Abstract
An immunologically mediated graft-versus-tumor (GVT) underlies the curative effect of reduced intensity allografts in acute myeloid leukaemia (AML) and other haematologic malignancies. Cancer testis antigens (CTA) represent a family of immunodominant proteins that are variably expressed in haematological malignancies and represent a potential target of a GVT response. Importantly a number of CTA genes demonstrate promoter hypermethylation in solid tumours which can be reversed using demethylating agents such as azacitidine. We have therefore examined whether donor T cell responses to CTAs are observed in patients allografted for AML and multiple myeloma (MM) and whether epigenetic therapies can be used to manipulate T cell mediating killing of haemopoietic targets.
We screened 37 patients with AML and 8 patients with MM, who had not received demethylating agent treatment, for T cell responses to 25 peptides derived from 10 CTA genes, including BAGE, LAGE, MAGE-A1, MAGE-A2, MAGE-A3, MAGE-A4, MAGE-C2, RAGE-1, by interferon-γ cytokine secretion assay (IFN-γ CSA). We found CTA specific T cells in 11.1% of patients (5 of 45) with frequencies ranging from 0.0005% to 0.2% (median 0.024%). Subsequently, we studied expression of 15 cancer-testis antigens (CTA) at the RNA and protein levels in AML, MM and Hodgkins’ lymphoma cell lines before and after exposure to demethylating agent 5-aza-2′-deoxycytidine (Aza) and histone deacetylase inhibitor sodium valproate (VPA), as single agents and in combination. We found that expression of CTAs HAGE, SACA3, SPANXB, LAGE, XAGE, MAGEA3 could be induced in a dose dependent manner by Aza alone but not with VPA alone. We also observed that expression induced by Aza treatment was increased further by combination treatment with VPA. Induction of CTAs was confirmed in vitro in primary AML cells and in vivo in 2/6 patients on VPA/Aza trial. Furthermore, using interferon-γ ELISA assay we observed that Aza-induced expression of the CTA MAGEA3 in MM cell lines was accompanied by increased recognition by MAGEA3-specific T cells.
These studies confirm the importance of members of the CTA family as targets of a T cell mediated immune response. Our data demonstrate that the expression of these putative immunodominant antigens in haematological malignancies in disease such as AML and myeloma, can be significantly up-regulated by epigenetic therapies with functional increases in target cell killing and support the use of adjunctive epigenetic therapies after allogeneic transplantation with the aim of augmenting a GVL response. A Phase II clinical trial combining post transplant azacitidine with a reduced intensity allograft is currently ongoing in patients with AML.
Spontaneous CD4+and CD8+T-cell responses directed against cancer testis antigens are present in the peripheral blood of testicular cancer patients