PHA eludes macrophage suppression to activate CD8⁺ T cells

Area of Science:

• Immunology
• Cancer Biology
• Cellular Immunology

Background:

• Tumor microenvironments often contain immune-suppressive cells and molecules that hinder anti-cancer responses.
• Activating T cells to combat cancer within these suppressive conditions is a significant challenge.
• Previous work showed T cell receptor (TCR) ligation fails to activate T cells in C57BL/6 J peritoneal cell cultures unless interferon-gamma (IFNγ) is neutralized or inducible nitric oxide synthase (iNOS) is inhibited.

Purpose of the Study:

• To investigate alternative methods for T cell activation in immune-suppressive tumor microenvironments.
• To evaluate the potential of phytohemagglutinin (PHA) as a T cell activator in macrophage-dense models.
• To explore the role of macrophages in PHA-mediated T cell expansion.

Main Methods:

• Utilized C57BL/6 J peritoneal cell culture models mimicking macrophage-dense tumors.
• Tested phytohemagglutinin (PHA) for T cell activation, comparing it to T cell receptor (TCR) ligation.
• Assessed T cell expansion, interferon-gamma (IFNγ) production, PD-L1 expression, and cell binding (macrophages and CD44hi T cells) to PHA.
• Investigated the effect of peritoneal cells on spleen T cell responses to PHA.

Main Results:

• Phytohemagglutinin (PHA) markedly expanded CD8 T cells without requiring IFNγ neutralization or iNOS inhibition.
• PHA induced lower IFNγ production and PD-L1 expression compared to TCR ligation.
• Macrophages and CD44hi T cells demonstrated binding to PHA.
• Peritoneal cells significantly enhanced PHA-induced spleen T cell responses, indicating macrophages promote T cell expansion.

Conclusions:

• Phytohemagglutinin (PHA) is a potent mitogen for expanding CD8 T cells in macrophage-dense environments.
• PHA may offer a strategy to enhance anti-tumor immunity by overcoming immune suppression.
• Macrophages play a crucial role in augmenting PHA-driven T cell expansion.