Immunological approaches in the gene therapy of cancer

Background : despite vigorous efforts at curbing tobacco consumption and aggressive combined modality treatment programmes, both incidence and mortality from lung cancer have remained virtually unchanged in the last 10 years and there is a clear need for more effective innovative therapies. The direct transfer of tumour suppressor genes or toxic gene products that specifically promote tumour cell death and spare non-malignant cells is a potentially novel anticancer treatment approach that should be investigated. Purpose : based on compelling preclinical data, we conducted a phase I study in humans to evaluate the feasibility, tolerance and clinical, biological and immunological effects of the intratumoral administration of a recombinant, replication-deficient adenovirus (Ad RSVB-gal), using the RSV promoter to drive transcription of the Escherichia coli lacZ marker gene that encodes for the bacterial enzyme beta-galactosidase (B-gal), in patients with inoperable lung cancer and an endobronchial lesion accessible by bronchoscopy. The first single dose level was 10 7 (3 patients), the second was 10 8 (3 patients) and the third was 10 9 plaque forming unit (pfu) (2 patients). Biopsies of tumour and surrounding mucosa, performed at days 8, and at 1, 2 and 3 months following injection, were analysed using PCR and X-gal staining. Patients and medical staff were monitored for wildtype and rAd infections by PCR, culture and serologic analyses. Patients remained in TL2 isolation until negative results of PCR and cultures of biologic fluid specimens were confirmed. All patients received concomitant chemotherapy. Results : seven patients with NSCLC and one with neuroendocrine tumour entered this ongoing study. Expression of B-gal was observed in five out of eight tumour biopsies (one at 10 7 , two at 10 8 and two at 10 9 dose level). Bronchoalveolar lavage collected immediately after injection were positive for recombinant adenovirus by culture and PCR. All biological fluids were negative by PCR after day 12. The three and two patients treated at 10 8 and 10 9 pfu respectively had PCR positive blood samples on day 1. Patients were in isolation for a median of 17 days. Moderate bleeding (two patients) during bronchoscopy and fever (four patients) were the most common toxicities. Endoscopic and clinical objective tumour responses were seen in five patients. The three patients treated at the second dose level, all with stage IIIB disease, were deemed resectable after chemotherapy. They all had a complete surgical resection of their tumour 112–152 days after viral injection. Hospital staff remained negative for recombinant adenovirus infection throughout the study. Conclusion : this ongoing study demonstrates that a marker gene can be safely introduced into humans using an rAd vector and that the gene product is expressed by host lung tumour cells. We will continue our programme by using this methodology to study the antitumour effects mediated by transfer of tumour suppressor or cytokine genes into endobronchial lesions in lung cancer patients.