D-Erythro-sphingosyl phosphoinositol is a lipid nanoparticle covalently linked to antibodies, with potential for targeted compound delivery. It enhances compound accumulation in specific cell types and may serve as a ligand to boost antibody efficacy in immunosuppression. Additionally, D-Erythro-sphingosyl phosphoinositol can be utilized for studying mechanisms related to cell signaling and lipid metabolism.