# Massively Scalable Single-cell Multiomic Profiling of T Cell Repertoire with REFLEX

## TL;DR

REFLEX is a new method for studying T cells at a large scale, combining T cell receptor sequencing with multiomic data to better understand immune responses.

## Contribution

REFLEX introduces a scalable, cost-efficient method for single-cell multiomic profiling with paired-chain TCR sequencing.

## Key findings

- REFLEX captured TCR sequences and multiomic data from over 1.4 million T cells.
- The method identified many putative novel CMV reactive clonotypes.
- REFLEX enables unprecedented scale and depth in T cell repertoire analysis.

## Abstract

Single-cell profiling of T cell state with immune repertoire is critical for understanding heterogenous T cell phenotypes and responses to antigen, however, existing technologies struggle to generate this information at sufficient throughput to match biological complexity. We present “REFLEX”, a novel single-cell method enabling highly scalable, cost-efficient, multiomic profiling with paired-chain TCR sequencing. REFLEX utilizes in-situ reverse transcription with integrated sample multiplexing barcodes in a way that merges seamlessly with the commonly used 10x FLEX platform to allow capture of TCR sequences at unprecedented scale and depth. We profile >2 million cells from CMV-peptide-pulsed T cell expansions, capturing TCR sequences and rich multiomic information from 1.4M T cells, identifying many putative novel CMV reactive clonotypes and illustrating the scale and transformative impact on our understanding of T cell mediated adaptive immunity achievable with REFLEX.