The present invention relates to the field of organ transplant and the issues associated with transplant rejection. Antibody-mediated rejection (AMR) is associated with a poor transplant outcome. Pathogenic alloantibodies are usually directed against human leucocyte antigens (HLAs). However, evidence of AMR in the absence of anti-HLA antibodies suggests the presence of non-anti-HLA antibodies, identified as anti-endothelial cell antibodies (AECAs). The inventors have demonstrated that kidney recipients who experienced acute rejection with microvascular inflammation within the first 3 months after transplantation in the absence of anti-HLA donor-specific antibodies, carried, before transplantation, unknown AECAs in their sera that specifically targeted the glomerular microvascular endothelium. Thus, the present invention relates to in vitro methods and kits for determining the likelihood of occurrence of an acute microvascular rejection (AMVR) against a renal allograft in an individual.rnrnScientific publication(s):rnJ Am Soc Nephrol, 2019 Apr, Delville M. et al., Early Acute Microvascular Kidney Transplant Rejection in the Absence of Anti-HLA Antibodies Is Associated with Preformed IgG Antibodies against Diverse Glomerular Endothelial Cell Antigens, doi: 10.1681/ASN.rn