Aptamer-Targeted Attenuation of IL-2 Signaling in CD8⁺ T Cells Enhances Antitumor Immunity

Immune responses elicited against cancer using existing therapies such as vaccines or immune stimulatory antibodies are often not curative. One way to potentiate antitumor immunity is to enhance the long-term persistence of anti-tumor CD8⁺ T cells. Studies have shown that the persistence of activated CD8⁺ T cells is negatively impacted by the strength of interleukin 2 (IL-2) signaling. Here, we used small interfering RNAs (siRNAs) against CD25 (IL-2Rα) to attenuate IL-2 signaling in CD8⁺ T cells. The siRNAs were targeted to 4-1BB-expressing CD8⁺ T cells by conjugation to a 4-1BB-binding oligonucleotide aptamer. Systemic administration of the 4-1BB aptamer-CD25 siRNA conjugate downregulated CD25 mRNA only in 4-1BB-expressing CD8⁺ T cells promoting their differentiation into memory cells. Treatment with the 4-1BB aptamer-CD25 siRNA conjugates enhanced the antitumor response of a cellular vaccine or local radiation therapy. Indicative of the generality of this approach, 4-1BB aptamer-targeted delivery of an Axin-1 siRNA, a rate-limiting component of the β-catenin destruction complex, enhanced CD8⁺ T cell memory development and antitumor activity. These findings show that aptamer-targeted siRNA therapeutics can be used to modulate the function of circulating CD8⁺ T cells, skewing their development into long-lasting memory CD8⁺ T cells, and thereby potentiating antitumor immunity.