Natural killer cell-dependent apoptosis of peripheral murine hematopoietic progenitor cells in response to Fas cross-linking: involvement of tumor necrosis factor-alpha

TNF-α has tropic rather than apoptotic activity in human hematopoietic progenitors: involvement of TNF receptor-1 and caspase-8

Tumor necrosis factor-α (TNF-α) has been suggested to exert detrimental effects on hematopoietic progenitor function that might limit the success of transplants. In this study, we assessed the influences of TNF-α and its two cognate receptors on the function of fresh umbilical cord blood (UCB) and cryopreserved mobilized peripheral blood (mPB). CD34(+) progenitors from both sources are less susceptible to spontaneous apoptosis than lineage-committed cells and are not induced into apoptosis by TNF-α. Consequently, the activity of UCB-derived severe combined immune deficiency (SCID) reconstituting cells and long-term culture-initiating cells is unaffected by this cytokine. On the contrary, transient exposure of cells from both sources to TNF-α stimulates the activity of myeloid progenitors, which persists in vivo in UCB cell transplants. Progenitor stimulation is selectively mediated by TNF-R1 and involves activation of caspase-8, without redundant activity of TNF-R2. Despite significant differences between fresh UCB cells and cryopreserved mPB cells in susceptibility to apoptosis and time to activation, TNF-α is primarily involved in tropic signaling in hematopoietic progenitors from both sources. Cytokine-mediated tropism cautions against TNF-α neutralization under conditions of stress hematopoiesis and may be particularly beneficial in overcoming the limitations of UCB cell transplants.

Tumor necrosis factor receptors support murine hematopoietic progenitor function in the early stages of engraftment

Tumor necrosis factor (TNF) family receptors/ligands are important participants in hematopoietic homeostasis, in particular as essential negative expansion regulators of differentiated clones. As a prominent injury cytokine, TNF-alpha has been traditionally considered to suppress donor hematopoietic stem and progenitor cell function after transplantation. We monitored the involvement of TNF receptors (TNF-R) 1 and 2 in murine hematopoietic cell engraftment and their inter-relationship with Fas. Transplantation of lineage-negative (lin(-)) bone marrow cells (BMC) from TNF receptor-deficient mice into wild-type recipients showed defective early engraftment and loss of durable hematopoietic contribution upon recovery of host hematopoiesis. Consistently, cells deficient in TNF receptors had reduced competitive capacity as compared to wild-type progenitors. The TNF receptors were acutely upregulated in bone marrow (BM)-homed donor cells (wild-type) early after transplantation, being expressed in 60%-75% of the donor cells after 6 days. Both TNF receptors were detected in fast cycling, early differentiating progenitors, and were ubiquitously expressed in the most primitive progenitors with long-term reconstituting potential (lin(-)c-kit(+) stem cell antigen (SCA)-1(+)). BM-homed donor cells were insensitive to apoptosis induced by TNF-alpha and Fas-ligand and their combination, despite reciprocal inductive cross talk between the TNF and Fas receptors. The engraftment supporting effect of TNF-alpha is attributed to stimulation of progenitors through TNF-R1, which involves activation of the caspase cascade. This stimulatory effect was not observed for TNF-R2, and this receptor did not assume redundant stimulatory function in TNFR1-deficient cells. It is concluded that TNF-alpha plays a tropic role early after transplantation, which is essential to successful progenitor engraftment.

Fas transduces dual apoptotic and trophic signals in hematopoietic progenitors

Stem cells and progenitors are often required to realize their differentiation potential in hostile microenvironments. The Fas/Fas ligand (FasL) interaction is a major effector pathway of apoptosis, which negatively regulates the expansion of differentiated hematopoietic cells. The involvement of this molecular interaction in the function of hematopoietic stem and progenitor cells is not well understood. In the murine syngeneic transplant setting, both Fas and FasL are acutely upregulated in bone marrow-homed donor cells; however, the Fas(+) cells are largely insensitive to FasL-induced apoptosis. In heterogeneous populations of lineage-negative (lin(-)) bone marrow cells and progenitors isolated by counterflow centrifugal elutriation, trimerization of the Fas receptor enhanced the clonogenic activity. Inhibition of caspases 3 and 8 did not affect the trophic signals mediated by Fas, yet it efficiently blocked the apoptotic pathways. Fas-mediated tropism appears to be of physiological significance, as pre-exposure of donor cells to FasL improved the radioprotective qualities of hematopoietic progenitors, resulting in superior survival of myeloablated hosts. Under these conditions, the activity of long-term reconstituting cells was not affected, as determined in sequential secondary and tertiary transplants. Dual caspase-independent tropic and caspase-dependent apoptotic signaling place the Fas receptor at an important junction of activation and death. This regulatory mechanism of hematopoietic homeostasis activates progenitors to promote the recovery from aplasia and converts into a negative regulator in distal stages of cell differentiation. Disclosure of potential conflicts of interest is found at the end of this article.

Comparison of morphological and functional characteristics of primary-cultured human conjunctival epithelium and of Wong–Kilbourne derivative of Chang conjunctival cell line

PURPOSE

To analyze the relevance of a human conjunctival cell line in a study of conjunctival epithelium. We investigated and compared the effects of IFNgamma and TNFalpha in a primary culture of human conjunctiva and in a human conjunctival cell line.

