Use of a Humanized Mouse Model System in the Validation of Human Radiation Biodosimetry Standards

Abstract

After a planned or unplanned radiation exposure, determination of absorbed dose has great clinical importance, informing treatment and triage decisions in the exposed individuals. Biodosimetry approaches allow for determination of dose in the absence of physical measurement apparatus. The current state-of-the-art biodosimetry method is based on the frequency of induced dicentric chromosomes in peripheral blood T cells, which is proportional to the absorbed radiation dose. Since dose-response curves used for obtaining absorbed dose for humans are based on data sourced from in vitro studies, a concerning discrepancy may be present in the reported dose. Specifically, T-cell survival after in vitro irradiation is much higher than that measured in humans in vivo and, in addition, is not dose dependent over some dose ranges. We hypothesized that these differences may lead to inappropriately inflated dicentric frequencies after in vitro irradiation when compared with in vivo irradiation of the same samples. This may lead to underestimation of the in vivo dose. To test this hypothesis, we employed the humanized mouse model, which allowed direct comparison of cell depletion and dicentric frequencies in human T cells irradiated in vivo and in vitro. The results showed similar dicentric chromosome induction frequencies measured in vivo and in vitro when assessed 24 h postirradiation despite the differences in cell survival. These results appear to validate the use of in vitro data for the estimation of the absorbed dose in human radiation biodosimetry.

Development of the FAST-DOSE assay system for high-throughput biodosimetry and radiation triage

“…In the event of a radiological catastrophe, immediate triage would be accomplished through a combination of physical dosimetry, history of an individual's location, clinical signs and symptoms, and individual hematology assessment, along with other biodosimetry methods 34 . The development of FDA-approved biodosimeters for early population triage has the potential to save hundreds of thousands of lives following a mass-casualty nuclear disaster.…”

“…Previously, we used Hu-NSG mice as an alternative model to validate human radiation biodosimetry standards and used the human hematopoietic system to investigate candidate protein marker expression in vivo after radiation exposure 8,34 . In the present study, we engrafted NSG mice with human fetal CD34+ stem cells to enrich the number of human cells in the mouse blood 41 .…”

“…Peripheral whole blood samples were collected from each mouse by cardiac puncture using a heparin-coated syringe. Human leukocyte, T cell and B cell counts were determined by flow cytometry using 20 μL of heparinized blood following the standard flow cytometry (CytoFLEX, Beckman Coulter, Pasedena, CA) surface staining protocol as mentioned previously 5,34 . Blood cells were stained with the following human surface biomarkers: CD45, (white blood cell marker, clone HI30, Biolegend, San Diego, CA), CD3 (T cell marker, clone UCHT1; Biolegend), CD20 (B cell marker, clone 2H7; Biolegend).…”

“…Mice were successfully engrafted by 4–5 months and human cell engraftment was tested according to previous work 34 . X-ray irradiation was performed using X-RAD 320 biological irradiator (Precision X-Ray Inc., North Branford, CT) operated at 320 kVp, a current of 12.5 mA and dose rate of 0.88 Gy/min.…”

Cytogenetic Damage of Human Lymphocytes in Humanized Mice Exposed to Neutrons and X Rays 24 h After Exposure

“…The objective of the present work was to quantify chromosomal DNA damage in human T lymphocytes in vivo in hematopoietically humanized (Hu-NSG) mice [Lee et al, 2018;Pujol-Canadell et al, 2019] exposed to total body neutron (0.3 Gy) and X-ray (1 Gy) irradiations. Cytogenetic assays for MN and DIC were used to analyze chromosome aberrations in human T lymphocytes in vivo, 24 h after exposure.…”