In this work, biocompatible and biodegradable poly(D-L-lactide-co-glycolide) (PLGA) composite microparticles with potential use as carrier for vaccines and other drugs to the lungs were developed using supercritical CO2-assisted spray-drying (SASD). Bovine serum albumin (BSA) was chosen as model vaccine, and L-leucine as a dispersibility enhancer, and their effects on the particle characteristics were evaluated. The dry powder formulations (DPFs) were characterized in terms of their morphology and aerodynamic performance using an in vitro aerosolization study - Andersen cascade impactor (ACI) - to obtain data such as the fine particle fraction (FPF) with percentages up to 43.4%, and the mass median aerodynamic diameter (MMAD) values between the 1.7 and 3.5 mu m. Additionally, pharmacokinetic and cytotoxicity studies were performed confirming that the produced particles have all the necessary requirements for potential pulmonary delivery.