An All-in-One Photothermal Nanocomposite Hydrogel for Controlling Inducible Transgene Expression

We have developed a remotely near-infrared (NIR)-activated, implantable fibrin hydrogel for the controlled induction of transgene expression, designed to decouple the therapeutic efficacy of rapamycin from its systemic toxicity. Rapamycin, a drug widely used in clinical practice as an immunosuppressant and antiproliferative agent, is a potent transcriptional inducer that enables tightly regulated temporal transgene expression through chemically induced dimerization. However, its utility as a dimerizer is hindered by the unintended systemic immunosuppression and off-target effects inherent to its conventional administration. To address this, we developed poly(lactic-co-glycolic acid) (PLGA) nanoparticles to encapsulate rapamycin, aiming to facilitate localized delivery and enhance drug stability. Engineered cells harboring a dual heat- and dimerizer-responsive gene switch exhibited robust reporter transgene expression following nanoparticle treatment and thermal activation. Nanoencapsulation preserved rapamycin activity against thermal and hydrolytic degradation, enabling superior, long-term dimerizer function compared to the free drug. To create a remotely actuated platform, we developed photothermal hydrogels by incorporating hollow gold nanoparticles and rapamycin-loaded PLGA nanoparticles within a fibrin matrix hosting the reporter cells. In mice, NIR irradiation of subcutaneously implanted constructs achieved transgene induction levels comparable to systemic administration of rapamycin. Notably, nanoparticle-mediated delivery resulted in negligible circulating rapamycin concentrations. Furthermore, localized rapamycin release initially promoted a pro-healing M2 macrophage phenotype, followed by a late-stage transition toward an M1-dominant profile that likely facilitated the clearance of scaffold degradation products. In hydrogels incorporating cells harboring a gene switch to control human VEGF165 production, NIR irradiation triggered a robust angiogenic cascade characterized by transient erythema followed by an increase in CD31⁺ microvascular density. Collectively, these data demonstrate the potential of this light-triggered and rapamycin-dependent platform as a customizable and safe tool for achieving the control required to advance the next-generation of site-specific, transgenic protein therapies.