Hormone Receptor-Positive Breast Cancer Sensitive to Pembrolizumab: Evidence of the Pathogenicity of the MLH1 Variant 1835del3

A woman with estrogen/progesterone receptor-positive, ERBB2-negative metastatic breast cancer developed progressive disease despite treatment with multiple hormonal and chemotherapeutic modalities. She carried a germline variant of MLH1 (1835del3), also known as c.1835_1837del and v612del, the pathogenicity of which has not been conclusively determined. MLH1 staining was not seen on immunohistochemical staining of her tumor tissue. The patient experienced a >5-year dramatic response to 4 doses of pembrolizumab. Family studies revealed multiple other relatives with the MLH1 1835del3 variant, as well as multiple relatives with colon cancer. The one relative with colon cancer who underwent genetic testing demonstrated the same variant. Laboratory studies revealed that the patient's tumor showed loss of heterozygosity (LOH) in the MLH1 region, high levels of microsatellite instability, and a high tumor mutational burden. LOH in the MLH1 region, along with the remarkable clinical response to pembrolizumab treatment and the presence of the same MLH1 variant in affected relatives, supports the hypothesis that the MLH1 1835del3 variant is pathogenic. Given the patient's family history, this likely represents an uncommon presentation of Lynch syndrome. Physicians should be alert to evaluate patients for targetable genetic variants even in unlikely clinical situations such as the one described here.

Birds of a Feather? Genetic Counseling, Genetic Testing, and Humanism

Humanism is a philosophy that emphasizes rational, scientific, and empiric analysis of the world we live in to improve the physical, social, and psychological life of humanity. Although individual genetic counselors may or may not identify as humanists, genetic counseling and genetic testing are primarily humanistic endeavors because they are situated in the context of humanistic medicine in the westernized world. Humanistic goals are also implicit and explicit in the profession and practice of genetic counselors. This review examines the relationship between humanism and genetic counseling, highlighting situations in which the two may be discordant, and suggests ways that genetic counselors can reconcile these discordances.

The effect of referral for genetic counseling on genetic testing and surgical prevention in women at high risk for ovarian cancer: Results from a randomized controlled trial

BACKGROUND

Guidelines recommend genetic counseling and testing for women who have a pedigree suggestive of an inherited susceptibility for ovarian cancer. The authors evaluated the effect of referral to genetic counseling on genetic testing and prophylactic oophorectomy in a randomized controlled trial.

METHODS

Data from an electronic mammography reporting system identified 12,919 women with a pedigree that included breast cancer, of whom 625 were identified who had a high risk for inherited susceptibility to ovarian cancer using a risk-assessment questionnaire. Of these, 458 women provided informed consent and were randomized 1:1 to intervention consisting of a genetic counseling referral (n = 228) or standard clinical care (n = 230).

RESULTS

Participants were predominantly aged 45 to 65 years, and 30% and 20% reported a personal history of breast cancer or a family history of ovarian cancer, respectively. Eighty-five percent of women in the intervention group participated in a genetic counseling session. Genetic testing was reported by 74 (33%) and 20 (9%) women in the intervention and control arms (P < .005), respectively. Five women in the intervention arm and 2 in the control arm were identified as germline mutation carriers. Ten women in the intervention arm and 3 in the control arm underwent prophylactic bilateral salpingo-oophorectomy (P < .05).

CONCLUSIONS

Routine referral of women at high risk for ovarian cancer to genetic counseling promotes genetic testing and prophylactic surgery. The findings from the current randomized controlled trial demonstrate the value of implementing strategies that target women at high risk for ovarian cancer to ensure they are offered access to recommended care. CA Cancer J Clin 2016. © 2016 American Cancer Society, Inc. Cancer 2016;122:3509-3518. © 2016 American Cancer Society.

