# A pooled CRISPR screen identifies the Tα2 enhancer element as a driver of TRA expression in a subset of mature human T lymphocytes

## TL;DR

This study identifies the Tα2 enhancer as a key driver of TCRα expression in some mature human T cells using a CRISPR screen.

## Contribution

The study reveals the Tα2 enhancer's role in TRA expression, resolving conflicting prior findings about regulatory elements in T cells.

## Key findings

- No sgRNAs targeting the 5’ J region affected TRA expression.
- sgRNAs targeting Tα2 reduced TCRα expression in Jurkat E6.1 and some primary T cells.
- The Tα2 enhancer drives TRA expression in a subset of mature human T lymphocytes.

## Abstract

The T cell receptor (TCR) is crucial for immune responses and represents a pivotal therapeutic target for CAR T cell therapies. However, which enhancer elements drive the constitutive expression of the TCRα chain in mature, peripheral T cells has not been well defined. Earlier work has suggested that enhancer alpha is inactive in mature peripheral T cells and that an alternative enhancer element in the 5’ J region was driving TRA expression, while more recent findings indicated the opposite. Here, we applied a pooled CRISPR screen to probe a large genomic region proximal to the human TRA gene for the presence of regulatory elements. Interestingly, no sgRNA targeting the 5’ J region was identified that influenced TRA expression. In contrast, several sgRNAs targeting enhancer alpha element Tα2, were identified that compromised the expression of the TCRα chain in Jurkat E6.1, as well as in a subset of human primary T cells. Our results provide new insights into the regulation of TRA in human peripheral T cells, advancing our understanding of how constitutive TRA expression is driven and regulated.