Phase I Study of a Poxviral TRICOM-Based Vaccine Directed Against the Transcription Factor Brachyury

Abstract

Purpose: The transcription factor brachyury has been shown in preclinical studies to be a driver of the epithelial-to-mesenchymal transition (EMT) and resistance to therapy of human tumor cells. This study describes the characterization of a Modified Vaccinia Ankara (MVA) vector-based vaccine expressing the transgenes for brachyury and three human costimulatory molecules (B7.1, ICAM-1, and LFA-3, designated TRICOM) and a phase I study with this vaccine.Experimental Design: Human dendritic cells (DC) were infected with MVA-brachyury-TRICOM to define their ability to activate brachyury-specific T cells. A dose-escalation phase I study (NCT02179515) was conducted in advanced cancer patients (n = 38) to define safety and to identify brachyury-specific T-cell responses.Results: MVA-brachyury-TRICOM-infected human DCs activated CD8⁺ and CD4⁺ T cells specific against the self-antigen brachyury in vitro No dose-limiting toxicities were observed due to vaccine in cancer patients at any of the three dose levels. One transient grade 3 adverse event (AE) possibly related to vaccine (diarrhea) resolved without intervention and did not recur with subsequent vaccine. All other AEs related to vaccine were transient and ≤grade 2. Brachyury-specific T-cell responses were observed at all dose levels and in most patients.Conclusions: The MVA-brachyury-TRICOM vaccine directed against a transcription factor known to mediate EMT can be administered safely in patients with advanced cancer and can activate brachyury-specific T cells in vitro and in patients. Further studies of this vaccine in combination therapies are warranted and planned. Clin Cancer Res; 23(22); 6833-45. ©2017 AACR.

Figure 1

(A) Flow cytometric analysis of CD80 (B7.1), CD54 (ICAM-1), and CD58 (LFA-3) expression in human DCs infected with indicated vectors (10 MOI, 24-hour). Shown is the percent positive cells for each marker and the mean fluorescence intensity (MFI). (B) Western blot analysis of brachyury expression in protein lysates of indicated DC cultures. GAPDH is used as a loading control protein for each sample. (C) Immunofluorescence analysis of brachyury expression in indicated DC cultures; green corresponds to brachyury and blue corresponds to DAPI-stained nuclei. Magnification 20X.

Figure 2

(A) DCs infected with 10 MOI of MVA-WT, MVA-TRICOM, or MVA-brachyury-TRICOM vectors were used for stimulation of allogeneic, brachyury-specific CD8⁺ T cells generated against a brachyury-specific 9-mer peptide. After 24 hours, supernatants were collected and evaluated for IFN-γ production by ELISA assay. Shown are the IFN-γ levels (pg/mL) after subtraction of background in response to T cells only. One-way ANOVA p=0.0036. Shown p-values for comparison between indicated groups were calculated by the Tukey’s multiple comparisons test. (B) DCs infected with 10 MOI of MVA-brachyury-TRICOM vector were used for stimulation of autologous PBMCs, as described in detail in the Materials and Methods section. Following two cycles of stimulation, CD4⁺ T cells were isolated and stimulated in the presence of autologous PBMCs pulsed with control HSA protein or a recombinant, purified His-brachyury protein. Shown is the proliferation of CD4⁺ T cells measured as [³H] thymidine incorporation (cpm = counts per minute) for two representative donors. One-way ANOVA p= 0.0046 (top panel) and p=0.004 (bottom panel). (C) Supernatants from autologous T cells were collected at 72–96 hours and assayed for IFN-γ production by ELISA. One-way ANOVA p= 0.0329 (top panel) and p=0.0007 (bottom panel). In all panels, p-values for comparison between indicated groups were calculated by the Tukey’s multiple comparisons test.

Figure 3

Progression-free survival on combination of vaccine and erlotinib. Patient 11 was treated on vaccine DL2, with time on vaccine of 15.9 months, for a total of 21.5 months on erlotinib. Patients 28, 34, and 36 were treated on vaccine DL3. Patient 28 was on vaccine study for 21.8+ months, and total time on erlotinib was 41.9+ months at the time of data lock for this publication. Patient 34 was on vaccine for 19.8 months, and total time on erlotinib was 35.0 months. Patient 36 was on vaccine study for 20+ months, with a total time on erlotinib of 32+ months at the time of data lock for this publication.