Cancer Risk Awareness and Concern among Women with a Family History of Breast or Ovarian Cancer

Women with a documented deleterious mutation in BRCA1 or BRCA2 are at substantially elevated risk for ovarian cancer. To understand what percentage of women with high-risk family histories know their risk is elevated we surveyed 1,885 women with a high- or moderate-risk family history and no personal history of breast or ovarian cancer, and asked about their perceived risk of breast and ovarian cancer. Among high-risk women, fewer than 20% reported use of genetic counseling, and knowledge of elevated risk of ovarian cancer was low. Prior genetic counseling was associated with greater perceived risk for ovarian cancer. Results suggest that most high-risk women (>75%) do not know their risk for ovarian cancer. Identification of potentially high-risk women for referral to genetic counseling may improve informed ovarian cancer risk management.

Abstract POSTER-CTRL-1214: Systematic identification of high risk women for genetic counseling and surgical prevention of ovarian cancer

Objectives: Information technology provides an opportunity for systematic identification of high-risk patients for appropriate referral. We conducted a randomized controlled trial to test whether routine identification of women at high risk for epithelial ovarian cancer using an electronic database and subsequent referral to genetic counseling would promote genetic testing and prophylactic surgery.

Methods: Electronic data in a mammography reporting system from a large community hospital in Seattle was used to identify women at increased risk for ovarian cancer based on personal and family cancer history. Following secondary confirmation of eligibility and consent, women were randomly assigned to an intervention consisting of a genetic counseling referral, or to standard clinical care.

Results: A total of 458 women were enrolled. Compared to standard clinical care systemic identification and referral of high risk women to genetic counseling increased the number of women who elect to undergo genetic testing (75 vs 20, p&lt;0.005) and prophylactic surgery (OR: 3.5, p=0.05).

Conclusions: Our results demonstrated that systematic identification of high-risk women for referral to genetic counseling is feasible and increases utilization of risk-appropriate prevention strategies.

Citation Format: Robert Resta, MS CGC; Charles W. Drescher, MD; David Beatty, MD; M Robyn Andersen, PhD; Kate Watabayashi, BA; Jason Thorpe, MSc; Hannah Purkey, BS; Jessica Chubak, PhD; Nancy Hanson, MS CGC; Diana S.M. Buist, MPH PhD; Nicole Urban, ScD. Systematic identification of high risk women for genetic counseling and surgical prevention of ovarian cancer [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-CTRL-1214.

Prophylactic oophorectomy rates in relation to a guideline update on referral to genetic counseling

OBJECTIVE

We sought to determine whether prophylactic oophorectomy rates changed after the introduction of a 2007 health plan clinical guideline recommending systematic referral to a genetic counselor for women with a personal or family history suggestive of an inherited susceptibility to breast/ovarian cancer.

METHODS

We conducted a retrospective cohort study of female members of Group Health, an integrated delivery system in Washington State. Subjects were women aged ≥ 35 years during 2004-2009 who reported a personal or family history consistent with an inherited susceptibility to breast/ovarian cancer. Personal and family history information was collected on a questionnaire completed when the women had a mammogram. We ascertained oophorectomies from automated claims data and determined whether surgeries were prophylactic by medical chart review. Rates were age-adjusted and age-adjusted incidence rate ratios (IRR) and 95% confidence intervals (CI) were computed using Poisson regression.

RESULTS

Prophylactic oophorectomy rates were relatively unchanged after compared to before the guideline change, 1.0 versus 0.8/1000 person-years, (IRR=1.2; 95% CI: 0.7-2.0), whereas bilateral oophorectomy rates for other indications decreased. Genetic counseling receipt rates doubled after the guideline change (95% CI: 1.7-2.4) from 5.1 to 10.2/1000 person-years. During the study, bilateral oophorectomy rates were appreciably greater in women who saw a genetic counselor compared to those who did not regardless of whether they received genetic testing as part of their counseling.

CONCLUSION

A doubling in genetic counseling receipt rates lends support to the idea that the guideline issuance contributed to sustained rates of prophylactic oophorectomies in more recent years.

