Bifunctional conjugate compositions are provided comprising a Signal-1 moiety bound to a first polymer carrier, wherein the combined size of the Signal-1 moiety and the first polymer carrier is about 1 nanometer to about 500 nanometers； and a Signal-2 moiety bound to a second polymer carrier, wherein the combined size of the Signal-2 moiety and the second polymer carrier is about 1 nanometer to about 500 nanometers. In some embodiments, the Signal-1 moiety and the Signal-2 moiety are bound to the same polymer carrier. Associated methods are also provided.
