Therapy-induced senescence (TIS) halts tumor growth and enhances treatment outcomes in numerous preclinical cancer models. However, it also alters tumor biology and reshapes the tumor environment, thereby contributing to treatment resistance and tumor relapse. Several studies have described the complex and dynamic relationship between senescent tumors and the host immune system, yet the molecular mechanisms underlying this interaction remain unclear, and its impact on treatment efficacy contingent upon cancer type. Consequently, elucidating the interplay between senescent tumor cells and the host immune system is a critical priority for improving cancer therapy, including the development of novel senolytic immunotherapies.

We employed RNA and proteome analyses, along with immunophenotyping by flow cytometry, in various pediatric tumor mouse models and human tumor cell lines before and after DNA-damaging therapy to characterize TIS-associated changes in tumor biology. To further investigate the interaction between TIS tumor cells and different cells of the host immune system (e.g., macrophages, T cells, and NK cells) in vivo, we utilized immune mass cytometry (IMC) and spatial multiplex immunofluorescence imaging (MACSima). Additionally, we applied genetic and pharmacological approaches to modulate T-cell interactions with TIS tumor cells and alter T-cell cytotoxicity in senolytic therapies.

Upon TIS, various mouse and human cancer cell lines exhibited increased expression of immunologic gene sets and surface markers associated with immune system activation. Investigation of in vivo tumor-host interactions by spatial imaging revealed that TIS promotes the infiltration of both CD4⁺ and CD8⁺ T cells into senescent tumor sites, facilitating their direct interaction with TIS cells. Immunophenotyping of these T cells identified Fas ligand (FasL) overexpression as a key actionable moiety that induces apoptosis in Fas receptor (FasR)-positive TIS cells. To further elucidate the significance of this interaction in senolytic therapies and treatment outcomes, we employed in vivo and in vitro genetic and pharmacological approaches to manipulate FasL–FasR binding, demonstrating its crucial role in TIS-targeted therapeutic strategies and treatment outcome.

This study elucidates the impact of TIS on tumor cell immunogenicity, demonstrating enhanced immune system activation and increased susceptibility to T cell–mediated apoptosis through direct interaction of both CD4⁺ and CD8⁺ T cells via the FasL–FasR pathway. These findings highlight novel actionable moieties to enhance the efficacy of senescence-based immunotherapies across different cancer types.