Fludarabine/Treosulfan/Thiotepa/ATG Conditioning Leads To High Rates Of Long-Term Engraftment and Low Toxicity Enabling The Use Of Mismatched and Unrelated Donors For Transplantation In Haemoglobinopathies

Blood and marrow transplantation (BMT) is the only proven curative treatment available for haemoglobinopathies. From October 2010 to May 2013 thirty-eight patients with haemoglobinoapathies received a BMT at St. Mary’s Hospital, London. The conditioning included fludarabine 160 mg/m², treosulfan 42 g/m², thiotepa 10 mg/kg and ATG (Thymoglobulin) 7.5 mg/kg or 11.25 mg/kg (FTTA). GvHD prophylaxis was ciclosporin for six months and MMF until molecular evidence of donor engraftment. Patients with SCD received clonazepam CNS prophylaxis whilst on immunosuppression. Endogenous haemopoiesis was suppressed with hypertransfusions for at least six weeks pre-transplantation to minimise the risk of rejection. All patients had iron load assessed by MRI T2* and FerriScan and hepatic fibrosis staged by liver biopsy pre-transplantation. Patients with liver fibrosis Ishak ≥3 were given defibrotide prophylaxis.

Twenty-six patients suffered from thalassaemia major (TM) and from 12 sickle cell disease (SCD). Patients with TM were Pesaro class I or II. Patients with SCD were transplanted for stroke or recurrent vaso-oclusive crisis and/or acute chest syndrome not responding to hydroxycarbamide. The median age was 7 years (range 2-17). The median follow-up was 10.18 months (range 1.02 -25.1).

Thirty-six patients received stem cells from a related donor (31 matched sibling bone marrow, 2 matched other relatives, two 9/10 mismatched siblings, and one 9/10 mismatched other relative) and 2 from unrelated donors (1 fully matched and one 9/10 mismatch). The source of stem cells was bone marrow (BM) in 32 patients, mixed BM and cord blood (CB) in 3 patients, CB in 2 patients and PBSC in one patient. The median cell dose 3.61 x10⁸ TNC/kg (range 0.58 -9.77) and 5.99 x10⁸ TNC/kg (range 1.15 -14.23).

All patients engrafted, though one related CB transplant suffered secondary graft failure on day +26 due to disseminated adenovirus infection. The median neutrophil engraftment occurred on day +12 (range 9-21). Three patients (7.8%) suffered VOD, presenting at a median of 9 days (7-11) which was successfully treated with defibrotide. Acute GvHD grade 1 occurred in 1 patient (2.6%) and grade ≥2 in 5 patients (13.2%), which resolved in all patients including 2 who received MSC. cGVHD >day +100 post-transplantation was limited in 2 (7.9%) and extensive in 2 patients (5.3%) and fully resolved in all cases with appropriate treatment. Two patients have died of a transplant related cause: a related CB transplant for TM of disseminated adenovirus infection on day +31 and a related BM transplant for SCD of an intracranial haemorrhage on day +185 due to immune thrombocytopenia and parvovirus B19 infection.

Chimerism studies in whole blood demonstrated donor haemopoiesis as follows: day +28: 94% >95% and 6% >90-95%; day +90: 93.2% >95%, 3.4% >90-95% and 3.4% >80-90%; day +120: 84% >95%, 8% >90-95%, 4% >50-80% and 4% <20%; day +150: 64% >95%, 24% >90-95%, 4% >80-90%, 4% >50-80% and 4% <20%; day +180: 62.5% >95%, 25% >90-95%, 8.3% >80-90% and 4.3% >50-80%; day +360: 61.5% >95%, 30.8% >90-95% and 7.7% >30-50%. Donor T-cell lymphopoiesis was day +28: 100% (28 – 100), day +90: 99% (16-100), day +150: 96% (36-100), day +180: 96% (54-100) and day +360: 94.5% (78-100).

In conclusion, FTTA leads to high levels of long-term donor engraftment and enables the use of mismatched and unrelated donors for transplantation in haemoglobinopathies with limited toxicity