Carla Fowler

Peripheral CD8+ T cell tolerance to self-proteins is regulated proximally at the T cell receptor.

CD8(+) T cell tolerance, although essential for preventing autoimmunity, poses substantial obstacles to eliciting immune responses to tumor antigens, which are generally overexpressed normal proteins. Development of effective strategies to overcome tolerance for clinical applications would benefit from elucidation of the immunologic mechanism(s) regulating T cell tolerance to self. To examine how tolerance is maintained in vivo, we engineered dual-T cell receptor (TCR) transgenic mice in which CD8(+) T cells recognize two distinct antigens: a foreign viral-protein and a tolerizing self-tumor protein. Encounter with peripheral self-antigen rendered dual-TCR T cells tolerant to self, but these cells responded normally through the virus-specific TCR. Moreover, proliferation induced by virus rescued function of tolerized self-tumor-reactive TCR, restoring anti-tumor activity. These studies demonstrate that peripheral CD8(+) T cell tolerance to self-proteins can be regulated at the level of the self-reactive TCR complex rather than by central cellular inactivation and suggest an alternate strategy to enhance adoptive T cell immunotherapy.

Abrogation of Src Homology Region 2 Domain-Containing Phosphatase 1 in Tumor-Specific T Cells Improves Efficacy of Adoptive Immunotherapy by Enhancing the Effector Function and Accumulation of Short-Lived Effector T Cells In Vivo

T cell expression of inhibitory proteins can be a critical component for the regulation of immunopathology owing to self-reactivity or potentially exuberant responses to pathogens, but it may also limit T cell responses to some malignancies, particularly if the tumor Ag being targeted is a self-protein. We found that the abrogation of Src homology region 2 domain-containing phosphatase-1 (SHP-1) in tumor-reactive CD8+ T cells improves the therapeutic outcome of adoptive immunotherapy in a mouse model of disseminated leukemia, with benefit observed in therapy employing transfer of CD8+ T cells alone or in the context of also providing supplemental IL-2. SHP-1−/− and SHP-1+/+ effector T cells were expanded in vitro for immunotherapy. Following transfer in vivo, the SHP-1−/− effector T cells exhibited enhanced short-term accumulation, followed by greater contraction, and they ultimately formed similar numbers of long-lived, functional memory cells. The increased therapeutic effectiveness of SHP-1−/− effector cells was also observed in recipients that expressed the tumor Ag as a self-antigen in the liver, without evidence of inducing autoimmune toxicity. SHP-1−/− effector CD8+ T cells expressed higher levels of eomesodermin, which correlated with enhanced lysis of tumor cells. Furthermore, reduction of SHP-1 expression in tumor-reactive effector T cells by retroviral transduction with vectors that express SHP-1–specific small interfering RNA, a translatable strategy, also exhibited enhanced antitumor activity in vivo. These studies suggest that abrogating SHP-1 in effector T cells may improve the efficacy of tumor elimination by T cell therapy without affecting the ability of the effector cells to persist and provide a long-term response.

SHP-1 in T Cells Limits the Production of CD8 Effector Cells without Impacting the Formation of Long-Lived Central Memory Cells

During responses against viruses and malignancies, naive CD8 T lymphocytes expand to form both short-lived effector cells and a population containing cells with the potential to be long-lived and participate in memory responses (memory precursor effector cells). The strength of antigenic, costimulatory, and cytokine signals during responses impacts the magnitude and type of CD8 populations formed. In vitro studies have revealed that the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1 (SHP-1) regulates signal transduction from receptors on T cells including the TCR, helping set the activation threshold, and therefore may shape responses of mature CD8 T cells in vivo. Analysis of CD8 T cells from motheaten mice, which are globally deficient in SHP-1, proved problematic due to cell-extrinsic effects of SHP-1 deficiency in non-T cells on CD8 T cells. Therefore, a conditional knockout of SHP-1 in mature single-positive T cells was developed to analyze cell-intrinsic consequences of complete and partial SHP-1 deficiency on CD8 T cell responses to acute viral infection. The results demonstrated that SHP-1 has disparate effects on subpopulations of responding cells, limiting the magnitude and quality of primary and secondary responses by reducing the number of short-lived effector cells generated without affecting the size of the memory precursor effector cell pool that leads to formation of long-term memory.