Human Adenovirus (HAdV) infection/reactivation may cause life-threatening complications in recipients of hematopoietic stem cell transplantation (HSCT), the highest risk being observed in pediatric recipients of a T-cell depleted allograft from haploidentical family donor. The effectiveness of pharmacological therapy for HAdV infection is still suboptimal. It has been recently demonstrated that cell therapy may offer a unique opportunity to restore antiviral immune surveillance, leading to clearance of infection and prevention/treatment of disease. However, infusion of HAdV-specific T-cells in the haplo-HSCT cohort poses the concern that GVHD may ensue as a consequence of T-cell transfer. We have conducted scale-up experiments to validate a method of in vitro culture to expand T-cells specific for HAdV, based on stimulation of donor peripheral blood mononuclear cells (PBMC) with a pool of 5 30-mer peptides derived from HAdV5 hexon protein, for use in recipients of haplo-HSCT (
Veltrop-Duits et al, Eur J Immunol 36, p2410; 2006
). A total of 20 T-cell lines were generated, starting from a median of 20 × 106 donor PBMC, that yielded a median of 80 × 106 cells. Most of the cell lines obtained included a majority of CD4+ T-lymphocytes, with a lower % CD8+ cells (median and range: 78, 19–94 and 18, 5–58, respectively) but 5/20 lines contained a high number of CD8+ T cells (ranging between 43% and 58%), which were CD56+ and/or TCRγδ+, and in 1 case also 44% NK cells. Eighteen of the 20 T-cell lines were HAdV-specific, since they showed a median proliferation to the HAdV hexon peptide pool and inactivated HAdV of 14615 (95%CI 8924–31532) and 11103 (95%CI 8805–30174) cpm/105 cells after subtraction of background (responders+irradiated autologous PBMC), respectively. HAdV-specific lysis >10% at a 2:1 effector to target (E:T) ratio was observed in 50% of the T-cell lines. The 2 non-specific, as well as the 3 T-cell lines with lower specific activity, included >40% CD8+ T-cells. Production of IFNγ in an ELIspot assay to HAdV hexon peptide pool above 40 SFU/105 cells was observed in 9 out of 13 tested T-cell lines. Evaluation of specific response to hexon peptides in showed a majority of responses to II42 (80%), with 50–60% responses to II50, II57, II61, and II64. Only 2 out of the 20 T-cell lines tested were prevalently alloreactive against the recipient. Of the 18 HAdV-specific lines, 1 showed higher proliferation to patient PBMC than to HAdV (13518 vs 11717 mean cpm), and would have thus been discarded as unsuitable for in vivo use, while the other 17 showed no alloreactivity (14) or alloreactivity between 10 and 23% of specific proliferation (3). None of these 18 T-cell lines showed lysis >5% against recipient PHA blasts in the cytotoxicity assay. Our data show that PBMC stimulation with HAdV hexon protein-derived 30-mer peptides is able to reproducibly induce the generation of HAdV-specific CD4+ T-cell lines with efficient in vitro antiviral response in most HLA-mismatched HSCT donors. The majority of these T-cell lines show low/undetectable alloreactivity against recipient targets, and could therefore be safely employed for adoptive treatment of HAdV complications developing after HSCT from a HLA-haploidentical donor.
