Antioxidant activity of 2-mercaptoethanol protects against CD8+ T cell overstimulation or accelerated exhaustion: evidence from an in vitro exhausted CD8+ T model and in vivo adoptive cell transfer.

BACKGROUND

CD8+ T cell exhaustion in the tumor microenvironment acts as a barrier to tumor immunotherapy development. Therefore, studying that cell in vitro and in vivo is essential for developing a successful cancer immunotherapeutic drug.

METHODS

While repeated stimulation of CD8+ T cells in vitro is a must to acquire their exhaustion state, it is important to keep that to a limit that allows for exhaustion of the CD8+ T cells without accelerated cell death, so we can obtain enough exhausted CD8+ T cells to be studied. In the current study, we demonstrated the role of 2-mercaptoethanol (2-ME) as an essential media component by performing repeated CD8+ T cell stimulation with or without 2-ME.

RESULTS

In the absence of 2-ME, CD8+ T cell suffers from overstimulation that allows for their accelerated death. Mechanistically, the absence of 2-ME elevates the oxidative stress on the CD8+ T cells, leading to a shift in their metabolic pathways by adopting lipid peroxidation, which hastens CD8+ T cells' terminal differentiation and over-activates the AKT-mTOR signaling pathway, and finally, cell death. These findings were reflected in our in vivo experiment, where adoptive transfer of antigen-specific CD8+ T cells that have been in vitro activated without 2-ME experienced a lower tumor infiltration frequency and diminished stemness characteristics and effector functions.

CONCLUSION

Our study confirms the importance of 2-ME as a media component for CD8+ T cells stimulation and supports the potential of antioxidant agents to be used with immunotherapeutic agents to generate enhanced effects.