Therapeutic Cancer Vaccination Targeting Shared Tumor Associated Antigens in Combination with Azacitidine for High Risk Myelodysplastic Syndrome - a Phase I Clinical Trial

Background: Standard care for patients with high risk myelodysplastic syndrome (MDS) is hypomethylating agents, such as azacitidine (AZA). AZA can induce expression of silenced genes, including methylated tumor associated antigens. Such tumor associated antigens may be recognized by T cells, and therefore exploited for immunotherapeutic targeting. To our knowledge, this is the first clinical study that combine hypomethylating agents with a multi-peptide therapeutic cancer vaccine in a hematological malignancy.

Method: In this open label phase 1 trial (ClinicalTrials.gov NCT02750995), we combine AZA with a peptide vaccine targeting antigens encoded from NY-ESO-1, MAGE-A3, PRAME and WT-1, which have previously been demonstrated to be upregulated by AZA treatment. Four long synthetic peptides containing previously described class I and class II epitopes for a variety HLA types was emulsified in Incomplete Freund's Adjuvant for subcutaneous injection. Patients were included following verified treatment response to six courses of AZA monotherapy.

Result: Five patients were included in the study and treated with the vaccine. The combination therapy showed only few adverse events during the study period, whereof none classified as serious. There was one instance of grade 4 toxicity; a case of neutrophil count decrease, requiring administration of prophylactic antibiotics, and two instances of grade 3 toxicity; platelet count decrease and neutrophil count decrease. No vaccine-specific immune response could be detected using intracellular cytokine staining or ELISpot assays, however changes in the phenotypic composition of immune cells and their expression of stimulatory and inhibitory markers were identified in individual patients. All patients progressed to AML with a mean time to progression from inclusion (TTP) of 4.9 months (range 2.8 to 7.6). Survival was 17 months (range 10.9 to 30.6) from MDS diagnosis. Sequencing of bone marrow showed clonal evolution of malignant cells, as well as appearance of novel mutations.

Conclusion: The patients progressed to AML with an average time of only five months after initiating the combination therapy. This may be unrelated to the experimental treatment, but the trial was terminated early as there was no sign of clinical benefit or immunological response.

Figure 1. (a) Trial design. All participants received six courses of AZA prior to inclusion and were evaluated with bone marrow biopsy for treatment response. Vaccination was given together with the next three courses of AZA. (b) Vaccine composition. Synthetic long peptides from NY-ESO-1, PRAME, MAGE-A3 and WT-1 were emulsified in adjuvant Montanide ISA 51.