Nanoconfinement of microvilli alters gene expression and boosts T cell activation

Abstract

T cells sense and respond to their local environment at the nanoscale by forming small actin-rich protrusions, called microvilli, which play critical roles in signaling and antigen recognition, particularly at the interface with the antigen presenting cells. However, the mechanism by which microvilli contribute to cell signaling and activation is largely unknown. Here, we present a tunable engineered system that promotes microvilli formation and T cell signaling via physical stimuli. We discovered that nanoporous surfaces favored microvilli formation and markedly altered gene expression in T cells and promoted their activation. Mechanistically, confinement of microvilli inside of nanopores leads to size-dependent sorting of membrane-anchored proteins, specifically segregating CD45 phosphatases and T cell receptors (TCR) from the tip of the protrusions when microvilli are confined in 200-nm pores but not in 400-nm pores. Consequently, formation of TCR nanoclustered hotspots within 200-nm pores allows sustained and augmented signaling that prompts T cell activation even in the absence of TCR agonists. The synergistic combination of mechanical and biochemical signals on porous surfaces presents a straightforward strategy to investigate the role of microvilli in T cell signaling as well as to boost T cell activation and expansion for application in the growing field of adoptive immunotherapy.

Mechanosurveillance: Tiptoeing T Cells

“…In summary, it is evident that microvilli form a restricted reaction volume harboring the necessary molecules for T-cell activation. An exciting observation was recently made by Klotzsch and colleagues, who demonstrated the ability of the T cell to reach into narrowly confined spaces and who showcased the very dynamic nature of their microvillar protrusions and their ability to scan for occluded antigens ( 85 ). Interestingly, when T cells reached into micropits below 200 nm in diameter, a slight yet quantifiable antigen-independent cytokine upregulation started.…”

The solid tumor microenvironment—Breaking the barrier for T cells

“…[57,58] Our recent publication using nanoporous substrates, led to a strongly enhanced T cell activation and proliferation, compared to flat substrates. [59] Together the signal processes mediated through microvilli represent potential targets for immune therapies as well as to facilitate an enhanced tumor infiltration and killing capacity.…”

Understanding immune signaling using advanced imaging techniques

“…The triggering of the T-cell receptor (TCR) occurs within a few seconds of cell–cell contact [ 1 ], which involves reorganization of membrane proteins over 20–100 nm [ 3 ] and the fast motion of finger-like microvilli structures [ 4 , 5 ] that continuously change in shape [ 6 ]. These conditions all together present highly technical imaging challenges.…”