PD-1+ and TIM-3+ T cells widely express common γ-chain cytokine receptors in multiple myeloma patients, and IL-2, IL-7, IL-15 stimulation up-regulates PD-1 and TIM-3 on T cells.

Background: Immune checkpoint ligand-receptor interactions appear to be associated with multiple myeloma (MM) progression. Simultaneously, previous studies showed the possibility of PD-1 and TIM-3 expression on T cells upon stimulation with common γ-chain family cytokines in vitro and during homeostatic proliferation. The aim of the present work was to study the impact of homeostatic proliferation on the expansion of certain T cell subsets up-regulating PD-1 and TIM-3 checkpoint molecules.

Methods: The expression of CD25, CD122, CD127 common γ-chain cytokine receptors, phosphorylated signal transducer and activator of transcription-5 (pSTAT5) and eomesodermin (EOMES) was comparatively assessed with flow cytometry in PD-1- and TIM-3-negative and positive T cells before the conditioning and during the first post-transplant month in peripheral blood samples of MM patients.

Results: Substantial proportions of PD-1- and TIM-3-positive T lymphocytes expressed common γ-chain cytokine receptors and pSTAT5. Frequencies of cytokine receptor expressing cells were significantly higher within TIM-3⁺ T cells compared to PD-1⁺TIM-3^- subsets. Considerable proportions of both PD-1-/TIM-3-negative and positive CD8⁺ T cells express EOMES, while only moderate frequencies of CD4⁺ PD-1⁺/TIM-3⁺ T cells up-regulate this transcription factor. Besides, the surface presence of CD25 and intranuclear expression of EOMES in CD4⁺ T cells were mutually exclusive regardless of PD-1 and TIM-3 expression. The stimulation with common γ-chain cytokines up-regulates PD-1 and TIM-3 during the proliferation of initially PD-1/TIM-3-negative T cells but fails to expand initially PD-1⁺ and TIM-3⁺ T cell subsets in vitro.

Conclusions: Both PD-1 and TIM-3 expressing T cells appear to be able to respond to homeostatic cytokine stimulation. Differences in common γ-chain cytokine receptor expression between PD-1⁺ and TIM-3⁺ T cells may reflect functional dissimilarity of these cell subsets. Checkpoint blockade appears to alleviate lymphopenia-induced proliferation of PD-1⁺ T cells but may raise the possibility of immune-mediated adverse events.