Deletion of the protein tyrosine phosphatase PTPN22 for adoptive T cell therapy facilitates CTL effector function but promotes T cell exhaustion
Authors: Teagle Alexandra R. , Castro-Sanchez Patricia , Brownlie Rebecca J. , Logan Nicola , Kapoor Simran S. , Wright David , Salmond Robert J. , Zamoyska Rose 
Published: June 2023

ABSTRACTBackgroundAdoptive 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 anti-tumor efficacy in ACT. We tested whetherPtpn22KOcytolytic T cells (CTL) were also more effective thanPtpn22WTCTL in controlling tumors in scenarios that favor T cell exhaustion.MethodsTumor control byPtpn22WTandPtpn22KOCTL 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. Anin vitroassay was established to compare CTL function in response to acute and chronic re-stimulation with antigen-pulsed tumor cells. The expression of effector and exhaustion-associated proteins byPtpn22WTandPtpn22KOT cells was followed over timein vitroandin vivousing the ID8 tumor model. Finally, the effect of PD-1 and TIM-3 blockade onPtpn22KOCTL tumor control was assessed using monoclonal antibodies and CRISPR/Cas9-mediated knockout.ResultsDespite having improved effector function at the time of transfer,Ptpn22KOCTL became more exhausted thanPtpn22WTCTL, 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 inPtpn22KOcells. Anti-tumor responses ofPtpn22KOCTL were improved following PD-1 blockadein 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 inPtpn22KOCTL.ConclusionsThis 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.What is already known on this topicT cell exhaustion in the tumor microenvironment is a major factor limiting the potential success of adoptive cell therapy (ACT) in the treatment of solid tumors.Deletion of the phosphatase PTPN22 in CD8+T cells improves their response to tumors, but it is not known whether this influences development of exhaustion.What this study addsUnder conditions which promote exhaustion, CTL lacking PTPN22 exhaust more rapidly than WT cells, despite displaying enhanced effector function in their initial response to antigen.Ptpn22KOCTL express high levels of the inhibitory receptor TIM-3, but TIM-3 signaling does not directly contribute toPtpn22KOCTL dysfunction.Ptpn22KOT cells are more responsive to IL-2 through JAK-STAT signaling, which induces TIM-3 expression via the transcription factor NFIL3.How this study might affect research, practice or policyStrategies aimed at augmenting T cell effector function for ACT should balance improved responses against an increased risk of T cell exhaustion.