# Empowerment of CAR-T Cells by IL-7 and IL-15 Boosts Their Efficacy Against HER2-Positive Tumors with Enhanced Expansion and Persistence

## TL;DR

Adding IL-7 and IL-15 to CAR-T cell production improves their ability to fight HER2-positive tumors by boosting expansion and persistence.

## Contribution

The study shows that IL-7 and IL-15 supplementation enhances CAR-T cell function and longevity against solid tumors.

## Key findings

- CAR-T cells expanded with IL-7 and IL-15 showed enhanced proliferation and cytotoxicity.
- Supplemented CAR-T cells retained stem cell-like features and sustained antitumor activity.
- CD57+ CAR-T cells from supplemented cultures retained full function despite CD57 expression.

## Abstract

Chimeric antigen receptor (CAR)-T cell therapy has achieved remarkable clinical success in B cell malignancies. However, its efficacy in solid tumors remains limited, in part due to suboptimal expansion, persistence, and restrained effector function. Strategies that promote durable CAR-T cell fitness are therefore required to overcome these barriers. In this study, we generated HER2-CAR-T cells targeting human breast cancer cells and evaluated the impact of different cytokine supplementation strategies on CAR-T cell phenotype and function. We analyzed gene expression patterns and performed repetitive tumor killing assays to assess the ability of CAR-T cells expanded with IL-2 + IL-7 + IL-15 compared with IL-2 alone to maintain proliferation and cytotoxic function across multiple rounds of tumor cell exposure. Compared with IL-2 alone, supplementation with IL-7 and IL-15 significantly enhanced CAR-T cell expansion, preserved stem cell-like features prior to antigen encounter, and promoted superior proliferative capacity. Moreover, CAR-T cells cultured with IL-7+15 or IL-2+7+15 maintained sustained cytotoxicity and exhibited increased antitumor cytokine production during repeated tumor challenges. Notably, IL-7 and IL-15 supplementation induced a CD57+ CAR-T cell population that, unlike the immunosenescent CD57+ cells reported previously, retained full proliferative and cytotoxic capacity, with CD57 expression being dynamically downregulated upon antigen stimulation. Collectively, these findings demonstrate that incorporation of IL-7 and IL-15 into CAR-T cell manufacturing protocols substantially improves expansion, persistence, and effector function, supporting their use as a strategy to enhance CAR-T cell performance against solid tumors.