METHODS

A primary-cultured human conjunctival epithelium and a human conjunctival cell line (Chang cells) were treated for 72 hr with 20, 200, 400 and 600 U ml(-1) IFNgamma or with 1100 and 11,000 U ml(-1) TNFalpha. Then, the expression of HLA DR, CD40, CD44, CD63, CD80, CD86, Fas receptor, E-cadherin, ICAM-1, MUC1, cytokeratins and vimentin were investigated by flow cytometry. Cell morphology was studied with phalloidin staining. Apoptosis was detected by flow cytometry with Annexin V and via cell cycle analysis.

RESULTS

The primary culture of human conjunctival epithelium expressed cytokeratin K4, non-keratinized squamous epithelial marker. Chang cells presented a more dedifferentiated phenotype and were cytokeratin K4 negative. In primary-cultured cells, IFNgamma (600 U ml(-1)) induced only a low level of apoptosis and a significant upregulation of most tested proteins such as HLA DR, Fas, ICAM-1, CD40 and CD63. In the Chang cell line, IFNgamma induced a significant level of apoptosis at concentrations of 200, 400 and 600 U ml(-1). HLA DR and CD63 were induced at lower levels than in primary-cultured cells. Other proteins were modified in a similar manner after IFNgamma treatment in both systems. In the primary-cultured cells, TNFalpha induced an important upregulation of ICAM-1, Fas and CD40 whereas CD44 and CD63 were significantly decreased. Conversely, only a very weak alteration of CD63 and ICAM-1 was observed in the Chang cell line after TNFalpha treatment.

CONCLUSIONS

A primary culture of a human conjunctival epithelium demonstrated well-defined epithelial features. TNFalpha and IFNgamma, two inflammatory cytokines, induced different effects in both cellular systems, in a primary-cultured conjunctival epithelium and a human conjunctival cell line. Inflammation-related molecules were highly upregulated in the primary culture and, to a lesser extent, in the Chang cell line. Thus, the Chang cell line differs in certain features from a primary culture of human conjunctival epithelium, a fact which emphasizes the complexity of interpretation of in vitro data and this should be taken into consideration in in vitro studies of human conjunctival epithelium.

Cytokine and chemokine networks influencing stem cell proliferation, differentiation, and marrow homing

The hematopoietic stem cell (HSC) is an attractive target for gene therapy of genetic diseases of the immune and hematopoietic system, and for drug-resistance strategies in which genes conferring resistance to a variety of chemotherapeutic agents can be transduced. Stem cells are relatively easy to obtain; e.g., by marrow aspiration or G-CSF mobilization into the peripheral blood, and can be enriched e.g., by the use of anti-CD34 + monoclonal antibody. For conventional retroviral transduction, normally quiescent HSC must be activated into the cell cycle by priming with appropriate cytokines, and it has been critical to identify cytokine combinations that preserve the self-renewal capacity of long-term repopulating HSC. It has become apparent that strategies designed to optimize HSC cycling and proviral integration can compromise the capacity of transduced HSC to compete in vivo against endogenous HSC or HSC that have not been activated into cell cycle. Lentiviral vectors can integrate genes into non-cycling cells but there is an increased efficiency of transduction if Go HSC are activated into G1-phase of the cell cycle. This reduced efficiency of long-term engraftment of ex vivo cultured HSC may be due to impaired self-renewal capacity or reduced marrow homing efficiency. The latter may be attributed to down modulation of chemokine receptors necessary for chemotactic homing to the marrow. Alternatively, or in addition, there may be down modulation of (1) HSC adhesion molecules necessary for endothelial adhesion and egress from the circulation: (2) metalloproteinases secreted by HSC that facilitate their migration through extracellular matrix and promote release of critical soluble regulatory factors in the marrow microenvironment. A more controversial view is that cell death pathways, for example those involving FasR (CD95) may be activated in cycling HSC, resulting in their selective destruction upon transplantation and localization to sites rich in Fas ligand such as the liver.

Aggressive Epstein-Barr virus-associated, CD8+, CD30+, CD56+, surface CD3-, natural killer (NK)-like cytotoxic T-cell lymphoma

We report an unusual case of aggressive natural killer (NK)-like cytotoxic T-cell lymphoma in a previously healthy immunocompetent West African male. He presented with a fever of unknown origin, subsequently developed erythematous skin nodules, generalized lymphadenopathy, and hepatosplenomegaly, and then died of multiple organ failure. A skin nodule and lymph node biopsy showed an infiltrate of pleomorphic atypical medium and large lymphoid cells with extensive necrosis and prominent apoptosis. Peripheral blood and ascites also harbored these cells, with cytology revealing irregular nuclear folding and basophilic cytoplasm, and some with azurophilic cytoplasmic granules. Flow cytometry and immunohistochemistry demonstrated the expression of CD2, CD7, CD8, CD30, CD56, and cytoplasmic but not surface CD3. In situ hybridization demonstrated Epstein-Barr virus transcripts. A monoclonal T-cell receptor gamma chain gene rearrangement was detected by polymerase chain reaction. This is the first reported case of an NK-like T-cell lymphoma with these unusual features, making precise classification difficult. Some features suggest an NK1.1 or NKT lymphocyte origin. Because the earliest clinical manifestation was splenomegaly and abnormal liver function, the normal cellular counterpart may be a distinct subset of NK1.1 cells normally present in hepatosplenic sinusoids. This tumor disseminated early and pursued a fulminant clinical course, thus emphasizing the importance of early recognition and diagnosis.