Raunak Kar

India

Understanding the biology of CD4 cytotoxic T lymphocytes (CD4-CTLs) in humans

Raunak Kar1, Shreya Sinha1, Anjali Sharma2, Veena S. Patil1
1. National Institute of Immunology, New Delhi, India
2. VMMC and Safdarjung Hospital, New Delhi

Abstract

Background

The acquisition of immunological memory to infection is a hallmark of protective immunity. Naïve T-cells (TN) during a primary immune response differentiate into memory cells (TM), that are characterized by their enhanced capacity to generate response to a secondary infection, and can be broadly categorized into long-lived (TSCM, TCM) or short-lived effector memory (TEM, TEMRA). Based on their functionality, conventionally, T-cells have been segregated into cytotoxic CD8-T cells and helper CD4-T cells (TH). But in cases of various infectious diseases, cancers and vaccination regimes, CD4-CTLs (cytotoxic T lymphocytes) have been shown to be the correlates of protective immune responses. However, compared to other CD4+ TH subsets, the molecular and epigenetic landscapes that drive the differentiation, maintenance, and function of human CD4-CTLs are still elusive.

Methods

In this study we performed a multi-factorial analysis of CD4 memory subsets with focus on the CD4-CTLs in humans. A combination of transcriptomics, epigenomics (open-chromatin analysis) and TCR-repertoire analysis at both bulk and single-cell level was performed on ex vivo isolated memory compartments including naive cells. Flow cytometry analysis was used to compare protein expression. In addition, an in vitro differentiaion protocol was established to generate CD4-CTLs from naive cells to elucidate the precise trajectory and identify early factors responsible for fate commitment.

Results

The combination of immunological and multiomics tools helped unravel the breadth of molecular factors that govern their development and differentiation. Interestingly, we observed that the CD4-CTLs were molecularly and functionally indistinguishable from the CD8-CTLs. A notable discovery is the identification of stem-like T-cell memory-precursors of CD4-CTLs, hence delineating their developmental trajectory. Further we developed an in vitro model to generate CD4-CTLs with long-term survival ability that has the capacity to secrete effector cytokines and cytolytic molecules. This property can be further explored in cell therapy to treat various diseases.

Conclusions

The knowledge base from this study not only delineate the overall memory development process but also serve as the resource for the vaccine development for various viral infections.