Generation n + 1: Projected numbers of babies born to women with PKU compared to babies with PKU in the United States in 2009

Newborn PKU screening has been available since the mid-1960s, and the first group of screened babies is now a complete reproductive cohort (age 15-44). Untreated maternal PKU (MPKU) often results in significant developmental and physical disabilities in exposed fetuses, and could potentially offset some or all of the benefits produced by newborn PKU screening and dietary treatment. Based on the age distribution of the United States population in 2009, and using different estimates of PKU frequency (1/10,000; 1/15,000; 1/20,000), the projected number of babies born to women with PKU was compared to the projected number of babies born with PKU. In 2009, there were about 62,000,000 women age 15-44, with a fertility rate of 66.7 births/1,000 women. Of these women, depending on the incidence of PKU, 3,097-6,195 were estimated to have PKU, and they would have delivered 207-413 babies. In that same year, the number of births was 4,118,055, which would have resulted in 206-412 babies with PKU. Thus, in the United States, at all estimates of PKU frequency, the number of babies exposed to MPKU is equal to the number of babies born with PKU. This ratio varies with the fertility rate but is not dependent on the incidence of PKU. The benefits of newborn PKU screening and treatment could be significantly curtailed if adequate resources, education, and funding are not available to follow and monitor women with MPKU and their babies.

Physical exercise in young patients with congenital heart disease

The aim of this paper is to clarify two important aspects about patients affected by congenital heart disease. Their functional status plays a dominant role in the definition of quality of life related to health status, because of its implication in working and recreational activities. In the first part, we explain their cardiovascular adaptation on exercise, based on pathology (Tetralogy of Fallot, transposition of great arteries, univentricular heart). In the second part, we explain the risk of sudden death from congenital heart disease due to exercise, because of electrical cardiac instability and/or the structural abnormalities of the cardiovascular parietal walls.

Incidence of and Predictive Factors for Recovery of Ovarian Function on Letrozole in ER-Positive Breast Cancer Patients in Their Forties Who Cease Menstruating with Adjuvant Chemotherapy

Background: We conducted an open-label pilot study of 2 years of aromatase inhibitor (AI) therapy in women in their 40's with ER-positive breast cancer who had ceased menstruating with adjuvant cyclophosphamide-based chemotherapy, had postmenopausal serum estradiol (E2) levels, and had been on tamoxifen (Tam) for at least 1 year. The primary objective was to determine if serial FSH levels while on letrozole predicted for ovarian recovery (resumption of menses or premenopausal E2/FSH levels) and secondary objectives included evaluation of serial E2, inhibin A and B levels and osteopenia on baseline DEXA scan as predictors of ovarian failure.Patients and Methods: Patients who had ceased menstruating and who had a postmenopausal estradiol level on tamoxifen at study entry were treated for up to 2 years with letrozole following at least 1 year of Tam; patients who were on another AI at study entry were permitted to continue on that therapy. All patients underwent evaluation of serum FSH and E2 levels every 3 months for 1 year and then every 6 months during Year 2; baseline and end of Year 1 inhibin A and B levels; and baseline assessment of bone mineral density (BMD). Patients consented to strict birth control measures and stopped letrozole therapy at evidence of ovarian function recovery.Results: 173 patients were enrolled on study and we report now on the findings in the 30 patients &lt;45 years old (mean age 43). 96% of the patients were on letrozole. Median time from end of cyclophosphamide to start of letrozole was 23 months and median duration of Tam treatment prior to starting letrozole was 18 months. Seven patients (23%) resumed menses; 5 additional patients (17%) developed both premenopausal levels of FSH (&lt;23 IU/L) and E2 (&gt;31 pg/mL) without menses; and an additional 6 patients (20%) had isolated premenopausal E2 levels. The average time to recovery of ovarian function as above on letrozole was 14 months (range 2.4 - 29 months). Postmenopausal baseline inhibin A and B levels did not accurately predict for lack of ovarian recovery. Of the 18 patients with menses or biochemical evidence of ovarian recovery, 5 (28%) had osteopenia (T score &lt;-1) at study entry while 4 of 12 patients (33%) without ovarian recovery had baseline osteopenia. In patients who had ovarian recovery on letrozole, FSH levels that were suppressed on Tam tended to rise over 6-10 months on letrozole and then return to premenopausal levels.Conclusion: Women &lt;45 years of age who have persistent amenorrhea with adjuvant chemotherapy followed by Tam have a high incidence of ovarian recovery on letrozole. After initial rises in FSH levels following the switch from Tam to letrozole, subsequent declines in FSH levels predict for ovarian recovery.Supported, in part, by Novartis Pharmaceuticals, Corp., East Hanover, NJ.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6097.

