Purpose of review <p>To evaluate and summarize the current landscape of peripheral blood monitoring and immunophenotyping of patients following heart and lung transplantation, highlighting recent advances in monitoring which may help to predict and improve clinical outcomes.</p> Recent findings <p>Immunological contributions to primary graft dysfunction, acute allograft dysfunction, and chronic allograft dysfunction are reviewed. In heart transplantation, novel diagnostic approaches like donor-derived cell-free DNA (dd-cfDNA) and gene expression profiling (GEP) show promise as alternatives to invasive biopsies for detecting rejection. Following lung transplantation, various immune cell populations—including NK cells, T cells, B cells, and regulatory T cells—demonstrate distinct dynamics between peripheral blood and the allograft compartment. Key findings include associations between circulating immune cell phenotypes and chronic lung allograft dysfunction (CLAD), donor-specific antibodies correlating with graft survival, and telomere length serving as a potential biomarker.</p> Summary <p>Immune cells in circulation do not always phenotypically reflect immune cells in the allograft. While some promising markers for allograft dysfunction exist, further studies are needed to correlate them with disease severity and/or progression.</p>