Thymosin‑alpha‑1 (Tα1) doesn't change cancer cells much, but it does tweak the activity of several immune cells, especially boosting the gene activity in activated CD8+ T cells, which are important for fighting tumors.

The immune-balancing role of thymosin alpha 1 (Tα1) is well-recognized in contexts of immune dysregulation. Within the anti-tumor context, Tα1 demonstrated to act as an immune-enhancer, with potential roles in immunotherapy-based treatments. However, Tα1 immunomodulatory potential on tumor cells is poorly understood. Additionally, Tα1 pleiotropic effects on immune cells require in-depth investigations to unravel its specific impact on different immune cell populations. Thus, we first aimed to investigate whether Tα1 treatments influenced the transcriptional immune profile of various cancer cell lines. Alongside, CD4⁺ T, CD8⁺ T, B, and natural killer cells from healthy donors (HDs) were treated individually with Tα1, to assess its direct effects on each immune cell population. Cutaneous melanoma, glioblastoma, and pleural mesothelioma cell lines and HD immune cell subsets were treated with Tα1 for 48 hours. Total RNA was subsequently isolated, and gene expression profiles were analyzed by the nCounter^® SPRINT Profiler. Genes with a log2ratio ≥0.58 and ≤-0.58 in Tα1-treated vs untreated cells were defined as differentially expressed (DEGs) and subsequently evaluated for the enrichment of Gene Ontology terms to identify biological processes potentially affected by Tα1 in tumor and immune cells. Tα1 minimally changed cancer cell DEGs and immune-related biological processes, suggesting a comprehensive lack of transcriptional immunomodulatory potential on the tumor counterpart. Conversely, Tα1 exhibited to directly affect the proliferation and/or transcription processes of each studied immune cell subset, with the greatest transcriptional impact observed for activated CD8⁺ T cells, crucial players in anti-tumor immunity. Our findings question the tumor immunomodulatory properties of Tα1, simultaneously underscoring the importance of further investigating Tα1 influence on specific immune cell subsets in the periphery or within the tumor microenvironment of cancer patients. This would contribute to understand Tα1 potential in immunotherapy-based combination strategies, within the anti-tumor setting.