These infiltrates are nodular in appearance and are often referred to as tertiary lymphatic organs, ectopic lymphoid tissue, or lymphoid neogenesis because of their amazing resemblance to the lymphatic organization seen in the germinal centers of lymph nodes and spleen (8, 9). immunoglobulin gene somatic recombination machinery usually restricted to highly activated lymphocytes in germinal centers and lymphomas. An analogy can be made between the inescapable antigenic drive in chronic contamination versus that in an allograft, both of which may lead to emergence of dominant B-cell clones and even lymphoid malignancy. Keywords: transplantation, combinatorial antibody libraries, next-generation sequencing Although kidney L67 rejection following allotransplantation had been considered to be largely a T-cell mediated phenomenon (1, 2), there is growing evidence that B?cells and antibodies may play a role in the process (3C5). In this regard, the nature of the lymphoid cells that infiltrate into the transplanted kidney is usually of special interest (6, 7). These infiltrates are nodular in appearance and are often referred to as tertiary lymphatic organs, ectopic lymphoid tissue, or lymphoid L67 neogenesis because of their amazing resemblance to the lymphatic business seen in the germinal centers of lymph nodes and spleen (8, 9). Fgf2 The similarity of these nodules to those in lymphoid organs goes beyond simple morphology in that they include the full spectrum of T?cell, B?cell, and dendritic cell components present in the organized nodules of spleen and lymph nodes and have been shown to produce alloantibodies (10, 11). Indeed, it has been suggested that this gene expression pattern of the lymphoid infiltrates in rejected kidneys recapitulates the ontogenic program of the embryo during development of the secondary lymphoid organs (10). Some other studies have suggested that these infiltrates are associated with poor survival of the transplanted kidney (12, 13). Despite their frequent occurrence and potential role in kidney rejection, little is known about the molecular nature of these infiltrates, particularly as it relates to their B-cell receptors (BCRs). One wonders about the stage of differentiation of these B?cells, whether they are of restricted L67 diversity, differ in kidneys that function well versus those that are rejecting, and have shared antibody specificity amongst different patients. These issues arise because of the unique selective pressure that a transplanted organ exerts around the evolution of an immune response. Many questions concerning the nature of the B?lymphocytes that infiltrate transplanted kidneys can now be addressed using combinatorial antibody libraries. Such libraries allow one to characterize the diversity of the entire antibody repertoire of B-cell populations (14C16). Here, we report creation of combinatorial antibody libraries from two different pools of RNA isolated from 20 biopsies of transplanted human kidneys. One pool was from 10 patients biopsied by protocol where the graft was performing well and histology was normal (TX) and the other was from 10 patients with the progressive renal dysfunction of chronic allograft nephropathy (CAN) and histology confirming interstitial fibrosis and tubular atrophy (IFTA) (17). In addition, matched libraries were prepared from the transplanted kidneys and peripheral blood lymphocytes of three patients. Analysis of these libraries showed that this B-cell response in patients with kidney transplants is usually highly restricted to dominant germ line genes and complementarity determining region 3 (CDR3) and the lymphocytes within a cluster appear to be clonal. Both the infiltrating B?cells and peripheral blood of transplant patients have dominant clones, but L67 those in the blood differ from those in the kidney. Results Patient Populations Studied. Kidney biopsies and peripheral blood samples were obtained from 23 patients who gave informed consent under a protocol previously described (18, 19). Human subject research protocols were approved by the institutional review board (IRB) of The Scripps Research Institute and the IRBs of collaborating centers. The kidneys were classified as.