A 'rescuable' plasmid containing globin gene sequences allowing recombination with homologous chromosomal sequences has enabled us to produce, score and clone mammalian cells with the plasmid integrated into the human beta-globin locus. The planned modification was achieved in about one per thousand transformed cells whether or not the target gene was expressed.

A recombinant retroviral vector (MFG-GC) was used to study the efficiency of transduction of the human gene encoding glucocerebrosidase (GC; D-glucosyl-N-acylsphingosine glucohydrolase, EC 3.2.1.45), in mouse hematopoietic stem cells and expression in their progeny. Transfer of the GC gene to CFU-S (spleen cell colony-forming units) in primary and secondary recipients was virtually 100%. In mice 4-7 months after transplantation, highly efficient transfer of the human gene to bone marrow cells capable of long-term reconstitution was confirmed by detection of one or two copies per mouse genome in hematopoietic tissues and in cultures of pure macrophages. Expression of the human gene exceeded endogenous activity by several fold in primary and secondary CFU-S, tissues from long-term reconstituted mice, and explanted macrophages cultures. These studies are evidence of the feasibility of efficient transfer of the GC gene to hematopoietic stem cells and expression in their progeny for many months after reconstitution. The results of this study strengthen the rationale for gene therapy as a treatment for Gaucher disease.

The role of Ikaros in early stages of natural killer (NK) cell differentiation was investigated using an in vitro system that promotes proliferation and differentiation of NK cell precursors into mature NK1.1+ cells. Day 14.5 fetal liver cells from mice, either homozygous for Ikaros Null or dominant negative (DN) mutations, had severe 55- to 79-fold reductions in functional NK cell precursors. Although there was no statistically significant difference between values for +/+ and +/– Null mice, the mean precursor frequency for DN mutant (+/–) mice was significantly above that for DN –/– mice and below that for DN +/+ mice. The NK activity values for cells generated from the NK cell precursors followed the same respective relationships found for NK cell precursor frequencies. These data suggest that the deficiency of mature NK cells in Ikaros mutant mice is related to lack of functional precursors.

SummaryTransplantation of untreated F344 rat bone marrow into irradiated B10 mouse recipients (non-TCD F344 -> B10) to produce fully xenogeneic chimeras resulted in stable xenogeneic lymphoid chimerism, ranging from 82% to 97% rat . Survival of animals was excellent, without evidence for GVH disease. The specificity of tolerance which resulted was highly donor-specific ; MHC disparate third party mouse and rat skin grafts were promptly rejected while donor-specific F344 grafts were significantly prolonged (MST >130 days) . Multi-lineage rat stem cell-derived progeny including lymphoid cells (T and B-lymphocytes), myeloid cells, erythrocytes, platelets, and natural killer (NK) cells were present in the fully xenogeneic chimeras up to 7 months after bone marrow transplantation . Immature rat Tlymphocytes matured and acquired the a/# Tcell receptor in the thymus of chimeras in a pattern similar to normal rat controls, suggesting that immature Tlymphocytes of rat origin could interact with the murine xenogeneic thymic stroma to undergo normal maturation and differentiation . This model may be useful to study the mechanisms responsible for the induction and maintenance of donor-specific transplantation tolerance across a species barrier.

A B S T R A C T This study was designed to approach two primary questions concerning hematopoietic stem cells (HSC) in mice: what is the concentration of HSC with extensive proliferative potential in marrow, and how long can an HSC continue to function in an intact animal? The assay system was the W/W" mouse, a mouse with an inherited HSC defect, reflected in a reduction in all myeloid tissue and most particularly in a macrocytic anemia.A single chromosomally marked HSC will reconstitute the defective hematopoietic system of the W/Wv.The concentration of HSC in normal littermate (+/ +) marrow was assayed by limiting dilution calculation using cure of W/Wv as an end point (correction of anemia and erythrocytes' macrocytosis) and found to be -10/105. This is significantly less than spleen colony forming cell (CFU-S) concentration: -220/105 in +/+ and ranging from 50 to 270/105 in various other studies. Blood values were studied at selected intervals for as long as 26 mo. Of 24 initially cured mice, which were observed for at least 2 yr, 75% remained cured. However, of all cured mice, 17 lost the cure, returning to a macrocytic anemic state. Cured mice had normal numbers of nucleated and granulocytic cells per humerus and a normal concentration of CFU-S. However, cure of secondary W/WV recipients by this marrow was inefficient compared with the original +/+ marrow. These studies suggest the CFU-S assay overestimates extensively proliferating HSC or perhaps does not assay such a cell. A single such HSC can not A preliminary report of this work has been published in abstract form in 1978. Blood. 52: 222a.

