PO-408 New targets for the immunotherapy of adult B-cell acute lymphocytic leukaemia

Abstract

IntroductionB-cell acute lymphocytic leukaemia (B-ALL) is a rare heterogeneous disease characterised by excess lymphoblasts of the B-lineage in the bone marrow. The most effective treatment to date is allogeneic stem cell transplant which can improve overall survival rates. This may in part be due to a ‘graft-versus-leukaemia’ effect via antigens that are are specifically expressed by leukaemic cells. However, few of the cancer antigens have been identified in adult B-ALL which could act as targets for immunotherapy.Material and methodsThrough literature evaluation we identified potential target antigens for the immunotherapy of adult B-ALL. We wanted to determine which known antigens would act as comparators for novel antigens we are identifying through the use of antibody specific profiling on sera samples. We used an existing microarray dataset (GSE38403) to examine whether the expression of the antigens we had identified as promising, by proto-array and in silico methods, were frequently expressed in 215 B-ALL patient samples and correlated with survival. Real-time quantitative (RQ)-PCR and immunocytochemistry were used to confirm the expression of the most promising antigens in our patient samples.Results and discussionsBy real-time PCR we examined a total of 12 different antigens in adult B-ALL patient samples and healthy volunteers. We found that only survivin and WT1 were expressed in B-ALL patient samples (7/11 and 6/11, respectively) but not normal donor control samples (0/8). RQ-PCR showed that survivin was the only antigen whose transcript exhibited significantly higher expression in the B-ALL samples (n=10) compared with healthy controls (n=4) (p=0.015). Immunolabelling detected SSX2, SSX2IP, survivin and WT1 protein expression in all 10 B-ALL samples examined, but survivin was not detectable in healthy volunteer samples. To determine whether these findings were supported by the analyses of a larger cohort of patient samples, we performed metadata analysis on an already published microarray dataset. By microarray analyses, survivin (p=0.013, ANOVA) was found to be frequently over-expressed in B-ALL patient samples versus normal pre-B cells. In addition, we also found that having HAGE and SSX2IP gene expression were poor prognostic markers for the probability of overall survival, although neither reached statistical significance.ConclusionFurther analysis of patient samples and healthy donor lymphoblasts will determine whether survivin remains the most promising target for the immunotherapy of adult B-ALL.