Oncogene addiction provides ideal targets for immunotherapy. We previously described MondoA (also known as MLXIP, MAX like protein X interacting protein) as a metabolic stress sensor, required for leukemogenesis. Here we report on the expression of MondoA in common acute lymphoblastic leukemia (cALL) compared to other malignancies, its role in malignancy of cALL in vivo, downstream pathways and correlation with relapse risk. Given the non-accessibility of transcription factors by drugs or chimeric antigen receptor transgenic T cells (CARs), we tested the targetability of MondoA by allo-restricted, peptide specific T cells.

Our human/murine xenotransplantation model with immunodeficient RAG2-/-gc-/- mice was used (Richter et al. 2009). NALM6 and 697 cALL lines were lentivirally transduced with MondoA short hairpin RNA (shRNA). Upon successful MondoA knock down (KD), KD and control lines were injected into the mice; CD10+ blasts in blood, spleen and marrow were assessed. MondoA specific T cells were generated by priming of donor HLAA0201 negative (A2-) T-cells with A2+ dendritic cells bearing MondoA peptides, multimer-based sorting and subcloning of A2-CD8+ T-cells. For priming of T cells, five MondoA peptides were chosen by SYMPEITHI, BIMAS and NetCTL1.2. analyses. Peptide 428 stabilized best A2 expression on TAP-deficient T2 cells. Specificity and functionality of T cell clones were tested by ELISpot interferon gamma (IFg) and granzyme B assays with six MondoA+ leukemia lines (A2+, A2-). Off target effects of MondoA specific T-cell clones were assessed by IFg reactivity against the MondoA expressing A2+ NALM6 cell line vs. A2+ and A2- EBV immortalized lymphoblastoid cell lines from six donors. Peptide homology was assessed with BLAST algorithms in SWISSPROT.

We found MondoA to be most strongly expressed in pediatric cALL and AML. Moreover MondoA expression was high in gastrointestinal stromal tumors and alveolar rabdomyosarcoma. MondoA KD in cALL cell lines and their subsequent analysis in xenograft mice resulted in a reduced number of leukemic blasts in blood, marrow and spleen. Spleen size and weight normalized in treated mice after MondoA KD. Further microarray analysis revealed an induction of aerobic glycolysis switch genes and hypoxia-response by MondoA. Consequently, HIF1A stabilization required MondoA expression and tied to these results, MondoA overexpression correlated with relapse risk; its expression was 63% higher in the very high-risk group as compared to the non-high-risk group of cALL. Therapeutically, MondoA-derived peptide antigens and A2+ cALL lines were successfully recognized and killed by specific, allo-restricted CD8+ T cells.

In conclusion, our findings demonstrate that MondoA maintains leukemic burden and aggressiveness of cALL in vivo possibly by modulating metabolic and hypoxia stress response. Moreover, we identified MondoA as a promising target for immunotherapy of cALL.

Citation Format: Alexandra Sipol, Thomas G. P. Grunewald, Juliane Schmaeh, David Schirmer, Monique L. den Boer, Rebeca Alba Rubío, Michaela Baldauf, Caroline Wernicke, Hans-Jochem Kolb, Martin Horstmann, Gunnar Cario, Guünther Richter, Stefan Burdach. MondoA mediates in vivo aggressiveness of common ALL and may serve as a T-cell immunotherapy target. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2462.