Tetanus toxoid provides efficient T-cell help for the induction of HA-1^H cytotoxic T cells

BACKGROUND:  In vitro generation and expansion of leukemia-reactive T cells may improve the efficacy and specificity of cellular immunotherapy against hematologic malignancies in the context of allogeneic stem cell transplantation. Since the expression of minor histocompatibility antigen HA-1^H is limited to hematopoietic cells, ex vivo generated HA-1^H-specific CD8+ cytotoxic T lymphocytes (CTLs) can be used for adoptive immunotherapy.

STUDY DESIGN AND METHODS:  Numerous studies have shown that primary CTL induction from naïve precursors requires professional antigen-presenting cells. Here, the feasibility of ex vivo induction of HA-1^H-specific CD8+ CTLs is demonstrated from unfractionated peripheral blood mononuclear cells (PBMNCs) from healthy blood donors when CD4+ T-cell help is provided during primary stimulation. As a stimulus for the induction of T-cell help, tetanus toxoid (TT) was used.

RESULTS:  After the second restimulation cycle, approximately 1 percent of CD8+ T cells stained positively with the HLA-A*0201/HA-1^H pentamer. Positive T cells were further expanded more than 1000-fold by antigen-independent stimulation with anti-CD3/CD28 monoclonal antibodies. HA-1^H-induced T cells showed the classical phenotype for CD8+ memory effector cells: the phenotype changed from a mixed CD45RA/RO phenotype to an activated phenotype characterized by high expression of CD45RO and no expression of CCR7. The generated T cells revealed a very potent CTL response, even at low E:T ratios.

CONCLUSION:  This study demonstrates that TT provides a very potent and cost-effective tool for the in vitro induction of antigen-specific CTLs from precursor PBMNCs that can easily be adapted to GMP conditions for translational purposes.