Recovery from severe immunosuppression requires hematopoietic stem cell reconstitution and effective thymopoiesis to restore a functional immune cell repertoire. Herein, a model of immune cell reconstitution consequent to potentially lethal doses of irradiation is described, which may be valuable in evaluating potential medical countermeasures. Male rhesus macaques were total body irradiated by exposure to 6.00 Gy 250 kVp x-radiation (midline tissue dose, 0.13 Gy min−1), resulting in an approximate LD10/60 (n = 5/59). Animals received medical management, and hematopoietic and immune cell recovery was assessed (n ≤ 14) through 370 d post exposure. A subset of animals (n ≤ 8) was examined through 700 d. Myeloid recovery was assessed by neutrophil and platelet-related parameters. Lymphoid recovery was assessed by the absolute lymphocyte count and FACS-based phenotyping of B- and T-cell subsets. Recent thymic emigrants were identified by T cell receptor excision circle quantification. Severe neutropenia, lymphopenia, and thrombocytopenia resolved within 30 d. Total CD3+ cells μL−1 required 60 d to reach values 60% of normal, followed by subsequent slow recovery to approximately normal by 180 d post irradiation. Recovery of CD3+4+ and CD3+8+ cell memory and naïve subsets were markedly different. Memory populations were ≥ 100% of normal by day 60, whereas naïve populations were only 57% normal at 180 d and never fully recovered to baseline post irradiation. Total (CD20+) B cells μL−1 were within normal levels by 77 d post exposure. This animal model elucidates the variable T- and B-cell subset recovery kinetics after a potentially lethal dose of total-body irradiation that are dependent on marrow-derived stem and progenitor cell recovery, peripheral homeostatic expansion, and thymopoiesis.
*University of Maryland, School of Medicine, Dept. of Radiation Oncology, Baltimore, MD; †NIAID Integrated Research Facility, Frederick, MD.
The authors declare no conflicts of interest.
For correspondence contact: Ann M. Farese, 10 S. Pine Street, MSTF Rm 6‐34D, Baltimore, MD 21201, or email at email@example.com.
This project has been funded in whole or in part with Federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under R01 A167503‐1. Authors gratefully acknowledge the superb technical assistance of Carrie Redinger, Michael E. Flynn, and all the members of our Preclincial Radiobiology Laboratory for their dedication to the health and wellbeing of our animals.
(Manuscript accepted 26 June 2015)