Very Early Adoptive Transfer of Ex Vivo Generated Multi-Virus Specific T Cells Is a Safe Strategy for Prevention of Viral Infection after Allogeneic T Cell Depleted Stem Cell Transplantation

Abstract

▪Background: Reactivation of latent viruses post-allogeneic stem cell transplant (SCT) negatively affects outcomes and increases non-relapse mortality. We have reported over 80% early CMV reactivation rate and significant additional costs in recipients of T cell depleted (TCD) SCT. Ex vivo generated multi-virus specific T cells (MVSTs) are effective as a therapy of active infection, but have not been evaluated as prophylaxis early after transplant. In a Phase I study (NIH 14-H-0182) we transferred MVSTs targeting immunodominant viral proteins of CMV, Epstein-Barr virus (EBV), BK and adenovirus (Ad) immediately post SCT as a novel approach to prevent viral reactivation post-SCT.Methods: All subjects were enrolled in HLA-matched T cell depleted (TCD) transplant protocol (NIH 13-H-0144). MVSTs cells were manufactured from SCT sibling donors by stimulation of elutriated lymphocytes for 14 days with seven overlapping peptide libraries (pepmixes) pulsed onto autologous dendritic cells (DCs) in presence of IL-7, IL-15 and IL-2. MVSTs were infused as early as possible (day 0 to +60) post SCT. A Phase I 3+3 dose escalation design was used as follows: Cohort 1 - 1x10e5 total nucleated cells (TNC)/kg, Cohort 2 - 5x10e5 TNC/kg, Cohort 3 - 1x10e6 TNC/kg. Three additional subjects received MVST cells manufactured using pepmix-pulsed mononuclear cells as stimulators (Cohort 3A; 1x10e6TNC/kg) under an amended protocol. The primary safety endpoint at day 42 post infusion was the occurrence of dose limiting toxicity (DLT) defined as Grade IV GVHD or any other severe adverse even (SAE) deemed to be at least “probably” or “definitely” related to the MVST infusion. Patients were followed to day +100 post SCT for secondary outcomes of efficacy, immune reconstitution and GVHD biomarkers (ST2, REG3). CDR3 sequencing (ImmunoSEQ) was performed on selected MVST products and peripheral blood samples post MVST and compared to control SCT recipients. GVHD biomarkers were analyzed pre- and post-treatment.Results: Twelve subjects were treated: nine received MVSTs generated using DCs and three subjects using mononuclear cells (cohort 3A). Median time from SCT to MVST administration was 13 days (range D +2 to +52 post-SCT). Median time to MVST for subjects in Cohort 3A was 3 days (range 2-7). There were no immediate infusion-related adverse events or DLT at the highest dose level. De novo grade II-III aGVHD post-MVST infusion was seen in three subjects (one in Cohort 1 and two in Cohort 3A), but GVHD biomarker elevation predated MVST infusion. CMV reactivation post-MVST occurred in 6 out of 12 subjects (50%) vs. 45 out of 52 patients (50% vs 87%) in a historical group of recipients of T cell depleted SCT. In all cases CMV reactivation occurred in the context of high dose steroids and in two subjects MVSTs were derived from CMV seronegative donors with minimal anti-CMV activity. One subject experienced rapidly rising AdV viremia (asymptomatic) and received an additional infusion of MVSTs. We saw self-limiting low level EBV replication in 8 cases and one BK viremia, but no disease. CDR3 sequencing of MVST products and serial peripheral blood from subjects revealed a robust contribution of ex vivo expanded cells to the overall repertoire, in contrast to untreated controls where the repertoire of (sham) MVST cell products generated from the transplant donors did not significantly overlap with the immune repertoire in peripheral blood of TCD-SCT recipients in the early post SCT period. Only at day +180 some convergence of repertoires became visible indicating spontaneous immune reconstitution (Figure). Detailed CDR3 analysis of cytokine-captured CMV pp65 and IE-1 specific CD4+ and CD8+ T cells was performed in a representative subject clearly demonstrating the detrimental effect of high-dose steroids on frequency of anti-viral T cells, precipitating CMV reactivation.Conclusions: This is the first report demonstrating safety and feasibility of using MVST immediately post-SCT to rapidly reconstitute anti-viral immunity and ameliorate the detrimental impact of the early viral reactivation in SCT recipient. No DLTs were seen and a minimal risk of aGVHD was observed, as there was no correlation with GVHD biomarkers. As revealed by serial CDR3 sequencing, MVSTs robustly contributed to the T cell repertoire. Our results suggest efficacy of this strategy in reducing viral reactivation. A Phase II study is warranted. DisclosuresNo relevant conflicts of interest to declare.