Generation of good manufacturing practice grade virus-specific T cells for the management of post-transplant CMV infections

Adoptive transfer of antigen-specific T cells has recently emerged as a successful strategy to treat viral infections following hematopoietic cell transplantation (HCT). Ex-vivo expanded donor-derived virus-specific T cells (VSTs) can be safe and effective, devoid of all the drug-related adverse effects. The study aimed to manufacture cGMP grade VSTs from healthy donors, characterize the VST product and demonstrate its safety and efficacy. Peripheral blood mononuclear cells (PBMCs) collected from six healthy donors were stimulated with pepmix that mimics the pp65 antigenic epitope of CMV and cultured for 14 days in G-Rex culture tubes. Post pepmix exposure and expansion the median CD3% was 98.8% (range:95.5% to 99.9%) while the median CD4% and CD8% were 49.1% (range:21.3% to 86.6%) and 43.9% (range:12.7% to 75.5%) respectively. The percentage of IFNγ+ cells was much higher among the CD8+ T cells (median - 18.47%; range 6.50% - 45.82%) when compared to CD4+ T cells (median - 2.74%; range 0.47% - 18.58%) and there was a switch from the CD45RA+ naive phenotype to CD45RA- effector memory phenotype in the 4 samples that achieved a >5 fold expansion. The VSTs were cytotoxic to the pepmix pulsed lymphoblasts (efficacy) while they did not induce cytolysis in the lymphoblasts that were not exposed to the pepmix (safety). This feasibility exercise helped us optimize the starting cell dose for the culture and clinical grade culture strategies, subset characterization and cytotoxicity assays. The approach could be applied to the clinical practice where virus-specific T cell infusions could be given for post-transplant viral infections.