Interleukin-17 and transplant immunology: clinical evidence from hematopoietic cell transplantation

Interleukin-17 (IL-17), a proinflammatory cytokine primarily produced by Th17 cells, plays a complex role in transplant immunology. Its involvement in graft-versus-host disease (GvHD) and immune regulation following hematopoietic cell transplantation (HCT) has garnered significant clinical interest, though findings remain inconsistent.

This narrative review summarizes clinical studies in human HCT recipients investigating IL-17 cytokine levels, Th17 cell activity, and IL-17 gene polymorphisms associated with transplant outcomes. While several studies report associations between elevated IL-17 or Th17 levels and increased GvHD risk, results vary widely due to differences in study design, patient populations, and measurement methods.

IL-17 is a promising, though context-dependent, biomarker and therapeutic target in HCT. Its dual roles in promoting inflammation and supporting antimicrobial defense complicate therapeutic modulation. Future studies should focus on standardized assays, multi-omics approaches, and longitudinal designs to clarify its clinical utility. Tailored strategies that modulate IL-17 without impairing immune reconstitution or graft-versus-leukemia effects are likely to guide future interventions.