Survivin-specific CD4+ T cells are decreased in patients with survivin-positive myeloma

Abstract

Background: Survivin is a small protein inhibitor of apoptosis and a tumor associated antigen. Survivin expression in multiple myeloma is associated with poor prognosis, disease progression, and drug resistance. The CD4+ response against survivin remains uncharacterized. Methods: In order to better understand the anti-tumor immune response to survivin, and optimize vaccination strategies, we characterized the spontaneous CD4+CD25- T cell response against survivin in healthy donors and myeloma patients using survivin derived peptide pools. Results: Healthy donors and myeloma patients' CD4+CD25- T cells exhibited a proliferative and IFN-gamma response against survivin peptides loaded onto autologous dendritic cells. We employed limiting dilution analysis to quantify the precursor frequency of survivin reactive CD4+CD25- T cells. Multiple myeloma patients (range 0% to 2.2x10-3%, n=12) had fewer survivin reactive CD4+CD25- T cells than healthy blood donors (range 1.1x10-3 to 8.4x10-3%, n=10), p=0.021. The survivin reactive CD4+CD25- T cell precursor frequency was inversely associated with tumor survivin mRNA expression (p=0.0028,r=-1.0,n=6), and survivin tumor protein expression by IHC (p=0.0295,r=-0.67,n=10). A full length mutant survivin protein-pulsed dendritic cell vaccine expanded survivin reactive CD4+CD25- T cells after 12 days of in vitro culture (range 0-540x,median=42x), and expansion was achieved even in patients with low baseline survivin reactive CD4+ precursors. Conclusions: We have, for the first time, quantified the circulating CD4+CD25- precursor frequency against survivin and demonstrated this is lower in myeloma patients than healthy donors. The number of survivin reactive CD4+CD25- T cells is inversely associated with tumor survivin expression suggesting suppression of survivin responsive CD4+CD25- T cells. Further exploration of a full length mutant survivin protein vaccine which expands survivin reactive CD4+ cells independent of the survivin reactive precursor frequency is warranted.