The CD7(-) subset of CD4(+) memory T cells is prone to accelerated apoptosis that is prevented by interleukin-15 (IL-15)

Intestinal epithelial cell-derived IL-15 determines local maintenance and maturation of intra-epithelial lymphocytes in the intestine

Interleukin-15 (IL-15) is a cytokine critical for maintenance of intestinal intra-epithelial lymphocytes (IELs), especially CD8αα + IELs (CD8αα IELs). In the intestine, IL-15 is produced by intestinal epithelial cells (IECs), blood vascular endothelial cells (BECs) and hematopoietic cells. However, the precise role of intestinal IL-15 on IELs is still unknown. To address the question, we generated two kinds of IL-15 conditional knockout (IL-15cKO) mice: villin-Cre (Vil-Cre) and Tie2-Cre IL-15cKO mice. IEC-derived IL-15 was specifically deleted in Vil-Cre IL-15cKO mice, whereas IL-15 produced by BECs and hematopoietic cells was deleted in Tie2-Cre IL-15cKO mice. The cell number and frequency of CD8αα IELs and NK IELs were significantly reduced in Vil-Cre IL-15cKO mice. By contrast, CD8αα IELs were unchanged in Tie2-Cre IL-15cKO mice, indicating that IL-15 produced by BECs and hematopoietic cells is dispensable for CD8αα IELs. Expression of an anti-apoptotic factor, Bcl-2, was decreased, whereas Fas expression was increased in CD8αα IELs of Vil-Cre IL-15cKO mice. Forced expression of Bcl-2 by a Bcl-2 transgene partially restored CD8αα IELs in Vil-Cre IL-15cKO mice, suggesting that some IL-15 signal other than Bcl-2 is required for maintenance of CD8αα IELs. Furthermore, granzyme B production was reduced, whereas PD-1 expression was increased in CD8αα IELs of Vil-Cre IL-15cKO mice. These results collectively suggested that IEC-derived IL-15 is essential for homeostasis of IELs by promoting their survival and functional maturation.

The i-AAA protease YME1L and OMA1 cleave OPA1 to balance mitochondrial fusion and fission

OPA1 processing by YEM1L and OMA1 is dispensable for mitochondrial fusion and instead drives mitochondrial fragmentation, which is crucial for mitochondrial integrity and quality control.

Mitochondrial fusion and structure depend on the dynamin-like GTPase OPA1, whose activity is regulated by proteolytic processing. Constitutive OPA1 cleavage by YME1L and OMA1 at two distinct sites leads to the accumulation of both long and short forms of OPA1 and maintains mitochondrial fusion. Stress-induced OPA1 processing by OMA1 converts OPA1 completely into short isoforms, inhibits fusion, and triggers mitochondrial fragmentation. Here, we have analyzed the function of different OPA1 forms in cells lacking YME1L, OMA1, or both. Unexpectedly, deletion of Oma1 restored mitochondrial tubulation, cristae morphogenesis, and apoptotic resistance in cells lacking YME1L. Long OPA1 forms were sufficient to mediate mitochondrial fusion in these cells. Expression of short OPA1 forms promoted mitochondrial fragmentation, which indicates that they are associated with fission. Consistently, GTPase-inactive, short OPA1 forms partially colocalize with ER–mitochondria contact sites and the mitochondrial fission machinery. Thus, OPA1 processing is dispensable for fusion but coordinates the dynamic behavior of mitochondria and is crucial for mitochondrial integrity and quality control.

T cells expanded in presence of IL-15 exhibit increased antioxidant capacity and innate effector molecules

Persistence of effector cytotoxic T lymphocytes (CTLs) during an immunological response is critical for successfully controlling a viral infection or tumor growth. Various cytokines are known to play an important part in regulating the immune response. The IL-2 family of cytokines that includes IL-2 and IL-15 are known to function as growth and survival factors for antigen-experienced T cells. IL-2 and IL-15 possess similar properties, including the ability to induce T cell proliferation. Whereas long-term IL-2 exposure has been shown to promote apoptosis and limit CD8(+) memory T cell survival and proliferation, it is widely believed that IL-15 can inhibit apoptosis and helps maintain a memory CD8(+) T-cell population. However, mechanisms for superior outcomes for IL-15 as compared to IL-2 are still under investigation. Our data shows that human T cells cultured in the presence of IL-15 exhibit increased expression of anti-oxidant molecules glutathione reductase (GSR), thioredoxin reductase 1 (TXNDR1), peroxiredoxin (PRDX) and superoxide dismutase (SOD). An increased expression of cell-surface thiols, intracellular glutathione, and thioredoxins was also noted in IL-15 cultured T cells. Additionally, IL-15 cultured T cells showed an increase in cytolytic effector molecules. Apart from increased level of Granzyme A and Granzyme B, IL-15 cultured T cells exhibited increased accumulation of reactive oxygen (ROS) and reactive nitrogen species (RNS) as compared to IL-2 cultured T cells. Overall, this study suggests that T cells cultured in IL-15 show increased persistence not only due to levels of anti-apoptotic proteins, but also due to increased anti-oxidant levels, which is complimented by increased cytolytic effector functions.

