HOUSTON – Allogeneic hematopoietic stem cell transplantation (allo-HCT) following a novel reduced-intensity conditioning regimen was largely successful in a heterogeneous cohort of 29 adults and children with primary immunodeficiency in a prospective clinical trial.
At 1 year after transplant, overall survival was 98% and the estimated graft failure–free and graft-versus-host disease (GVHD)–free survival was 82% among the participants, who had various underlying primary immunodeficiencies (PIDs),, reported at the Transplantation and Cellular Therapy Meetings.
GVHD-free survival was defined in this National Institutes of Health study as the absence of steroid-refractory grade 3-4 acute GVHD and chronic GVHD, noted Dr. Dimitrova of the NIH.
All patients, including 19 adults and 10 children (median age, 25 years), received a serotherapy-free, radiation-free, reduced-intensity conditioning regimen designed to optimize immune reconstitution, minimize toxicity and GVHD, reduce the risk of infectious complications, and enable successful use of alternative donors.
The conditioning platform included pentostatin on day –11 and day –7 at 4 mg/m2 along with 8 days of low-dose cyclophosphamide and 2 days of pharmacokinetically dosed busulfan at 4,600 mmol/min. GVHD prophylaxis included posttransplantation cyclophosphamide, mycophenolate mofetil (MMF), and sirolimus.
All patients received T cell–replete bone marrow or peripheral blood stem cell allografts; 72% received alternative donor grafts, Dr. Dimitrova said.
Two patients died, including one with bacterial sepsis and invasive aspergillosis who died on day +44 and one with presumed viral encephalitis who died on day +110. The patients were high risk overall (median HCT–comorbidity index score of 3, with a range of 0-11), and the two who died had HCT-CI scores of 6 and 8, respectively.
An additional accidental death occurred at 18 months after transplant “in the setting of continued remission, good graft function, and no transplant-related complications,” she said.
Neutrophil recovery occurred at a median of 17 days after transplant; three patients experienced graft failure, including one primary failure with autologous recovery on day +14 and two secondary graft failures.
“Two patients with known underlying difficult-to-engraft diseases required second transplants using different nonmyeloabalative platforms, and nevertheless required donor lymphocyte infusions to avoid threatened secondary graft failure,” she said. “The third patient actually had sufficiently improved infectious disease control and has not needed a second transplant to date.”
Overall GVHD incidence using the novel platform has been extremely low, she said, noting that 14% of patients had grade 2-4 GVHD and 3% had grade 3-4 acute GVHD. There was no steroid-refractory GVHD or chronic GVHD.
Among the infectious complications, other than those that led to the two deaths, were cytomegalovirus reactivation in 7 of 16 patients at risk, BK virus–associated hemorrhagic cystitis in 19 of 22 patients at risk, and a suspected case of viral cardiomyopathy that ultimately resolved.
“Importantly, although many patients had Epstein-Barr virus [EBV] control issues prior to transplant, no patients received preemptive EBV-directed therapy, and no patients had EBV-PTLD [posttransplant lymphoproliferative disorder],” she said.
Additionally, blood stream infections were detected in five patients, there were two cases of confirmed aspergillosis, and one child developed cutaneous candidiasis. Other complications and toxicities appeared to relate to underlying pretransplant issues in the affected organ or exuberant immune responses to existing infection.
“Phenotype reversal was evident to some degree in all evaluable patients, even in those with mixed chimerism or unknown underlying genetic defect,” Dr. Dimitrova said.
All 10 patients with malignancy or lymphoproliferative disease as an additional indication for allo-HCT remain in remission, and most patients who required immunoglobulin replacement therapy prior to transplant have been able to discontinue it, she noted.
The findings of this study are of note, because while it has been known for decades that allo-HCT is a potentially curative therapy for patients with PIDs that arise from defects in cells of hematopoietic origin, it frequently fails because of complicating factors or is not an option, Dr. Dimitrova said.
“These patients will often enter transplant with multiple comorbidities and disease sequelae, particularly as diagnosis of PIDs increases in older children and adults following years of illness,” she explained, adding that related donor options may be limited if family members are also affected.
For this reason, and with the goal of improving access to allo-HCT to all who require it, the novel conditioning platform used in this study was developed.
The platform was well tolerated overall, Dr. Dimitrova said, emphasizing the “notably low” GVHD rates.
“Currently we are investigating reduced MMF with the goal of promoting earlier immune reconstitution, and a separate protocol has opened that includes several modifications to this platform aimed at patients with increased risk of graft failure who may not tolerate mixed chimerism early on,” she said, noting that both protocols are currently enrolling.
The meeting was held by the American Society for Blood and Marrow Transplantation and the Center for International Blood and Marrow Transplant Research. At its meeting, the American Society for Blood and Marrow Transplantation announced a new name for the society: American Society for Transplantation and Cellular Therapy (ASTCT).
Dr. Dimitrova reported having no financial disclosures.
SOURCE: Dimitrova D et al. TCT 2019, .