CD70 identifies alloreactive T cells and represents a potential target for prevention and treatment of acute GVHD.

Graft-versus-host disease (GVHD) remains a major challenge after allogeneic hematopoietic stem cell transplantation (allo-HSCT), and further understanding of its immunopathology is crucial for developing new treatments. CD70 interacts with CD27 and is upregulated transiently on T cells after recent T-cell receptor (TCR) engagement. Here, we investigated the functional and clinical significance of CD70 expression on T cells during the early posttransplantation period. CD70 was expressed on a subset of highly activated memory T cells within the first 2 weeks after transplant, which then gradually declined in most patients. CD70+ T cells exhibited an open chromatin landscape and a transcriptional profile indicative of intense Myelocytomatosis oncogene (MYC)-driven glycolysis and proliferation. CD4+ and CD8+CD70+ T-cell numbers increased by ninefold and fourfold, respectively, during acute GVHD (aGVHD) and displayed an oligoclonal TCR repertoire. These cells expressed CCR4 and CCR6 chemokine receptors and were markedly increased in aGVHD tissue samples. Furthermore, CD70+ T cells demonstrated alloreactive specificity in vitro, and proliferative and inflammatory cytokine responses were markedly attenuated by CD70 blockade. These findings identify CD70 as a marker of highly activated alloreactive T cells and reveal the potential therapeutic importance of inhibiting CD27-CD70 costimulation in both the prophylaxis and treatment of aGVHD.