Delivery of IL-2 to the T Cell Surface Through Phosphatidylserine Permits Robust Expansion of CD8 T Cells.

Alana Macdonald,T.-C Wu,Louise Ferrall,Brandon Lam,Ya Chea Tsai,John Lin,Yu Jui Kung,Chien-Fu Hung

doi:10.3389/fimmu.2021.755995

Alana Macdonald, T.-C Wu + Show 6 more

Open Access

https://doi.org/10.3389/fimmu.2021.755995

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Abstract

The phospholipid phosphatidylserine (PS) is naturally maintained on the cytoplasmic side of the plasma membrane. Independent of apoptosis, PS is redistributed to the surface of CD8 T cells in response to TCR-mediated activation. Annexin V (AnnV) is a protein known to bind PS with high affinity and has been effectively utilized to anchor antigen to the surface of CD8 T cells. To expand these studies, we aimed to exploit TCR activation driven PS exposure as a target to deliver cytokine, namely interleukin-2 (IL-2), to the surface of CD8 T cells. This was accomplished using a novel chimeric fusion protein of annexin V and interleukin 2 (AnnV-IL2). In vitro analysis revealed that AnnV-IL2 is able to specifically bind PS on the T cell surface following TCR stimulation. Consequently, AnnV-IL2 proved to be significantly more effective at enhancing T cell activation compared to recombinant IL-2. In vivo, AnnV-IL2 promotes robust expansion of antigen-specific cells capable of interferon gamma (IFNγ) production when administered following peptide vaccination. Importantly, upon antigen rechallenge, AnnV-IL2 treatment mice demonstrated a stronger secondary expansion, indicating durability of AnnV-IL2 mediated responses. Our data supports the use of AnnV-IL2 to modulate antigen-specific T cell immunity and demonstrates that the PS-AnnV axis is a feasible mechanism to target diverse cargo to CD8 T cells.

Highlights

The adaptive immune system is critical for defense against pathogens and providing long-term immunological protection
We utilized naïve CD8 T cells isolated from murine spleens and lymph nodes and in vitro generated memory cells to understand how both cell types respond to T cell receptor (TCR) stimulation
Both antigen inexperienced and experienced cells upregulated CD69, a marker of early T cell activation, and Annexin V (AnnV) staining indicated that PS was externalized following TCR crosslinking (Figure 1A)

Summary

Introduction

The adaptive immune system is critical for defense against pathogens and providing long-term immunological protection. CD8 and CD4 T cells are an important arm of the adaptive immune system and the T cell repertoire is incredibly diverse with the potential for 107-108 unique T cell receptors poised to respond to a pathogenic challenge [1]. CD8 T cells function to recognize and remove infected and malignant cells through antigen receptor mediated recognition of peptides presented on MHC class I molecules (pMHC). The local cytokine milieu present during T cell priming is commonly referred to as “signal 3” and helps skew CD4 and CD8 T cells to the appropriate effector cell phenotype to. High concentrations of IL-2 present during antigen receptor activation is associated with the development of a shortlived, terminal effector cell phenotype, while in contrast, low concentrations of IL-2 are associated with the formation of longlived memory cells [4]

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