The compositions and methods provide herein include, inter alia, antibodies attached to single-stranded oligoribonucleotides. Two antibodies are capable of forming complexes in vivo through hybridization of the respective complementary oligoribonucleotides they are bound to. For example, a first antibody bound to a first oligoribonucleotide through a first chemical linker may be administered to a subject, bind to a cell surface antigen in vivo and subsequently form an antibody complex in vivo with a second antibody bound to a second oligoribonucleotide through a second chemical linker, through complementary base-pairing between the first and the second oligoribonucleotide. The compositions and methods provided herein are, inter alia, useful for diagnostic and therapeutic purposes, for example, the treatment of cancer or autoimmune disease.