Disclosed are immunopotentiating agents, and vaccines thereof, which enhance and/or otherwise modify immune responses, and method for their preparation and use in vivo. Immunopotentiating agents can be single agents that act directly, adjuvants added concurrently with the agents, or heteroconjugates wherein the immunopotentiating agent is chemically coupled to the compound against which an immune response is desired. Examples of immunopotentiating agents include monoclonal antibodies, such as anti-CD3, anti-CD2) and anti-CD5 antibodies, and proteins derived from microorganisms (e.g., enterotoxins) which activate T cells. The compounds against which an immune response can be generated, which may be the second component in a heteroconjugate, include compound from abnormal or diseased tissues such as tumors, or infectious agents, such as viruses, bacteria, fungi, protozoal or metozoal parasites, and can be obtained by natural or recombinant means. Methods of using the invention to prepare monoclonal antibodies are particularly disclosed.