Temporal Evolution of Functional Immune Reconstitution after Allogeneic HSCT

Immune reconstitution (IR) following allogeneic hematopoietic stem cell transplantation (allo-HSCT) is currently monitored by measuring the absolute number of immune effectors. However, this approach does not capture functional immune capacities. In this study, we aimed to evaluate the temporal evolution of functional IR alongside traditional immune cell count measurements. Whole-blood stimulation with TruCulture tubes (Myriad Rbm, Austin, TX, USA) containing lipopolysaccharides or staphylococcal enterotoxin B was performed on 55 allo-HSCT recipients at 6 and 12 months post-transplant, and on 10 healthy volunteers. The expression of 144 immune-related genes was quantified using NanoString technology (NanoString Technologies, Seattle, WA, USA) . The temporal follow-up of functional immune profiles was analyzed over time according to demographics, clinical characteristics, and immune cell counts. The evaluation of IR in allo-HSCT recipients up to 12 months post-transplant showed a significant discrepancy between quantitative and qualitative assessments. While immune cell counts improved, eg. the proportion of recipients reaching normal CD4⁺ T cell values, increasing from 25% to 46%, transcriptomic profiles showed persistent functional alterations. More than 78% of less-induced genes observed at 6 months still exhibited a reduced expression at 12 months post-transplant. Transcriptomic immune profiling divulged diverse functional outcomes linked to clinical characteristics, which were not reflected by cell count assessments alone. Herein, we emphasize that quantitative assessment of immune effectors alone is not informative enough to classify allo-HSCT recipients regarding functional immune capacity. Our findings highlight the value of implementing immune functional assay (IFA) as an additional tool for a comprehensive understanding of functional IR post-allo-HSCT, which could serve as a straightforward and efficient method for enabling personalized post-transplant management.