IN-VIVO ALLOREACTIVE POTENTIAL OF EX-VIVO EXPANDED PRIMARY T-LYMPHOCYTES

Background. We are presently investigating the therapeutic potential o f herpes simplex-thymidine kinase-expressing donor T cells in the sett ing of a T cell-depleted allogeneic bone marrow transplantation, The g eneration, expansion, and selection of the gene-modified T cells requi re a 12-day ex vivo culture period in high-dose interleukin (IL)-2 tha t could significantly alter their in vivo alloreactivity, Methods. We evaluated the alloreactive potential of such cultured cells in a murin e allogeneic bone marrow transplantation model. Results. The present s tudies demonstrate that ex vivo-expanded cultured T cells are capable of strong alloreactivity as evidenced by the occurrence of lethal acut e graft-versus-host disease (GVHD). However, GVHD mortality after admi nistration of the cultured T cells occurred later than after the admin istration of a same number of fresh T cells. Similar kinetics of GVHD- induced mortality between cultured and fresh T cells required a 10-fol d increase in the number of cultured T cells, indicating a reduced all oreactive potential of these cells. The addition of a a-day ''resting' ' period in low-dose IL-2 resulted in T cells with enhanced alloreacti ve potential identical to the alloreactivity observed with fresh T cel ls. Conclusion. Ex vivo IL-2-expanded T cells are capable of significa nt in vivo alloreactivity, However, an increase in the number of cultu red T cells administered or the introduction of a short resting cultur e period prior to infusion is necessary in order to achieve in vivo al loreactivity identical to the alloreactivity observed with fresh T cel ls.