CD8 T cell responses to viral infections and tumors contribute significantly to the immune responses that
dictate the clinical outcomes of such pathologies. The functional integrity of CD8 T cell responses depends on
the characteristic properties of CD8 effector (Teff) and memory (Tmem) populations. However, during chronic
viral infections and cancer, antigen persistence without clearance precludes effective Teff and Tmem
development, instead biasing CD8 T cell differentiation towards an epigenetically distinct “exhausted” lineage
(Tex). Tex exhibit progressive dysfunction and loss of effector properties, proliferation capacity, and memory
potential, as well as a sustained increase in co-expression of PD1 and multiple other inhibitory receptors (IRs).
Interrogating the fundamental mechanisms that initiate and maintain the Tex epigenetic state is of central
importance to understanding Tex biology and identifying strategies to selectively target or modulate Tex.
However, the field generally lacks a detailed mechanistic understanding of Tex-specific epigenetic processes. In
models of exhaustion during chronic infection and of dysfunctional tumor-specific T cells, the transcription factor
TOX is essential for the initiation of Tex development, repressing terminal Teff differentiation and potentiating
epigenetic commitment to the Tex lineage. This proposal seeks to identify and interrogate the mechanistic details
of Tex regulation by TOX that would be required to begin developing immunotherapy approaches to
epigenetically reprogram Tex and improve immunotherapy clinical outcomes.
The molecular transactions TOX employs to exert its effects remain largely unknown. Understanding the details
of TOX activity remains limited by a lack of functional characterization of its N- and C-terminal domains (“NTD”
and “CTD”) in relation to its HMG-box DNA binding domain. My preliminary data demonstrate in vitro that loss of
either the TOX NTD or CTD is sufficient to abrogate the increase in surface PD1 expression that is
characteristically driven by full-length (“FL”) TOX, suggesting important, as yet unknown roles for these domains.
The central hypothesis of this proposal is that distinct features of TOX activity are attributable to its N-
vs. C-terminal domains and that NTD- or CTD-specific perturbations will enable selective modulation of
Tex responses to chronic viral infection. This proposal tests this hypothesis by interrogating features of TOX’s
interactions and domain-level function at the Pdcd1 locus (encoding PD1), by defining the extent to which the
NTD and CTD exhibit global differences in their Tex-specific roles, by defining how the NTD and CTD program
the Tex epigenetic state, and by determining which NTD- and CTD-mediated protein interactions TOX uses to
regulate Tex transcription. This proposal will thus advance fundamental knowledge of how the molecular
processes regulating exhaustion may be manipulated to improve CD8 T cell responses during chronic viral
infections and cancer.