The depths of PD-1 function within the tumor microenvironment beyond CD8⁺ T cells

Area of Science:

• Immunology and Cancer Research
• Cellular and Molecular Medicine

Background:

• Programmed cell death-1 (PD-1; CD279) is a key immune checkpoint receptor expressed on various immune cells.
• While PD-1's role in CD8+ T cells is well-studied, its function in other immune cells remains less understood.
• Current PD-1 based therapies primarily focus on enhancing CD8+ T cell responses in cancer.

Purpose of the Study:

• To review the role and therapeutic potential of PD-1 in non-CD8+ T cell-mediated anti-cancer immunity.
• To explore PD-1 expression and function in CD4+ T helper cells, myeloid cells, and innate lymphoid cells (ILCs).
• To guide patient stratification for PD-1 based therapies by understanding immune cell-specific PD-1 functions.

Main Methods:

• Literature review of fundamental and translational studies on PD-1 expression and function.
• Analysis of PD-1's role in various non-CD8+ immune cell subsets within the tumor microenvironment.
• Discussion of therapeutic strategies to leverage PD-1 in T cell-independent anti-cancer responses.

Main Results:

• PD-1 plays a significant role in modulating immune responses beyond CD8+ T cells.
• Understanding PD-1's function in CD4+ T cells, myeloid cells, and ILCs is crucial for comprehensive cancer immunotherapy.
• PD-1 based therapies can be optimized to enhance diverse immune cell-mediated anti-tumor activities.

Conclusions:

• Targeting PD-1 in non-CD8+ immune cells offers a promising strategy to broaden the efficacy of cancer immunotherapies.
• Tailoring PD-1 based treatments based on immune cell-specific PD-1 activity can improve outcomes for various cancers.
• Further research into PD-1's role in innate and adaptive non-CD8+ immune cells will unlock new therapeutic avenues.