Key Points Partially HLA-matched third-party CMV-specific T cells provide long-term viral control in HSCT patients with resistant CMV infection. Viral control occurs in the setting of recovery of CD8+ terminally differentiated effector T cells.

Objectives. Adoptive immunotherapy using donor-derived antigen-specific T-cells can prevent and treat infection after allogeneic haemopoietic stem cell transplant (HSCT). Methods. We treated 11 patients with a prophylactic infusion of 2 9 10 7 cells per square metre donor-derived T-cells targeting seven infections (six viral and one fungal) following HSCT. Targeted pathogens were cytomegalovirus (CMV), Epstein-Barr virus (EBV), adenovirus, varicella zoster virus, influenza, BK virus (BKV) and Aspergillus fumigatus. Results. T-cell products were successfully generated in all patients with 10 products responsive to 6 or 7 infections. T-cell infusions were associated with increases in antigen-experienced activated CD8 + T-cells by day 30. CMV, EBV and BKV reactivation occurred in the majority of patients and was well controlled except where glucocorticoids were administered soon after T-cell infusion. Three patients in that circumstance developed CMV tissue infection. No patient required treatment for invasive fungal infection. The most common CMV and EBV TCR clonotypes in the infusion product became the most common clonotypes seen at day 30 post-T-cell infusion. Donors and their recipients were recruited to the study prior to transplant. Grade III/IV graft-versus-host disease developed in four patients. At a median follow-up of 390 days post-transplant, six patients had died, 5 of relapse, and 1 of multi-organ failure. Infection did not contribute to death in any patient. Conclusion. Rapid reconstitution of immunity to a broad range of viral and fungal infections can be achieved using a

Current techniques to assess chimerism after hematopoietic stem cell transplantation (HSCT) are limited in both sensitivity and precision. These drawbacks are problematic in the context of cellular therapies that frequently result in microchimerism (donor chimerism <1%). We have developed a highly sensitive droplet digital PCR (ddPCR) assay using commercially available regents with good performance throughout the range of clinically relevant chimerism measurements, including microchimerism. We tested the assay using spiked samples of known donor-recipient ratios and in clinical samples from HSCT recipients and patients enrolled on clinical trials of microtransplantation and third-party virus-specific T cells (VSTs). The levels of detection and quantification of the assay were .008% and .023%, with high levels of precision with samples of DNA content ranging from 1 to 300 ng DNA. From the panel of 29 insertion-deletion probes multiple informative markers were found for each of 43 HSCT donor-recipient pairs. In the case of third-party cellular therapies in which there were 3 DNA contributors (recipient, HSCT donor, and T-cell donor), a marker to detect the cellular product in a background of recipient and donor cells was available for 11 of 12 cases (92%). Chimerism by ddPCR was able to quantify chimerism in HSCT recipients and comparison against standard STR analysis in 8 HSCT patients demonstrated similar results, with the advantage of fast turnaround time. Persistence of donor microchimerism in patients undergoing microtransplantation for acute myeloid leukemia was detectable for up to 57 days in peripheral blood and bone marrow. The presence of microtransplant product DNA in bone marrow T cells after cell sorting was seen in the 1 patient tested. In patients receiving third-party VSTs for treatment of refractory viral infections, VST donor DNA was detected at low levels in 7 of 9 cases. ddPCR offers advantages over currently available methods for assessment of chimerism in standard HSCT and cellular therapies.