Dielectric anomalies in ferroelectric nanostructures

First-principles-based methods are used to determine the external dielectric susceptibility (i.e., the polarization response to the external electric field) and the internal susceptibility (i.e., the polarization response to the average internal field) in ferroelectric dots, wires, and films, as a function of the electrical boundary conditions. While the external susceptibility is obviously positive, we find that the internal one is negative over a wide range of boundary conditions for all kinds of nanostructures. A Landau-type phenomenological model provides a rationale for all of our findings.

A new definition of Genetic Counseling: National Society of Genetic Counselors' Task Force report

The Genetic Counseling Definition Task Force of the National Society of Genetic Counselors (NSGC) developed the following definition of genetic counseling that was approved by the NSGC Board of Directors: Genetic counseling is the process of helping people understand and adapt to the medical, psychological and familial implications of genetic contributions to disease. This process integrates the following: Interpretation of family and medical histories to assess the chance of disease occurrence or recurrence. Education about inheritance, testing, management, prevention, resources and research. Counseling to promote informed choices and adaptation to the risk or condition. The definition was approved after a peer review process with input from the NSGC membership, genetic professional organizations, the NSGC legal counsel, and leaders of several national genetic advocacy groups.

Orbital magnetization in periodic insulators

Working in the Wannier representation, we derive an expression for the orbital magnetization of a periodic insulator. The magnetization is shown to be comprised of two contributions, an obvious one associated with the internal circulation of bulklike Wannier functions in the interior, and an unexpected one arising from net currents carried by Wannier functions near the surface. Each contribution can be expressed as a bulk property in terms of Bloch functions in a gauge-invariant way. Our expression is verified by comparing numerical tight-binding calculations for finite and periodic samples.

Orbital Magnetization in Extended Systems

While the orbital magnetic dipole moment of any finite sample is well-defined, it becomes ill-defined in the thermodynamic limit as a result of the unboundedness of the position operator. Effects due to surface currents and to bulk magnetization are not easily disentangled. The corresponding electrical problem, where surface charges and bulk polarization appear as entangled, was solved about a decade ago by the modern theory of polarization, based on a Berry phase. We follow a similar path here, making progress toward a bulk expression for the orbital magnetization in an insulator represented by a lattice-periodic Hamiltonian with broken time-reversal symmetry. We therefore limit ourselves to the case where the macroscopic (i.e. cell-averaged) magnetic field vanishes. We derive an expression for the contribution to the magnetization arising from the circulating currents internal to the bulk Wannier functions, and then transform to obtain a Brillouin zone integral involving the occupied Bloch orbitals. A version suitable for practical implementation in discretized reciprocal space is also derived, and the gauge invariance of both versions is explicitly shown. However, tests on a tight-binding model indicate the presence of additional edge currents, and it remains to be determined whether these can be related to the bulk band structure.

