Cytomegalovirus HLA antigen load as a new potential predictive factor after haploidentical stem cell transplantation

Among the complications occurring after allogeneic hematopoietic stem cell transplantation (HSCT), infection by human Cytomegalovirus (CMV) represents one of the most relevant in terms of morbidity/mortality and specific management is required by either monitoring viral load and administer anti-CMV therapies. Due to the physiological role of the Human Leucocyte Antigen (HLA) system in presenting foreign antigens to the adaptive immune system to enhance viral clearance, we measured here the HLA antigen load for two immunodominant CMV peptides and correlate with transplant outcome in 238 consecutive adult patients undergoing haploidentical HSCT at a single center. Interestingly, a higher class I antigen load (i.e. above the median) for protein IE1 correlated with an inferior absolute incidence of CMV infection; moreover, a statistically significant correlation with lower non-relapse mortality and higher overall survival was observed (HR: 0.32, 0.12-0.84, p = 0.02; 0.34 (0.17-0.69, p = 0.003; respectively), with a protective effect in patients with high antigen load values. Despite additional research is needed, our exploratory data support the role of the HLA polymorphism on CMV infection and survival after HSCT. The introduction of CMV antigen load as a new potential predictive factor might contribute to further define the post-transplant risk on an individualised basis.