Tumor Necrosis Factor Receptors Support Murine Hematopoietic Progenitor Function in the Early Stages of Engraftment

Abstract

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-a 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 2 ) 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 2 ckit). BM-homed donor cells were insensitive to apoptosis induced by TNF-a and Fasligand and their combination, despite reciprocal inductive cross talk between the TNF and Fas receptors. The engraftment supporting effect of TNF-a 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-a plays a tropic role early after transplantation, which is essential to successful progenitor engraftment.

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

“…19,20,22 Resistance of human UCB progenitors to receptor-mediated apoptosis, consistently observed in mobilized-peripheral blood cells 22,27 and murinebone marrow, [17][18][19]21 evolves as an inherent characteristic of hematopoietic precursors. 20 Furthermore, we demonstrate by direct measurements of viability and functional hematopoieticreconstitution assays that TNF-induced Fas expression in 40% of the CD34 + progenitors does not sensitize to apoptosis induced by receptor cross-linking, similar to observations in murine-bone marrow.…”

“…20 Furthermore, we demonstrate by direct measurements of viability and functional hematopoieticreconstitution assays that TNF-induced Fas expression in 40% of the CD34 + progenitors does not sensitize to apoptosis induced by receptor cross-linking, similar to observations in murine-bone marrow. 18 Hematopoietic cells progressively acquire sensitivity to receptor-mediated apoptosis in the course of differentiation, which becomes the dominant mechanism of physiologicalnegative regulation of the mature progeny. [18][19][20][21][22] Differential sensitivities of progenitors and differentiated cells to receptormediated apoptosis can be employed to improve the outcome of UCB transplants.…”

“…In contrast to apoptotic signaling in differentiated cells that mediates homeostatic negative regulation, murine and human precursors are inherently insensitive to apoptosis. [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.…”

“…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.…”

“…[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. [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.…”