Genetic Evaluation and Counseling of Couples with Recurrent Miscarriage: Recommendations of the National Society of Genetic Counselors

The objective of this document is to provide recommendations for genetic evaluation and counseling of couples with recurrent miscarriage (RM). The recommendations are the opinions of the multidisciplinary Inherited Pregnancy Loss Working Group (IPLWG), with expertise in genetic counseling, medical genetics, maternal fetal medicine, internal medicine, infectious disease, cytogenetics, and coagulation disorders. The IPLWG defines RM as three or more clinically recognized consecutive or non-consecutive pregnancy losses occurring prior to fetal viability (<24 weeks gestation). These recommendations are provided to assist genetic counselors and other health care providers in clinical decision-making, as well as to promote consistency of patient care, guide the allocation of medical resources, and increase awareness of the psychosocial and cultural issues experienced by couples with RM. The IPLWG was convened with support from the March of Dimes Western Washington State Chapter and the University of Washington Division of Medical Genetics. The recommendations are U.S. Preventive Task Force Class III, and are based on clinical experiences, review of pertinent English-language published articles, and reports of expert committees. This document reviews the suspected causes of RM, provides indications for genetic evaluation and testing, addresses psychosocial and cultural considerations, and provides professional and patient resources. These recommendations should not be construed as dictating an exclusive course of medical management, nor does the use of such recommendations guarantee a particular outcome. The professional judgment of a health care provider, familiar with the circumstances of a specific case, should always supersede these recommendations.

Single nucleotide polymorphism in prohibitin 3' untranslated region and breast-cancer susceptibility

The RNA encoded by the 3' untranslated region of the prohibitin gene arrests cell proliferation by blocking the transition between the G1 and S phases of the cell cycle. The product of a variant allele (T allele) is inactive. We did a case-control study of prohibitin genotype in 205 women with breast cancer and 1046 healthy controls. The results showed an association between the T allele and breast cancer in women who reported a first-degree relative with the disease (odds ratio 2.5, p=0.005). An even stronger association was found in a subset of women diagnosed at or before age 50 years (4.8, p=0.003). These data suggest that prohibitin genotyping has value in assessing risk of breast cancer in women aged 50 years or younger with at least one first-degree relative with the disease.

Metabolites from apoptotic thymocytes inhibit thymopoiesis in adenosine deaminase-deficient fetal thymic organ cultures

Murine fetal thymic organ culture was used to investigate the mechanism by which adenosine deaminase (ADA) deficiency causes T-cell immunodeficiency. C57BL/6 fetal thymuses treated with the specific ADA inhibitor 2'-deoxycoformycin exhibited features of the human disease, including accumulation of dATP and inhibition of S-adenosylhomocysteine hydrolase enzyme activity. Although T-cell receptor (TCR) Vbeta gene rearrangements and pre-TCR-alpha expression were normal in ADA-deficient cultures, the production of alphabeta TCR(+) thymocytes was inhibited by 95%, and differentiation was blocked beginning at the time of beta selection. In contrast, the production of gammadelta TCR(+) thymocytes was unaffected. Similar results were obtained using fetal thymuses from ADA gene-targeted mice. Differentiation and proliferation were preserved by the introduction of a bcl-2 transgene or disruption of the gene encoding apoptotic protease activating factor-1. The pan-caspase inhibitor carbobenzoxy-Val-Ala-Asp-fluoromethyl ketone also significantly lessened the effects of ADA deficiency and prevented the accumulation of dATP. Thus, ADA substrates accumulate and disrupt thymocyte development in ADA deficiency. These substrates derive from thymocytes that undergo apoptosis as a consequence of failing to pass developmental checkpoints, such as beta selection.

