In Vivo Alloreactive Potential of Ex Vivo Expanded Primary T Lymphocytes

Background. We are presently investigating the therapeutic potential of herpes simplex-thymidine kinase-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 period in high-dose interleukin (IL)-2 that could significantly alter their in vivo alloreactivity, Methods. We evaluated the alloreactive potential of such cultured cells in a murine allogeneic bone marrow 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 potential of these cells. The addition of a a-day ''resting'' period in low-dose IL-2 resulted in T cells with enhanced alloreactive potential identical to the alloreactivity observed with fresh T cells. Conclusion. Ex vivo IL-2-expanded T cells are capable of significant in vivo alloreactivity, However, an increase in the number of cultured T cells administered or the introduction of a short resting culture period prior to infusion is necessary in order to achieve in vivo alloreactivity identical to the alloreactivity observed with fresh T cells. [References: 22]

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