Production and characterization of the extracellular domain of human CD7 antigen: further evidence that CD7 has a role in T cell signaling

The clinical importance of CD4+ CD7- in human diseases

The CD7 antigen is a member of the immunoglobulin superfamily that expresses on the surface of all thymocytes, a majority of mature T cells, and also natural killer cells. Interestingly, under physiological and different pathological conditions, the loss of CD7 antigen occurred in the subset of CD4⁺ memory T cells. Various functions have been proposed for CD7, including its role in the activation and intercellular adhesiveness of T cells. Several studies indicate that the number of CD4⁺ CD7^- T cells increases in diseases such as chronic inflammation and T-cell malignancies, these being skin inflammatory lesions. Therefore, this can be useful for the diagnosis of cancer cells, especially with reference to blood origin, treatment monitoring, and establishment of new therapies. Therefore, a comprehensive review could be useful to increase our knowledge about the clinical importance of these cells in human disease.

Cancer stem cell marker glycosylation: Nature, function and significance

Glycans are essential for the maintenance of normal biological function, with alterations in glycan expression being a hallmark of cancer. Cancer stem cells (CSCs) are a subset of cells within a tumour capable of self-renewal, cellular differentiation and resistances to conventional therapies. As is the case with stem cells, marker proteins present on the cell surface are frequently used to identify and enrich CSCs, with the expression of these markers statistical correlating with the likelihood of cancer recurrence and overall patient survival. As such CSC markers are of high clinical relevance. The majority of markers currently used to identify CSC populations are glycoproteins, and although the diverse biological roles for many of these markers are known, the nature and function of the glycan moiety on these glycoproteins remains to be fully elucidated. This mini-review summarises our current knowledge regarding the types and extent of CSC marker glycosylation, and the various roles that these glycans play in CSC biology, including in mediating cell adhesion, metastasis, evading apoptosis, tear shear resistance, tumour growth, maintaining pluripotency, self-renewal, trafficking, maintaining stability, maintaining enzymatic activity and aiding epithelial mesenchymal transitioning. Given that CSCs markers have multiple diverse biological functions, and are potentially of significant diagnostic and therapeutic benefit the search for new markers that are uniquely expressed on CSCs is vital to selectively target/identify this subset of cancer cells. As such we have also outlined how high-throughput lectin microarrays can be used to successfully profile the glycosylation status of CSC and to identify glyco-markers unique to CSCs.

Receptors and ligands implicated in human T cell costimulatory processes

It is well established that full activation of T cells that recognize antigens requires additional signals. These second signals are generated by the interaction of costimulatory ligands expressed on antigen presenting cells with their receptors on T cells. In addition, T cell activation processes are negatively regulated by inhibitory costimulatory pathways. Interaction of members of the B7 and the TNF superfamilies with members of the CD28 and TNF-R-superfamilies plays major roles in costimulatory processes. However, a large number of molecules that do not belong to these families have been reported to be involved in the generation of T cell costimulatory signals. In addition to well-defined costimulatory pathways, where both receptors and ligands are known, there are many T cell surface molecules that have been described to generate a second signal under certain experimental conditions, f.i. when ligated with antibodies. Furthermore there are several ligands that have been shown to positively or negatively modulate T cell activation by interacting with as of yet unknown T cell receptors. Here we give a comprehensive overview of molecules that have been implicated in human T cell activation processes and propose criteria that define genuine T cell costimulatory pathways.

Simvastatin regulates non-neuronal cholinergic activity in T lymphocytes via CD11a-mediated pathways

Lymphocyte function associated antigen-1 (LFA-1; CD11a/CD18) is an important mediator of leukocyte migration and T cell activation. We previously showed that antithymocyte globulin stimulates an independent, non-neuronal cholinergic system in T cells via LFA-1-mediated pathways, as evidenced by increases in acetylcholine (ACh) synthesis and choline acetyltransferase (ChAT) mRNA expression. The cholesterol-lowering drug simvastatin inhibits LFA-1 signaling by binding to an allosteric site on CD11a (LFA-1 alpha chain), which leads to immunomodulation. In the present study, we investigated whether simvastatin modulates lymphocytic cholinergic activity in T cells. We found that anti-CD11a monoclonal antibody (mAb) increased ChAT activity, ACh synthesis and release, and expression of ChAT and M5 muscarinic ACh receptor mRNA in MOLT-3 cells, a human leukemic T cell line. Simvastatin abolished these anti-CD11a mAb-induced increases in lymphocytic cholinergic activity in a manner independent of its cholesterol-lowering activity. These results indicate that LFA-1 contributes to the regulation of lymphocytic cholinergic activity via CD11a-mediated pathways, and suggest that simvastatin exerts its immunosuppressive effects in part via modification of lymphocytic cholinergic activity.

