Immune Analysis of Radium-223 in Patients With Metastatic Prostate Cancer.

Background: Radium223 (Ra223) delivers high-energy radiation to osteoblastic metastasis of prostate cancer, resulting in irreparable double-stranded DNA damage. The effects of Ra223 on CD8+ T cell subsets in patients with prostate cancer is unknown.

Patients And Methods: Fifteen men with metastatic prostate cancer with clinical indication for Ra223 without any autoimmune or immune deficiency conditions were enrolled. Patients received a course of Ra223 50 kBq/kg. Concurrent use of prednisone ≤ 10 mg a day was allowed. Peripheral blood samples were collected before and 3 to 4 weeks after the first dose of Ra223 50 kBq/kg. Peripheral blood mononuclear cells were purified and analyzed for the phenotypic and functional characteristics of CD8 T cells using flow cytometry.

Results: One Ra223 treatment did not result in significant change in the overall frequencies of CD8 T cells and their subsets including naive, central memory, and effect memory cells. However, the mean frequency of programmed cell death protein 1-expressing EM CD8 T cells decreased after 1 Ra223 treatment from 20.6% to 14.6% (P = .020), whereas no significant change was observed in the frequencies of CD27-, CD28-, or CTLA4-expressing T cells. One Ra223 treatment was not associated with any significant change in the frequencies of CD8 T cells producing IFN-γ, TNF-α, and IL-13.

Conclusion: One Ra223 treatment is associated with a decreased mean frequency of programmed cell death protein 1-expressing effect memory CD8 T cell without affecting other immune checkpoint molecules or cytokine production. Further investigations are warranted to elucidate the immunologic and clinical significance of our observations and its long-term effects after multiple treatments.