Validation of lymphoma-associated antigens identified using autoantibody profiling and protein arrays

Diffuse large B-cell lymphoma (DLBCL) is an aggressive lymphoma subtype with heterogeneous clinical outcome and a significant number of patients still die of their disease. Characterising lymphoma patients’ autoantibody repertoires represent one approach to improve the understanding of their disease biology. Our hypothesis was that characterisation of antigens eliciting humoural immune responses in lymphoma patients may provide insights into mechanisms of lymphomagenesis and identify novel diagnostic/therapeutic targets.HIP1R was validated as a novel B-NHL autoantigen by immunoblotting with patients’ sera. No response was identified to the related HIP1 protein. Consistent with this finding, more widespread expression of HIP1R, compared to HIP1, was observed in lymphoma cell lines. Expression studies, at both transcript (qRT-PCR and analysis of microarray datasets) and protein levels (blotting and immunolabelling), identified abundant HIP1R in normal B cells and low level expression in a poor prognosis activated B-cell (ABC)-like DLBCL subtype. Upregulation of HIP1R expression was observed in activated non-malignant B cells at both transcript and protein levels, suggesting that downregulation of HIP1R expression in ABC-DLBCL might be a disease-related process. Despite its potential for DLBCL subtyping, HIP1R protein expression was not statistically significantly associated with patients’ survival in a series of 256 DLBCL. Short FOXP1 isoforms were identified as one mechanism repressing HIP1R transcription in an ABC-DLBCL cell line. Phenotypic analysis of HIP1R-depleted B-cell lymphoma cells indicated that HIP1R silencing could increase the surface levels of B-cell receptor (BCR) components such as IgM and CD79b.HIP1R represents a novel lymphoma autoantigen and cell-of-origin marker for distinguishing germinal centre- versus ABC-DLBCL subtypes. As ABC-DLBCL survival is dependent on chronic BCR signalling, future studies will address whether HIP1R silencing plays a fundamental role in disease pathogenesis by promoting BCR signalling.