Coadministration of a Clinically Relevant Dexamethasone Dosage With Ablative Radiation Therapy Reduces Peripheral Lymphocytes But Does Not Alter In Vivo Intratumoral Lymphocyte Phenotype or Inhibit Efficacy of Radiation Therapy in a Murine Colorectal Tumor Model.

PURPOSE: Dexamethasone is commonly given during radiation therapy (RT) to manage toxicities. Our study examines if dexamethasone coadministration with RT inhibits the RT-induced antitumor T cell response in mouse. METHODS AND MATERIALS: Intramuscularly implanted MC38 tumors were irradiated with 15 Gy after establishing for 7 days. Tumor bearing mice were administered dexamethasone using multiple schedules and doses. Peripheral lymphocyte reduction was monitored by complete blood count and intratumoral and tumor draining lymph node (tdLN) populations by flow cytometry. Effector phenotype and function of ex vivo stimulated tumor-infiltrating lymphocytes (TILs) and naïve splenocytes as well as in vivo TILs with or without dexamethasone were monitored by flow cytometry and ELISA. RESULTS: Long course high dose, short course high dose, and short course human equivalent dose dexamethasone reduced peripheral lymphocytes yet did not inhibit survival after irradiation. Short course high dose administration decreased TIL and tdLN lymphocyte activation as well as tdLN mass but did not affect TIL frequencies or change tdLN cell population composition. Dexamethasone inhibited effector function of ex vivo stimulated naïve splenocytes and TILs, but magnitude of IFN-γ secretion was consistently higher in TILs regardless of dexamethasone dose. In vivo analysis of TILs after irradiation and HE dexamethasone treatment showed that TILs had a similar effector phenotype compared with vehicle controls. CONCLUSIONS: Dexamethasone reduces blood and tdLN lymphocytes. Dexamethasone also suppresses TIL activation/effector function yet does not affect survival in irradiated MC38 tumor bearing mice, which depend on RT-induced immune responses for therapy efficacy. Additional study in human subjects is warranted.

Role of Axl in T-Lymphocyte Survival in Salt-Dependent Hypertension.

OBJECTIVE: Survival of immune and nonimmune cells relies on Axl, a receptor tyrosine kinase, which is implicated in hypertension. Activated T lymphocytes are involved in regulation of high blood pressure. The goal of the study was to investigate the role of Axl in T-lymphocyte functions and its contribution to salt-dependent hypertension. APPROACH AND RESULTS: We report increased apoptosis in peripheral blood from Axl(-/-) mice because of lower numbers of white blood cells mostly lymphocytes. In vitro studies showed modest reduction in interferon gamma production in Axl(-/-) type 1 T helper cells. Axl did not affect basic proliferation capacity or production of interleukin 4 in Axl(-/-) type 2 T helper cells. However, competitive repopulation of Axl(-/-) bone marrow or adoptive transfer of Axl(-/-) CD4(+) T cells to Rag1(-/-) mice showed robust effect of Axl on T lymphocyte expansion in vivo. Adoptive transfer of Axl(-/-) CD4(+) T cells was protective in a later phase of deoxycorticosterone-acetate and salt hypertension. Reduced numbers of CD4(+) T cells in circulation and in perivascular adventitia decreased vascular remodeling and increased vascular apoptosis in the late phase of hypertension. CONCLUSIONS: These findings suggest that Axl is critical for survival of T lymphocytes, especially during vascular remodeling in hypertension.

Role of Axl in early kidney inflammation and progression of salt-dependent hypertension.

The Gas6/Axl pathway regulates many cell functions and is implicated in hypertension. In this study, we aimed to investigate the role of Axl in immune cells on initiation and progression of salt-dependent hypertension. Deoxycorticosterone acetate (75 mg/60 days release)-salt hypertension was induced for 1 week or 6 weeks in Axl chimeras generated by bone marrow transplant to restrict Axl deficiency to hematopoietic or nonhematopoietic compartments. Depletion of Axl in hematopoietic cells (Axl(-/-) →Axl(+/+)) reduced (133 ± 2 mm Hg) increase in systolic blood pressure compared with other Axl chimeras (≈150 mm Hg) 1 week after deoxycorticosterone acetate-salt. Urine protein and renal oxidative stress were lowest in Axl(-/-) →Axl(+/+) at 1 week after deoxycorticosterone acetate-salt. Compensatory increase in Gas6 in kidneys of recipient Axl(-/-) may affect kidney function and blood pressure in early phase of hypertension. Flow cytometry on kidneys from Axl(-/-) →Axl(+/+) showed increase in total leukocytes, B, and dendritic cells and decrease in macrophages compared with Axl(+/+) →Axl(+/+). These immune changes were associated with decrease in proinflammatory gene expression, in particular interferon γ. Systolic blood pressure returned to baseline in Axl(-/-) →Axl(+/+) and Axl(-/-) →Axl(-/-) but remained increased in Axl(+/+) →Axl(+/+) and Axl(+/+) →Axl(-/-) chimeras after 6 weeks of deoxycorticosterone acetate-salt. Vascular apoptosis was increased in the global Axl(-/-) chimeras in the late phase of hypertension. In summary, we found that expression of Axl in hematopoietic cells is critical for kidney pathology in early phase of salt-dependent hypertension. However, Axl in both hematopoietic and nonhematopoietic lineages contributes to the late phase of hypertension.