Methods and compositions for using N-hydroxysuccinimide and N-hydroxysulfosuccinimide to covalently couple protein(s) to the surface of red blood cells universally, rapidly and conveniently are provided. In one embodiment, the compositions promote immune tolerance in a subject. One embodiment provides autologous or allogenic red blood cells having whole protein(s) of interests conjugated to proteins on or within the plasma membrane of the red blood cells, wherein the conjugated proteins display at least one antigen to which immune tolerance is desired. The proteins are conjugated to the RBCs using carbodiimide chemistry. In a preferred embodiment, the whole proteins are conjugated using EDC in combination with NHS or sulfo-NHS.
