Little is known about the immune responses induced by recombinant adenoviral (Ad) vectors in humans. The humoral and cellular immune responses were therefore analyzed in 21 patients with localized malignancy (mesothelioma), who received intrapleurally high doses of a replication-defective Ad5 vector carrying a suicide gene. Eight of 21 patients had pretreatment titers of neutralizing antibodies (NAb) to Ad at > or =1:100. Peripheral blood mononuclear cells (PBMCs) proliferated in response to adenoviral 5 structural proteins before treatment in 17 of 21 patients. Preexisting humoral and cellular immunity did not preclude gene transfer. Vector instillation induced high titers of nonneutralizing and neutralizing anti-Ad antibody (4- to 341-fold increase in 18 of 20 patients) in a dose-dependent manner. Three patients generated antibodies to the transgene, herpes simplex virus thymidine kinase. Ad5-specific proliferation of PBMCs increased significantly (>3-fold) after vector administration in 12 of 21 patients in a dose-dependent manner. Thus, replication-defective Ad5 administered intrapleurally induced significant humoral and cellular immune responses that induced no obvious adverse clinical sequelae.

ObjectiveThe authors demonstrate the ability of an adenovirus vector expressing the herpes simplex thymidine kinase (HSVtk) gene to treat human malignant mesothelioma growing within the peritoneal cavity of severe combined immunodeficient (SCID) mice.

Metabolic cooperation via gap junctional intercellular comtransduced with HSVtk via either retrovirus or adenovirus munication (GJIC) is an important mechanism of the vectors. This augmentation of bystander effect could also bystander effect in gene therapy using the herpes simplex be seen in vivo. HSVtk-transduced tumors in mice treated virus thymidine kinase/ganciclovir (HSVtk/GCV) 'prodrug' with the combination of GCV and retinoids were signifisystem. Since retinoids have been reported to increase cantly smaller than those treated with GCV or retinoids GJIC by induction of connexin expression, we hypothesalone. These results provide evidence that retinoids can ized that these compounds could be used to augment the augment the efficiency of cell killing with the HSVtk/GCV HSVtk/GCV bystander effect. Addition of all-trans retinoic system by enhancing bystander effects and may thus be acid increased GJIC in tumor cell lines, augmented a promising new approach to improve responses in gene expression of connexin 43, and was associated with more therapy utilizing the HSVtk/GCV system to treat tumors or efficient GCV-induced in vitro bystander killing in cells vascular restenosis.

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Previous studies have shown adenoviral transfer of the herpes simplex virus thymidine kinase (HSVtk) gene followed by the anti-viral drug ganciclovir (GCV) can be used to successfully treat established human mesothelioma tumors growing within the peritoneal cavities of severe combined immune deficient (SCID) mice. These findings raised a number of questions important to the applicability, efficiency, and safety of this treatment strategy. In this report, we have further characterized the use of recombinant adenovirus carrying the HSVtk gene to treat mesothelioma and other localized malignancies. Our results indicate that the Ad.RSVtk/GCV system is effective in causing tumor regression in animals inoculated with another mesothelioma cell line and a lung cancer cell line and that animals with bulky disease can be successfully treated. Effects are seen at a wide range of virus doses and significant anti-tumor activity is present at doses of ganciclovir that are clinically achievable. Finally, this treatment approach appears safe, with limited dissemination of virus using a sensitive RT-PCR detection system. These studies further characterize the use of adenoviral transfer of the HSVtk gene to treat experimental mesothelioma and suggest that clinical trials using this approach may be feasible.