12 - Prospective Study of Changes in Circulating Immune Regulatory Cells in Infants with Hypoxic Ischemic Encephalopathy Undergoing Therapeutic Hypothermia.

Poster Number: 12
Publication Number: 12.510

Background: Hypoxic ischemic encephalopathy (HIE) is the leading cause of acquired neonatal brain injury in Canada, commonly resulting in cerebral palsy, developmental delays, and/ or death. In HIE, perinatal disruption of oxygenation to the brain triggers a potent secondary inflammatory cascade, causing neuronal cell death. Immature myeloid cells which expand under inflammatory conditions, exert profound anti-inflammatory responses and may dampen this secondary neuronal cell death. At birth, there are high numbers of circulating CD34+ hematopoietic stem/progenitor and immune-regulatory cells which soon exit circulation in healthy newborns. We postulate that these potently immunosuppressive populations can be manipulated to reduce the inflammatory cascade in HIE to provide an adjuvant strategy to therapeutic hypothermia (TH).

Objective: We aim to investigate the feasibility of using myeloid growth factors, such as G-CSF, to expand/prolong circulation of CD34+ cells allowing the delivery of immune-regulatory signals to the brain during the critical period of post-hypoxia inflammation. We measured circulating CD34+ and immune regulatory cells to establish baselines for an interventional trial of G-CSF-induced expansion of autologous regulatory myeloid cells.

Design/Methods: Nineteen infants with HIE treated by TH were enrolled. Circulating CD34+ and immune-regulatory cells were measured daily over four time points during cooling and after rewarming by flow cytometry. The degree of brain injury was scored by standard scoring published by Weeke et al.

Results: Of the 19 infants, 3 (16%), 14 (74%), and 2 (10%) presented with mild, moderate, and severe encephalopathy respectively. Granulocytic myeloid-derived suppressor cells (G-MDSCs) (CD15/HLA-DR-/LOX-1+), normally not in circulation, are present at birth (avg =1689, range=394-3887 cells/µl) and decline (avg= 371, range=112-727 cells/µl; p<.05) by 96 hours. This suppressive population seems to be elevated in HIE infants with severe brain injury compared to those with less injury. Monocytic myeloid-derived suppressor cells (M-MDSCs) (CD33+, CD14+, HLA-DR-) are also elevated compared to healthy individuals and remain stable over the cooling period (avg. = 212 cells/µl, range = 6 cells/ µl - 1175 cells/ µl).

Conclusion(s): Our findings confirm the persistence of immune regulatory cells which correlates with the severity of brain injury. Next steps would be to explore supplemental G-CSF administration as a tool to amplify the regulatory phenotype of these cells as an autologous cellular approach to minimize the second phase of inflammatory toxicity in these infants.