This 2019 worldwide discussion among 18 experts concerned T cell exhaustion:
“‘T cell exhaustion’ is a broad term that has been used to describe the response of T cells to chronic antigen stimulation, first in the setting of chronic viral infection but more recently in response to tumours.
Key questions remain about the potential to reverse the epigenetic programme of exhaustion and how this might affect the persistence of T cell populations.”
There were nearly a dozen viewpoints on even “What do we mean by T cell exhaustion and/or dysfunction and how would you define this state?” 🙂
Answers to the question “What are the key controversies and outstanding research questions?” included:
- “What are the cellular signalling and transcriptional pathways that drive the conversion to an exhausted T cell phenotype, and how can the chromatin and transcriptional changes of exhaustion be reversed in individual exhausted cells?
- Whether and how we can manipulate signalling pathways to both activate and maintain T cell responses remain open questions, as does the question of whether pharmacological manipulations can reverse the epigenetic changes associated with exhaustion versus expand less-exhausted populations.
- We need to define better the effects of the microenvironment on the induction of T cell exhaustion, the developmental trajectories of exhaustion and the point at which and extent to which exhaustion can be reversed. Understanding the consequences of unleashing T cells from exhaustion will also be crucial to designing the most effective therapeutic interventions.
- When and how exhausted T cell populations are formed. The original view that they are terminally differentiated descendants of formerly ‘normal’ effector T cells has been challenged.
- Whether the predysfunctional T cells themselves, or their more differentiated (and phenotypically dysfunctional) progeny, form the ultimate effector pool for control of human tumours.
- How do the functions and states (subpopulations) of exhausted T cells change over time? Can the epigenetic state of exhaustion be reversed to form true effector or memory T cells, and is this required for improved cancer immunotherapy?
- There is no definitive marker for exhausted T cells, although TOX may prove to be useful. Transcriptional profiles are informative, but epigenetic changes are more specific and robust. A major clinical question is whether exhausted T cells can be, or indeed need to be, reprogrammed to achieve therapeutic benefit.”
https://www.nature.com/articles/s41577-019-0221-9 “Defining ‘T cell exhaustion'” (not freely available)