CD8+ T Cells Specific for Cancer-Testis Antigens Are Found in Many Patients with Multiple Myeloma and Correlate with Disease Burden.

Proteins from the family known as ‘cancer-testis antigens’ (CTAg) are expressed in some cases of multiple myeloma and subsets of acute myeloid leukaemia. CTAg can stimulate CD8+ T cell responses in patients with melanoma but there are no reports of CTAg-specific immune response in patients with haematological malignancy. Such information is critical to assess whether or not these antigens act as targets for tumour-specific immunity or if they could be used as targets for immunotherapy. We have used twelve peptide epitopes from a range of cancer-testis antigens which have been previously defined as epitopes for CD8+ T cells. These were used to screen for tumour-specific T-cells in blood of patients with multiple myeloma at various stages of their disease. The IFNγ cytokine secretion assay was used to detect functional responses and magnetic selection was employed to increase the sensitivity of detection. FACS analysis was used to quantitate the frequency of responding cells. 37 patients were screened with an age range of between 45 and 88 years. Blood samples were taken at monthly intervals and the percentage of CD8+ T cells responding to each peptide was calculated. 13 patients responded to 1 or more of the peptides with a range between 0.01% and 0.7% of the total CD8+ T cell pool. The frequency of the tumour-specific response fluctuated during treatment in individual patients. Analysis of the CTAg-specific immune response in relation to disease course revealed that the immune response was generally correlated with tumour burden as revealed by the paraprotein level. CTAg HLA-peptide tetramers incorporating peptides from LAGE-1 and MAGE-2 were able to directly visualize CTAg-reactive T cells in PBMC. CTAg-specific CD8+ T cells may have been primed and expanded by expression of CTAg on tumour cells or following ‘cross presentation’ through dendritic cells. In conclusion, T cells specific for cancer-testis antigens are present in the blood of a subset of patients with multiple myeloma. The clinical significance of this observation is currently being addressed.