Safety and survival with GVAX pancreas prime and Listeria Monocytogenes-expressing mesothelin (CRS-207) boost vaccines for metastatic pancreatic cancer

Abstract

Purpose: GVAX pancreas, granulocyte-macrophage colony-stimulating factor-secreting allogeneic pancreatic tumor cells, induces T-cell immunity to cancer antigens, including mesothelin. GVAX is administered with low-dose cyclophosphamide (Cy) to inhibit regulatory T cells. CRS-207, live-attenuated Listeria monocytogenes-expressing mesothelin, induces innate and adaptive immunity. On the basis of preclinical synergy, we tested prime/boost vaccination with GVAX and CRS-207 in pancreatic adenocarcinoma.

Patients and methods: Previously treated patients with metastatic pancreatic adenocarcinoma were randomly assigned at a ratio of 2:1 to two doses of Cy/GVAX followed by four doses of CRS-207 (arm A) or six doses of Cy/GVAX (arm B) every 3 weeks. Stable patients were offered additional courses. The primary end point was overall survival (OS) between arms. Secondary end points were safety and clinical response.

Results: A total of 90 patients were treated (arm A, n = 61; arm B, n = 29); 97% had received prior chemotherapy; 51% had received ≥ two regimens for metastatic disease. Mean number of doses (± standard deviation) administered in arms A and B were 5.5 ± 4.5 and 3.7 ± 2.2, respectively. The most frequent grade 3 to 4 related toxicities were transient fevers, lymphopenia, elevated liver enzymes, and fatigue. OS was 6.1 months in arm A versus 3.9 months in arm B (hazard ratio [HR], 0.59; P = .02). In a prespecified per-protocol analysis of patients who received at least three doses (two doses of Cy/GVAX plus one of CRS-207 or three of Cy/GVAX), OS was 9.7 versus 4.6 months (arm A v B; HR, 0.53; P = .02). Enhanced mesothelin-specific CD8 T-cell responses were associated with longer OS, regardless of treatment arm.

Conclusion: Heterologous prime/boost with Cy/GVAX and CRS-207 extended survival for patients with pancreatic cancer, with minimal toxicity.

Fig 1.

CONSORT diagram. Percentages are based on number of participants treated in each arm and overall, except where indicated with asterisk (*).

Fig 2.

Kaplan-Meier estimates of overall survival (OS) according to treatment group. (A) OS for full analysis set (patients receiving ≥ one dose of cyclophosphamide [Cy]); median OS was 6.1 months in group receiving Cy/GVAX followed by CRS-207 and 3.9 months in group receiving Cy/GVAX alone. (B) OS for per-protocol analysis set (patients receiving ≥ three doses [≥ two doses of Cy/GVAX and one dose of CRS-207 in arm A or three doses of Cy/GVAX in arm B]); median OS was 9.7 months in group receiving Cy/GVAX followed by CRS-207 and 4.6 months in group receiving Cy/GVAX alone. Solid circles represent censored survival time for alive patients. HR, hazard ratio.

Fig 3.

Forest plot of treatment effect on overall survival in subgroup analyses. Horizontal lines represent 95% CIs. Position of each square represents point estimate of hazard ratio for treatment effect. Cy, cyclophosphamide; ECOG, Eastern Cooperative Oncology Group; FAS, full analysis set; PD, progressive disease; PP, per-protocol analysis set; SD, stable disease.

Fig 4.

Carbohydrate antigen 19-9 (CA 19-9) responses. (A) CA 19-9 kinetics; in patients with abnormal baseline tumor marker CA 19-9 (> 37 U/mL), the following definitions to distinguish stable or responding (SR) from progression (PR) were used: SR if < 50% increase for all assessments through 120 days, and PR if ≥ 50% increase in first 120 days for any assessment. (B) Overall survival based on CA 19-9 responses. HR, hazard ratio; N/A, not applicable.

Fig 5.

Mesothelin-specific T-cell responses. Mesothelin-specific CD8 T cells were quantified in peripheral blood lymphocytes (PBLs) using interferon gamma enzyme-linked immunosorbent spot assays at baseline (C1W1), 3 weeks after two treatments with cyclophosphamide (Cy)/GVAX (C1W7), and 3 weeks after each subsequent dose of either CRS-207 (arm A) or Cy/GVAX (arm B; C1W10, C1W13, C1W16, and C1W20) in 44 HLA-A1–, HLA-A2–, and/or HLA-A3–positive patients who received ≥ one treatment of Cy/GVAX. CD8 T-cell responses to mesothelin peptides were considered enhanced when post-treatment T-cell levels were > five per 1 × 10⁵ CD8⁺ PBLs and increased by ≥ two-fold compared with baseline levels. Cumulative numbers of T cells measured against each HLA-matched mesothelin peptide are reported for each sample. (A) Mesothelin-specific CD8 T-cell levels per 1 × 10⁵ CD8⁺ PBLs in patients separated by treatment arm. (B) Mesothelin-specific CD8 T-cell levels per 1 × 10⁵ CD8⁺ PBLs in patients separated by overall survival (OS) > or < 6 months. (C) Size of enhanced post-treatment mesothelin-specific CD8 T-cell repertoire in patients separated by OS > or < 6 months.

Fig A1.

Heterologous prime/boost of GVAX and Listeria-based vaccines induces robust antigen-specific T-cell immunity and delays tumor growth in experimental mouse pancreatic tumor model. (A) AH1-specific T-cell responses at peak of response in BALB/c mice. On day 0, BALB/c mice (n = 5) were immunized with either 5 × 10⁶ colony-forming units (CFUs) of Lm-AH1 (Lm) intravenously (IV) or 1 × 10⁶ cells of GVAX subcutaneously (SC). On day 14, specific groups were boosted IV with 5 × 10⁶ CFUs of Lm. Seven days after prime and 5 days after boost, spleens from mice were obtained, and interferon gamma (IFN-γ) AH1-specific immune responses were assessed by intracellular cytokine staining. (B) Therapeutic antitumor efficacy of combination of GVAX and Lm in C57BL/6 mice. On day 0, C57BL/6 mice (n = 10) were implanted SC with 1 × 10⁶ Panc02 cells. On day 3, GVAX animals were pretreated with cyclophosphamide 100 mg/kg and PC-61 50 μg. On day 4, mice were vaccinated either SC with 6 × 10⁶ cells of GVAX (3 × 10⁶ irradiated Panc02 cells plus 3 × 10⁶ irradiated B78H1 cells) or IV with 5 × 10⁶ CFUs of Lm-mouse mesothelin (Lm-mMeso). Fourteen days after vaccination, indicated groups were boosted IV with 5 × 10⁶ CFUs of Lm-mMeso. Mice were monitored over time, and tumor growth was measured twice per week. HBSS, Hank's balanced salt solution.

Fig A2.

Kaplan-Meier estimates of overall survival (OS) at interim analyses according to treatment group. (A) OS for full analysis set (patients receiving ≥ one dose of cyclophosphamide [Cy]); median OS was 6.0 months in group receiving Cy/GVAX followed by CRS-207 and 3.4 months in group receiving Cy/GVAX alone. (B) OS for per-protocol analysis set (patients receiving ≥ three doses [≥ two doses of Cy/GVAX and one dose of CRS-207 in arm A or three doses of Cy/GVAX in arm B]); median OS was 7.3 months in group receiving Cy/GVAX followed by CRS-207 and 4.6 months in group receiving Cy/GVAX alone. Solid circles represent censored survival time for alive patients.