The present disclosure provides nucleic acid carriers comprising one or more layers comprising multiple monomers, wherein each monomer comprises: a first and a second oligonucleotide; wherein a central portion of each of the first and second oligonucleotides is complementary to each other, forming a double-stranded region, wherein the two terminal portions of the first oligonucleotide are not complementary to the two terminal portions of the second oligonucleotide, forming four terminal arms; and at least one targeting agent conjugated to at least one peripheral terminal arm, wherein when the at least one targeting agent is an miRNA. The present disclosure also provides pharmaceutical composition comprising any of the nucleic acid carriers described herein, and a pharmaceutically acceptable vehicle. The present disclosure also provides methods of inducing an immune response in an animal comprising administering to the animal any of the nucleic acid carriers described herein.