Poor graft function can be durably and safely improved by CD34⁺-selected stem cell boosts after allogeneic unrelated matched or mismatched hematopoietic cell transplantation

Insufficient production of leukocytes, thrombocytes and erythrocytes after allogeneic peripheral blood stem cell transplantation (PBSCT) represents a life-threatening complication.

In 20 adult patients with poor graft function (PGF defined as transfusion-dependent platelet counts <20,000/µl, or leukocytes <1500/µl, or transfusion-dependent anemia) and variable causes of PGF after allogeneic PBSCT, immunomagnetically selected CD34⁺ stem cell boosts (SCB) from matched unrelated (n = 8), mismatched unrelated (n = 11) or haploidentical (n = 1) donors were applied without prior conditioning.

Patients received a median of 4.6 × 10⁶ CD34⁺ cells per kilogram bodyweight (1.9–9.1 × 10⁶) and low T cell numbers (median 0.2 × 10⁴, range 0.04–0.6 × 10⁴). All patients showed responses in at least one hematopoietic lineage. Engraftment for platelets, leukocytes and hemoglobin was 88, 88 and 100 % after a median of 14, 13 and 18 days, respectively. With regard to the complete cohort, 90 % (n = 18) showed an increase in platelets (median 76,500/µl, range −7000 to 223,000/µl), 95 % (n = 19) had an increase in leukocytes (median 3110/µl, range 150–13,740/µl) and 90 % (n = 18) improved with regard to hemoglobin (median 1.9 g/dl, range −0.9 to 5.1 g/dl). Due to effective T cell depletion, only one patient developed graft versus host disease (GvHD, grade III) after SCB. Patients were followed for a median of 7.5 months (1–74 months) with 11 patients being alive and disease free with normalized peripheral blood counts at the end of follow-up.

CD34⁺-selected SCB are safe and effective and can durably improve PGF even in patients receiving grafts from unrelated matched or mismatched donors with low incidence of GvHD.