Cytotoxicity of human RNase-based immunotoxins requires cytosolic access and resistance to ribonuclease inhibition

Immunotoxins are targeted therapeutics designed to kill cancer cells. The targeting moiety of an immunotoxin selectively binds to a tumor cell and targets it for death via an attached toxin. Because the toxins are typically of plant or bacterial origin, their clinical use is limited by immunogenicity and nonspecific toxicity. To circumvent these problems, we have begun to engineer immunotoxins containing human pancreatic ribonuclease. Here we describe the generation of ribonuclease mutants designed to evade a ubiquitous cytosolic inhibitor that would otherwise block cytotoxicity. Two mutants retained catalytic activity and were relatively resistant to the inhibitor. To deliver them to human T leukemic cells, these ribonuclease variants were fused to a single chain Fv fragment specific for CD 7. The ribonuclease-sFv fusion proteins bound CD 7(+) T cells and were internalized yet were not cytotoxic. Transfection of the proteins directly into the cytosol reduced cell viability, suggesting that the failure of the immunotoxins to kill cells when added externally resulted from the inability of the ribonuclease moiety to access the cytosol efficiently. Our results indicate appropriate intracellular routing, as well as resistance to inhibition, is critical to the cytotoxicity of human ribonuclease-based immunotoxins.

In vitro culture of skin-homing T lymphocytes from inflammatory skin diseases

We, in this study, describe how T lymphocytes in a skin biopsy can proliferate in vitro for up to 3 months by using T-cell growth factors - interleukin-2 (IL-2) and IL-4 yielding approximately 100-160 million T lymphocytes within 1 month. We established cell lines from three tuberculin skin tests, four positive patch tests, 15 of 16 biopsies from atopic dermatitis (AD), 15 of 19 biopsies from mycosis fungoides (MF), 12 of 24 biopsies from psoriasis vulgaris, which was significantly less than AD (P < 0.05), and with a reduced cumulative number of lymphocytes (P < 0.05). Omitting IL-2 and IL-4 led to immediate halt of proliferation. Blood mononuclear cells from patients and biopsies from healthy persons never gave cell lines. All cells were T lymphocytes expressing CD45RO+, HLA-DR+ and CD150. The CD7 expression was significantly increased in cell lines from AD (P < 0.05). T-cell receptor beta-chain studies by using reverse transcription-polymerase chain reaction showed that all T lymphocytes had access to the skin compartment. Single-stranded conformational analysis showed clonally expanded T cells numbering between 40 and 60 clones. After approximately 2 months of growth, the mean CD4+ : CD8+ ratio was for AD 1.20, MF 0.65 and psoriasis 0.85. Patients with AD treated with cyclosporin-A had almost no growth of CD8+ cells in vitro. Our findings indicate a changed homeostasis among skin-homing lymphocytes for in vitro culture. Our culture system of skin-homing T lymphocytes leads to a prominent cellular expansion allowing for a range of studies of in vivo activated skin T lymphocytes.

Effects of human antithymocyte globulin on acetylcholine synthesis, its release and choline acetyltransferase transcription in a human leukemic T-cell line

Lymphocytes possess an independent, nonneuronal cholinergic system. In the present study, we investigated the short- and long-term effects of antithymocyte globulin (ATG)-Fresenius (ATG-F), a human antithymocyte globulin that binds to CD2, CD7 and CD11a, on acetylcholine (ACh) synthesis and transcription of choline acetyltransferase (ChAT) in CCRF-CEM cells, a human leukemic T-cell line. In the short-term (6 h), ATG-F enhanced ACh release, likely through transient increases in intracellular Ca(2+) ([Ca(2+)](i)) mediated by CD7, which led to declines in intracellular ACh content. By 48 h, however, the ACh content had increased as compared to control due to up-regulation of ChAT expression mediated by CD11a.

Variable CD7 expression on T cells in the leukemic phase of cutaneous T cell lymphoma (Sézary syndrome)

CD7, a molecule normally expressed on 90% of normal CD4+ T cells, is often deficient on the malignant T cells of cutaneous T cell lymphoma. To investigate the clinical and biologic implications of CD7 expression, blood lymphocytes from 42 patients with the leukemic phase of cutaneous T cell lymphoma (CD4/CD8 ratio of 10 or more with evidence of a T cell clone in the blood) were analyzed for level of expression of CD7 by flow cytometry. CD7 expression by cells did not clearly segregate into two distinct subgroups that are either CD7 positive or CD7 negative as generally thought; however, nine of 17 patients with a predominantly CD4+CD7+ tumor population on early studies became CD4+CD7- over time whereas the converse situation was not observed. In addition, of three patients with evidence of large tumor cells in the blood coexisting with smaller cells, discordant CD7 expression was observed in one instance. In lymph node specimens, the percentage of cells expressing CD7 and other T cell markers did not correlate with histologic evidence of involvement. CD7 expression on blood lymphocytes also did not correlate with patients' survival nor to serum IgE levels or blood eosinophil counts, a finding suggesting that this marker does not identify functional cell subsets that produce serum interleukin-4 or -5, respectively. We speculate that the level of CD7 expression on malignant T cells may be the effect of sustained antigen stimulation in vivo analogous to what has been proposed to occur with normal T cells during aging.

