Herpes simplex virus (HSV)-mediated ICAM-1 gene transfer abrogates tumorigenicity and induces anti-tumor immunity

Background: Costimulatory and cellular adhesion molecules are thought to be essential components of antigen presentation in the immune response to cancer. The current studies examine gene transfer utilizing herpes viral amplicon vectors (HSV) to direct surface expression of adhesion molecules, and specifically evaluate the potential of a tumor-expressing intercellular adhesion molecule-1 (ICAM-1) to elicit an anti-tumor response. Materials and Methods: The human ICAM-1 (hICAM1) gene was inserted into an HSV amplicon vector and tested in a transplantable rat hepatocellular carcinoma and in a human colorectal cancer cell line. Cell surface ICAM-1 expression was assessed by flow cytometry. Lymphocyte binding to HSV-hICAM1-transduced cells was compared with that to cells transduced with HSV not carrying the ICAM gene. Tumorigenicity of HSV-hICAM1-transduced tumor cells were tested in syngeneic Buffalo rats. Additionally, immunization with irradiated (10,000 rads) HSV-hICAM1-transduced tumor cells was performed to determine its effect on tumor growth. Results: A 20-min exposure of tumor cells at a multiplicity of infection (MOI) of 1 resulted in high-level cell surface expression of human ICAM in approximately 25% of tumor cells. Transduced rat or human tumor cells exhibited significantly enhanced binding of lymphocytes (p < 0.05). HSV-hICAM1-transduced cells elicited an increase in infiltration by CD4⁺ lymphocytes in vivo and exhibited decreased tumorigenicity. Immunization with irradiated HSV-hICAM1-transduced cells protected against growth of subsequent injected parental tumor cells. Conclusions: HSV amplicon-mediated gene transfer is an efficient method for modifying the cell surface expression of adhesion molecules. Increased tumor expression of ICAM-1 represents a promising immune anti-cancer strategy.