CD73 expression and fyn-dependent signaling on murine lymphocytes

CD73 is a glycosyl phosphatidylinositol-anchored protein with both ecto-enzyme activity (ecto-5'-nucleotidase) and signal transducing capabilities for human T lymphocytes. We now report an analysis of the distribution and function of CD73 in murine lymphoid tissues made possible by the development of the first monoclonal antibodies (mAb) specific for murine CD73. Subsets of T and B lymphocytes are CD73+ and the level of expression increases with lymphocyte maturation in both species. Among B cells, CD73 is largely restricted to cells which have undergone isotype switching. The signal transmitting function of CD73 is also conserved, as splenic T cells treated with anti-CD73 mAb plus phorbol 12-myristate 13-acetate proliferate and secrete IL-2. Fyn-/- mice are unresponsive to CD73 ligation, however, demonstrating the requirement for this tyrosine kinase in CD73-mediated signal transduction. CD73 is down-regulated after mAb plus cross-linking, suggesting that expression may be controlled by interaction with a ligand. Only small numbers of thymocytes are CD73+, so CD73 receptor functions are unlikely to be important for developing T cells. However, immunohistochemical analysis reveals that reticular and vascular cells throughout the thymus and other lymphoid tissues are markedly CD73+. Therefore, CD73 might mediate lymphocyte-stromal cell interactions or condition the local microenvironment to facilitate lymphocyte development and/or function.

Ecto-enzyme and signaling functions of lymphocyte CD73

CD73 or ecto-5'-nucleotidase (5'-NT) is a widely expressed ecto-enzyme which catalyzes the dephosphorylation of AMP and other nucleoside monophosphates. CD73 participates in purine salvage through this enzymatic activity, supplying cells with precursors for energy metabolism and nucleic acid biosynthesis. As an enzyme that produces adenosine, CD73 can also regulate adenosine receptor engagement in many tissues. However, CD73 also has functions independent of its enzyme activity. Like many glycosyl phosphatidylinositol (GPI)-anchored molecules, it transmits potent activation signals in T cells when ligated by antibodies. Less compelling evidence suggests that CD73 may function as a cell adhesion molecule. In the human immune system, CD73 is expressed on subsets of T and B cells, on germinal center follicular dendritic cells, and on thymic medullary reticular fibroblasts and epithelial cells. Many challenging areas remain to be explored before the role of CD73 in the immune system will be fully understood. These include an evaluation of the role of adenosine receptors in lymphoid development, the identification of physiological CD73 ligands, a functional assessment of the GPI anchor, and an analysis of the intricate cell-type-specific and developmental regulation of CD73 expression.

Methotrexate and sulfasalazine promote adenosine release by a mechanism that requires ecto-5'-nucleotidase-mediated conversion of adenine nucleotides

We and others have shown that an increased extracellular concentration of adenosine mediates the antiinflammatory effects of methotrexate and sulfasalazine both in vitro and in vivo, but the mechanism by which these drugs increase extracellular adenosine remains unclear. The results of the experiments reported here provide three distinct lines of evidence that adenosine results from the ecto-5'-nucleotidase- mediated conversion of adenine nucleotides to adenosine. First, pretreatment of a human microvascular endothelial cell line (HMEC-1) with methotrexate increases extracellular adenosine after exposure of the pretreated cells to activated neutrophils; the ecto-5'-nucleotidase inhibitor alpha, beta-methylene adenosine-5'-diphosphate (APCP) abrogates completely the increase in extracellular adenosine. Second, there is no methotrexate-mediated increase in extracellular adenosine concentration in the supernate of cells deficient in ecto-5'-nucleotidase, but there is a marked increase in extracellular adenosine concentration in the supernates of these cells after transfection and surface expression of the enzyme. Finally, as we have shown previously, adenosine mediates the antiinflammatory effects of methotrexate and sulfasalazine in the murine air pouch model of inflammation, and injection of APCP, the ecto-5'-nucleotidase inhibitor, abrogates completely the increase in adenosine and the decrement in inflammation in this in vivo model. These results not only show that ecto-5'-nucleotidase activity is a critical mediator of methotrexate- and sulfasalazine-induced antiinflammatory activity in vitro and in vivo but also indicate that adenine nucleotides, released from cells, are the source of extracellular adenosine.

