The respective iGeneTRAiN study designs and characteristics for subjects recruited with existing GWAS data are outlined in Table 1. In total, there are over 16494 recipients with 11669 donors across the 4 solid organs. The existing GWAS include participants with a wide geographic representation across the United States, The Netherlands, United Kingdom, Ireland, Spain, and Australia. The majority of transplant recipients in the studies are adults with the exception of 2 cohorts, which comprise approximately 1060 pediatric subjects. The study designs are primarily single or multisite prospective cohorts, and although a small number are retrospective in recruitment approach, most are continuing to accrue longitudinal transplant phenotypes and outcome events. Approximately 18900 samples were subjected to GWAS using a transplant-specific genomewide genotyping array (described below) and approximately 8600 additional samples genotyped using conventional GWAS arrays. The iGeneTRAiN studies range in size from less than 100 D-R pairs to several thousands of recipients. All kidney studies and 2 liver studies have varied proportions of living donor versus deceased donors. Of the 16494 recipients, approximately 81.3%, 12.1%, 1.7%, and 4% are of are of European, African, Asian, and Hispanic ancestry, respectively, with the remainder classified as “other,” and approximately 62% of D-R pairs have conventional 2- or 4-digit HLA typing available. Table S1 (SDC, http://links.lww.com/TP/B191) outlines information regarding specific clinical HLA typing performed, pretransplant anti-HLA immunization status, including peak panel-reactive antibody (PRA), and posttransplant recording of de novo anti-HLA antibodies across each of the 22 studies.