# DUSP6 ablation restores CAR T-cell fitness impaired by tumor CD58 loss through invigoration of AP-1 signaling

## TL;DR

Researchers found that blocking DUSP6 can restore the effectiveness of CAR T-cells weakened by tumor CD58 loss, improving their function and survival.

## Contribution

The study identifies DUSP6 as a novel target to enhance CAR T-cell fitness by restoring AP-1 signaling and mitochondrial function.

## Key findings

- DUSP6 blockade restores AP-1 signaling and mitochondrial fitness in CAR T-cells impaired by tumor CD58 loss.
- DUSP6 ablation reduces CAR T-cell apoptosis and enhances long-term cytotoxicity and proliferation.
- DUSP6 downregulation correlates with positive patient outcomes in T-cell-based immunotherapy.

## Abstract

Primary resistance to chimeric antigen receptor (CAR) T-cell therapies has limited their widespread application. Our prior genome-wide CRISPR/Cas9 screening revealed that the loss of CD58, a crucial intrinsic resistance factor in tumors, resulted in insufficient immune synapse formation and impaired CAR T-cell activation and cytotoxicity. However, the specific signaling pathway and transcriptional changes associated with CAR T-cell dysfunction have not been addressed. Here, we revealed that AP-1-mediated activation was attenuated in CAR T cells impaired by tumor CD58 loss, driving a decrease in mitochondrial biogenesis, metabolic kinetic impairment, mitochondrial membrane potential loss and ROS accumulation. Moreover, this AP-1 attenuation triggered death receptor-independent apoptosis through the intrinsic mitochondrial pathway. In seeking therapeutic strategies, we pharmacologically and genetically blocked three distinct inhibitory phosphatases positioned upstream of AP-1 signaling. Multifaceted validation has demonstrated that dual specificity phosphatase 6 (DUSP6) blockade is an effective approach to supplement AP-1 signaling while notably reducing CAR T-apoptosis and enhancing mitochondrial fitness, proliferation and long-term cytotoxicity. The transcriptomic profiles of DUSP6-ablated CAR T cells revealed markedly upregulated T-cell activation signatures and enriched metabolic pathways. Clinically, bulk and single-cell RNA-seq analyses revealed that DUSP6 was downregulated in patients who responded to T-cell-based immunotherapy, implying its relevance to patient outcomes. Our findings repositioned CD58 not merely as an immune synapse component but also a metabolic checkpoint in CAR T-cell biology, the loss of which triggers AP-1-dependent mitochondrial derangement and creates a permissive landscape for intrinsic apoptosis, which can be ameliorated by ablation of the inhibitory phosphatase DUSP6. Crucially, DUSP6 ablation represents a promising engineering target to potentiate CAR T-cell efficacy in broader applications.