Injectable and viscoelastic click alginate hydrogels for spatio-temporal T cell administration in vivo.

T cell therapies have shown limited success in solid tumors, mainly due to the difficulty of T cells to penetrate the tumor tissue. Here, we develop injectable and viscoelastic click alginate hydrogels for local and sustained delivery of T cells, with the goal to improve T cell administration, viability, proliferation, and persistence in vivo. Oxidized alginate (Alg), functionalized with norbornene and tetrazine for inverse electron demand Diels-Alder covalent click crosslinking, at varying low (1% Alg) and high (2% Alg) alginate concentration were used. 1% Alg hydrogels showed better injectability in a fully crosslinked state, characterized by lower stiffness, larger mesh size, viscoelastic behavior, lower injection forces and higher cell viability upon injection. In vitro experiments demonstrated that 1% Alg supported T cell viability and proliferation, and promoted sustained release for 10 days. Using an in vivo chick chorioallantoic membrane (CAM) model, hydrogel-based T cell administration exhibited better local delivery, proliferation and persistence over time compared to bolus injection, with 1% Alg showing enhanced T cell release compared to 2% Alg. Further, in a murine model with a local injection in the mammary gland, 1% Alg showed enhanced T cell persistence within the mammary gland and high tissue integration. In conclusion, we engineered injectable, viscoelastic click alginate hydrogels that support T cell administration, local injection, viability, proliferation and persistence in vivo, opening future opportunities for spatio-temporal control of T cell immunotherapies.