title: Role of tyrosine phosphatase PTPN22 in CTL responses to tumours and T cell exhaustion
title: Role of tyrosine phosphatase PTPN22 in CTL responses to tumours and T cell exhaustion
titleType: AlternativeTitle
title: The role of tyrosine phosphatase PTPN22 in CTL responses to tumours and T cell exhaustion
titleType: AlternativeTitle
Creators: name: Teagle, Alexandra Rose
Publisher: name: The University of Edinburgh
Year: 2024
Subjects: subject: CTL
subject: tumours
subject: T cell exhaustion
subject: T cells
subject: immune response to tumours
subject: T cell receptors (TCRs)
subject: chimeric antigen receptor (CAR) T cells
subject: non-small cell lung cancer (NSCLC)
subject: immunosuppressive tumour microenvironment (TME)
subject: inhibitory receptors (IRs)
subject: tumour infiltrating lymphocytes (TILs)
subject: Adoptive cell therapy (ACT)
subject: protein tyrosine phosphatase non-receptor type 22 (PTPN22)

description: Despite advances in detection and treatment in recent decades, cancer remains the leading cause of death in the UK. The central role of T cells in the immune response to tumours has been recognised for several decades, and their presence in tumours correlates with more favourable outcomes. The T cell response to tumours relies on recognition of tumour antigens by highly specialised and specific T cell receptors (TCRs). Successive breakthroughs have brought novel T cell-based immunotherapies, such as “immune checkpoint” blocking monoclonal antibodies (mAbs) and chimeric antigen receptor (CAR) T cells. These therapies have realised significantly improved outcomes for patients, particularly for those with haematological malignancies and solid tumours with high mutational burdens such as melanoma and non-small cell lung cancer (NSCLC). However, T cells face many challenges in the immunosuppressive tumour microenvironment (TME), including recruitment to the tumour of suppressive immune cells, release of immunosuppressive cytokines and other mediators, and the induction of expression of inhibitory receptors (IRs). In addition, the continuous exposure of tumour infiltrating lymphocytes (TILs) to tumour antigens leads to chronic stimulation of the TCR, which induces a state of dysfunction termed T cell exhaustion. This exhaustion is characterised by high expression of IRs and the progressive loss of proliferative capacity and effector functions, and is a major challenge precluding success of cancer immunotherapy for many patients. Adoptive cell therapy (ACT) is a novel immunotherapy strategy, in which donor or autologous T cells are taken from the peripheral blood or tumour itself (TILs) and genetically modified ex vivo, before being expanded and infused to the patient. Such modifications include insertion of a TCR or CAR specific to a known tumour antigen. Another major benefit of this strategy is that it allows modifications to be made that enhance T cell effector function or endow T cells with capability to overcome some of the TME challenges. The protein tyrosine phosphatase non-receptor type 22 (PTPN22) dephosphorylates multiple targets involved in proximal TCR signalling, leading to downregulation of the TCR signal and subsequent T cell response. In humans, polymorphisms in the PTPN22 gene are associated with increased risk of autoimmune disease yet decreased risk of many cancers, making it an attractive target for cancer immunotherapy. Previous work from our lab has shown that deletion of Ptpn22 in mouse CD8+ T cells enhances response to weak, or self-, antigens, and leads to improved tumour control following adoptive transfer of CTL, naïve or memory Ptpn22ᴷᴼ T cells. Other groups have additionally demonstrated that germline knockout of Ptpn22 leads to an augmented tumour response, as well as synergistically enhanced response to immune checkpoint blockade. However, systematic evaluation of the longer-term fate of Ptpn22ᴷᴼ effector CTL in the face of persisting tumour challenge has not previously been carried out. We therefore modelled chronic antigen exposure in established tumours to test whether Ptpn22ᴷᴼ CTL are more effective than Ptpn22ᵂᵀ CTL in controlling tumours in scenarios that favour T cell exhaustion. Somewhat unexpectedly, we found that adoptive transfer of small numbers of Ptpn22ᴷᴼ CTL to mice with established tumours led to impaired control of tumour growth compared to Ptpn22ᵂᵀ CTL. This was associated with a more exhausted phenotype in response to persistent antigen exposure. Adoptively transferred Ptpn22ᴷᴼ OT-1 CTL controlled weak SIITFEKL (T4) ovalbumin peptide expressing MC38 tumour growth less effectively than Ptpn22ᵂᵀ OT-1 CTL, despite having improved cytokine and cytotoxic effector function at the time of transfer. In response to repeated re-stimulation with antigen, Ptpn22ᴷᴼ CTL were characterised by more rapid loss of these effector functions than Ptpn22ᵂᵀ CTL, which coincided with earlier and higher expression of IRs. Blockade of the IR PD-1 improved the anti-tumour response of Ptpn22ᴷᴼ CTL in vivo. In contrast, despite Ptpn22ᴷᴼ cells having significantly elevated expression of TIM-3, an IR and marker of terminal exhaustion, knock out or mAb blockade of TIM-3 did not improve but instead further impaired tumour control by Ptpn22ᴷᴼ CTL, suggesting that TIM-3 signalling itself does not drive the diminished function seen in Ptpn22ᴷᴼ CTL. Using TIM-3 as a readout of the underlying pathways leading to Ptpn22ᴷᴼ CTL exhaustion, we identified increased expression of the high affinity IL-2 receptor in Ptpn22ᴷᴼ cells, as well as enhanced IL- 2 signalling mediated by JAK phosphorylation of STAT5. Furthermore, abundance of the transcription factor NFIL3, which is known to induce Havcr2 (the gene for TIM-3) transcription, was greater in Ptpn22ᴷᴼ T cells than Ptpn22ᵂᵀ counterparts. Finally, activity of the key metabolic regulator Myc was elevated in Ptpn22ᴷᴼ cells, leading to increased expression of several nutrient transporters and driving metabolic changes implicated in terminal effector differentiation and exhaustion. Our findings demonstrate that although deletion of Ptpn22 in T cells improves antitumour responses, if tumours are not rapidly eliminated and antigen persists, the loss of restraint on TCR signalling in Ptpn22ᴷᴼ CTL may conversely drive the cells more rapidly to exhaust. PTPN22 deletion is therefore a viable strategy for cancer immunotherapy such as adoptive cell therapy, however this work highlights the need for careful consideration of the differentiation state of the T cells targeted in ACT, in order to balance short-term augmented effector function with longer-term protection. Ultimately, in the “arms race” between cancer cells and the immune system, adopting an approach which boosts multiple T cell phenotypes is likely to be preferable.