B-cell biomarkers in transplantation--from genes to therapy

An increased understanding of the mechanisms by which the immune system mounts a response to transplanted organs has allowed the development of immunosuppressive regimens that limit acute T-cell-mediated rejection (TCMR). However, the treatment of acute and chronic antibody-mediated rejection (ABMR) in kidney transplants remains sub-optimal. The occurrence and severity of antibody-mediated graft pathology are variable, and genetic polymorphisms that affect the magnitude and nature of the B-cell response, as well as effector functions of antibody, are likely to contribute to such phenotypic variation. Here we review current efforts to understand and quantify the contribution of B cells to renal transplant pathology by studying variation in DNA, mRNA and proteins. Large genetic studies with information on B-cell-specific genetic variants are scarce. At a transcriptomic level, there is evidence that B cells are essential contributors to transplant tolerance and may protect against TCMR and ABMR. In contrast, at the protein level, the detection of donor-specific human leukocyte antigen (HLA) antibodies and an assessment of their capacity to bind complement allow patients of high immunological risk to be identified. Other biomarkers, such as serum B-cell-activating factor (BAFF) or interleukin (IL)-10-producing B cells, may allow this risk stratification to be refined. An increased understanding of the significance of these biomarkers should allow a more accurate assessment of how an individual patient's B cells will impact allograft responses and thereby allow clinicians to adjust therapeutic strategies appropriately.