SummaryIn this report, we describe a novel long-term bone marrow culture (LTBMC) system to study the origin and generation of natural killer (NK) cells from NK precursors. Rat bone marrow was cultured for 4 wk in RPMI 1640 with 5% fetal calf serum and 2-mercaptoethanol to allow the forrpation of an adherent stromal cell layer containing NK precursor cells . After addition of interleukin 2 (IL-2), the LTBMC generated high numbers (up to 100-fold expansion in 7 d) of pure 3.2.3+ large granular lymphocytes with lytic activity against NK-sensitive and -resistant tumor targets, as well as antibody-dependent cellular cytotoxicity. NK activity in LTBMC could be detected 3 d after addition of as little as 1 U/ml rIL-2, whereas lymphokine-activated killer activity was found 5 d after addition of at least 10 U/ml rIL-2. In vivo depletion and in vitro complement lysis studies showed that the NK precursor cells in LTBMC did not express the NK-associated surface markers asialo GK or 3.2.3 . We also found that LTBMC cells did not exhibit colony growth in granulocyte/macrophage or spleen colony-forming unit assays. The generation of NK cells from NK precursors required, in addition to IL-2, a second growth/ maturation factor(s), which was present in the conditioned medium of the LTBMC. This LTBMC system provides a unique in vitro model to study the development of NK cells from precursor cells, the role ofthe bone marrow stromal microenvironment in this development, and the lineage relationship of NK cells to other hematopoietic cells.

The role of recombinant hematopoietic growth factors in radiation repair has become a subject of increasing interest in both clinical and basic radiobiology. Combinations of cytokines such as hepatocyte growth factor, interleukin (IL)-3, IL-11, kit ligand, GM-CSF and erythropoietin were used to study the in vitro radiation dose response of human cord blood CD34+ hematopoietic progenitor cells using clonogenic survival assays. CD34+ cells were isolated by immunomagnetic selection and irradiated at 8 cGy/min. Irradiated cells were plated in methylcellulose with or without added cytokines, and hematopoietic colonies including CFU-GM, BFU-E and CFU-GEMM were scored on day 14. The radiation response characteristics of BFU-E and CFU-GEMM were similar for all culture conditions tested. The D0 values for BFU-E ranged between 1.29 and 2.40 Gy and n between 1.0 and 1.4. The D0 values for CFU-GEMM ranged from 86 cGy to 2.02 Gy and n between 1.0 and 1.5. The D0 for CFU-GM grown without added factors was 1.03 Gy. With single cytokine stimulation (IL-3, IL-11 or varying concentrations of HGF), D0 values ranged from 1.11 to 1.44 Gy. With the combination of IL-3, GM-CSF, kit ligand and HGF, D0 values were not significantly altered and ranged between 1.61 and 2.60 Gy. In contrast, the combination of IL-11 and HGF produced an increase in the shoulder of the radiation survival curve (n = 3.35). No increase in the shoulder was detected for any of the other conditions tested (n = 1.0-1.7). Thus the combination of HGF and IL-11 increased the radiation survival of hematopoietic progenitor cells forming CFU-GM. Understanding the mechanism by which combinations of early-acting growth factors support postirradiation recovery of primitive clonogenic hematopoietic cells may be relevant to the design of clinical protocols for improving hematopoietic recovery after total-body irradiation.

In the search for ways to augment current brain tumor therapies many have sought to exploit the fact that adult brain tissue is virtually lacking in cell division. This endorses a special appeal to therapeutic approaches which target the dependence on cell division for brain tumor growth. Polyamines play an essential role in the proliferation of mammalian cells and depletion results in inhibition of growth. As a result, there are investigations into the feasibility of controlling tumor growth by targeting the enzymes in polyamine metabolism with specific enzyme inhibitors. DFMO, an inhibitor of putrescine synthesis, is a cytostatic agent which in combination with tritiated radioemitters or cytotoxic agents such as, MGBG or BCNU is an effective antitumor agent, but the effectiveness of DFMO in vivo is reduced by tumor cell uptake of polyamines released into the circulation by normal cells and from gut flora or dietary sources. However, DFMO therapy combined with elimination of exogenous polyamines inhibits tumor growth but also results in body weight loss, reduced protein synthesis and evidence of toxicity. Furthermore, tumor growth recurs upon termination of treatment. In contrast, competitive polyamine analogs function in the homeostatic regulation of polyamine synthesis but fail to fulfill the requirements for growth and they continue to inhibit tumor growth for several weeks after cessation of treatment. Analogs are now in clinical trials. However, their action may be highly specific and differ from one cell type to another. We suggest that the effectiveness of polyamine based therapy would be enhanced by two approaches: local delivery by intracerebral microdialysis and tumor cell killing by internal radioemitters such as tritiated putrescine or tritiated thymidine which are taken up in increased amounts by polyamine depleted tumor cells. The growth inhibition by polyamine depletion prevents the dilution of the radioactive putrescine and thymidine. The overload of radioactivity kills the growth inhibited cells so that growth cannot recur when treatment terminates.