Cytokines for Immune Protection from Acute Irradiation

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The threat of terrorist attacks involving radioactive material and the potential for radiation accidents require the development of improved treatment strategies for victims of radiation exposure. Hematopoietic cells are highly sensitive to radiation damage, and their loss after radiation exposure results in lethal infections. Development of treatment that prevents immune damage from radiation and reconstitutes immune function after radiation exposure would be a significant advance. The aim of this project is to study four promising, clinical-grade cytokines that are likely to significantly improve immune reconstitution after lethal dose irradiation in the well-established dog model. The four cytokines are fms-like tyrosine kinase-3 ligand (Flt3 ligand [FL]), keratinocyte growth factor (KGF), interleukin (IL)-7, and transferrin (Tf) given alone or in combination either before or after exposure to lethal doses of total body irradiation (TBI). All four cytokines have anti-apoptotic activity after gamma irradiation and have direct or indirect beneficial effects on lymphocytes and other immune cells. We will study these cytokines in the dog since (1) the dog model of radiation exposure and hematopoiesis has been highly predictive of human clinical outcomes, (2) there is extensive preliminary data with cytokines for radioprotection of the dog after acute radiation, (3) all four of the human cytokines we have proposed are cross-reactive in the dog, and (4) these cytokines have been studied in humans and are in various stages of clinical development. The goal is to achieve survival of dogs after an otherwise lethal dose of irradiation with sustained immune reconstitution without hematopoietic stem cell (HSC) transplantation. In Specific Aim 1, cytokines will be given after TBI and in Specific Aim 2, cytokines will be given before and after TBI. In Aim 1, we will give 500 cGy TBI and treat dogs with G-CSF plus each study cytokine. In this model, a radioprotective cytokine is defined as achieving significantly improved survival compared to G-CSF alone. In the subsequent experiments, the TBI dose will be successively increased by 100 cGy increments and dogs will be treated with a combination of radioprotective cytokines. The primary endpoint is recovery of hematopoiesis and survival beyond day 30. The secondary endpoint is immune reconstitution. Upon study completion, we will have identified the optimal cytokine treatment and the highest dose of TBI that can be reliably survived without HSC support.