Comparison of Cesium-137 and X-ray Irradiators by Using Bone Marrow Transplant Reconstitution in C57BL/6J Mice

Abstract

Mice are used extensively in transplantation studies involving bone marrow ablation. Due to the increasing security issues and expenses involved with γ irradiators, self-contained X-ray irradiators have been increasing in popularity. We hypothesized that bone marrow ablation by irradiation of mice with a (137)Cs irradiator would be comparable to that from an X-ray source irradiator. A lethal-dose curve was obtained by irradiating C57BL/6J mice with 500, 700, 900, and 1100 cGy from either source. These data were used to determine the lethal radiation exposure range for a noncompetitive bone marrow engraftment curve for each source. At 90 d after reconstitution, the bone marrow engraftment curves revealed significant differences between the 2 sources in the establishment of B cell, myeloid, and T cell lineages. Murine B cell reconstitution after exposure to a (137)Cs source was greater than that after X-ray exposure at each dose level, whereas the converse was true for myeloid cell reconstitution. At the 1050- and 1100-cGy doses, mice irradiated by using the X-ray source demonstrated higher levels of T cell reconstitution but decreased survival compared with mice irradiated with the (137)Cs source. We concluded that although both sources ablated endogenous bone marrow sufficiently to enable stem cell engraftment, there are distinct physiologic responses that should be considered when choosing the optimal source for use in a study and that irradiation from the (137)Cs source was associated with lower overall morbidity due to opportunistic infection.

Figure 1.

Acrylic divider insert with lid (top) and standard shoebox mouse cage with divider insert viewed from above without the lid (bottom). The lid limited the mouse movement vertically to increase X-ray uniformity. To prevent mice from moving it, the lid was made of 1/4-in. acrylic, compared with the 1/8-in. material of the divider walls.

Figure 2.

¹³⁷Cs lethal-dose curve over 30 d. Doses of 900 and 1100 cGy were 100% lethal.

Figure 3.

X-ray lethal-dose curve with acrylic insert and height-limiting lid (top) over 30 d. Doses of 700, 900, and 1100 cGy were 100% lethal

Figure 4.

¹³⁷Cs irradiation with bone-marrow transplantation survival curve over 30 d. Mice that lived past 30 d lived to 90 d and demonstrated recovered hematopoiesis (¹³⁷Cs: 900 cGy, n = 8; 950 cGy, n = 6; 1000 cGy, n = 7; 1050 cGy, n = 8; 1100 cGy, n = 5).

Figure 5.

X-ray irradiation with bone marrow transplant survival curve over 30 d. Mice that lived past 30 d lived to 90 d. (X-ray: 900 cGy, n = 7; 950 cGy, n = 6; 1000 cGy, n = 6; 1050 cGy, n = 6; 1100 cGy, n = 7)

Figure 6.

Percentage (mean ± SEM) of peripheral engraftment at 90 d after bone marrow transplantation with CD45.1 allotype donor. The only statistically significant difference (*, P = 0.008) in engraftment was between X-ray and ¹³⁷Cs irradiation at 1100 cGy.

Figure 7.

Percentage (mean ± SEM) of peripheral engraftment of donor B cells at 90 d after bone marrow transplantation with Cd45.1 allotype donor. Engraftment was significantly (*, P < 0.005) greater after ¹³⁷Cs irradiation than after X-ray irradiation at all exposure levels.

Figure 8.

Percentage (mean ± SEM) of peripheral engraftment of donor myeloid cells at 90 d after bone marrow transplantation with Cd45.1 allotype donor. Engraftment was significantly (*, P < 0.01) greater after ¹³⁷Cs irradiation than after X-ray irradiation at all exposure levels.

Figure 9.

Percentage (mean ± SEM) of peripheral engraftment of donor T cells at 90 d after bone marrow transplantation with Cd45.1 allotype donor. Engraftment was significantly (*, P < 0.05) greater after X-ray irradiation than after ¹³⁷Cs irradiation at exposure levels of 1000, 1050, and 1100 cGy.