Abstract
Targeting negative regulators downstream of the TCR represents a novel strategy to improve cancer immunotherapy. Two proteins that serve as critical inhibitory regulators downstream of the TCR are diacylglycerol kinase ζ (DGKζ), a regulator of Ras and PKC-θ signaling, and Casitas b-lineage proto-oncogene b (Cbl-b), an E3 ubiquitin ligase that predominantly regulates PI(3)K signaling. We sought to compare the signaling and functional effects that result from deletion of DGKζ, Cbl-b, or both (double knockout) in T cells and to evaluate tumor responses generated in a clinically relevant orthotopic pancreatic tumor model. We found that whereas deletion of Cbl-b primarily served to enhance NF-κB signaling, deletion of DGKζ enhanced TCR-mediated signal transduction downstream of Ras/Erk and NF-κB. Deletion of DGKζ or Cbl-b comparably enhanced CD8+ T cell functional responses, such as proliferation, production of IFN-γ, and generation of granzyme B when compared with wild type T cells. Double-knockout T cells demonstrated enhanced function above that observed with single-knockout T cells after weak, but not strong, stimulation. Deletion of DGKζ, but not Cbl-b, however, resulted in significant increases in numbers of activated (CD44hi) CD8+ T cells in both nontreated and tumor-bearing mice. DGKζ-deficient mice also had enhanced control of pancreatic tumor cell growth compared with Cbl-b–deficient mice. This represents a direct comparison between mice of these genotypes and suggests that T cell immunotherapies may be better improved by targeting TCR signaling molecules that are regulated by DGKζ as opposed to molecules regulated by Cbl-b.
Footnotes
This work was supported by National Institutes of Health Grant K08-CA151893 (to M.J.R.) and an American Cancer Society Institutional Award (to M.J.R.).
Abbreviations used in this article:
- Cbl-b
- Casitas b-lineage proto-oncogene b
- DAG
- diacylglycerol
- DGKζ
- diacylglycerol kinase ζ
- DKO
- double-knockout
- DN
- double negative
- DP
- double positive
- KO
- single-knockout
- LCMV
- lymphocytic choriomeningitis virus
- Treg
- regulatory T cell
- WT
- wild type.
The online version of this article contains supplemental material.
- Received October 9, 2017.
- Accepted March 12, 2018.
- Copyright © 2018 The Authors
This article is distributed under the terms of the CC BY 4.0 Unported license.