Evaluation of the Effects of 50 Hz Magnetic Field Exposure on the Human Hematopoietic System in Humanized Mice.

Accumulating evidence from experimental animal studies is essential for clarifying the causal relationship between exposure to power-frequency magnetic fields (MFs) and childhood leukemia. In this study, we developed a 50 Hz MF exposure system for experimental animals. To ensure uniform whole-body exposure of multiple animals placed at the center of the coil, we fabricated a Merritt-type coil. The maximum MF output inside the coil was 5 mT(rms), and spatial variation remained within ±2.5% of the target intensity. The system enabled stable exposure of experimental animals to uniform 50 Hz MFs while eliminating equipment-related artifacts. We then conducted exposure experiments using humanized mice, in which a human-like hematopoietic system was established by transplanting human hematopoietic stem and progenitor cells (HSPCs), to a 50 Hz, 5 mT(rms) MF for 2 months. After exposure, the chimerism rates of human leukocytes in hematopoietic organs of the MF-exposed group were comparable to those in the control group. Furthermore, exposure to the 50 Hz MF did not affect early differentiation of human B cells in the bone marrow of humanized mice. These findings support our previous in vitro results and validate the use of humanized mice for evaluating the effects of power-frequency MFs on human hematopoiesis. This system is expected to evaluate the effects of 50 Hz MFs not only on normal human hematopoiesis in humanized mice but also under abnormal conditions such as preleukemic state induced by transplanting genetically modified HSPCs.