Potentiating tumor immunity using aptamer-targeted RNAi to render CD8⁺ T cells resistant to TGFβ inhibition

Abstract

TGFβ secreted by tumor cells and/or tumor infiltrating stromal cells is a key mediator of tumor growth and immune suppression at the tumor site. Nonetheless, clinical trials in cancer patients targeting the TGFβ pathway exhibited at best a modest therapeutic benefit. A likely reason, a common limitation of many cancer drugs, is that the physiologic roles of TGFβ in tissue homeostasis, angiogenesis, and immune regulation precluded the dose escalation necessary to achieve a profound clinical response. Murine studies have suggested that countering immune suppressive effects of TGFβ may be sufficient to inhibit tumor growth. Here we describe an approach to render vaccine-activated CD8 T cells transiently resistant to TGFβ inhibition using an siRNA against Smad4 to inhibit a key step in the canonical TGFβ signaling pathway. The siRNA was targeted to vaccine activated CD8 T cells in the mouse by conjugation to a 4-1BB binding oligonucleotide (ODN) aptamer ligand (4-1BB-Smad4 conjugate). the 4-1BB-Smad4 conjugate rendered T cells partially resistant to TGFβ inhibition, and treatment of tumor bearing mice with systemically administered 4-1BB-Smad4 conjugate enhanced vaccine- and irradiation-induced antitumor immunity. Limiting the inhibitory effects of TGFβ to tumor-specific T cells will not interfere with its multiple physiologic roles and hence reduce the risk of toxicity.

Non-viral siRNA delivery to T cells: Challenges and opportunities in cancer immunotherapy

“…Recent studies have shown successful delivery of aptamer-conjugated siRNAs (AsiCs) to T lymphocytes in vivo [19,22,[179][180][181][182]. For example, Gilboa et al reported moderate gene silencing levels (30-40%) in CD8 + T lymphocytes using AsiC targeted towards the 4-1BB receptor, a co-stimulatory receptor expressed on activated T cells, to enhance anti-tumor responses in mouse tumor models [179][180][181][182]. Other approaches include the use of CTLA-4 targeting AsiCs to silence STAT3 expression (~75% knockdown) in CTLA4 + T cells to reduce metastasis and tumor growth in various murine tumor models [181].…”

Aptamers, the Nucleic Acid Antibodies, in Cancer Therapy

“…4-1BB aptamer has also been used in conjugation with an siRNA against Smad4 in the TGFβ signaling pathway, the signaling of which mediates immune suppression at the tumor microenvironment. The 4-1BB aptamer-Smad4 siRNA conjugates rendered T cell resistant to TGFβ inhibition, and systemic administration of the conjugates to tumor-bearing mice boosted irradiation-and vaccine-induced antitumor immunity [162].…”

Aptamer-Mediated Nanotheranostics for Cancer Treatment: A Review

“…These aptamers were further explored to regulate more benefits. Together with other therapeutic RNAs, several aptamer–siRNA conjugates have been utilized for the in vivo delivery of such cargoes to elicit an antitumor immune response. , Even with the repertoire of such therapeutic ligands, challenges due to spatial and temporal control over delivery, displaying modest clinical response, exist. This obstacle can be overcome by functionalizing it with potential nanocarriers because nanomedicine has escalated the efficiency of cancer immunotherapy.…”