Antigen
In immunology, antigens (Ag) are structures (aka substances) specifically bound by antibodies (Ab) or a cell surface version of Ab ~ B cell antigen receptor (BCR). The term antigen originally described a structural molecule that binds specifically to an antibody only in the form of native antigen. It was expanded later to refer to any molecule or a linear molecular fragment after processing the native antigen that can be recognized by T-cell receptor (TCR). BCR and TCR are both highly variable antigen receptors diversified by somatic V(D)J recombination. Both T cells and B cells are cellular components of adaptive immunity. The Ag abbreviation stands for an antibody generator.
Bette Korber
Several of the major variations are included in each molecule of protein, thus producing a variant protein antigen that probably does not exist in the wild virus population but should cross-react with variants that do exist.  Korber has taken two different approaches to designing such antigens.  Her group has developed a computer algorithm to choose epitopes to combine into a mosaic molecule for the mosaic antigens. In 2009, she described a designed mosaic protein this way: "People didn't know if it would fold properly, if it would be antigenic, or if it would have the same sites that recognized by killer T cells". They found that the newly designed antigens did fold properly and acted as a strong antigen, and were recognized by the cytotoxic T cells (killer cells). Also, Korber and her collaborators have developed a graphical analysis called Epigraph that can generate promising antigens with a mixture of epitopes. Korber explains that the approach of designing a protein via computer, combining bits of known proteins that provoke immune responses, had never been tried. She says, "Even after it worked, it was hard to convince people that this novel thing could be a vaccine because it hadn't been done before".