Pre-Transplantation Suppression of Haemopoiesis Is Associated with a High Rate of Macrophage Activation Syndrome in Ptcy Haploidentical Transplantation for Haemoglobinopathies

Post infusion of stem cell cyclosphosphamide (PTCy) has enable transplantation across the HLA barrier and with the use of reduced intensity conditioning protocols. This constitutes a very important development for conditions affecting populations poorly represented in the donor registries, like haemoglobinopathies. However, PTCy in haemoglobinopathies is associated with a high risk of primary graft failure using standard regimens unless additional interventions are applied: suppression of haemopoiesis pre-transplantation with hydroxycarbamide and azathioprine, and the addition of thiotepa. We report for the first time an unexpected high rate of macrophage activation syndrome with this approach.

Three centres (two in India and one in London, UK) used a common protocol to undertake 87 haploidentical bone marrow transplants for patients with haemoglobinopathies. The backbone of the conditioning regimen was provided by the reduced intensity PTCy approach developed by John Hopkins University for haploidentical transplantation in SCD (Bolaños-Meade, Blood 2012). This included the use of ATG 0.5 mg/kg day -9 and 2 mg/kg days -8 and -7 (total dose 4.5 mg/kg), fludarabine 30 mg/m² days -6 to -2 (total dose 150 mg/m²), cyclophosphamide 14.5 mg/kg days -6 and -5 (total dose 29 mg/kg) and TBI 200 cGy days -1. Post-transplantation patients received two doses of cyclophosphamide 50 mg/kg on days +3 and +4 to delete alloreactive T cells whilst preserving haempoietic stem cells, and GvHD prophylaxis was provided from day +5 with MMF until day +35 and sirolimus targeting 10 - 15 ng/mL. The source of stem cells was bone marrow harvested following priming with filgrastim 10 mg/kg/day for five days and aiming to obtain a cell dose of >8 x 10⁸ TNC/kg. Supportive care recommendations included granulocyte colony-stimulating factor commenced on day +7 and continued until neutrophils maintained independently >1 x 10⁹/L. The additional components added to the backbone to reduce graft failure included strategies previously found effective in achieving such aim in transplantation for thalassaemia major: (1) suppression of the expanded endogenous haemopoiesis with hypertransfusions, hydroxycarbamide 30 mg/kg and azathioprine 3 mg/kg and for a minimum of 42 days pre-transplantation (Sodani, Blood 2004; Shen Eur Radiol 2008; Capelli, Br J Haematol. 2009) and (2) addition of thiotepa 10 mg/kg on day -7 to the conditioning regimen (Bernardo, Blood 2012).

Eleven patients (12.6%) suffered from macrophage activation syndrome, resulting in death in seven of the patients. Six patients had sickle cell disease and five thalassaemia. Patients presented with persistent fever not responding to broad spectrum antibiotics and antifungals in 6 cases, unexplained cytopenias in three cases and both persistent fever and cytopenias in two cases. The majority of the patients developed haemophacytosis with cytopenias, elevated ferritin (median 54,200 mg/L, range 2,026 - 128,844), triglycerides (median 3 mmol/L, range 1.78 - 7.92) and all but two had organomegaly. The presence of rash was a rare feature, only found in two patients and fever was not found in three patients. HHV6 infection in the bone marrow was found in 6 patients in whom it was specifically looked for, the other five had concomitant infection with CMV in three patients, adenovirus in one patient and JC was found in a case presenting with ataxia. Those surviving presented later (median 80 days, range 22- 143 days) with preservation of the bone marrow cellularity (>50% with no further reduction) and responded to treatment with dexamethasone 10 mg/m² and antivirals and had resolution within 50 days of presentation; whereas those who did not survive presented early (median 42 days, range 17 - 258 days) with a bone marrow cellularity <50% eventually leading to secondary graft failure (<5% of hematopoietic cells in the bone marrow), and only had a partial response to dexamethasone, antivirals and targeted monoclonal antibodies, which was not sustained.

In conclusion, PTCy transplants for haemoglobinopathies receiving pre-transplantation strategies to reduce graft failure have a high risk of macrophage activation syndrome. This has not been previously recognized and has a high risk of death (two third of the cases) despite targetted treatment. We postulate that the pre-transplantation treatment allows alloreactive T cells escape the use of PTCy.