Identification of CD7 as a cognate of the human K12 (SECTM1) protein

CD7 is a 40-kDa protein found primarily on T, NK, and pre-B cells; the function of the CD7 protein in the immune system is largely unknown. The K12 (SECTM1) protein was originally identified by its location just upstream of the CD7 locus. The K12 gene encodes a transmembrane protein of unknown function. In order to clone a K12-binding protein, we generated a soluble version of the human K12 protein by fusing its extracellular domain to the Fc portion of human IgG(1). Flow cytometry experiments showed that the K12-Fc fusion protein bound at high levels to both human T and NK cells. Precipitation experiments using K12-Fc on (35)S-radiolabeled NK cells lysates indicated that the K12 cognate was an approximately 40-kDa protein. A human peripheral blood T cell cDNA expression library was screened with the K12-Fc protein, and two independent, positive cDNA clones were identified and sequenced. Both cDNAs encoded the same protein, which was CD7. Thus, K12 and CD7 are cognate proteins that are located next to each other on human chromosome 17q25. Additionally, we have cloned the gene encoding the mouse homologue of K12, shown that it maps near the mouse CD7 gene on chromosome 11, and established that the mouse K12 protein binds to mouse, but not human, CD7. Mouse K12-Fc inhibited in a dose-dependent manner concanavalin A-induced proliferation, but not anti-TcRalpha/beta induced proliferation, of mouse lymph node T cells. Human K12-Fc stimulated the up-regulation of CD25, CD54, and CD69 on human NK cells in vitro.

Prognostic factors in Sézary syndrome: a multivariate analysis of clinical, haematological and immunological features

BACKGROUND

Sézary syndrome (SS) prognostic factors are not well defined because of the rarity of this disease. The specific goal of this prospective study was to assess by multivariate analysis the predictive value with respect to survival of a series of clinical, haematological and immunological parameters taken at SS diagnosis.

PATIENTS AND METHODS

A cohort of 62 SS patients diagnosed and followed since 1975 was examined, and 51 were included in the multivariate analysis model.

RESULTS

The median survival time was 31 months (range: 1 month-15.7+ years), and the five-year survival rate 33.5%. The following variables were found by univariate analysis to be associated with a poor prognosis at the time of SS diagnosis: previous history of mycosis fungoides (P = 0.013), high number of circulating leukocytes (P = 0.001), Sézary cells (SC) (P < 0.001) and CD4+ cells (P < 0.001), presence of large circulating SC (P < 0.001), above normal range LDH serum levels (P = 0.015), presence of PAS-positive inclusions in the cytoplasm of circulating SC (P < 0.001), high CD4/CD8 ratio (P = 0.004) and a CD7 negative circulating SC phenotype (P < 0.001). Among them, the stepwise multivariate analysis selected as adverse independent prognostic factors: PAS-positive cytoplasmic inclusions (P = 0.001), CD7 negative phenotype (P = 0.018) and presence of large circulating SC (P = 0.045).

CONCLUSIONS

Two low-/high-risk groups have been singled out on the basis of the risk index. Patients with no or one adverse prognostic feature(s) (risk index < or = 1; n = 31) share a slow disease course and a relatively favorable prognosis (five-year survival: 58%); on the other hand, patients with 2 or 3 adverse prognostic feature (risk index > 1; n = 20) are characterized by an aggressive disease course not modifiable by traditional therapies (five-year survival: 5%).

CD4+ CD7- T cells: a separate subpopulation of memory T cells?

The CD7 molecule is apparently involved in T cell activation but is absent in a substantial subpopulation of human T cells under physiological and certain pathological conditions. The majority of CD7- T cells expresses TCR alpha/beta and is of CD4+ helper and CD45R0+CD45RA- memory phenotype. After birth, percentages and absolute numbers of circulating CD7- T cells increase significantly during aging. A number of molecules thought to be involved in organ-specific T cell homing are preferentially expressed within the subset of CD4+CD7- T cells. Specific absence of CD7 antigen expression on T cells is observed in a variety of pathologic conditions such as cutaneous T cell lymphoma, HIV infection, rheumatoid arthritis, and kidney transplantation. Current in vitro results suggest that specific downregulation of CD7 antigen expression in T cells reflects a separate and stable differentiation state occurring late in the immune response. Expansion of CD7- T cells in vivo has been found in certain diseases associated with chronically repeated T cell stimulation. The potential pathophysiological significance of this T cell subset in certain human diseases is discussed.