Selective growth advantage of wild-type lymphocytes in X-linked SCID recipients.

The cytokine receptor common gamma chain (gamma c) plays a pivotal role in multiple interleukin signaling, and gamma c gene mutations cause an X-linked form of SCID (X-SCID). Recently, gamma c gene transfer into the autologous X-SCID BM achieved appreciable lymphocyte reconstitution, contrasting with the limited success in previous gene therapy trials targeting hematopoietic stem cells. To understand the mechanisms underlying this success, we examined the repopulating potential of the wild-type (WT) BM cells using an X-SCID mouse model. Limited numbers of WT cells were infused into non-ablated WT and X-SCID hosts. Whereas no appreciable engraftment was observed in WT recipients, donor-derived lymphocytes repopulated well in X-SCID, reaching 37% (10(6)cells given) and 53% (10(7) cells given) of the normal control value 5 months post BMT. A lineage analysis showed a predominance of the donor-derived lymphocytes (CD4(+) T, CD8(+) T, B and NK cells) in X-SCID while the donor-derived granulocytes and monocytes engrafted poorly. These results showed a selective advantage of WT cells in X-SCID, and that the advantage was restricted to lymphocytes. In human gene therapy for X-SCID, an analogous growth advantage would greatly enhance the repopulation of lymphocytes derived from a very small number of gamma c gene-supplemented precursors.

Human homologues of Delta-1 and Delta-4 function as mitogenic regulators of primitive human hematopoietic cells.

Delta-mediated Notch signaling controls cell fate decisions during invertebrate and murine development. However, in the human, functional roles for Delta have yet to be described. This study reports the characterization of Delta-1 and Delta-4 in the human. Human Delta-4 was found to be expressed in a wide range of adult and fetal tissues, including sites of hematopoiesis. Subsets of immature hematopoietic cells, along with stromal and endothelial cells that support hematopoiesis, were shown to express Notch and both Delta-1 and Delta-4. Soluble forms of human Delta-1 (h Delta-1) and h Delta-4 proteins were able to augment the proliferation of primitive human hematopoietic progenitors in vitro. Intravenous transplantation of treated cultures into immune-deficient mice revealed that h Delta-1 is capable of expanding pluripotent human hematopoietic repopulating cells detected in vivo. This study provides the first evidence for a role of Delta ligands as a mitogenic regulator of primitive hematopoietic cells in the human. (Blood. 2001;97:1960-1967)

The notch ligand jagged-1 represents a novel growth factor of human hematopoietic stem cells.

The Notch ligand, Jagged-1, plays an essential role in tissue formation during embryonic development of primitive organisms. However, little is known regarding the role of Jagged-1 in the regulation of tissue-specific stem cells or its function in humans. Here, we show that uncommitted human hematopoietic cells and cells that comprise the putative blood stem cell microenvironment express Jagged-1 and the Notch receptors. Addition of a soluble form of human Jagged-1 to cultures of purified primitive human blood cells had modest effects in augmenting cytokine-induced proliferation of progenitors. However, intravenous transplantation of cultured cells into immunodeficient mice revealed that human (h)Jagged-1 induces the survival and expansion of human stem cells capable of pluripotent repopulating capacity. Our findings demonstrate that hJagged-1 represents a novel growth factor of human stem cells, thereby providing an opportunity for the clinical utility of Notch ligands in the expansion of primitive cells capable of hematopoietic reconstitution.

Large amount of vitamin A has no major effects on thyroidal hormone synthesis in two-stage rat thyroid carcinogenesis model using N-bis(2-hydroxypropyl)nitrosamine and thiourea.

In our previous investigation, which focused on two-stage carcinogenicity in the thyroid, rats were administered N-bis(2-hydroxypropyl)nitrosamine (DHPN), followed by thiourea (TU) over an experimental period of 19 weeks. Simultaneous treatment with a high level of vitamin A (VA) enhanced the induction of proliferative lesions that originated from the thyroidal follicular epithelium. To examine whether hormone synthesis in the thyroid could be inhibited by simultaneous treatment with a large amount of VA and TU, all of the rats were initially given a single subcutaneous injection of 2,800 mg DHPN/kg followed by a supply of 0% TU + 0% VA (DHPN only, control group), 0.2% TU in their drinking water (DHPN/TU group), 0.1% VA in their diet (DHPN/VA group), or 0.2% TU + 0.1% VA (DHPN/TU + VA group) during an experimental period of 4 weeks. Results obtained indicate that the iodine uptake and organification, namely iodination of tyrosine residue in thyroglobulin, of the thyroid, were significantly decreased in the DHPN/TU group compared to the DHPN control group. The variation in these values was attributable to the inhibitory effect of TU upon thyroid hormone synthesis. Results obtained from the DHPN/TU + VA and DHPN/TU groups were comparable. Therefore, the possibility that modification of hormone synthesis contributes to the enhancing effect of simultaneous treatment with a large amount of VA on thyroidal tumor induction by TU is considered to be very minimal.