and the mucosal immune system. In addition to MHC class I and II antigens, intestinal epithelia constitutively express the nonclassical MHC molecule CD1d, a transmembrane molecule with a short cytoplasmic tail expressed as a beta(2)-microglobulin-associated 48-kDa glycoprotein and novel beta(2)-microglobulin-independent 37-kDa nonglycosylated protein on intestinal epithelia. At present, it is not known whether extracellular ligands can signal intestinal epithelial CD1d. To define signaling of CD1d cytoplasmic tail, retrovirus-mediated gene transfer was used to generate stable cell lines expressing wild-type CD1d or a chimeric molecule (extracellular CD1d and cytoplasmic CD1a), and surface CD1d was triggered by antibody crosslinking. Although wild-type CD1d was readily activated (tyrosine phosphorylation), no demonstrable signal was evident in cell lines expressing the chimeric molecule. Subsequent studies revealed that anti-CD1d crosslinking specifically induces epithelial IL-10 mRNA and protein and is blocked by the tyrosine kinase inhibitor genistein. Further studies addressing epithelial-derived IL-10 revealed that anti-CD1d crosslinking attenuates IFN-gamma signaling and that such attenuation is reversed by addition of functionally inhibitory IL-10 antibodies. These results define signaling through surface CD1d, and, importantly, they demonstrate that this pathway may serve to dampen epithelial proinflammatory signals.

Critical role of cAMP response element binding protein expression in hypoxia-elicited induction of epithelial tumor necrosis factor-alpha.

Tissue hypoxia is intimately associated with a number of chronic inflammatory conditions of the intestine. In this study, we investigated the impact of hypoxia on the expression of a panel of inflammatory mediators by intestinal epithelia. Initial experiments revealed that epithelial (T84 cell) exposure to ambient hypoxia evoked a time-dependent induction of the proinflammatory markers tumor necrosis factor-alpha (TNF-alpha), interleukin-8 (IL-8), and major histocompatibility complex (MHC) class II (37 +/- 6.1-, 7 +/- 0.8-, and 9 +/- 0.9-fold increase over normoxia, respectively, each p < 0.01). Since the gene regulatory elements for each of these molecules contains an NF-kappaB binding domain, we investigated the influence of hypoxia on NF-kappaB activation. Cellular hypoxia induced a time-dependent increase in nuclear p65, suggesting a dominant role for NF-kappaB in hypoxia-elicited induction of proinflammatory gene products. Further work, however, revealed that hypoxia does not influence epithelial intercellular adhesion molecule 1 (ICAM-1) or MHC class I, the promoters of which also contain NF-kappaB binding domains, suggesting differential responses to hypoxia. Importantly, the genes for TNF-alpha, IL-8, and MHC class II, but not ICAM-1 or MHC class I, contain cyclic AMP response element (CRE) consensus motifs. Thus, we examined the role of cAMP in the hypoxia-elicited phenotype. Hypoxia diminished CRE binding protein (CREB) expression. In parallel, T84 cell cAMP was diminished by hypoxia (83 +/- 13.2% decrease, p < 0.001), and pharmacologic inhibition of protein kinase A induced TNF-alpha and protein release (9 +/- 3.9-fold increase). Addback of cAMP resulted in reversal of hypoxia-elicited TNF-alpha release (86 +/- 3.2% inhibition with 3 mM 8-bromo-cAMP). Furthermore, overexpression of CREB but not mutated CREB by retroviral-mediated gene transfer reversed hypoxia-elicited induction of TNF-alpha defining a causal relationship between hypoxia-elicited CREB reduction and TNF-alpha induction. Such data indicate a prominent role for CREB in the hypoxia-elicited epithelial phenotype and implicate intracellular cAMP as an important second messenger in differential induction of proinflammatory mediators.

Polarized expression and function of the costimulatory molecule CD58 on human intestinal epithelial cells.

