Redirected CD4⁺ T Cells towards HLA Class I-Restricted WT1 Epitope Successfully Display Multifactorial Helper Function for the Enhancement of Antileukemia Efficacy Mediated by Redirected T-Cell Based Immunocelltherapy.

In antitumor adoptive immunotherapy, the utility of tumoricidal CD8⁺ T cells are mainly highlighted, while in tumor immunity, the importance of tumor-reactive CD4⁺ T cells is also well documented. However, because the number of well-characterized tumor-associated epitopes recognized by CD4⁺ T cells still remains small, application of tumor-reactive CD4⁺ T cells is limited. In order to circumvent this drawback, redirection of CD4⁺ T cells to well-characterized HLA class I-restricted CD8⁺ T-cell epitope seems promising. In this study, using an HLA class I-restricted and WT1-specific T-cell receptor (TCR) gene transfer, we, in detail, examined helper functions mediated by those gene-modified CD4⁺T cells in redirected T cell-based antileukemia adoptive immunotherapy.

HLA-A*2402-restricted and WT1_235–243-specific TCR α/β genes were inserted into our unique retroviral vector encoding shRNAs for endogenous TCRs (WT1-siTCR vector), and was employed for gene-modification both of CD4⁺ and CD8⁺ T cells to express WT1-specific TCR. (1) WT1 epitope-responsive cytokine production mediated by WT1-siTCR-transduced CD4⁺ T cells (WT1-siTCR/CD4) was measured using bead-based immunoassay and ELISA assay. (2) WT1 epitope-ligation induced co-stimulatory molecules by WT1-siTCR/CD4 was assessed using flow cytometry. (3) Impacts on WT1 epitope and leukemia-specific responses; cytocidal activity, proliferation and differentiation into memory T-cell phenotype, mediated by WT1-siTCR-transduced CD8⁺ T cells (WT1-siTCR/CD8) provided by concurrent WT1-siTCR/CD4 were assessed using ⁵¹Cr-release assay, CD107a/intracellular IFN-γ assay, CFSE dilution assay and flow cytometry. (4) WT1 epitope-ligation triggered chemokine production mediated by WT1-siTCR/CD4 was assessed using real-time PCR, then chemotaxis mediated by WT1-siTCR/CD8 in response to those chemokines was assessed using a transwell experiment. (5) In vivo tumor trafficking mediated by WT1-siTCR/CD4 was assessed using bioluminescence imaging assay. (6) Finally, WT1-siTCR/CD4-caused in vivo augmentation of antileukemia functionality mediated by WT1-siTCR/CD8 was assessed similarly using a xenografted mouse model.

WT1-siTCR/CD4 showed a terminal effector phenotype; positive for transcription factor T-bet, but negative for Bcl-6 or Foxp3. Upon recognition of WT1 epitope, WT1-siTCR/CD4 produced Th1, but not Th2 cytokines in the context of HLA-A*2402, which simultaneously required HLA class II molecules on target cells. WT1 epitope-ligation enhanced WT1-siTCR/CD4 to express cell-surface OX40. In the presence of WT1-siTCR/CD4, but not non-gene-modified CD4, effector functions mediated by WT1-siTCR/CD8 in response to WT1 epitope and leukemia cells, including cytocidal activity based on CD107a expression and IFN-γ production was enhanced. Such augmentation was mediated by humoral factors produced by WT1 epitope-ligated WT1-siTCR/CD4. Additionally, proliferation and differentiation into memory phenotype, notably CD45RA- CD62L⁺ central memory phenotype, mediated by WT1-siTCR/CD8 in response to both WT1 epitope and leukemia cells were also augmented, accompanied with increased expression of intracellular Bcl-2 and cell-surface IL-7R. Next, CCL3/4 produced by activated WT1-siTCR/CD4 triggered chemotaxis of WT1-siTCR/CD8 which express the corresponding receptor, CCR5. Using bioluminescence imaging, intravenously infused WT1-siTCR/CD4 successfully migrated towards leukemia cells inoculated in a NOG mouse. Finally, co-infused WT1-siTCR/CD4 successfully augmented immediate accumulation towards leukemia cells and antileukemia reactivity mediated by WT1-siTCR/CD8 in a xenografted mouse model.

Using GMP grade WT1-siTCR vector, redirected CD4⁺ T cells to HLA class I-restricted WT1 epitope successfully recognized leukemia cells and augmented in vivo antileukemia functionality mediated by similarly redirected CD8⁺ T cells, encompassing tumor trafficking, cytocidal activity, proliferation and differentiation into memory cells. The latter seem to support the longevity of transferred antileukemia efficacy. Taking together, coinfusion of redirected CD4⁺ T cells to HLA class I-restricted WT1 epitope seems feasible and advantageous for the successful WT1-targeting redirected T cell-based immunotherapy against human leukemia.

No relevant conflicts of interest to declare.