Antitumor activity of T cells expressing a novel anti-folate receptor alpha (FOLR1) costimulatory antigen receptor (CoStAR) in a human xenograft murine solid tumor model and implications for in-human studies.

Abstract

2535 Background: ITIL-306 is an autologous tumor-infiltrating lymphocyte (TIL) therapy that integrates T-cell receptor (TCR)-specific antigen recognition (Signal 1) with robust costimulation via the novel CoStAR transgene upon engagement with FOLR1 (Signal 2; Sukumaran, et al. JITC. 2021;9:198). Here, we assessed IL-2 independent effector function by anti-FOLR1 CoStAR T cells in vitro and evaluated activity in a novel, more representative murine solid tumor model. Methods: For in vitro studies, healthy donor T cells were manufactured to express anti-FOLR1 CoStAR or left nontransduced (NTD). Product cells were stimulated with a single (Day [D]0; ±IL-2) or serial (D0, 7, 14, 21; no IL-2) addition of target cells expressing membrane-anchored OKT3 (Signal 1) and FOLR1 (Signal 2). T-cell activation and proliferation were measured. For in vivo studies, the carcinoembryonic antigen (CEA)-positive (Signal 1) H508 cell line was engineered to express FOLR1 (Signal 2) and injected into 6 mice/group (D–21). NTD or healthy donor T cells expressing HLA-A*02-restricted anti-CEA TCR only, anti-FOLR1 CoStAR only, or dual TCR+CoStAR were given intravenously (D0), and compared with PBS control. Tumor growth, survival, and T-cell expansion were assessed in 2 donors to D96. Results: After single and serial stimulation, only anti-FOLR1 CoStAR T cells showed sustained proliferation without exogenous IL-2. PD-1 positivity was low ( < 10%) on anti-FOLR1 T cells up to D24. In vivo, T-cell persistence on D14 was increased in dual TCR+CoStAR vs anti-CEA TCR only mice ( P<.001) and all other groups ( P<.01-.001). Tumor growth up to D58 was significantly lower in dual TCR+CoStAR ( <.5 cm3) vs all other groups (each > 2 cm3; P<.0001). Survival was significantly longer in dual TCR+CoStAR ( P<.01) vs all other groups; only dual TCR+CoStAR mice were alive at D58, with 5/6 alive at D96. The second donor showed similar tumor control irrespective of exogenous IL-2 in responder mice, with > 50% alive at D96, and robust T-cell expansion in dual TCR+CoStAR mice. Conclusions: When combined with TCR-specific binding, CoStAR significantly enhanced T-cell proliferation, persistence, and antitumor activity in vivo vs TCR alone, resulting in tumor control and prolonged survival. Effects were not observed with CoStAR alone, underscoring that signaling through CoStAR alone does not induce T-cell effector function. The sustained proliferation of anti-FOLR1 CoStAR T cells without exogenous IL-2 support in vitro and in vivo supports a clinical TIL regimen free of high-dose IL-2. These results suggest that CoStAR may improve the clinical performance and benefit/risk profile of TILs, whereby fewer toxicities are expected with the removal of post-TIL IL-2 support. This will be explored in an upcoming first-in-human clinical study with ITIL-306.

Folate Receptor Alpha—A Novel Approach to Cancer Therapy

“…According to an abstract published in ASCO 2022, a study evaluating IL-2 independent effector function by anti-FOLR1 CoStAR T cells (ITIL-306) in vitro found that tumor growth was significantly reduced and survival was improved by this treatment, with five out of six mice alive at day 96 [ 42 ]. Although there are many obstacles to the use of this receptor in treatments and imperfections in its application, it has been shown in many studies that the use of this receptor can pave the way to success.…”

Tumor-Infiltrating Lymphocyte Therapy in Melanoma: Facts to the Future

“…27). Including a synthetic costimulatory antigen receptor (CoStAR) molecule with dual CD28 and CD40 domains on healthy donor T cells targeting the tumor-associated antigen CEA led to increased T-cell activation and long-term proliferation even in the absence of IL2 (99,100). Furthermore, the enhancement of cytokine-induced immune activation may be accomplished through the local delivery of cytokines outside of IL2 (Fig.…”

776 ITIL-306–201: A multicenter, first-in-human phase 1a/1b study of ITIL-306, an engineered autologous tumor-infiltrating lymphocyte (TIL) cell therapy product, in adults with advanced solid tumor

“…5 In a murine model with a human solid tumor xenograft, the anti-folate receptor alpha (FRa) costimulatory antigen receptor (CoStAR) significantly enhanced T-cell proliferation, persistence, and antitumor activity without exogenous IL-2 support, resulting in enhanced tumor control and prolonged survival. 6 ITIL-306 is an engineered autologous TIL cell therapy that supplements native TCR-specific antigen recognition with synthetic costimulation upon engagement with FRa. ITIL-306-201 is a multicenter, single-arm, phase 1a/1b dose escalation and expansion study evaluating the safety and feasibility of ITIL-306 in adult patients with advanced epithelial ovarian cancer (EOC), nonsmall cell lung cancer (NSCLC), and renal cell carcinoma (RCC) who relapsed from or are refractory to !1 prior line of systemic therapy.…”