Quantitative studies in T and B cell epitope mimicry

For a peptide vaccine to be effective in generating an antibody response, it generally must incorporate both B cell epitopes, against which the antibody response is to be directed, and T cell epitopes, which are responsible for stimulating helper T cells. The first part of this work is concerned with the question, How well can a T cell epitope replace the carrier protein from which it is derived?" To answer this question two studies were done: an initial, direct comparison between a protein (the Fab' fragment of murine monoclonal anti-fluorescein antibody 9-40) coupled to hen egg lysozyme (HEL) and the same protein coupled to the immunodominant T cell epitope from HEL for BIO.A (H-2a) mice, along with negative controls, and a second, dose response study with fluorescein (FL) as the B cell epitope attached to a multiple antigenic peptide (MAP) version of this T cell epitope, along with positive and negative controls (HEL and a MAP in which the epitope sequence was replaced by glycine residues, respectively). This study showed a half-sigmoidal curve for the FL-(T epitope) immunogen, no response to the negative control except at the highest dose used, and a fairly constant and high response for both the experimental MAP and the fluoresceinated HEL. The initial study described above gave a very specific anti-idiotype response for the (9-40)Fab'-HEL construct. Another, follow-up study comparing a peptide mimic based on an important idiotope, the third complementarity determining region of the heavy chain (the CDR-H3 loop), to the intact idiotype was also conducted. In this study the peptide mimic of the CDR-H3 loop was the B cell epitope; it was also coupled to HEL. The question being addressed was, "How well can an idiotope peptide mimic replace its parent idiotype?" B10.A mice were immunized with (B epitope)-HEL, (9-40)Fab'-HEL, (B epitope) + HEL mixed together, or just the B epitope. The essential issue was crossreactivity, and this was observed to increase with succeeding immunizations. Molecular dynamics simulations with generalized Born implicit solvation or particle mesh Ewald electrostatics were also used to provide insight into the structural basis of idiotopic phenomena.