The diagnosis of Sézary syndrome on peripheral blood by flow cytometry requires the use of multiple markers

BACKGROUND

Diagnosis of Sézary syndrome (SS)-defining blood involvement is hampered by the lack of Sézary cell-specific markers and nonspecific morphology of the tumour cells.

OBJECTIVES

To identify the most reliable and easy to use markers for the diagnosis of SS-defining blood involvement.

METHODS

We studied 17 patients with SS and 11 control patients. We used flow cytometry for the detection of T-cell antigens (CD3, CD4, CD7 and CD8), expression of the Sézary cell-associated marker CD158k and T-cell receptor (TCR)-Vbeta chain. Additionally, Sézary cells were identified by peripheral blood smear for lymphocytes with cerebriform nuclei.

RESULTS

It was not possible to diagnose blood involvement in all patients with SS by a single marker or method, although none of the markers was increased in the control population. Sézary cells were detected by blood smears in 13 of 17 (76%), by flow cytometry by their CD4+ CD7- CD3(dim) phenotype (> 1000 cells microL(-1)) in 13 of 17 (76%) and by expression of CD158k in 11 of 17 (65%) patients with SS. A specific T-cell clone was identified by identical TCR-Vbeta chain expression in 12 of 17 (71%) patients with SS. The identification of Sézary cells in individual patients varied for the different markers investigated.

CONCLUSIONS

The combination of identifying CD4+ CD7- CD3(dim) cells, TCR-Vbeta chain and CD158k expression allowed a definite identification of SS-defining blood involvement in every individual patient. All of these markers can be measured by flow cytometry which would avoid time-consuming analysis of blood smears. These markers would also be suitable to monitor tumour cell load during therapy.

New insights into the molecular biology and targeted therapy of cutaneous T-cell lymphomas

Cutaneous T-cell lymphoma is an extra-nodal non-Hodgkin lymphoma of mature T cells. These tumor cells home to and persist in the skin,producing a broad spectrum of clinical entities. Recent results of basic research on tumor biology and tumor immunology as well as molecular genetics of cutaneous T-cell lymphoma have fostered the development of new therapeutic approaches. Several clinical trials testing these targeted therapies have shown encouraging results. This article provides an overview of recent research developments and therapeutic strategies for cutaneous T-cell lymphoma.

Galectin-1 receptors in different cell types

Galectins are a family of animal lectins defined by two properties: shared amino acid sequences in their carbohydrate-recognizing domain, and beta-galactoside affinity. A wide variety of biological phenomena are related to galectins, i.e., development, differentiation, morphogenesis, tumor metastasis, apoptosis, RNA splicing, and immunoregulatory function. In this review, we will focus on galectin-1 receptors, and some of the mechanisms by which this lectin affects different cell types. Several galectin-1 receptors are discussed such as CD45, CD7, CD43, CD2, CD3, CD4, CD107, CEA, actin, extracellular matrix proteins such as laminin and fibronectin, glycosaminoglycans, integrins, a beta-lactosamine glycolipid, GM1 ganglioside, polypeptide HBGp82, glycoprotein 90 K/MAC-2BP, CA125 cancer antigen, and pre-B cell receptor.

Expression of apoptosis regulators in cutaneous T-cell lymphoma (CTCL) cells

This study examined cutaneous T-cell lymphoma (CTCL) cell lines and cutaneous lesions for the presence of Bcl-2 gene family members and found that the two apoptosis-inhibiting members Bcl-xL and Mcl-1 and the two apoptosis-supporting members Bad and Bax were expressed. However, Bad was at least partially inactivated by phosphorylation. In skin lesions, the translocation of Bad from the nucleus to the cytoplasm may reflect the Bad inactivation by phosphorylation identified in vivo. Bax is also ineffective, as the non-steroidal anti-inflammatory drug sulindac, whose cytotoxic effect is mediated by Bax, could not induce apoptosis in CTCL cell lines. The expression of Bcl-2, Bcl-xL, and Mcl-1 may therefore be sufficient to guarantee the survival of malignant CTCL cells. The Bcl-x, Mcl-1, Bad, and Bax proteins were also expressed in all CTCL skin lesions tested. In two patients from whom two biopsies from two different time points of the disease were available, a significant increase in Mcl-1 expression was found in the later-stage skin lesion. Overexpression of Mcl-1 and synthesis of non-functional Bax may be responsible for the resistance of CTCL cells to the anti-cancer drugs chlorambucil and sulindac.

CD4+CD7- leukemic T cells from patients with Sézary syndrome are protected from galectin-1-triggered T cell death

In early stages of cutaneous T cell lymphoma (Sézary syndrome) both CD4+CD7- and CD4+CD7+ T cells clonally expand whereas in late stages of the disease CD7- cells are predominant in number, giving rise to the question whether CD7- T cells have a survival advantage in the skin. Galectin-1, a cell-bound lectin, was recently reported to trigger apoptosis in activated CD7+ T cells. Here, we demonstrate that in contrast to activated CD7(+) T cells, quiescent and activated CD69+ CD7- T cells from healthy donors and from Sézary patients are resistant to galectin-1-mediated cell death. CD7- T cells are apoptosis-resistant even during coculture with IFN-gamma-stimulated endothelial cells that constitutively express galectin-1 in high amounts. These data imply that resistance of CD7- T cells to galectin-1-induced apoptosis may contribute to the accumulation of CD7- Sézary T cells during progression of the disease.