or within minutes to hours of administration of each other by u201c antigen u201d is meant a molecule that contains one or more epitopes that will stimulate a host 39 s immune system to elicit a humoral antibody response or cellular antigen specific immune response when the antigen is presented normally an epitope will include between about 3 15 generally about 5 15 amino acids for purposes of the present invention antigens can be derived from any of several known viruses bacteria parasites and fungi the term also is intended to encompass any of the various tumor antigens furthermore for purposes of the present invention an u201c antigen u201d includes those with modifications such as deletions additions and substitutions generally conservative in nature to the native sequence so long as the protein polypeptide or polysaccharide maintains the ability to elicit an immunological response these modifications may be deliberate as through site directed mutagenesis or may be accidental such as through mutations of hosts that produce the antigens an u201c immune response u201d to an antigen or composition is the development in a subject of a humoral and or a cellular immune response to molecules present in the composition of interest for purposes of the present invention a u201c humoral immune response u201d refers to an immune response mediated by antibody molecules while a u201c cellular immune response u201d is one mediated by t lymphocytes and or other white blood cells one important aspect of cellular immunity involves an antigen specific response by cytolytic t cells u201c ctls u201d ctls have specificity for peptide antigens that are presented in association with proteins encoded by the major histocompatibility complex mhc and expressed on the surfaces of cells ctls help induce and promote.