# Chimeric Antigen Receptor (CAR) T Cells Releasing Soluble SLAMF6 Isoform 2 Gain Superior Anti-Cancer Cell Functionality in an Auto-Stimulatory Fashion

## TL;DR

Engineered CAR T cells that release a specific form of SLAMF6 show improved long-term anti-cancer activity against solid tumors.

## Contribution

CAR T cells engineered to release soluble SLAMF6 isoform 2 demonstrate enhanced functionality and persistence in solid tumors.

## Key findings

- SLAMF6-secreting CAR T cells showed increased IFN-γ secretion and CD25 upregulation on CD4+ T cells.
- These CAR T cells exhibited superior cytotoxic capacity and a central memory phenotype with reduced exhaustion markers.
- The auto-stimulatory loop of SLAMF6-secreting CAR T cells boosts their anti-tumor activity in solid cancers.

## Abstract

T cells equipped with chimeric antigen receptors (CARs) have evolved into an essential pillar of lymphoma therapy, reaching second-line treatment. In solid cancers, however, a dearth of lasting CAR T cell activation poses the major obstacle to achieving a substantial and durable anti-tumor response. To extend T cell cytotoxic capacities, we engineered CAR T cells to constitutively release an immunostimulatory variant of soluble SLAMF6. While wild-type SLAMF6 induces T cell exhaustion, CAR T cells with the soluble Δ17-65 SLAMF6 variant exhibited refined, CAR redirected functionality compared to canonical CAR T cells. CD28-ζ CAR T cells releasing soluble SLAMF6 increased IFN-γ secretion and augmented CD25 upregulation on CD4+ CAR T cells upon CAR engagement by pancreatic carcinoma and melanoma cells. Moreover, under conditions of repetitive antigen encounter, SLAMF6-secreting CAR T cells evinced superior cytotoxic capacity in the long term. Mechanistically, SLAMF6-secreting CAR T cells showed predominantly a central memory phenotype, a PD-1- TIGIT- double negative profile, and reduced expression of exhaustion-related transcription factors IRF-4 and TOX with augmented amplification and persistence capacities. Overall, CAR T cells engineered with the release isoform 2 SLAMF6 establish an auto-stimulatory loop with the potential to boost the cytolytic attack against solid tumors.