(396a) Programmable Immunotherapeutic Biomaterials to Potentiate Chemotherapy

Introduction: Acute Myeloid Leukemia (AML) has a very poor prognosis, with a 5-year survival of about 25%. While cytotoxic chemotherapy is successful at inducing remission of acute myeloid leukemia (AML), the disease has a high probability of relapse with chemo-resistant cells. One strategy to prevent relapse is to vaccinate mice against AML. Key to this strategy is to sustain a cytotoxic CD8⁺T-cell response to eliminate residual cells after debulking by chemotherapy. In this study, we explored the development of a modular biomaterial-based vaccine with AML-specific antigens to prevent AML relapse.

Materials and Methods: Injectable macroporous alginate hydrogels were synthesized by low-temperature redox-induced free-radical polymerization. Granulocyte macrophage colony stimulating factor (GM-CSF), CpG ODN 1826, (5â?²-TCC ATG ACG TTC CTG ACG TT-3â?²) and ovalbumin (OVA), cell lysate or an immunogenic peptide of Wilmsâ?? tumor protein-1 (WT-1) were added to the mixture prior to cryopolymerization. A GFP-luciferase expressing MLL-AF9 AML knock-in cell line from a C57BL/6J mouse was used to induce AML without irradiation. One version of the cell line was transduced to express ovalbumin. Cytosine arabinoside (Ara-C 100mg/kg) and Doxorubicin (Dox 4mg/kg) were used for induction chemotherapy. Hydrogels were injected subcutaneously and the recruitment of immune cells to the scaffold was monitored by periodically harvesting the scaffolds. Antigen specific CD8⁺T-cells were monitored in blood. Secondary transplants were performed to test treatment efficacy.

Results and Discussion: In the MA-Alg/MA-PEG hydrogel, we observed an infiltration of neutrophils, dendritic cells and macrophages as early as 2 days after subcutaneous injection. There was an upregulation in activated dendritic cells at the site of the hydrogel, as well as in the draining lymph nodes. When used as an antigen prophylactically, the lysate of the bone marrow cells of leukemic mice prevented the engraftment of AML cells in mice. A western blot analysis of vaccinated mouse serum revealed the production of antibodies against a broad range of targets. When OVA was used as the antigen, paired with the OVA expressing AML cell line, the onset of leukemia was delayed significantly in prophylactically vaccinated mice, but not prevented altogether. SIINFEKL tetramer positive CD8⁺ cells were detected in peripheral blood and were maintained over the duration of the study, until the mice were terminal. An analysis of the hematopoietic compartments revealed the gradual loss of OVA expression on AML cells, suggesting immune escape through loss of antigen. A bolus subcutaneous injection transiently increased SIINFEKL tetramer positive CD8⁺, and delayed the onset of AML when challenged within that window â?? however it did not translate into increased survival. A known MHC class 1 restricted peptide fragment of a clinically defined AML antigen, WT-1, was incorporated in the vaccine as an antigen. When used prophylactically, WT-1 extended survival significantly, more than OVA, but not prevent AML associated mortality entirely. To mimic the clinical therapeutic management of AML, an induction chemotherapeutic regimen was used before the administration of the WT-1 vaccine. The chemotherapy significantly debulked the tumor, whereas the WT-1 vaccine prevented the relapse of AML in mice. WT-1 tetramer positive CD8⁺cells were detected in peripheral blood over the duration of the study. Secondary transplants were performed after 150 days and confirmed the eradication of AML.

Conclusions: The results indicate the promise of a programmable biomaterial vaccine with clinically defined leukemia antigen targets. When used prophylactically, the vaccine alone can extend survival by sustaining the cytotoxic CD8⁺T-cell response. When used in conjunction with cytotoxic chemotherapy, the biomaterial vaccine can potentially prevent the relapse of AML in a clinical setting.

Acknowledgements: The work was supported by the National Institutes of Health through grants U19HL129903 and R01EB014703 and R01EB015498.