Adhesion and niche residency factors in plasma cell differentiation and neoplasia

Haematological malignancies are incredibly complex due to the nature of immune cell maturation and the stages that malignancies can arise. Therefore, understanding the underlying mechanisms of survival, homing and migration to the survival niche will aid diagnosis and understanding of disease metastasis. This project aims to investigate cell surface phenotype during plasma cell differentiation of an adhesion signature. This adhesion signature was initially identified using RNA-sequencing and microarray. The adhesion signature was upregulated in plasmacytoma an isolated, cohesive tumour compared to plasmablastic lymphoma a dispersed, proliferative disorder. Along with a set of niche factors involved in homing and migration, there is a particular focus on the protocadherin-gamma (PCDH-γ) locus which we have shown to be epigenetically regulated in B-cells, this unique mechanism generates an identity code on the cell surface that may influence cell-cell interactions within the bone marrow microenvironment. My work uses a novel in vitro differentiation system to investigate the establishment of an adhesion surface phenotype throughout plasma cell differentiation from peripheral blood and malignant bone marrow samples. I aimed to elucidate how this pattern of expression is established in plasma cells and investigate what link this has to the microenvironment. Expression patterns throughout B-cell differentiation were assessed using an in vitro differentiation system to generate antibody-secreting plasma cells from naïve and memory B-cells isolated from peripheral blood of healthy volunteers. A distinct set of patterns for the niche factors was a standard feature of B-cell differentiation, irrespective of the niche conditions stimulating the PC programme with evidence of regulation both transcriptionally and post-transcriptionally. The first evidence for surface expression of the PCDH-γ locus was revealed for 3 of the 22 members of the gamma cluster. The pattern of PCDHGA6, PCDHGB4 & PCDHGB5 expression was consistent between donors and niche conditions. This is consistent with epigenetic regulation determining the expression patterns that are observed at the cell surface. The highest level of surface PCDH-γ expression was at the PC stage of differentiation correlating with mRNA expression. This provides evidence that the PCDHs may indeed act as a unique identity barcode on the surface of PC.