One Strategy for Vaccine Development Currently Under Investigation Is the Use

One strategy for vaccine development currently under investigation is the use of pathogen-derived T cell epitopes as a component of the vaccine. For viral pathogens, implementing this strategy involves scanning the predicted amino acid sequences of the viral proteins for likely peptide epitopes that would bind to MHC class I and MHC class II molecules. In addition to the complication of MHC sequence polymorphism in the human population, another complication of this strategy for peptide epitopes that would bind to MHC class II proteins is:

A) The importance of viral proteins containing peptides that are cleaved into 8-10 amino acid long fragments.
B) The ability of viruses to mutate their proteins to avoid MHC anchor residue sequences.
C) The fact that long peptides (>13 amino acids) are rapidly degraded in cells.
D) The fact that MHC class II proteins are intrinsically stable, even in the absence of binding to a peptide.
E) The absence of defined sequence motifs that predict peptide binding to MHC class II molecules.