Mesothelin peptide-specific CD8+ T cells were quantitated in pre- and post-treatment PBL using IFNγ ELISPOT assays. A) Mesothelin-specific T cell frequencies measured at baseline, following the first treatment, and at the peak of induction in 19 HLA-A1+ and/or HLA-A2+ patients receiving at least one treatment. B) Mesothelin-specific T cell frequencies measured at baseline, following the first treatment, at the peak of induction, and following the final treatment in 14 of the 19 patients who received at least two treatments. Patients in both treatment arms (Ipilimumab alone = open triangles; Ipilimumab + GVAX = solid circles) were grouped together based on survival of greater than or less than 4.3 months. Post-treatment T cell levels were compared to baseline levels using Wilcoxon sign-rank tests.