Deletion of the protein tyrosine phosphatase PTPN22 for adoptive T cell therapy facilitates CTL effector function but promotes T cell exhaustion.

BACKGROUND: Adoptive cell therapy (ACT) is a promising strategy for treating cancer, yet it faces several challenges such as lack of long-term protection due to T cell exhaustion induced by chronic TCR stimulation in the tumor microenvironment. One benefit of ACT, however, is that it allows for cellular manipulations, such as deletion of the phosphotyrosine phosphatase non-receptor type 22 (PTPN22), which improves CD8+ T cell antitumor efficacy in ACT. We tested whether Ptpn22KO cytolytic T cells (CTLs) were also more effective than Ptpn22WT CTL in controlling tumors in scenarios that favor T cell exhaustion. METHODS: Tumor control by Ptpn22WT and Ptpn22KO CTL was assessed following adoptive transfer of low numbers of CTL to mice with subcutaneously implanted MC38 tumors. Tumor infiltrating lymphocytes were isolated for analysis of effector functions. An in vitro assay was established to compare CTL function in response to acute and chronic restimulation with antigen-pulsed tumor cells. The expression of effector and exhaustion-associated proteins by Ptpn22WT and Ptpn22KO T cells was followed over time in vitro and in vivo using the ID8 tumor model. Finally, the effect of PD-1 and TIM-3 blockade on Ptpn22KO CTL tumor control was assessed using monoclonal antibodies and CRISPR/Cas9-mediated knockout. RESULTS: Despite having improved effector function at the time of transfer, Ptpn22KO CTL became more exhausted than Ptpn22WT CTL, characterized by more rapid loss of effector functions, and earlier and higher expression of inhibitory receptors (IRs), particularly the terminal exhaustion marker TIM-3. TIM-3 expression, under the control of the transcription factor NFIL3, was induced by IL-2 signaling which was enhanced in Ptpn22KO cells. Antitumor responses of Ptpn22KO CTL were improved following PD-1 blockade in vivo, yet knockout or antibody-mediated blockade of TIM-3 did not improve but further impaired tumor control, indicating TIM-3 signaling itself did not drive the diminished function seen in Ptpn22KO CTL. CONCLUSIONS: This study questions whether TIM-3 plays a role as an IR and highlights that genetic manipulation of T cells for ACT needs to balance short-term augmented effector function against the risk of T cell exhaustion in order to achieve longer-term protection.

Emerging Role of EGFR Mutations in Creating an Immune Suppressive Tumour Microenvironment.

Several types of tumours overexpress the Epidermal Growth Factor Receptor (EGFR) in either wild type or mutated form. These tumours are often highly aggressive and difficult to treat. The underlying mechanisms for this phenomenon have remained largely unresolved, but recent publications suggest two independent mechanisms that may contribute. According to one line of research, tumours that overexpress the EGFR grow autonomously and become "addicted" to growth factor signalling. Inhibition of this signal using EGFR inhibitors can, therefore, induce cell death in tumour cells and lead to tumour shrinkage. The other line of research, as highlighted by recent findings, suggests that the overexpression, specifically of mutant forms of the EGFR, may create an immune-suppressive and lymphocyte depleted microenvironment within tumours. Such a lymphocyte depleted microenvironment may explain the resistance of EGFR overexpressing cancers to tumour therapies, particularly to check-point inhibitor treatments. In this article, we discuss the recent data which support an immune modulatory effect of EGFR signalling and compare these published studies with the most recent data from The Cancer Genome Atlas (TCGA), in this way, dissecting possible underlying mechanisms. We thereby focus our study on how EGFR overexpression may lead to the local activation of TGFß, and hence to an immune suppressive environment. Consequently, we define a novel concept of how the mitogenic and immune modulatory effects of EGFR overexpression may contribute to tumour resistance to immunotherapy, and how EGFR specific inhibitors could be used best to enhance the efficacy of tumour therapy.