Homeostatic proliferation leads to telomere attrition and increased PD-1 expression after autologous hematopoietic SCT for systemic sclerosis

In the months that follow autologous hematopoietic stem cell transplantation (AHSCT), lymphopenia drives homeostaticproliferation, leading to oligoclonal expansion of residual cells. Here we evaluated how replicative senescent and exhausted cells associated with clinical outcomes of 25 systemic sclerosis (SSc) patients who underwent AHSCT. Patients were clinically monitored for skin (modified Rodnan’s skin score, mRSS) and internal organ involvement and had blood samples collected before and semiannually, until 3 years post-AHSCT, for quantification of telomere length, CD8+ CD28− and PD-1+ cells, and serum cytokines. Patients were retrospectively classified as responders (n = 19) and non-responders (n = 6), according to clinical outcomes. At 6 months post-AHSCT, mRSS decreased (P < 0.001) and the pulmonary function stabilized, when compared with pre-transplant measures. In parallel, inflammatory cytokine (IL-6 and IL-1β) levels and telomere lengths decreased, whereas PD-1 expression on T-cells and the number of CD8+ CD28− cells expressing CD57 and FoxP3 increased. After AHSCT, responder patients presented higher PD-1 expression on T- (P < 0.05) and B- (P < 0.01) cells, and lower TGF-β, IL-6, G-CSF (P < 0.01), and IL-1β, IL-17A, MIP-1α, and IL-12 (P < 0.05) levels than non-responders. Homeostaticproliferation after AHSCT results in transient telomere attrition and increased numbers of senescent and exhausted cells. High PD-1 expression is associated with better clinical outcomes after AHSCT.