Longitudinal Changes in Donor-Derived Cell-Free DNA With Tocilizumab Treatment for Chronic Antibody-Mediated Rejection

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.

Inclusion Criteria:

- Age ≥18 years

- Enrolled within one month of biopsy-proven evidence of chronic active ABMR defined by
Banff 2017 diagnostic criteria

- Evidence of DSA detected in the blood within 6 months prior to consent.

- Able to understand and provide informed consent.

Exclusion Criteria:

- Known contraindications for therapy with tocilizumab:

- Hypersensitivity

- Elevated liver enzymes

- Patients at risk for GI perforation

- Absolute neutrophil count <500/mm3

- Platelet count <50,000/mm3

- Active infection

- Contraindications for kidney transplant biopsy, including bleeding diathesis or
technical/anatomical infeasibility for biopsy.

- Contraindications to donor-derived cell-free DNA (AlloSure) testing:

- Recipient of multiple transplanted organs.

- Recipient of a transplant from an identical twin.

- Pregnant

- Under the age of 18.

- Less than two weeks post-transplant.