BACKGROUND & AIMS: Intestinal epithelial cells (IECs) can process foreign protein antigens and display antigenic peptides to CD4(+) T lymphocytes via HLA class II molecules. The purpose of this study was to determine the nature of the second, or costimulatory, signal provided by IECs. METHODS: We investigated surface expression of the costimulatory molecules CD58 (LFA-3), CD80 (B7-1), and CD86 (B7-2) by using flow cytometry, confocal microscopy, and vectorial biotinylation. Antibodies specific for CD58, CD80, and CD86 were used in blocking experiments to assess the role of these molecules in providing a costimulatory signal to CD4(+) T cells by IECs. RESULTS: CD58, but not CD80 or CD86, was observed to be expressed constitutively on both native IECs and in the IEC lines T84 and HT-29. The surface expression of CD58 was highly polarized and restricted to the basolateral surface of the cell. Antibodies against CD58, but not CD80 or CD86, inhibited the stimulation of CD4(+) T-cell proliferation mediated by IECs. CONCLUSIONS: CD58 is expressed by polarized IECs in a topologically restricted manner at the region of T-cell contact and can function as a costimulatory molecule in HLA class II-mediated antigen presentation.

Highly polarized HLA class II antigen processing and presentation by human intestinal epithelial cells.

The high concentration of foreign antigen in the lumen of the gastrointestinal tract is separated from the underlying lymphocytes by a single cell layer of polarized epithelium. Intestinal epithelial cells can express HLA class II antigens and may function as antigen-presenting cells to CD4(+) T cells within the intestinal mucosa. Using tetanus toxoid specific and HLA-DR-restricted T lymphocytes, we show that polarized intestinal epithelial cells directed to express HLA-DR molecules are able to initiate class II processing only after internalization of antigen from their apical surface. Coexpression of the class II transactivator CIITA in these cells, which stimulates highly efficient class II processing without the characteristic decline in barrier function seen in polarized monolayers treated with the proinflammatory cytokine gamma-IFN, facilitates antigen processing from the basolateral surface. In both cases, peptide presentation to T cells via class II molecules was restricted to the basolateral surface. These data indicate a highly polarized functional architecture for antigen processing and presentation by intestinal epithelial cells, and suggest that the functional outcome of antigen processing by the intestinal epithelium is both dependent on the cellular surface at which the foreign antigen is internalized and by the underlying degree of mucosal inflammation.

Impaired class II expression and antigen uptake in monocytic cells after HIV-1 infection.

Using the human macrophage hybridoma cell line 43 and primary monocytes, we investigated the regulation of class II expression and intracellular Ag trafficking after HIV-1 infection. The HIV-1-infected human macrophage hybridoma cell line, 43HIV, lost class II Ag expression, as determined by immunofluorescence, immunoprecipitation, and Northern blot analysis, 2 wk after infection. Class II expression could be restored by transfection with the full-length HLA-DR4 cDNA driven by a CMV IE promotor. However, even after transfection, the 43HIV cells were incapable of presenting Ag to MHC-matched Ag-specific T cells. This defect was associated with decreased formation of class II-Ag complexes, and similar findings were observed in primary HIV-1BaL-infected monocytes. We investigated Ag uptake using FITC-labeled tetanus, OVA, and keyhole limpet hemocyanin. There was decreased uptake of all three Ags after HIV-1 infection at different time points after Ag pulsing in the 43HIV cells and in primary HIV-1BaL-infected monocytes. There was colocalization of the FITC-labeled Ags with early (cathepsin D) and late endosomal markers (anti-mannose-6-phosphate receptor), lysosomal markers (CD-63), and acidic compartment markers (3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine) in the uninfected cells, but the level of colocalized Ag was reduced in the 43HIV cells and HIV-1BaL-infected monocytes. Our data suggest that class II expression, formation of class II-Ag complexes, and Ag uptake are impaired in chronically HIV-1-infected monocytic cells, which may contribute to the global immunosuppression observed in AIDS.

