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.