Reassessment of germline heavy chain transcripts from two murine VH families

While expression of functional heavy chain immunoglobulin mRNA requires rearrangement of variable (VH), diversity (D) and (JH) gene segments, these individual gene segments can be transcribed prior to their rearrangement. It has been proposed that the resulting germline, or sterile, transcripts play an important role in the rearrangement process because strong correlations between rearrangement frequency and sterile transcript levels have been observed in some studies. Murine VH genes have been grouped into families on the basis of coding sequence homology. VH families rearrange in a developmentally regulated manner, so that rearrangements of genes from several VH families are detected earlier than rearrangements of J558 family genes. Paradoxically, the only VH family for which sterile transcripts have been documented is the J558 family. We used RT-PCR analyses to ask whether sterile transcripts from other VH families could be detected in fetal liver samples prior to their rearrangement. While J558 family germline transcripts were easily detected, no sterile transcripts were observed from the S107 family. Our studies also revealed the ability of small quantities of degraded genomic DNA to nonspecifically prime cDNA synthesis, emphasizing the need for caution in interpreting RT-PCR data in which family-specific oligos are used for cDNA production. These results cast doubt on the idea that sterile transcripts are required for V(H)DJ(H) rearrangement.

Insights into thymic purine metabolism and adenosine deaminase deficiency revealed by transgenic mice overexpressing ecto-5'-nucleotidase (CD73)

The adenosine producing enzyme ecto-5'-nucleotidase (5'-NT) is not normally expressed during thymocyte development until the medullary stage. To determine whether earlier expression would lead to adenosine accumulation and/or be deleterious for thymocyte maturation, thymic purine metabolism, and T cell differentiation were studied in lckNT transgenic mice overexpressing 5'-NT in cortical thymocytes under the control of the lck proximal promoter. In spite of a 100-fold elevation in thymic 5'-NT activity, transgenic adenosine levels were unchanged and T cell immunity was normal. Inosine, the product of adenosine deamination, was elevated more than twofold, however, indicating that adenosine deaminase (ADA) can prevent the accumulation of adenosine, even with a dramatic increase in 5'-NT activity, and demonstrating the availability of 5'-NT substrates in the thymus for the first time. Thymic adenosine concentrations of mice treated with the ADA inhibitor 2'-deoxycoformycin (dCF) were elevated over 30-fold, suggesting that high ADA activity, rather than an absence of 5'-NT, is mainly responsible for low thymic adenosine levels. The adenosine concentrations in dCF-treated mice are sufficient to cause adenosine receptor-mediated thymocyte apoptosis in vitro, suggesting that adenosine accumulation could play a role in ADA-deficient severe combined immunodeficiency.

T cell signalling through CD73

CD73 (ecto-5'-nucleotidase), a glycosyl phosphatidylinositol (GPI) anchored purine salvage enzyme expressed on the surface of human T and B lymphocytes, catalyzes the conversion of purine and pyrimidine ribo- and deoxyribonucleoside monophosphates to the corresponding nucleosides. The cellular distribution, cDNA sequence, and structure of CD73 are reviewed. CD73 serves as a costimulatory molecule in activating T cells. A Jurkat.T cell line transfected with the CD73 cDNA revealed that neither enzymatic activity nor the GPI anchor is necessary for T cell activation in vitro via CD73, while expression of p56kk, CD45 and the T cell receptor are required. Models for the transmission of signals via CD73 and other GPI-anchored proteins are discussed. CD73 generated adenosine functions in cell signalling in many physiologic systems, including intestinal epithelium, ischemic myocardium, and cholinergic synapses. The hypothesis that CD73 produces adenosine that is important for T cell development is presented.

