TNF-α Has Tropic Rather than Apoptotic Activity in Human Hematopoietic Progenitors: Involvement of TNF Receptor-1 and Caspase-8

Abstract

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.

Negative selection by apoptosis enriches progenitors in naïve and expanded human umbilical cord blood grafts

“…27 Expression of the receptors was determined using mAb against human Fas (clone DX2, Miltenyi Biotec), TNF-R1 and TNF-R2 (clones 16803 and 22235, respectively, R&D Systems, Abingdon, UK). 22 Cell death and apoptosis were determined in cells incubated with 5 μg/mL 7-aminoactinomycin-D (7-AAD, Sigma, St Louis, MO, USA) and Annexin-V (IQ Products), respectively. 17 Engraftment of UCB cells in NOD.SCID xenochimeras was determined in the bone marrow after 12 weeks using antibodies against murine CD45 (clone 30-F11, eBioscience, San Diego, CA, USA) and human CD45 (clone ML2, IQ Products).…”

“…[17][18][19][20] Signaling mediated by the Fas, TNF and TNF-Related Apoptosis-Inducing Ligand (TRAIL) receptors triggers progenitor activity and synergizes with other inductive factors in promoting hematopoietic differentiation. 19,21,22 This mechanism links injury signals, including TNF-family ligands, with the activation of the hematopoietic system to ensure prompt recovery from hypoplasia. It also explains the marked upregulation of these receptors under conditions of stress hematopoiesis 23 and ubiquitous expression in most primitive progenitors.…”

“…17,20,21 The identified physiological roles of receptor/ligand interactions in the transplant setting include cell interaction with bone-marrow stroma 24 and autocrine-and paracrine-trophic signaling. [18][19][20][21][22] In addition to these early activities, hematopoietic progenitors deficient in Fas and TNF receptors fail to mediate durablemultilineage reconstitution. 17,18 Insensitivity of hematopoietic progenitors to apoptosis can be used to improve the outcome of transplants, conferring immune privilege to the graft 24,25 and fostering progenitor activity.…”

“…17,18 Insensitivity of hematopoietic progenitors to apoptosis can be used to improve the outcome of transplants, conferring immune privilege to the graft 24,25 and fostering progenitor activity. [19][20][21][22] A pretransplant apoptotic challenge with Fas-ligand (FasL) and TNF-α reduces significantly the incidence and severity of GvHD in haploidentical-and xenogeneic-murine transplants, 26,27 and improves early myeloid reconstitution. 20,22 In this study we assessed possible implementation of apoptotic signaling in several aspects of UCB cell transplantation.…”

“…[19][20][21][22] A pretransplant apoptotic challenge with Fas-ligand (FasL) and TNF-α reduces significantly the incidence and severity of GvHD in haploidentical-and xenogeneic-murine transplants, 26,27 and improves early myeloid reconstitution. 20,22 In this study we assessed possible implementation of apoptotic signaling in several aspects of UCB cell transplantation. Following documentation of the insensitivity of UCB progenitors to apoptotic signaling, 20 we assessed the influence of FasL, TNF-α and their combination on the various lineages as a possible approach to graft preparation for transplantation.…”