Generation of leukemia-specific T-helper type 1 cells applicable to human leukemia cell-therapy

A synthetic NOD2 agonist, muramyl dipeptide (MDP)-Lys (L18) and IFN-β synergistically induce dendritic cell maturation with augmented IL-12 production and suppress melanoma growth

BACKGROUND

A synthetic NOD2 agonist, muramyl dipeptide (MDP)-Lys (L18), mimics the bacterial peptidoglycan moiety and acts as a powerful adjuvant that induces cell-mediated immunity.

OBJECTIVE

To investigate the induction of antitumor immune response for malignant melanoma by IFN-β in combination with MDP-Lys (L18) (IFN-MDP-Lys (L18)).

METHODS

Human monocyte-derived DCs (MoDCs) are stimulated with IFN-MDP-Lys (L18) in vitro. We assess the expression of costimulatory molecules on MoDCs by FACS. Moreover, we investigate the induction of Th1 cytokines by real time PCR and ELISA. Further to confirm the anti tumor immune response of IFN-MDP-Lys (L18) therapy, we examine the growth of B16F10 melanoma in vivo.

RESULTS

The stimulation of human MoDCs with IFN-MDP-Lys (L18) significantly augmented the production of IL-12p70, TNF-α, and IL-6 compared to that with MDP or that with IFN-β alone. IFN-MDP-Lys (L18) increased the expression of IL-12p35, IL-12p40, IL-10, TNF-α, IL-6 and IL-1β mRNA by MoDC using real-time PCR. The expression of CD83 and costimulatory molecules CD40, CD80, and CD86 was also augmented in MoDC treated with IFN-MDP-Lys (L18), which resulted in their augmented allogeneic T cell stimulation. In vivo, the administration of IFN-MDP-Lys (L18) significantly suppressed the growth of B16F10 melanoma, while the monotherapy of IFN-β or MDP-Lys (L18) did not significantly affect the tumor growth.

CONCLUSION

These findings suggest that IFN-MDP-Lys (L18) can be a promising adjuvant therapy for malignant melanoma.

Aberrant dendritic cell differentiation initiated by theMll-Eenfusion gene does not require leukemic transformation

Dendritic cells (DCs), as specialized APCs, play a key role in the induction of anti-tumor immunity. They originate from bone marrow (BM) progenitors, which are frequently the targets of chromosomal translocations leading to development of leukemia. Aberrant DC differentiation and functions have been observed and are widely reported in patients with leukemia. It is not clear, however, whether such defects are a direct effect of a leukemic fusion gene or simply an outcome of the clinical disease. In this study, we demonstrate for the first time that knockin of the Mll-Een fusion gene can affect myeloid DC differentiation and functions directly, independent of the leukemic disease activities. We showed that the Mll-Een-expressing BM cells [enhanced green fluorescent protein+ (EGFP+)] from leukemic and nonleukemic mice had similarly impaired DC differentiation capacities with functional abnormalities. In contrast, BM cells without Mll-Een expression (EGFP(-)) showed normal DC differentiation and functions. A reduction in the frequency of CD11c+ DCs was also observed within the EGFP+ population in spleen and lymph nodes, and these cells were dysfunctional. Taken together, our findings suggest that the Mll-Een fusion gene can affect myeloid DC differentiation directly and functions in a cell-autonomous manner, where fully leukemic transformation of the hematopoietic progenitors is not required exclusively. Therefore, the study provides evidence for a direct causal relationship between leukemic gene fusion and abnormal DC differentiation, possibly contributing to the development of leukemia.

Vaccination with leukemia cells expressing cell-surface-associated GM-CSF blocks leukemia induction in immunocompetent mice

The fundamental basis for immunotherapy of leukemia is that leukemic cells express specific antigens that are not expressed by normal hematopoietic cells. However, the host immune system appears to be tolerant to leukemia cells. To overcome this tolerance, we vaccinated immunocompetent mice with murine leukemia cells (WEHI-3B and BCR-ABL+ 32D cells) transduced with a specifically constructed transmembrane form of granulocyte-macrophage colony-stimulating factor (tmGM-CSF). The transduced cells expressed tmGM-CSF on the cell-surface. To determine whether tmGM-CSF-expressing WEHI-3B leukemia cells would prevent leukemia formation as a vaccine, immunocompetent mice (BALB/c and C3H/HEJ) were immunized with lethally irradiated murine leukemia cells expressing cell-surface tmGM-CSF before challenging mice with murine leukemia cells. Two immunocompetent mouse models were investigated, either WEHI-3B cells in BALB/c mice or BCR-ABL+ 32D cells in C3H/HEJ mouse. The results showed that 100% of WEHI-3B/tmGM-CSF-vaccinated BALB/c mice and about 65% of 32D+ BCR-ABL/tmGM-CSF-vaccinated C3H/HEJ mice were protected from leukemia after leukemia cell challenge, whereas all non-vaccinated mice succumbed to leukemia. Spleen and marrow cell suspensions from vaccinated mice challenged with WEHI-3B cells lacked detectable GFP+ WEHI-3B cells at 82 days post-challenge. A significant delay of death was observed in C3H/HEJ mice challenged with the very aggressive DA-1 cell line expressing BCR-ABL. Vaccination of mice with WEHI-3B/CD40L cells protected 80% of the mice from the WEHI-3B challenge. Notably, 60% of the WEHI-3B/BALB/c mice were also protected from leukemia when WEHI-3B/tmGM-CSF vaccination was carried out after the leukemia challenge. In order to determine whether cellular immunity is involved in this vaccine-mediated protection, either CD4+ or CD8+ T cells were depleted from mice after the WEHI-3B/tmGM-CSF vaccination. The results indicate that CD8+ T-cells mediated the protective immune response provided by the irradiated tmGM-CSF-expressing WEHI-3B cells. In addition, vaccination of nude mice did not provide protection from WEHI-3B leukemia induction. Importantly, 80% of non-vaccinated mice were also protected from a WEHI-3B cell challenge after receiving spleen cells from vaccinated mice 1 day before challenge with leukemia cells. These results indicate that overexpression of tmGM-CSF on the leukemia cell-surface can enhance the recognition of leukemic cells by CD8+ T cells, and can either prevent or significantly delay leukemia induction. These findings suggest that injection of irradiated leukemia cells expressing cell-surface-bound GM-CSF has the potential as an immunological approach to treat leukemia.