# Differentiation-induced reduction in functional diversity restricts the ability of cytomegalovirus-specific CD8 T cells to eliminate virus-infected cells

## TL;DR

This study shows that HCMV can evade immune control by promoting the differentiation of CD8 T cells, which reduces their ability to fight virus-infected cells.

## Contribution

The study reveals how HCMV exploits CD8 T cell differentiation to escape immune detection and suggests implications for T-cell therapy and vaccine development.

## Key findings

- High-frequency NLV-T cells show advanced differentiation and reduced ability to eliminate HCMV-infected cells.
- Low-frequency NLV-T cells maintain functional diversity and can kill HCMV-infected cells even when HLA is downregulated.
- HCMV may use CD8 T cell differentiation to evade immune protection and control reactivation.

## Abstract

Human cytomegalovirus (HCMV) is one of the pathogens with the most significant impact on the immune system's composition, including the expansion of virus-specific CD8 T cells. Nevertheless, it remains unclear why individuals with expanded CD8 T cells recognising the pp65-HLA-A∗02:01–restricted viral epitope NLVPMVATV (NLV-T cells) exhibit weakened immune control of HCMV reactivation.

Here, we characterised NLV-T cells from 116 healthy HCMV-positive donors, dividing them into two groups: those with low and those with high NLV-T cell frequencies (LF and HF, respectively). We phenotyped the cells using multi-colour spectral flow cytometry and single-cell RNA sequencing coupled with TCR profiling and examined their killing properties against peptide-loaded and virus-infected target cells.

Our comprehensive multimodal analysis revealed that NLV-T cells from HF donors exhibited a phenotype of advanced differentiation, marked by high levels of granzyme B and perforin expression, and efficiently eliminated peptide-loaded targets and HCMV-infected cells as long as cell surface HLA expression was unaffected. However, NLV-T cells from LF donors, possessing a less differentiated granzyme K-intermediate phenotype, demonstrated enhanced cytokine secretion and the ability to eliminate HCMV-infected cells, even in the presence of virus-induced HLA class-I downregulation.

Overall, these findings suggest that HCMV exploits CD8 T cell differentiation to evade immune protection. These data are crucial for understanding the previously observed decline in HCMV reactivation control in individuals with NLV-T cell accumulation. Moreover, our findings have clinical implications and could guide future research on adoptive T-cell therapy, and the potential use of HCMV as a vaccine vector.

10.13039/501100001659Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)–Projects number 390874280 and FO334/7-2.