Effect of CD28 costimulation on tumour killing by activated CD8 cytotoxic T cells.

Abstract

Due to their ability to differentiate tumour cells from healthy cells and induce cytotoxicity, cytotoxic T cells (CTLs) are key mediators of tumour immunity. Multiple attempts have been made to boost tumour immunity via enhancing CTL activity. One often explored route is the provision of costimulation, in particular, via the CD28 axis. CD28 is a key costimulatory receptor of T cells that is crucial in T cell activation, the process where naïve T cells become activated and differentiate into CTLs. Despite the interest around the therapeutic potential of CD28, its exact role in CTLs post activation is less defined.
In this study, we aim to study the effect of CD28 costimulation on the anti-tumour function of CTLs. CD28 stimulation was achieved via provision of its natural ligand CD86. In a co-culture of CTLs and tumour cells, we observed that CD86 expression on tumours did not enhance tumour killing, but slightly elevated IFN-γ production by CTLs, if a strong antigen stimulus is present. However, without a strong antigen tumour, both killing and IFN-γ production were elevated by ligation of CD86 to CD28.
Secondly, we also explored the synthetic CD28 costimulation, via the CD28/CD40 chimeric costimulatory antigen receptor (CoStAR). The CoStAR has been shown to enhance cytokine production and CTL survival in anti-tumour responses. Here we seek to investigate its mechanism of action, focusing on its impact on CTL actin dynamics and ability to couple with tumour targets. By engaging the CoStAR, CTLs formed more stable cell couples with their tumour targets at higher frequencies. There were some signs of CoStAR recruiting more actin filaments to the immune synapse, but the results were eventually inconclusive due to the small dataset and low statistical significance. When observing actin clearance from the interface centre as a proxy for increased cytolytic granule release, CoStAR engagement did not result in any significant enhancement. Strong antigen stimuli remained the main factor in inducing cytolytic granule release.

Date of Award	2 Jun 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Christoph Wuelfing (Supervisor) & Borko Amulic (Supervisor)