Intestinal epithelial cells use two distinct pathways for HLA class II antigen processing.

Intestinal epithelial cells express a low level of HLA class II molecules constitutively, with elevated levels seen in the setting of mucosal inflammation including inflammatory bowel disease. The ability of intestinal epithelial cells to act as antigen presenting cells for alphabeta CD4(+) T lymphocytes was examined through a molecular analysis of the HLA class II antigen processing pathway. We have shown that intestinal epithelial cells contain abundant constitutive levels of the cathepsin proteases proven to function in HLA class II mediated antigen presentation. Activation of these cells by gamma-IFN induced the expression of invariant chain and HLA-DM alphabeta, thus facilitating the formation of compact, SDS-stable HLA- DR alphabeta heterodimers. Using HLA-DR-restricted T cells and retroviral mediated gene transfer of HLA-DR alleles into the intestinal epithelial cell lines HT-29 and T84, we demonstrated efficient antigen processing and presentation to CD4(+) T lymphocytes in the presence of the proinflammatory cytokine gamma-IFN. The class II processing pathway and presentation in the presence of gamma-IFN was indistinguishable from that observed with a conventional antigen presenting cell. Antigen processing also occurred in intestinal epithelial cells in the absence of gamma-IFN, and in contrast to that seen after stimulation with gamma-IFN, required high concentration of antigen and was not inhibited by the protease inhibitor leupeptin. These data suggest the use of two distinct pathways of HLA class II antigen processing in enterocytes with differential immunomodulatory properties in the presence or absence of mucosal inflammation.

T-cell receptor gamma delta diversity and specificity of intestinal intraepithelial lymphocytes: analysis of IEL-derived hybridomas.

The phenotype, T-cell antigen receptor (TCR) usage and specificity of intestinal intraepithelial lymphocytes (IEL), and hybridomas derived from IEL have been examined. In young conventionally reared mice, approximately 50% of the IEL express TCR alpha beta and 50% express TCR gamma delta, although there is considerable variation between individuals. Here we demonstrate that T-cell hybridomas can be prepared from freshly isolated BALB/c mouse IEL. The expressed TCR of these hybridomas reflects the TCR isotype distribution of the IEL population. Analysis of the gamma delta TCR expressed by the hybridomas demonstrates that IEL express a greater number of TCR V gene segments than has been reported for gamma delta T cells in several other epithelial sites. At least five types of gamma delta TCRs are expressed by a panel of BALB/c IEL hybridomas, although use of the gamma delta TCR V gene repertoire clearly is not random. Some TCR gamma delta cells and gamma delta hybridomas have been reported to recognize purified protein derivative (PPD); however, none of the IEL hybridomas secreted IL-2 in response to PPD. These data suggest that most TCR gamma delta IEL are not likely to be PPD reactive.

Depletion of mouse alpha beta T cell antigen receptor bearing lymphocytes by neonatal monoclonal antibody treatment.

Neonatal treatment with a monoclonal antibody specific for the alpha beta TCR results in mice with a long term, severe depletion in the number of alpha beta T cells in the periphery. Significant numbers of T cells reappear in the periphery about age 65 days, but these cells tend to lack expression of CD4 or CD8. Splenocytes of antibody-treated mice are less sensitive to mitogen stimulation or stimulation with MHC allogeneic cells. The level of serum IgG but not IgM was decreased by the treatment. Anti-alpha beta TCR antibody treatment decreased single-positive T lymphocytes that express high levels of the CD3/alpha beta TCR complex from the thymus, suggesting that the treatment could act in part by affecting negative selection of alpha beta TCR+ thymocytes. This treatment does not, however, detectably affect either the homing or the numbers of gamma delta T cells which are abundant in the intestinal epithelium, but which remain a minor population in the spleen and lymph nodes. This supports the hypothesis that gamma delta T cells are developmentally autonomous from alpha beta T cells. These mice provide an excellent model system for assessing the developmental and functional role of gamma delta T lymphocytes in vivo.

