IMMUNOGEN

n. antigen, substance which triggers an immune response, material which stimulates the production of antibodies

An antigen or immunogen is a molecule that stimulates an immune response. The word originated from the notion that they can stimulate antibody generation. We now know that the immune system does not only consist of antibodies. The modern definition encompasses all substances that can be recognized by the adaptive immune system.
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Noun
1. any substance or organism that provokes an immune response (produces immunity) when introduced into the body
(synonym) immunizing agent
(hypernym) antigen
(hyponym) vaccine, vaccinum

adj. immunogenetic, of immunogenetics, of the branch of immunology which studies the link between the immune system and genetic makeup

a foreign substance in the body (a bacterium, virus, or protein, for example) that can cause disease — and whose presence triggers an immune response (the formation of antibodies).