While a low frequency of myelin-specific IFN-γ-secreting spot-forming cells was detected when PBL from healthy controls (Figure 6(c)) and from MS patients (Figure 6(d)) were rechallenged with myelin-derived peptides, PBL were still able to secrete IFN-γ production following rechallenge with a CMV pp65-derived peptide pool in all conditions tested. This evidence concerns the gene IFNG and myeloid sarcoma.