Dual Activation of CD8+ and CD4+ T cells by a PD-1 targeted IL-15 Mutein in Viral Infection

Cytokines remain promising additions to immunotherapy to improve response rates; however, the low therapeutic index and associated side effects have hindered progress. In response to these challenges, immunocytokines, engineered fusion proteins that combine the specificity of antibodies with the immune-stimulatory properties of cytokines, have been employed to enable targeted delivery of cytokine signals to immune cells or the tumor microenvironment to minimize pathological consequences.

Here, we describe SAR445877 (SAR’877), a novel PD-1-targeted immunocytokine that fuses a high-affinity anti-PD-1 antibody with a detuned IL-15/IL-15Rα sushi domain complex. SAR’877 simultaneously blocks PD-1/PD-L1 and PD-1/PD-L2 interactions and delivers IL-15 signals selectively to PD-1+ T cells. This design enhances the proliferation and activation of antigen-experienced CD8⁺ and CD4⁺ T cells, as well as NK cells, while limiting systemic inflammatory cytokine release.