Breaking the rules? X-ray examination of hematopoietic stem cell grafts at international airports

Hematopoietic stem cells donated from unrelated subjects are increasingly used for restoration of bone marrow function after high-dose chemoradiotherapy for hematologic malignancies. Thus, thousands of stem cell grafts are transported via aviation by a courier, and, according to existing guidelines (eg, from the European Group for Blood and Marrow Transplantation1), they must not be exposed to the radiation of x-ray hand-luggage control systems at airports. Interestingly, we found no published data about the presumed adverse effect of x-rays emitted from hand-luggage control devices on the viability and proliferative capacity of the blood cells and their progenitors.

To change myths into facts, we exposed aliquots from peripheral blood progenitor cell collections (6 allogeneic, 5 autologous; mobilized by subcutaneous administration of granulocyte colony-stimulating factor) to radiation emitted from a widely used hand-luggage control device (HEIMANN HI-SCAN 6040A, Wiesbaden, Germany; radiation dosage 1.5 ± 0.6 μSv per single passage) at Innsbruck International Airport. After 0, 1, 2, 3, 5, and 10 passes through the x-ray device, the cells were checked for viability using trypan-blue dye exclusion. Mature hematopoietic progenitor cells (colony-forming cells [CFCs], including erythroid burst-forming units, granulocyte-macrophage colony-forming units, and megakaryocyte colony-forming units) and primitive progenitor cells (long-term culture-initiating cells) were enumerated in vitro as described.2 The in vitro expandability of the exposed mononuclear cells (MNCs) and CFCs was tested under serum-free conditions.3 After culturing the cells for 7 days in the presence of 1000 U/mL recombinant interleukin-2, we calculated the proliferation capacity of lymphocytes (T cells, natural killer [NK] cells) by fluorescence-activated cell-sorting analysis (CD3, CD56) and counting of the cells.

After up to 10 radiographical passes, neither cell viability nor the number of hematopoietic progenitor cells was affected (Table 1). The expandability of MNCs (no x-ray: 259 ± 108-fold, 5 passages: 285 ± 132-fold), of CFCs (no x-ray: 446 ± 223-fold, 5 passages: 495 ± 251-fold), of NK cells (no x-ray: 2.4 ± 0.3-fold, 1 passage: 2.4 ± 0.4-fold, 5 passages: 2.3 ± 0.3-fold, 10 passages: 2.4 ± 0.4-fold), and of T lymphocytes (no x-ray: 1.9 ± 0.2-fold, 1 passage: 1.9 ± 0.1-fold, 5 passages: 1.9 ± 0.2-fold, 10 passages: 1.8 ± 0.2-fold) was unaltered. Also, HLA-unrestricted (NK cell) cytotoxicity against the erythroleukemia cell line K562 (effector to target ratio 5:1 and 25:1) was comparable to that of the controls (Table 1). Endothelial cells could be generated from the irradiated samples (data not shown), indicating the preservation of progenitor cells with hematoendothelial differentiation capacity.4 These data suggest that the radiation emitted from hand-luggage security-check devices exerts no harmful effect on the cellular content of hematopoietic stem cell grafts.

The exposure of airplane personnel to radiation from extraterrestrial sources is 3 to 6 mSv/y, compared with 1 mSv at ground5 (a sievert [Sv] is a measure of the total radioactive dose, factoring in each type of radiation and its energy), and this may increase the incidence of malignant diseases. The risk of developing acute leukemia is 5.1-fold in those flying more than 5000 hours.6Pilots (and accordingly, their bone marrow) are exposed to a radiation dose of 60 μSv during a 10-hour flight, a dose that is roughly equivalent to 40 hand-luggage controls. Assuming 5 connecting flights, the radiation dose applied to hematopoietic stem cell grafts is 67.5 μSv (7.5 μSv in 5 security checks plus 60 μSv during a 10-hour overseas flight). This is approximately 1.3% of the dose acquired by pilots every year.

Only vigorously instructed personnel are authorized to obtain, handle (ie, couriers), and deliver hematopoietic stem cell transplants to human beings. Couriers are instructed by international guidelines to refuse the checking of stem cell transplants by means of x-ray–assisted devices. Thus, unsatisfying discussions are frequently entailed, ultimately resulting in the visual and tactual inspection of the graft by security staff who are unskilled to handle vital human organs. On the other hand, thick-walled containers containing human organs may be targets for bootlegging illegal goods or weapons. Our data suggest that the radiation emitted from x-ray hand-luggage control systems at airports does not harm the cellular components of peripheral blood stem cell grafts. Thus, a customary examination using x-ray devices should facilitate the delivery of stem cell grafts and minimize the risk for the graft, for the people obliged to check this, as well as for the passengers joining the flights.

We thank Ewald Dworschak and the security staff of the Innsbruck International Airport for their help.