In vivo alloreactive potential of ex vivo-expanded primary T lymphocytes.

Laboratoire de Therapeutique Immuno-moleculaire, Etablissement de Transfusion Sanguine de Franche-Comte ´, Service d'Anatomo-pathologie, Service de Radiotherapie-Oncologie, Service d'Hematologie, Centre Hospitalier Universitaire, 25000 Besancon, France, and NCI-FCRDC, Frederick, Maryland Background. We are presently investigating the therapeutic potential of herpes simplex-thymidine ki- nase-expressing donor T cells in the setting of a T cell-depleted allogeneic bone marrow transplantation. The generation, expansion, and selection of the gene- modified T cells require a 12-day ex vivo culture pe- riod in high-dose interleukin (IL)-2 that could signifi- cantly alter their in vivo alloreactivity. Methods. We evaluated the alloreactive potential of such cultured cells in a murine allogeneic bone mar- row transplantation model. Results. The present studies demonstrate that ex vivo-expanded cultured T cells are capable of strong alloreactivity as evidenced by the occurrence of lethal acute graft-versus-host disease (GVHD). However, GVHD mortality after administration of the cultured T cells occurred later than after the administration of a same number of fresh T cells. Similar kinetics of GVHD-induced mortality between cultured and fresh T cells required a 10-fold increase in the number of cultured T cells, indicating a reduced alloreactive po- tential of these cells. The addition of a 2-day "resting" period in low-dose IL-2 resulted in T cells with en- hanced alloreactive potential identical to the alloreac- tivity observed with fresh T cells. Conclusion. Ex vivo IL-2-expanded T cells are capa- ble of significant in vivo alloreactivity. However, an increase in the number of cultured T cells adminis- tered or the introduction of a short resting culture period prior to infusion is necessary in order to achieve in vivo alloreactivity identical to the alloreac- tivity observed with fresh T cells.