Characterisation of the expression of tumour antigens and biomarkers in myeloid leukaemia and ovarian cancer

Acute myeloid leukaemia (AML) and ovarian cancer (OVC) are two difficult to treat cancers. AML is often treatable however minimal residual disease (MRD) endures such that many patients who achieve remission eventually relapse and succumb to the disease. OVC affects approximately 7000 women in the U.K. every year. It can occur at any age but is most common after menopause. Diagnosis at an early stage of disease greatly improves the chances of survival however, patients tend to be diagnosed in the later stages of disease when treatment is often less effective. Immunotherapy has the potential to reduce MRD and delay or prevent relapse. In order for immunotherapy to work, tumour antigens need to be identified and characterised so they can be effectively targeted. Personalised treatments require the identification of biomarkers, for disease detection and confirmation, as well as to provide an indication of best treatment and the prediction of survival. PASD1 has been found to be frequently expressed in haematological malignancies and I wanted to determine if there was a correlation between the presence of antigen-specific T cells in the periphery of patients with AML and PASD1 protein expression in the leukaemic cells. The expression of other leukaemia antigens were concurrently examined as comparators. I performed RT-PCR on nine antigens and immunocytochemistry on PASD1 in 18 samples from AML patients. I found a correlation between PASD1 expression in AML samples and the presence of PASD1-specific T cells as detected on the pMHC array. OVC lacks suitable targets for immunotherapy with few CTAs having been identified. I examined the expression of SSX2IP and the CTAs PASD1 and SSX2 in OVC. I compared the protein expression of these known tumour antigens to the “gold standard” biomarker for the diagnosis of OVC, CA125 and two other proteins known to be promising in the diagnosis of OVC, HE4 and WT1. I analysed commercially available paraffin-embedded OVC multiple tissue arrays (MTAs) containing 191 samples, predominantly stage I (n= 166), II (n= 15) and III (n= 6) OVC as well as healthy donor (n= 8) and normal adjacent tissues (n= 8). Scoring was performed in a single blinded fashion. I found SSX2A to be expressed at a score level of 3 with a frequency (37/191) that exceeded that of CA125 (14/191), HE4 (14/191), WT1 (1//191) or PASD1 (0/191). To confirm this expression I used two additional commercially-available antibodies that recognise the region common to SSX2A and B, and an antibody specific for SSX2A. Using SSX2 peptides, I blocked the immunolabelling of SSX2 in SSX2-positive cell lines showing that the immunolabelling of SSX2 and SSX2A was specific. I demonstrated that the expression of SSX2 and specifically SSX2A was reproducible and restricted to ovarian cancer with little or no expression in endometrial tissues, or diseased or inflamed endometrial tissue. In summary, these studies demonstrated that PASD1 expression in leukaemia cells correlated with the presence of PASD1-specific T cells in the periphery of presentation AML patients. I have shown that PASD1 specific-T cells are present in AML patients at diagnosis and that immunotherapy targeting PASD1 could be used to break tolerance and clear residual leukaemia cells during first remission. Analysis of the expression of three antigens in OVC, identified the specific expression of SSX2, in particular SSX2A in OVC but not healthy or diseased endometrial tissues. The expression of SSX2A was more frequent and more specific to OVC, than HE4 and WT1, and more frequent at higher intensity, especially in early stage OVC, than CA125. SSX2 and explicitly SSX2A requires further investigation to determine whether the high level of background at score 2 can be reduced with better blocking of non-specific sites. This may require the use of different SSX2 antibodies or an improved staining protocol.