Isolation and characterization of the promoter of the human 5'-nucleotidase (CD73)-encoding gene

Ecto-5'-nucleotidase (NT, CD73) is a purine salvage-pathway enzyme located on the surface of various cell types, including subsets of human lymphocytes and certain leukemias and lymphomas. In addition to purine salvage, NT has proposed roles in lymphocyte maturation and activation, and its expression has been associated with the resistance of some tumor cell lines to chemotherapeutic agents. To better understand the regulation of NT gene expression in normal lymphocyte development and the elevated expression seen in some drug-resistant tumor cell lines, we isolated NT genomic clones containing the promoter region. The genomic DNA upstream from the NT start codon is high in G+C content, with one cAMP-responsive element and five consensus Sp-1 binding sites, but no TATAA box. RNase protection assays identified a cluster of potential transcription start points (tsp). One tsp, at -63 bp relative to the start codon, was confirmed as authentic by 5'-RACE (rapid amplification of cDNA ends) cloning. Transient transfection experiments utilizing luc as a reporter gene have demonstrated that a 155-bp NT genomic DNA segment inclusive of the tsp functions as a promoter in both NT+ (WI-L2 and MG) and NT- (Jurkat, Hela and Raji) cell lines. The addition of 5'-flanking sequences extending as far as -1.9 kb did not confer cell-type-specific expression to the core promoter. However, nuclear run-on analysis of nascent NT transcripts suggested that differential transcription initiation is at least partially responsible for the regulation of NT expression. Thus, additional information is necessary, either at the chromatin level, or within elements outside of the promoter region, to direct tissue-specific expression of NT.

Production and characterization of multiple antigenic peptide antibodies to the adenosine A2b receptor

A polyclonal antibody to the human adenosine A2b receptor (A2bR) was produced by immunizing a chicken with a multiple antigenic peptide consisting of eight copies of a 16-amino acid peptide, corresponding to the presumed second extracellular loop of the A2bR, linked to a branched lysine core. Western blotting with affinity-purified antibody revealed the human A2bR to be a protein of approximately 50-55 kDa, found in a variety of tissues including thymus, colon, and small intestine. The antibody also recognized mouse and rat A2bRs and revealed heterogeneity in size, with a 35-kDa protein being detected in small intestine in addition to the larger 50-52-kDa species in thymus, colon, and placenta. The chicken anti-human A2bR peptide antibody recognized the receptor in both frozen and formalin-fixed tissue sections. In human colon, the A2bR was highly expressed in epithelial cells of the crypts. A2bR immunoreactivity was also apparent in syncytiotrophoblast cells of human placental villi and in the basal zone of murine chorioallantoic placenta. These cell type-specific patterns of expression are consistent with the hypothesized roles of the A2bR in mediating electrogenic Cl- secretion and the resulting secretory diarrhea caused by colonic crypt abscesses and in regulating morphogenesis of the placenta. Insight into the multiple physiological consequences of A2bR engagement will be forthcoming from an analysis of the cell type-specific expression of this receptor in additional tissues.

Ecto-5'-nucleotidase activity is not required for T cell activation through CD73

It had previously been shown that CD73 (ecto-5'-nucleotidase) expressed on 30% of normal human peripheral T-lymphocytes can mediate costimulatory signals in T cell activation. To check for a possible contribution of the catalytic property of CD73 to this function transfected cell lines were created. Using site-directed mutagenesis on human CD73 cDNA the codons of His92 and His194 were exchanged for alanine codons. Wild type and mutant cDNAs were cloned into an expression vector and stably expressed in the T cell line Jurkat. Surface expression as quantitated by immunofluorescence with anti CD73 mAbs was comparable in wild type and mutant transfectant clones, whereas in contrast to the wild type both His to Ala mutants completely lacked enzymatic activity. The Jurkat transfectants were stimulated with a combination of soluble anti-CD73 mAb and PMA and their response was quantitated by IL-2 production. The responses of different clones of wild type and mutant transfectants varied within a wide range; however, the ranges of wild type and mutants overlap. It is concluded that in order to transmit costimulatory signals CD73 does not require its catalytic activity.