DNA-mediated adjuvant immunotherapy extends survival in two different mouse models of myeloid malignancies

Abstract

We have previously shown that a specific promyelocytic leukemia-retinoic acid receptor alpha (PML-RARA) DNA vaccine combined with all-trans retinoic acid (ATRA) increases the number of long term survivors with enhanced immune responses in a mouse model of acute promyelocytic leukemia (APL). This study reports the efficacy of a non-specific DNA vaccine, pVAX14Flipper (pVAX14), in both APL and high risk myelodysplastic syndrome (HR-MDS) models. PVAX14 is comprised of novel immunogenic DNA sequences inserted into the pVAX1 therapeutic plasmid. APL mice treated with pVAX14 combined with ATRA had increased survival comparable to that obtained with a specific PML-RARA vaccine. Moreover, the survival advantage correlated with decreased PML-RARA transcript levels and increase in anti-RARA antibody production. In HR-MDS mice, pVAX14 significantly improved survival and reduced biomarkers of leukemic transformation such as phosphorylated mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) 1. In both preclinical models, pVAX14 vaccine significantly increased interferon gamma (IFNγ) production, memory T-cells (memT), reduced the number of colony forming units (CFU) and increased expression of the adapter molecule signalling to NF-κB, MyD88. These results demonstrate the adjuvant properties of pVAX14 providing thus new approaches to improve clinical outcome in two different models of myeloid malignancies, which may have potential for a broader applicability in other cancers.

pVAX14DNA-mediated add-on immunotherapy combined with arsenic trioxide and all-trans retinoic acid targeted therapy effectively increases the survival of acute promyelocytic leukemia mice

“…As pVAX14 is acting as a nonspecific DNA adjuvant with the specificity coming from the tumor cells themselves, this immunotherapeutic strategy may be applicable to other malignancies. We have already demonstrated this to be the case in our preclinical model of high-risk MDS 8 and we predict that this approach will be applicable to solid tumors in combination with agents that induce immunogenic cell death to enable tumor antigen shedding/spreading and initiation of immune responses, which pVAX14 then potentiates.…”

“…These changes translated into enhanced cytotoxic T-cell responses with the inhibition of APL BM progenitor growth and cytotoxic T-lymphocytes targeting APL cells. We hypothesize that the pVAX14 sequences, which we have demonstrated to induce immune responses, 8 potentiate the immune responses already initiated by the release of the PML-RARA tumor antigen due to terminal differentiation and immunogenic cell death 15 induced by ATRA and ATO. An add-on adjuvant immunotherapy approach may have utility in preventing relapse and could be considered for the rare high-risk APL patients who fail to respond to ATO+ATRA therapy.…”

“…Using this preclinical model, we previously demonstrated the efficacy of combined fusion gene promyelocytic leukemia-retonoic acid receptor alpha (PML-RARA) DNA administration with ATRA on mouse survival and leukemia-initiating cell eradication. 7 , 8 , 9 , 10 , 11 We have recently reported the similar efficacy of a novel nonspecific DNA construct pVAX14 with adjuvant properties and with an equally effective impact on the survival of these APL mice in combination with ATRA. 8 …”

“…To further monitor the efficacy of pVAX14 with ATRA+ATO, a biomarker we have previously described, MyD88 transcript levels were investigated using primer sequences detailed in Supplementary Table S3 . 8 , 12 MyD88 is an adaptor protein that mediates numerous biologically important signal transduction pathways including pathways involved in DNA's mechanism of action. 12 Transcript levels of MyD88 were significantly ( P <0.017) higher in APL mice treated with pVAX14+ATO+ATRA ( n =15) compared with mice treated with Vehicle+ATO+ATRA only ( n =20) ( Figure 1c ).…”

“…Two functional assays were used to evaluate the cytotoxic activity of T cells against precursor bone marrow (BM) cells. First we applied the assay described by Quintarelli et al 13 and that we have previously used, 8 in which APL BM targets were cocultured with CD3+ spleen cells from either Vehicle+ATO+ATRA- ( n =4) or pVAX14+ATO+ATRA- ( n =5) treated APL mice. As shown in Figure 2d , the incubation of CD3+ spleen cells from pVAX14+ATO+ATRA mice with APL precursors leads to a significant ( P <0.02) reduction of colony-forming units (CFUs).…”