Molecular Follow-Up of Patients Treated with HSV-TK/ΔLNGFR Engineered Donor Lymphocytes after Allogeneic Stem Cell Transplantation.

Donor lymphocyte infusions (DLI) play a crucial role in promoting immune reconstitution and anti-tumor activity in patients treated with allogeneic hematopoietic stem cell transplantation (HSCT). The efficacy of DLI is, however, limited by the occurrence of graft-versus-host disease (GvHD). In three different clinical trials, we showed that the infusion of lymphocytes transduced by a retroviral vector expressing a suicide gene (HSV-TK) and a surface marker (ΔLNGFR) allows to control GvHD in 100% of cases, while preserving anti-tumor and antiviral activities. In >40 patients treated with TK-cells in the context of HLA identical and haplo-identical HSCT, we observed consistent expansion (up to 40% of circulating cells) and long-term persistence (>10 years) of transduced cells. No acute or chronic adverse or toxic effect due to the gene transfer procedure was observed in these patients, who were treated with a total of >1011 cells generated by >60 independent transductions. Analysis of vector integration sites was preformed by LM-PCR on lymphocytes obtained up to 10 years after treatment from 4 patients, and selected for ΔLNGFR expression. 60% of the sequences met our validity criteria and were unambiguously mapped onto the human genome by Ensembl BLAST analysis. Transduced T-cells were highly polyclonal, with vector integrations occurring preferentially within genes (52%), and particularly within the first intron (25%). Quantitative PCR analysis of selected integrations was performed to follow the dynamics of individual T-cell clones during time. Microchip analysis of the gene expression profile showed that <200 out of >22,000 genes (0.9%) were differentially expressed in ΔLNGFR+ vs. ΔLNGFR- T-cells from two different patients, suggesting that no significant perturbation was induced by retroviral transduction or HSV-TK/ΔLNGFR expression in human lymphocyte populations. Interestingly, these data also show the substantial biological identity of T-cell population generated by HSCT and those administered as DLI. Finally, the influence of proviral integration on the expression of targeted genes was studied in individual T-cell clones transduced in vitro or obtained ex vivo from treated patients by quantitative gene expression analysis.