Immune checkpoint protein and cytokine expression by T lymphocytes in pleural effusion of cancer patients receiving anti-PD-1 therapy.

Objectives: Pleural effusion (PE) occasionally develops in cancer patients during treatment with antibodies to programmed cell death-1 (PD-1) or to its ligand PD-L1 (hereafter, αPD-1 therapy). Such effusion often contains infiltrated mononuclear cells, although the types of immune cell present as well as the outcome of such patients have remained unclear.
Materials and Methods: We performed a multi-institutional, observational study to examine the clinical outcome of patients who develop PE after the onset of αPD-1 therapy. We compared the immune cell profiles and the immune status of lymphocytes in PE as determined by flow cytometry between nine patients who developed effusion during αPD-1 therapy (αPD-1 group) and 15 patients who developed PE during treatment with other anticancer agents (control group).
Results: Most mononuclear cells in PE were lymphocytes in both the αPD-1 and control groups. The frequency of both CD4 ⁺ and CD8 ⁺ T lymphocytes expressing the immune checkpoint proteins TIM-3 or TIGIT as well as that of CD8 ⁺ T lymphocytes expressing PD-L1 were increased in the αPD-1 group compared with the control group. αPD-1 therapy continued for a substantial period after the emergence of PE in six of the nine patients in the αPD-1 group, and the frequency of CD4 ⁺ T lymphocytes in PE expressing the immune checkpoint protein LAG-3 or the cytokine interkeukin-17 was lower for these patients than for those who did not receive a sustained treatment benefit.
Conclusion: Our results suggest a clinical benefit of continuing αPD-1 therapy in some patients who develop PE. We found that infiltrating T lymphocytes in PE manifest a more exhausted phenotype during αPD-1 therapy than during treatment with other cancer drugs, with subpopulations of these cells characterized by specific immune checkpoint protein and cytokine expression profiles possibly contributing to the antitumor immune response.
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