Abstract CT145: Systemic rintatolimod and interferon-α2b selectively reprogram local tumor microenvironment in patients with metastatic triple negative breast cancer for enhanced influx of cytotoxic T-lymphocytes but not regulatory T-cells

Abstract Background: Effective immune therapies depend on the presence of cytotoxic T-lymphocytes (CTLs) in the tumor microenvironment (TME). Our preclinical data showed synergy between TLR3 ligands and interferon-α (IFN-α) in reprogramming the TME, but not healthy tissues, to selectively enhance CTL attraction, providing rationale for their systemic application to enhance local CTL densities in “cold” tumors. The pilot study NCT03599453 evaluated the safety of systemic chemokine modulating regimen (CKM) composed of i.v. rintatolimod (Ampligen; selective TLR3 ligand) and IFN-α, and its ability to promote local CTL influx to mTNBC lesions. Methods: Six evaluable patients (33-75 years) with mTNBC received 6 doses of rintatolimod (200 mg i.v.), IFN-α (INTRON-A; 20MU/m2 i.v.) and COX-2 inhibitor (celecoxib; 2 x 200 mg, p.o.) over 2 weeks, with tumor biopsies obtained before (within 6 days) and after (within 5 days) CKM. All patients received follow-up pembrolizumab (200 mg, i.v, Q3 weeks). The primary endpoint was the change in the CTL marker CD8α in the TME with a planned interim analysis after 3 patients (α=0.03) and final analysis after 6 patients (α=0.084). Correlative studies analyzed additional markers of CTLs, regulatory T-cells (Tregs), and CTL- and Treg-attracting chemokines in the TME and blood. Results: Treatment was well tolerated with mostly grade 1/2 adverse events and one grade 3 clinically significant pneumonitis and immune thrombocytopenic purpura observed during follow up pembrolizumab treatment. We observed uniform increases of intratumoral type-1 immune markers upon treatment: CD8α mRNA (6.1-fold; p=0.034), GZMB (3.5-fold; p=0.058), ratios of CD8α/FOXP3 and GZMB/FOXP3 (5.7-fold; p=0.036, and 7.6-fold; p=0.024 respectively), and CTL attractants CXCL10 (2.6-fold; p=0.104) and CCL5 (3.3-fold; p=0.019), successfully meeting the primary endpoint. In contrast, neither Treg marker Foxp3 nor Treg attractants CCL22 or CXCL12 were enhanced. These TME changes were accompanied by transient decreases in circulating CD3+CD8+ CTLs and CD3-CD56+ NK cells (but not Tregs), selectively affecting the cells expressing CXCR3 (receptor for CXCL10), but not CCR4 or CXCR4 (receptors for CCL22 and CXCL12). Three patients had stable disease lasting 2.4, 2.5 and 3.8 months, as of September 1, 2021 cut-off. An additional patient had a partial response (breast auto-amputation) with massive tumor necrosis observed in the post-CKM biopsy. Conclusion: This proof-of-concept study shows that short-term systemic CKM followed by pembrolizumab is safe and selectively enhances local CTL infiltration in the TME, providing rationale for concurrent CKM and PD1 blockade in prospective phase II studies. Citation Format: Shipra Gandhi, Mateusz Opyrchal, Melissa Grimm, Ronald Slomba, Kathleen Kokolus, Sebastiano Battaglia, Kristopher Attwood, Adrienne Groman, Lauren Williams, Mary Lynne Tarquini, Paul Wallace, Kah Teong Soh, Tracey O'Connor, Amy Early, Ellis Levine, Igor Puzanov, Marc Ernstoff, Pawel Kalinski. Systemic rintatolimod and interferon-α2b selectively reprogram local tumor microenvironment in patients with metastatic triple negative breast cancer for enhanced influx of cytotoxic T-lymphocytes but not regulatory T-cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT145.