The CD8+ memory T-cell state of readiness is actively maintained and reversible

Area of Science:

• Immunology
• Cell Biology
• T-cell differentiation

Background:

• Immunologic memory enables rapid adaptive immune responses upon re-exposure to antigens.
• Acquisition of memory T-cell function was previously considered an irreversible differentiation process.
• The role of cell-cell interactions in maintaining the memory T-cell state was unclear.

Purpose of the Study:

• To investigate whether memory T-cell function is maintained by continuous signaling.
• To determine the factors involved in sustaining the functional phenotype of memory T cells.
• To explore the reversibility of the memory T-cell state.

Main Methods:

• Depriving antigen-specific CD8 memory T cells of dendritic cell contact.
• Assessing T-cell proliferation, costimulation dependence, and interferon-gamma production.
• Analyzing cell-cycle state (G0 vs. G1) and transcription factor activity (Foxo1).
• Investigating the role of tumor necrosis factor receptor superfamily members (CD27, 4-1BB) and phosphatidylinositol-3 kinase signaling.
• Utilizing CD27-deficient mice infected with vesicular stomatitis virus.

Main Results:

• Memory T cells lost functional characteristics and reverted to a G0 cell-cycle state when deprived of dendritic cells.
• Reverted cells responded to stimulation like naive T cells, despite retaining memory surface markers.
• Memory T-cell maintenance required signaling via CD27 and 4-1BB.
• Foxo1 transcription factor activity was linked to T-cell quiescence and regulated by CD27 signaling.
• In vivo maintenance of memory T cells was impaired in CD27-deficient mice.

Conclusions:

• The functional phenotype of memory T cells is not fixed and requires active, continuous signaling for maintenance.
• Dendritic cell contact and specific signaling pathways (CD27, 4-1BB) are crucial for sustaining T-cell memory.
• Understanding these maintenance mechanisms could inform strategies for enhancing adaptive immunity.