Replication-restricted vaccinia as a cytokine gene therapy vector in cancer: Persistent transgene expression despite antibody generation

Abstract

Background:As antitumoral immunity requires the generation of local immunity directed against tissue proteins, we attempted to recreate within tumors the same environment found within tissues affected by autoimmune diseases (i.e., prolonged cytokine expression). Vaccinia virus (VV) has not been widely used as a cytokine gene therapy vector because of presumed high immunogenicity that would likely make repeated injections impossible; therefore, we modified it by inserting the cytokine gene into the thymidine kinase region, rendering it replication-restricted. The cytokine chosen was human interleukin-2 (IL-2), a molecule with powerful antitumoral effects.Methods: Six patients with the treatment-resistant tumor malignant mesothelioma received intratumoral (i.t.) VV-IL-2 therapy for 12 weeks by injection of 10 7 plaque-forming units of VV-IL-2 per dose. Serial tumor biopsies, sputum, urine, and blood samples were tested for VV-IL-2 mRNA expression; VV culture and T-cell infiltrates were evaluated by immunohistochemistry. Patients and contacts of patients were monitored for changes in VV immunoglobulin G (IgG) levels and clinical evidence of VV infection.Results: VV-IL-2 was not excreted and was only cultured in one patient from tumor biopsies. A T-cell infiltrate was detected in 50% of tumor biopsies. VV-IL-2 mRNA expression was highest on days 1-3 postinjection and was detected for up to 3 weeks after each injection even though VV IgG levels rose in all patients. No significant toxicities, infection of patient contacts, or tumor regressions were observed.Conclusions: I.t. VV-IL-2 administration is safe, is associated with minimal toxicity, and results in i.t. expression of VV-IL-2 for up to 3 weeks postinjection regardless of the level of anti-VV IgG titers generated. This suggests that VV may be a good vector for repeated cytokine gene therapy of solid human cancer.

Cytokine-armed vaccinia virus infects the mesothelioma tumor microenvironment to overcome immune tolerance and mediate tumor resolution

“…injections of the VV-HA and cytokine contructs in a Cytokine-armed vaccinia can cure mesothelioma C Jackaman and DJ Nelson regimen that mimicked the clinical trial. 12 VV-HA did not provide a beneficial effect, as the tumors continued to grow at a similar, or faster, rate than the PBS controls (Figures 7a and b). In contrast, both VV-IL-2 and VV-IL-12 monotherapies slowed tumor growth rate.…”

“…administration of VV as per a recent clinical trial. 12 Macrophages dominate the AE17-induced tumor microenvironment and can represent up to 60% of the total tumor cellularity. [41][42][43] Therefore, these cells are highly likely to encounter any viral vector that is delivered by i.t.…”

“…[6][7][8][9][10][11] However, each viral vector offers specific advantages; the potential of pox viral vectors, specifically vaccinia vectors, in mesothelioma has been already shown. 12 To this effect, a phase I gene therapy trial in malignant mesothelioma patients involving weekly intratumoral (i.t.) injections of a replication-restricted vaccinia virus-IL-2 (VV-IL-2) vector was conducted 12 showing the feasibility and safety of such an approach.…”

“…12 To this effect, a phase I gene therapy trial in malignant mesothelioma patients involving weekly intratumoral (i.t.) injections of a replication-restricted vaccinia virus-IL-2 (VV-IL-2) vector was conducted 12 showing the feasibility and safety of such an approach. Despite the generation of an anti-VV antibody response, VV-IL-2 mRNA gene expression persisted in tumor biopsies for up to 3 weeks and induced a local T cell infiltrate.…”

“…approach remains a viable proposition. [14][15][16][17][18][19][20][21][22][23] Despite the apparent safety of the mesothelioma VV clinical trial, 12 safety issues continue to be a concern. Another member of the Poxviridae family, Fowlpox virus (FPV), undergoes abortive replication in the cytoplasm of mammalian cells allowing for transcription of inserted genes without production of functional FPV particles, thereby reducing safety concerns.…”