Abstract LB-081: In situ vaccination of low-grade lymphoma with intratumoral Flt3L and poly-ICLC with low-dose radiotherapy

Background: Lymphomas are the 5th most common cancer in the United States, 40% of these are cases are indolent non-Hodgkin9s lymphoma (iNHL) and are incurable with standard therapy. A previous trial of in situ vaccination in iNHLs, in which intratumoral CpG, the TLR9 agonist, was combined with low dose radiation to induce a systemic immune response against tumor. In this trial induction of tumor-specific CD8 T cell responses and durable clinical remissions of patients’ untreated sites of disease was seen in some patients. One limitation in this previous trial may have been the scarcity of intratumoral dendritic cells (DC) and the suppressive tumor microenvironment. DC are uniquely able to endocytose dying (e.g. irradiated) tumor cells for cross-presentation to anti-tumor CD8 T cells. In this new iteration of in situ vaccine, Flt3L is added as a priming step to increase the presence of intratumoral DCs ahead of vaccination. Fms-like tyrosin kinase 3 ligand (Flt3L) induces tumor leukocyte infiltration and regression in lymphoma tumors in pre-clinical trials, and CDX-301- a formulation of Flt3L - was shown to mobilize BDCA-1 and BDCA-3 myeloid DC subsets in an early phase trial. These DC subsets respond to several TLR agonists and cross-present antigens more effectively than plasmacytoid DCs. While pDCs are high expressors of TLR9, responsive to CpG, myeloid dendritic cells express a wider array of TLRs, including high levels of TLR3. Methods: This Phase I/II trial tests the hypothesis that this novel in situ vaccination will induce clinical remissions at distant (untreated) tumor sites in two cohorts of patients with either previously untreated or relapsed/refractory iNHL (n = 15 per group). Intratumoral CDX-301 25ug/kg is injected into a palpable lymph node for 9 days, followed 2Gy local radiotherapy on day 9 and 10 to the target lymph node. On day 10, following radiation therapy, intratumoral poly-ICLC 2mg is injected to activate local DCs. Poly-ICLC 2mg is then injected on day 14, day 17 (1 week after initial dose) and weekly thereafter for a total of 9 treatments over 8 weeks. Response is assessed with CT scans every three months as per the Revised Response Criteria for Malignant Lymphoma, also known as the Cheson criteria, and leukemic phase of lymphoma monitored by peripheral blood flow cytometry. The trial started accrual in January 2014 and is ongoing, 11 have been enrolled including 8 untreated patients and 3 with refractory disease. To perform correlative studies during the clinical trial we perform excisional biopsy of a distal lymph node before starting trial to assess baseline immunomodulatory or immunosuppressive characteristics of a patients tumor microenvironment. Fine needle aspirate (FNA) of the target tumor (site of Flt3L, Radiation and poly-ICLC administration) treatment at weeks 0, 2, 4 and 6, after which target tumor is significantly smaller and biopsy not typically possible. Blood is collected for immune monitoring at weeks 0, 2, 4, 6, 8, 12 to assess for transient enrichment of DC populations, and monitoring for tumor-specific effector T cell populations. Citation Format: Thomas U. Marron, Nina Bhardwaj, Linda Hammerich, Seunghee Kim-Schulze, Tibor Keler, Tom Davis, Elizabeth Crowley, Andres M. Salazar, Joshua Brody. In situ vaccination of low-grade lymphoma with intratumoral Flt3L and poly-ICLC with low-dose radiotherapy. [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 LB-081.