Nowadays, there have truly been spectacular advances in surgical techniques, the preservation of organs for transplants, the optimal and efficient selection of both donors and recipients, a more efficient diagnosis and prediction of possible complications of transplants, and important progress in the advances of pharmacological immunosuppression protocols and procedures. In this sense, survival rates after transplantation of various organs have been progressively increasing, especially in the case of lung transplants, whose average survival rate is usually lower than that of other types of solid organ transplants. Thus, detecting acute and subclinical rejection and chronic allograft rejection of any implant is important. This is important in all transplants, such as heart and lung transplants. In this last type of transplant, particularly, and due to the chronic dysfunction of the lung allograft, it is key to detect rejection early and on time, since it can reach close to half of the transplant patient population. Therefore, practical diagnostic tools are needed to visualize the level of allograft damage using genomic methods such as those that measure donor-derived cell-free DNA, where its amount increases in the plasma component of the transplant after tissue injury or due to allograft infection. This biomarker has become a key element with light and hope, but with some shadows of caution due to its use as a panacea. Our research team has experience in solid organ transplantation in quantifying this parameter in the progression of the lesion of the implanted allograft, and our experience and comparison with the published literature will be presented in the following review, discussing validated and non-validated results.

B cells have attracted increasing interest in the field of organ transplantation due to their newly discovered immunoregulatory properties in alloimmune responses. Traditionally, B cells have been primarily associated with adaptive immunity to foreign substances and alloreactive immune response to allografts, differentiating into antibody-producing plasma cells or memory cells upon antigen recognition and T cell collaboration. However, the existence of B cells with regulatory functions (Bregs) in humans has been widely confirmed, highlighting the presence of this subset, which has immunosuppressive properties and which might contribute to allograft tolerance, within the B cell compartment in humans and mice. In this mini review, we summarize all the information available in the published reports about the role of regulatory B cells in solid organ transplantation.

The Murcia Region unrelated donor (URD) registry was established in 1992 as part of the Spanish Bone Marrow Donor Registry (REDMO). This study aimed to comprehensively characterize the long-term evolution of URD recruitment, human leukocyte antigen (HLA) genetic diversity, allele and haplotype frequencies, and the spectrum of novel HLA alleles detected over the 34 years from 1992 to 2025. Recruitment trends, URD demographic characteristics, HLA allele and haplotype frequencies, and newly detected HLA alleles were analyzed retrospectively. HLA typing was performed using serological methods (1992–1996); PCR-SSO, PCR-SSP, and PCR-SSO Luminex (1997–2018); sequence-based typing (SBT, 2018–2021); and next-generation sequencing (NGS, 2021–2025). NGS was used to analyze a subset of 650 URDs to determine high-resolution HLA allele frequencies, Hardy–Weinberg equilibrium, expected heterozygosity, and extended HLA haplotypes. Newly detected HLA alleles were further characterized by the affected HLA locus and the localization of sequence variants within exons, introns, and the 3′-untranslated region (3′UTR). Between 1992 and 2025, 33.271 URDs were recruited, of whom 27.107 remained active in REDMO at the time of analysis. URD recruitment increased substantially following the implementation of the Spanish National Bone Marrow Plan in 2012 and reached a historical high in 2017. Additional recruitment peaks were associated with major regional public awareness campaigns. High-resolution HLA analysis of the NGS cohort demonstrated extensive immunogenetic diversity across all analyzed HLA loci, with a mean expected heterozygosity of 0.914. Ten frequent extended HLA haplotypes were identified, the most prevalent being HLA-A*29:02-C*16:01-B*44:03-DRB1*07:01-DQB1*02:02. Thirty-nine novel HLA alleles were characterized, exhibiting heterogeneous distributions among HLA loci and across coding and non-coding genomic regions. Exonic variants were predominantly detected in HLA-C, whereas intronic variants were mainly observed in HLA-C, HLA-DQB1, and HLA-A. This study integrates 34 years of URD recruitment with high-resolution immunogenetic characterization of the Murcia Region URD registry, providing new insights into the evolution of donor recruitment, HLA diversity, and the discovery of novel HLA alleles. The implementation of NGS enabled precise molecular characterization of HLA diversity and substantially expanded the detection and characterization of novel HLA alleles. Together, these findings provide a robust immunogenetic framework for the Murcia URD population, supporting donor recruitment strategies, optimization of URD searches, registry management, and future research in population genetics and hematopoietic stem cell transplantation.