BCR–ABL-specific CD4+ T-helper cells promote the priming of antigen-specific cytotoxic T cells via dendritic cells

Abstract

The advent of tyrosine kinase inhibitor (TKI) therapy markedly improved the outcome of patients with chronic-phase chronic myeloid leukemia (CML). However, the poor prognosis of patients with advanced-phase CML and the lifelong dependency on TKIs are remaining challenges; therefore, an effective therapeutic has been sought. The BCR-ABL p210 fusion protein's junction region represents a leukemia-specific neoantigen and is thus an attractive target for antigen-specific T-cell immunotherapy. BCR-ABL p210 fusion-region-specific CD4 T-helper (Th) cells possess antileukemic potential, but their function remains unclear. In this study, we established a BCR-ABL p210 b3a2 fusion-region-specific CD4 Th-cell clone (b3a2-specific Th clone) and examined its dendritic cell (DC)-mediated antileukemic potential. The b3a2-specific Th clone recognized the b3a2 peptide in the context of HLA-DRB1*09:01 and exhibited a Th1 profile. Activation of this clone through T-cell antigen receptor stimulation triggered DC maturation, as indicated by upregulated production of CD86 and IL-12p70 by DCs, which depended on CD40 ligation by CD40L expressed on b3a2-specific Th cells. Moreover, in the presence of HLA-A*24:02-restricted Wilms tumor 1 (WT1) peptide, DCs conditioned by b3a2-specific Th cells efficiently stimulated the primary expansion of WTI-specific cytotoxic T lymphocytes (CTLs). The expanded CTLs were cytotoxic toward WT1-peptide-loaded HLA-A*24:02-positive cell lines and exerted a potent antileukemic effect in vivo. However, the b3a2-specific Th-clone-mediated antileukemic CTL responses were strongly inhibited by both TKIs and interferon-α. Our findings indicate a crucial role of b3a2-specific Th cells in leukemia antigen-specific CTL-mediated immunity and provide an experimental basis for establishing novel CML immunotherapies.

Generation of TCR-Expressing Innate Lymphoid-like Helper Cells that Induce Cytotoxic T Cell-Mediated Anti-leukemic Cell Response

“…The expanded WT1-specific CTLs exhibited cytotoxic activity against WT1 peptide-loaded HLA-A24-expressing K562, but not against vehicle-loaded cells ( Figure 5 B, right panel). These data indicate that the activation of CD40L high CD4 + iPS-T cells by the b3a2 peptide induces DC-mediated cellular adjuvant properties that can increase leukemic antigen-specific CTL responses, which is consistent with the T helper function of the original CD4 + Th1 clone (SK) ( Ueda et al., 2016 ).

Figure 5 Induction of Leukemia Antigen-Specific CTLs By CD40L high CD4 + iPS-T Cells (A) Proliferative response of CD8 + T cells.

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“…CD4 + Th cells help in the priming of CD8 + CTLs via DC activation ( Bennett et al., 1997 , Ridge et al., 1998 , Schoenberger et al., 1998 , Ueda et al., 2016 ). To determine whether CD40L high CD4 + iPS-T cells can induce leukemia antigen-specific CTL responses, vehicle- or b3a2 peptide-loaded DCs were cultured with CD40L high CD4 + iPS-T cells, and differentially conditioned DCs were loaded with Wilms tumor 1 (WT1 235-243 ) peptide, irradiated, and cultured with CD8 + T cells ( Figure S8 A).…”

“…HLA-DR9-restricted b3a2-specific CD4 + Th1 clone (SK) ( Ueda et al., 2016 ) and HLA-DR53-restricted GAD65 113-131 peptide-specific CD4 + Th clone (SA32.5) ( Tabata et al., 1998 ) were reprogrammed to iPSCs by transduction of reprogramming factors by the Sendai viral system using pSeV[KOSM302L] (kindly provided by Dr. Nakanishi, AIST, Tsukuba, Japan) as described previously ( Kitayama et al., 2016 , Nishimura et al., 2013 ). The iPSC clones were negative for residual transgenes, showed pluripotency characterized by the expression of pluripotency-related molecules and teratoma formation in immunodeficient mice, and were confirmed to have a normal karyotype ( Figure S1 ).…”

“…In the present study, we established iPSCs from a CD4 + Th1 clone specific for the junction region of BCR-ABL p210 (b3a2), a leukemia antigen, which is restricted by HLA class II (HLA-DR9) ( Ueda et al., 2016 ). We induced re-differentiation of iPSCs to T-lineage cells expressing HLA class II-restricted TCR (iPS-T cells).…”

Antigen Targets for the Development of Immunotherapies in Leukemia

“…Furthermore, most patients with a Philadelphia-positive leukemia receive TKI therapy, which can lead to additional mutations in the BCR-ABL fusion protein in order to achieve resistance to the inhibitor, which in turn could lead to new neoantigens naturally presented on the cell surface. By the use of epitope prediction, several immunogenic BCR-ABL fusion region peptides were described, which could induce BCR-ABL-specific CD4 + and CD8 + T-cell responses [146,147,148]. These T cells were capable of controlling treatment-refractory Philadelphia-positive ALL in vivo after adoptive T-cell therapy [146].…”