Animal hematopoietic cell transplantation (HCT) models and several small clinical trials showed that successful engraftment can be achieved across HLA-haplotype difference after reduced-intensity conditioning (RIC). Furthermore, decreased graft-versus-host disease (GVHD) and transplantation-related mortality (TRM) after RIC was shown in a swine leukocyte antigen-haploidentical HCT experiment. Therefore, a protocol investigating the role of RIC in HLA-haploidentical familial donor HCT was initiated in April 2004 and 20 patients [13 male and 7 female; median age 26.5 years (16–65)] without HLA-matched donor enrolled until June 2007. The diagnosis were AML (n=9), ALL (n=4), acute biphenotypic leukemia (n=1), MDS (n=4), and SAA (n=2), and all patients had high-risk features, i.e. first complete remission (CR) but with high-risk chromosomal abnormality (n=1), first CR after salvage (n=1), second CR (n=6), recurrent/refractory state (n=7), immunotherapy failure (n=4), and high-risk MDS (RAEB-1, n=1). The RIC included iv busulfan 3.2 mg/kg × 2, fludarabine 30 mg/m2 × 6, plus anti-thymocyte globulin [Thymoglobuline 3 mg/kg (n=17) or Lymphoglobuline 15 mg/kg (n=3)] × 4. After receiving G-CSF, the donors (13 mothers; 5 offsprings; and 2 HLA-haploidentical siblings) underwent 2 or 3 daily leukapheresis, and the collected cells were given to patients without T cell depletion [medians of; 7.9 (3.7–12.1)×108/kg MNC, 6.9 (3.6–73.5)×106/kg CD34+ cells, and 4.6 (1.8–8.5)×108/kg CD3+ cells]. GVHD prophylaxis was cyclosporine 3 mg/kg/day iv from day -1 and a short course of methotrexate. As a part of separate phase 1 study, the two most-recently enrolled patients received additional donor CD34+ cell-derived NK cells 6 weeks after HCT. Except one patients with SAA who died due to K. pneumoniae sepsis on day 18, all 19 evaluable patients engrafted with ANC> 500/μl median 17 days (12–53) and platelet> 20,000/μl median 23 days (12–100) after HCT. Eight patients experienced acute GVHD (grades I, II, III, and IV; 2, 3, 2, and 1, respectively). Cumulative incidences (CI) of overall and grade II-IV acute GVHD were 40 and 30%, respectively. Eight patients experienced chronic GVHD (limited, 4; extensive, 4; CI, 51%). Fourteen showed positive CMV antigenemia, while 2 suffered CMV colitis, which resolved after treatment. As early as 2 weeks after HCT, 15 of 16 evaluable patients, and, by 4 weeks, all of 17 evaluable patients showed donor chimerism ≥95% on STR-PCR, which was maintained until 24 weeks in all 11 patients tested. Thirteen patients are alive after median follow-up of 13.6 months (1.5–37.9; Kaplan-Meier survival, 55.6%). Of 16 patients with acute leukemia and high-risk MDS, 8 remain alive without recurrence (event-free-survival, 40.9%). Two patients died of K. pneumoniae sepsis and grade IV acute GVHD, respectively (CI of TRM, 11%). Immune recovery in 10 patients without relapse for > 6 months showed robust lymphocyte contents and immunoglobulin levels at 6 months (means of; 1,060/ul CD3+, 222/ul CD4+, 767/ul CD8+ cells, and 1,317 mg/dl IgG) and 12 months. After RIC, consistent engraftment and durable complete donor hematopoietic chimerism can be achieved from HLA-haploidentical familial donor. The frequencies of GVHD and TRM were low.

Author notes

Disclosure: No relevant conflicts of interest to declare.