The present study aims to evaluate the usefulness of protocol biopsies in a cohort of renal transplant patients of high immunological risk for graft injury and loss.

This will be a prospective study undertaken at the Renal Transplant Unit of Hospital of Clinics of Porto Alegre. In addition to the routine evaluation commonly carried-out at this post-transplant period, protocol biopsies will be performed at the 10th-week post-transplantation in high-risk transplant recipients. Biopsy fragments will be evaluated for tissue immune aggression (mainly cellular and antibody-mediated rejections) and other conditions such as infections, particularly polyomavirus and cytomegalovirus and medication toxicities. The presence of donor-specific antibodies and graft-damaging infectious agents will also be searched in the peripheral blood at the time of biopsy.One hundred patients will be randomized to a protocol biopsy and noninvasive assessment or only for noninvasive assessment. The hypothesis of the study is that biopsies will lead to treatments that may allow better outcomes of renal transplants, related to lowering the progression of subclinical aggressions, avoiding or delaying graft loss and preserving or decreasing the rate of loss of the glomerular filtration rate. Therefore, this strategy has the possibility of reaching clinical practice routine and thus contribute positively to the management of renal transplant patients.

Inclusion Criteria:

Adult kidney transplants, with high immunological risk, who consented to participate in the study by signing the informed consent form. The high immune risk is defined by:

• Positive pre-transplant T-lymphocyte cross-test by flow cytometry (channel deviation greater than 62);
• Flow cytometry pre-transplantation positive B lymphocyte cross-test (channel deviation greater than 112);
• Calculated panel reactivity greater than 50% in class I and / or class II;
• Presence in the pre-transplantation serum of donor class I and / or II anti-Human Leukocyte Antigen antibodies with intensity and fluorescence greater than 1000;
• Occurrence of cellular or antibody-mediated rejection within 30 days prior to the date of the protocol biopsy.

Exclusion Criteria:

• Patients with contraindication to renal graft biopsy;
• Patients whose biopsy fragments are not representative;
• Patients with graft dysfunction in whom renal graft biopsy is indicated within 4 weeks prior to protocol biopsy.