Expand and pull: A new treatment paradigm for glioblastoma using a long-acting recombinant interleukin-7 and oncolytic viral therapy.
Authors: Li Yuping Derek , Hu Tong , Kesarwani Ashwani , Costa Amanda , Wolfarth Alexandra , Ferrando-Martinez Sara , Lee Byung Ha , Diamond Michael , Chheda Milan G 
Published: June 2024

2043 Background: Patients with glioblastoma (GBM) face three major challenges. First, the tumor itself as well as chemoradiation treatment result in lymphopenia, which is associated with shorter survival. Second, the tumor microenvironment (TME) has a paucity of T cells and consequently, immunotherapies have failed in multiple phase 3 clinical trials for GBM. Third, a treatment resistant population of cancer stem cells (CSCs) contribute to inevitable tumor recurrence. In preclinical models, we have shown that a long-acting IL-7, NT-I7, significantly increases peripheral CD8 T cells and separately, oncolytic Zika virus (ZIKV) directly targets CSC and induces an anti-tumor CD8 T cell response. The aim of this study was to determine whether we can leverage the NT-I7 driven T cell expansion peripherally and combine it with ZIKV therapy to pull immune cells into the TME to successfully treat a highly immunosuppressive mouse model of GBM. Methods: SB28 syngeneic tumor cells were intracranially implanted in C57BL/6J mice. Mice were treated with NT-I7 subcutaneously on days 7 and 10 post tumor implantation, followed by intratumoral ZIKV on day 14. Mice were monitored for survival and bled weekly to assess the systemic T-cell response to NT-I7. Immunoprofiling of brain, draining lymph node, and peripheral blood via flow cytometry was done on days 17 and 21. Results: NT-I7 significantly expanded peripheral T cells compared to control (5,623 cells/µL vs 136 cells/µL, p<0.05). Cytotoxic CD8 T cells were particularly increased (4,776 cells/µL vs 47 cells/µL, p<0.05), with the expansion peak at day 7 after the first dose of NT-I7 and persisting for 21 days. When ZIKV was administered at the peak of the NT-I7-driven CD8 T cell expansion, the combination resulted in significant improvement in survival compared to NT-I7 or ZIKV monotherapy (median 47 days vs 35 days and 33 days, respectively, p<0.05). Combined NT-I7 and ZIKV treatment significantly increased TME CD8 T cell infiltration (369,814 cells/g vs 23,947 cells/g and 63,961 cells/g, respectively) as well as increased expression of interferon-γ, TNF-α, perforin, and granzyme B (p<0.05). Long-term survivors were protected against tumor rechallenge, suggesting that this treatment strategy confers immune memory against tumor antigens. The addition of immune checkpoint blockade with anti-PD1 antibody resulted in nearly 80% complete tumor clearance. Conclusions: Timing the oncolytic ZIKV injection with the NT-I7-induced peak expansion of peripheral CD8 T cells greatly increased tumor infiltration of cytotoxic T cells and improved survival in the immunotherapy resistant SB28 glioma model. This work suggests a new “expand and pull” approach for the treatment of highly immunosuppressive tumors such as GBM: priming the systemic immune system with NT-I7, followed by an oncolytic stimulus to draw them into the TME to engage and clear tumor cells.