Controlled release of monoclonal antibodies from poly-l-lysine-coated alginate spheres within a scaffolded implant mitigates autoimmune responses to transplanted islets and limits systemic antibody toxicity.

Immunomodulatory monoclonal antibodies (IM-mAbs) are a cornerstone of modern immunotherapy; however, when administered systemically (i.e., via injection), these agents can generate a variety of negative side effects. For many diseases, systemic delivery of IM-mAbs is the most effective mode of treatment, but in instances where the cellular target occupies a limited, well-defined space (e.g., solid tumors or cellularized implants) local, controlled release of IM-mAbs might be desirable. Antibodies are highly sensitive to a variety of environmental conditions, which limit the kinds of polymers suitable for antibody retention and controlled release. The present study evaluates the release of antibodies from biocompatible, 2-mm diameter alginate spheres coated with poly-l-lysine and a thin outer layer of alginate (APA spheres). In vitro, rates of antibody release (including IM-mAbs) could be incrementally decreased and made linear by incrementally increasing the quantity of poly-l-lysine deposited on the alginate, with linear release lasting in one scenario for at least 46 days. To evaluate the bioactivity in vivo of IM-mAbs, APA spheres loaded with either anti-CD3ε or anti-CD95 mAb were incorporated into scaffolded islet implant (SI) test-beds and the SIs implanted into a mouse model of autoimmune (type 1) diabetes. Release of mAbs within the implanted SIs resulted in reduced autoimmune responses to both transplanted and native islets. Notably, mice implanted with APA spheres loaded with quantities of anti-CD95 mAb that would be lethal if given systemically showed immunomodulation with no toxic side effects. Collectively, our results indicate that APA spheres are a relatively simple means to evaluate the effects of local, controlled release of IM-mAbs in a way that preserves mAb function and limits systemic toxicity.