CD34+-selected stem cell boost for poor graft function after allogeneic hematopoietic stem cell transplantation: a large cohort study focusing on haploidentical transplantation

Poor graft function (PGF) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). CD34+-selected stem cell boost has shown promise; however, data in the haploidentical setting and after failure of thrombopoietin receptor agonists (TPO-RAs) are limited. Patients who received purified CD34+ boost for refractory PGF after HSCT at two centers were retrospectively analyzed. Outcomes included overall response rate (ORR), graft-versus-host disease (GVHD) and overall survival (OS). Among the 116 evaluable patients, 86.79% (103/116) received haploidentical transplants and 113 (97.4%) had received at least one platelet-stimulating agent, including TPO-RA and/or recombinant human thrombopoietin (rhTPO). The ORR was 67.24% (CR 62.93%, PR 4.31%). The 180-day cumulative recovery rates of neutrophils, hemoglobin, and platelets were 56.7%, 57.1%, and 65.7%, respectively. Active infection at the time of CD34+-selected stem cell boost was the sole independent predictor of lower ORR (OR = 3.786, 95% CI: 1.584-9.048, P = 0.003). The incidence of grade III-IV acute GVHD was 9.48%, and that of moderate-to-severe chronic GVHD was 11.21%. The OS was 64.66%. Responders had a significantly better OS than nonresponders (81.65% vs. 11.67%, P < 0.001). In conclusion, CD34+-selected stem cell boost is safe and highly effective for refractory PGF after allo-HSCT, including in haploidentical recipients and those who have failed TPO-RAs. Active infection at infusion predicts a poor treatment response, and non-responders have a dismal prognosis, underscoring the need for alternative strategies.