A novel immunodeficient mouse model--RAG2 x common cytokine receptor gamma chain double mutants--requiring exogenous cytokine administration for human hematopoietic stem cell engraftment.

Gene transduction into immature human hematopoietic cells collected from umbilical cord blood, bone marrow, or mobilized peripheral blood cells could be useful for the treatment of genetic and acquired disorders of the hematopoietic system. Immunodeficient mouse models have been used frequently as recipients to assay the growth and differentiation of human hematopoietic stem/progenitor cells. Indeed, high levels of human cell engraftment were first reported in human/murine chimeras using NOD/SCID mice, which now are considered as the standard for these types of experiments. However, NOD/SCID mice have some clear disadvantages (including spontaneous tumor formation) that limit their general use. We have developed a new immunodeficient mouse model by combining recombinase activating gene-2 (RAG2) and common cytokine receptor gamma chain (gamma c) mutations. The RAG2-/-/gamma c- double mutant mice are completely alymphoid (T-, B-, NK-), show no spontaneous tumor formation, and exhibit normal hematopoietic parameters. Interestingly, human cord blood cell engraftment in RAG2-/-/gamma c- mice was greatly enhanced by the exogenous administration of human cytokines interleukin-(IL-3) granulocyte-macrophage colony-stimulating factor, (GM-CSF), and erythropoietin in contrast to the NOD/SCID model. This unique feature of the RAG2-/-/gamma c- mouse model should be particularly well suited for assessing the role of different cytokines in human lymphopoiesis and stem/progenitor cell function in vivo.

Radiobiological features of acute myeloblastic leukemia: comparison of self-renewal versus terminally differentiated populations.

PURPOSE: To evaluate the radiosensitivity of self-renewing progenitor cells in acute myeloblastic leukemia (AML), we have compared the radiosensitivity of the cells grown either in methylcellulose alone for 7 days, or first in suspension culture for 7 days before being plated in methylcellulose. Methylcellulose selects for terminal-dividing cells and suspension cultures have been developed because they allow self-renewal to occur: The exponential growth of the progenitors of AML cultured in suspension is due to self-renewal. METHODS AND MATERIALS: Cells were harvested from previously untreated leukemic human bone marrows. The myeloblastic lineage of the colonies was assessed by morphological, cytochemical, and immunophenotypic analysis, and by the use of growth factors that did not stimulate the growth of T-lymphocytes. The cell-cycle distribution of the blasts was analyzed by flow cytometry and was comparable for all samples. The irradiation was performed with gamma-photons at a dose-rate of 0.05 Gy/min, similar to the clinical conditions used in our institution for total body irradiation (TBI). RESULTS: The culture methods selected aggressive leukemias. There were large variations of the individual radiosensitivity whatever culture method was used. The progenitor cells capable of self-renewal were more radiosensitive than terminal dividing cells. In two cases, a shoulder was found in the initial part of the cell-survival curves of cells capable of self-renewal. In these two cases, the best fit for the data was the linear quadratic model (survival = e-alpha D-beta D2) with alpha/beta values of 1.49 Gy and 3.12 Gy, respectively. CONCLUSION: The very low values of alpha/beta suggest a reduced antileukemic effect in case of fractionated TBI, and may lead to more reliable screening methods to determine the most appropriate technique for radiation ablation of bone marrow prior to bone marrow transplantation (BMT).

[Radiotherapy and cerebral stereotaxis. Examples of dosimetry with 3D reconstruction]. / Radiothérapie et stéréotaxie cérébrale. Exemples de dosimétrie avec reconstruction 3-D.

External stereotactic radiotherapy allows to irradiate a small and carefully delimited intracranial volume according to the spatial definition of the target. To determine the distribution of the dose in the volume irradiated, we developed a dosimetric programme adapted to our particular treatment conditions (arc therapy in the frontal and oblique planes converging onto the centre of the target volume with circular beams 8 to 20 mm in diameter using 18 MV X photons). The principle of the programme is a 3D reconstruction based on ten transverse CT slices. This reconstruction, related to the stereotactic coordinates defined during stereotactic localization, visualises the outline of each oblique frontal treatment plane and the outline of the three perpendicular reference planes passing through the centre of the target volume (i.e. transverse, sagittal, coronal). The isodose distribution is then calculated in the planes defined by these reconstructions. Under treatment conditions, we use the parameters measured for each beam with their additional collimation. We present an evaluation of this software performed on a phantom consisting of a skull containing a defined target.