Enhancement of tumor killing using a combination of tumor immunization andHSV-tk suicide gene therapy

Abstract

Tumor cells genetically modified with the herpes simplex virus thymidine kinase (HSV‐tk) gene in combination with ganciclovir (GCV) demonstrate a “bystander effect”. Previous attempts to enhance the bystander tumor killing by combining cytokine genes with HSV‐tk/GCV have met with varying results. The present study was designed to determine the effects of tumor immunization in combination with HSV‐tk gene‐modified tumor cells and GCV on tumor killing and to determine if the bystander tumor killing could be enhanced. Tumor‐bearing mice immunized with syngeneic tumor (KBALB) prior to treatment with an i.p. injection of xenogeneic HSV‐tk gene‐modified tumor cells (PA‐1STK) had prolonged animal survival (group 4, 56.4 days). In contrast, unimmunized tumor‐bearing mice (group 2) or tumor‐bearing mice immunized to the xenogeneic PA‐1STK tumor cells (group 5) showed a mean survival of about 27 days after receiving an i.p. injection of PA‐1STK cells and GCV. Control groups, which were either not immunized and did not receive HSV‐tk cells (group 1) or immunized but treated only with GCV (group 3) showed short survival (16–18 days). Analysis of tumors for cytokine mRNA expression revealed increased TNF‐α and IL‐1α mRNA expression in group 4 mice. Furthermore, IL‐2 mRNA expression was detectable on days 2 and 4 only in group 4 mice. Immunophenotypic analysis for tumor‐infiltrating lymphocytes demonstrated an increase in macrophage (4%, p = 0.0001) and T cells (1.8%, p < 0.001) in group 4 mice with an enhanced T‐cell response as compared with mice from groups 1, 2 and 3. Our results demonstrate that tumor immunization combined with HSV‐tk/GCV treatment results in increased animal survival with enhanced immune response. Furthermore, the cytokine milieu observed in the present study can modulate the tumor micro‐environment in vivo from one that is immunosuppressive to one that is immune‐stimulatory. Int. J. Cancer 80:380–386, 1999. © 1999 Wiley‐Liss, Inc.

Recombinant interferon α2a synergistically enhances ganciclovir-mediated tumor cell killing in the herpes simplex virus thymidine kinase system

“…In one example, immunization to tumor cells before treatment with the HSV-TK gene-modified cells and GCV resulted in prolonged animal survival. 14 Our results confirm and extend previous findings using IFN 15,16 by demonstrating the importance of this combination in a therapeutic tumor model and analyzing the underlying mechanism that leads to a synergistic antitumor effect. We have demonstrated that a low dose of IFN␣2a decreased the IC 50 of GCV from 0.03 M to 0.005 M in PA1STK cells.…”

“…Weeks after therapy, the dying GCV-exposed HSV-TK tumor cells lead to a delayed hypersensitivity immune response, because GCV is not immunosuppressive. 9,14 Thus, studies with IL-2 in combination with GCV therapy did not enhance the early phase bystander killing but did enhance the later long-term tumor immunity. Therefore, it would be expected that cytokines that enhance the early phase of the bystander effect (proinflammatory) would enhance the antitumor response.…”

Cytotoxicity of HSVtkand hrTNF-alpha fusion genes with IRES in treatment of gastric cancer

“…Expressed TNF-α activated and enhanced the proliferation of T lymphocytes, and combination of TNF-α can synergistically stimulate the anti-tumor immune response in vivo. [28][29][30][31] The experimental results confirmed that tk-TNF-α /GCV gene therapy could kill tumor cells markedly. If combined with TNF-α gene, they could boost the antitumor reaction, and produce powerful anti-tumor effects.…”

Treatment of mesothelioma with gene-modified PA1STK cells and ganciclovir: a phase I study

“…Experimental studies demonstrated this effect to be only present in vivo in immunocompetent animals, but not in immunodeficient mice. [7][8][9][10][11][12] It is believed that HSVtk suicide gene therapy converts an immunoinhibitory environment into an immunostimulatory microenvironment. 13 The use of viral vectors is complex and costly.…”