(641d) Engineering Immunomodulatory Nanobody Conjugates for Cancer Immunotherapy

Stimulator of interferon genes (STING) has emerged as a promising target to enhance antitumor immunity. However, the clinical application of STING agonists faces challenges related to pharmacological barriers affecting their utility, efficacy, and safety. To combat these challenges, we present a highly modular platform designed for the systemic administration of immunomodulators using nanobodies engineered for in situ hitchhiking of agonist cargo on serum albumin. Here, we use site-selective bioconjugation chemistries to generate molecularly defined products, and in our first application we discovered that covalent conjugation of a non-nucleotide STING agonist to anti-albumin nanobodies improved pharmacokinetics and enhanced cargo accumulation in tumor tissue. This approach stimulated innate immune programs, leading to increased infiltration of activated natural killer cells and T cells, resulting in potent inhibition of tumor growth across multiple mouse tumor models. Furthermore, we demonstrated the programmability of the platform by recombinantly integrating a second nanobody domain targeting programmed cell death ligand-1 (PD-L1). This modification not only increased cargo delivery to tumor sites but also effectively blocked immunosuppressive PD-1/PD-L1 interactions. The resulting bivalent nanobody carrier – in combination with the covalently conjugated STING agonist – not only triggered robust antigen-specific T cell responses and long-lasting immunological memory but also conferred enhanced therapeutic efficacy. Notably, this platform proved effective as a neoadjuvant treatment, improving responses to adoptive T cell transfer therapy. Our findings highlight albumin hitchhiking nanobodies as an enabling, multimodal, and programmable platform for the systemic delivery of STING agonists. This approach has the potential to augment responses to various immunotherapeutic modalities, offering a promising avenue for advancing cancer immunotherapy.