Chronic antibody-mediated rejection (ABMR) is now recognized as the leading cause of late kidney transplant failure (1). A number of new immunosuppressive medications have been introduced to the field of kidney transplantation over the last twenty years, leading to a reduction in early acute rejection rates (2). However, long-term graft survival has not improved, primarily because of failure to make a timely diagnosis of chronic ABMR and a lack of effective therapeutic options. To date, treatment options for chronic ABMR are limited and include intravenous immunoglobulin (IVIg), rituximab, and plasmapheresis. These agents are effective for treatment of acute ABMR; however, they are generally ineffective in sustaining kidney function and prolonging graft survival in chronic ABMR.
Interleukin-6 (IL-6) blockade has emerged as a promising therapy for chronic ABMR. Our group recently reported that tocilizumab, a humanized monoclonal antibody against the IL-6 receptor, administered monthly to patients with chronic ABMR is associated with a reduction in donor specific antibodies (DSA), stabilization of renal function, improvement in histologic features of chronic ABMR, and excellent patient and graft survival up to six years (3).
The diagnostic criteria for antibody-mediated rejection in kidney transplantation requires serologic evidence of donor-specific antibodies to human leukocyte antigen (HLA) or other antigens in conjunction with histologic findings of ABMR on biopsy for a definitive diagnosis of ABMR (4). The criteria recognize that the mere presence of DSA alone is not sufficient to classify a patient as having ABMR, as has been described previously (5). Among patients treated for ABMR, a reduction in DSA is associated with a favorable response but is only observed in a small percentage of treated patients (6). Among patients with chronic ABMR who are treated, there is a subset with persistence of high titer DSA, yet stable renal function and resolution of active lesions of ABMR on follow-up kidney biopsy. Although these patients may not warrant continuing therapy with tocilizumab, they cannot be distinguished from patients with persistently active ABMR without undergoing an additional allograft biopsy. A non-invasive test for ABMR is preferred, as allograft biopsies are invasive, resource-intensive, carry a risk of bleeding, and are time-consuming for the patient. If validated, non-invasive testing for ABMR can be useful for monitoring for a treatment response and may help guide therapy for ABMR.
Because donor-derived cell-free DNA (Allosure) is predictive of rejection n kidney transplantation, longitudinal changes in the percentage of donor-derived cell free DNA detected in plasma of kidney transplant recipients with chronic ABMR may correlate with a histologic and clinical response to treatment. The primary objective is to assess whether longitudinal changes in donor-derived cell-free DNA correlate with histologic and clinical response to treatment with tocilizumab for chronic ABMR. The secondary objectives are to assess the test performance of donor-derived cell-free DNA measured against histologic findings on biopsy, provide molecular evidence for response to tocilizumab therapy, and to describe the time course of treatment effect of tocilizumab in chronic ABMR.
