Generation of an efficient graft-versus-
leukemia (GVL) effect in patients with
hematological malignancies who relapse after allogeneic
bone marrow transplantation depends in part upon the number of infused T lymphocytes. Currently, a GVL reaction cannot be achieved without inducing concomitant
graft-versus-host disease (GVHD); thus, one strategy is to try to modulate this GVL/GVHD ratio. We engineered human T lymphocytes with herpes simplex virus-
thymidine kinase and
neomycin resistance genes, with an LXSN-derived vector that confers a
ganciclovir-specific sensitivity to the transduced T cells. We analyzed proliferation,
interleukin-2 production, alloreactivity in a mixed lymphocyte culture, and clonogenicity during the different stages of retroviral
infection and
G418 selection. Our results confirm that a sufficient number of transduced T lymphocytes can be obtained after selection for clinical studies. Their proliferative activity, alloresponsiveness, and ability to produce and respond to
interleukin-2 were retained. Compared with control populations, their clonogenicity, as assessed by limiting dilution assays, was reduced after retroviral
infection and
G418 selection by 1.6 and 2.9 logs, respectively, with both viral supernatant incubation and coculture procedures. This study shows that
infection and selection with the
thymidine kinase-
neomycin resistance gene retroviral vector significantly reduces the number of functional T lymphocytes. This finding should be taken into account when establishing the dose of T lymphocytes necessary to trigger a modulated GVL/GVHD effect.