Helper-suppressor T-cell leukemia: unusual phenotype controlled with low-dose deoxycoformycin.

Presented is an unusual case of chronic T-cell leukemia. Immunophenotypic profile revealed the leukemia cells to express T4 and T8 surface markers simultaneously. The patient was treated with low-dose deoxycoformycin and control of symptoms and lymphocyte levels shown to correlate with ADA and dATP/ATP levels.

Expression of functional epidermal growth factor receptors in a human hematopoietic cell line.

To test the feasibility of using the human epidermal growth factor receptor (EGFR) as a model for growth factor receptor action in human hematopoietic cells, we infected Burkitt lymphoma cells (Namalwa) with a recombinant amphotrophic retrovirus containing a thymidine kinase promoter-driven human EGFR complementary DNA and the neomycin resistance gene. Neomycin-resistant cells expressing surface EGFR were selected by cell sorting using anti-EGFR monoclonal antibody 225. The selected cells expressed a Mr 170,000 protein immunoprecipitated by monoclonal antibody 225 and apparently identical to EGFR from A431 carcinoma cells. Infected Namalwa cells expressed 42,000 epidermal growth factor (EGF) binding sites/cell, and Scatchard analysis showed two affinities (Kd approximately 5 nM and approximately 0.5 nM). EGFR autophosphorylation was detected using antiphosphotyrosine antibodies after 5 min exposure to EGF. EGF binding induced rapid EGFR internalization (t1/2 = 9 min) and mobilization of transferrin receptors to the cell surface within 1 min. In fetal bovine serum-containing and serum-free cultures, EGF did not stimulate Namalwa cell proliferation. However, in the presence of 1.25% dimethyl sulfoxide (DMSO), EGF caused a dose-dependent increase in DNA synthesis. DMSO induced a cell cycle block in G1, which was partially reversed by EGF. DMSO induced changes in some B-cell markers suggesting cellular differentiation and increased surface EGF receptor number. Cells grown in DMSO and EGF were established as an EGF-dependent cell line for greater than 12 weeks, whereas cells grown in DMSO without EGF died within 1-2 weeks. Namalwa cells expressing EGFR demonstrated more rapid tumor growth in athymic mice. These studies demonstrate expression of functional EGFR mediating early biochemical and growth responses in a human hematopoietic cell, and indicate that EGFR can be used as an effective model in human hematopoietic cells. Results using DMSO are consistent with studies in other human leukemia cells indicating that agents inducing differentiation can restore growth factor dependence in previously factor-independent leukemia cells.

Expression of the thymus leukemia antigen in mouse intestinal epithelium.

The Qa and Tla regions of the mouse major histocompatibility complex contain a series of genes encoding proteins with structural similarity to the class I transplantation antigens of the same complex. In contrast to the genes encoding the transplantation antigens, the Qa and Tla genes show very little polymorphism. Function(s) of the proteins encoded by the Qa and Tla loci remain an enigma. Recently, the protein products of the Qa and Tla loci, often referred to as class Ib major histocompatibility complex molecules, have been proposed to present antigen to gamma delta T cells. In mice, gamma delta T cells have been found concentrated in several epithelial barriers and in the skin; yet, expression of serologically detectable Tla antigens is believed restricted to thymocytes, activated T lymphocytes, and some T-cell leukemias. Here we report that luminal epithelial cells of the mouse small intestine express the thymus leukemia antigen (TLA). We also find that, unlike T cells in Peyer's patches, a significant fraction of intestinal epithelial lymphocytes also express TLA. RNA prepared from intestinal cells contains transcripts of the T18d gene, which encodes TLA. These data extend the known expression profile of TLA molecules to mature lymphocytes and to nonhematopoietic cells. These data also demonstrate the specific expression of TLA on antigen-presenting cells in a site enriched for T cells that express gamma delta T-cell antigen receptor.