Final outcomes from a phase 2 trial of posoleucel in allogeneic hematopoietic cell transplant recipients

Allogeneic hematopoietic cell transplantation (allo-HCT) recipients are susceptible to viral infections. We conducted a phase 2 trial evaluating the safety and rate of clinically significant infections (CSIs; viremia requiring treatment or end-organ disease) after infusion of posoleucel, a partially HLA-matched, allogeneic, off-the-shelf, multivirus-specific T-cell investigational product for preventing CSIs with adenovirus, BK virus, cytomegalovirus, Epstein-Barr virus, human herpesvirus-6, or JC virus. This open-label trial enrolled allo-HCT recipients at high risk based on receiving grafts from umbilical cord blood, haploidentical, mismatched, or matched unrelated donors; post-HCT lymphocytes of <180/mm3; or use of T-cell depletion. Posoleucel dosing was initiated within 15 to 49 days of allo-HCT and subsequently every 14 days for up to 7 doses. The primary end point was the number of CSIs due to the 6 target viruses by week 14. Of the 26 patients enrolled, only 3 (12%) had a CSI by week 14, each with a single target virus. In vivo expansion of functional virus-specific T cells detected via interferon-γ enzyme-linked immunosorbent spot assay was associated with viral control. Persistence of posoleucel-derived T-cell clones for up to 14 weeks after the last infusion was confirmed by T-cell-receptor deep sequencing. Five patients (19%) had acute graft-versus-host disease grade 2 to 4. No patient experienced cytokine release syndrome. All 6 deaths were due to relapse or disease progression. allo-HCT recipients at high risk who received posoleucel had low rates of CSIs from 6 targeted viruses. Repeat posoleucel dosing was generally safe and well tolerated and associated with functional immune reconstitution. This trial was registered at www.ClinicalTrials.gov as #NCT04693637.