Showing papers by "Timothy L. Ratliff published in 1997"

Effect of Canarypox Virus (ALVAC)-Mediated Cytokine Expression on Murine Prostate Tumor Growth

Abstract: BACKGROUND Canarypox virus, ALVAC, does not replicate in infected mammalian cells and has potential as a vector for gene therapy in the treatment of cancer. PURPOSE Recombinant viruses carrying DNA sequences encoding interleukin 2 (ALVAC-IL-2), interferon gamma (ALVAC-IFN gamma), tumor necrosis factor-alpha (ALVAC-TNF-alpha), or the co-stimulatory molecule B7-1 (ALVAC-B7-1) were investigated as agents for the treatment of a newly defined mouse prostate tumor model. METHODS RM-1 mouse prostate cancer cells, which are syngeneic (i.e., same genetic background) to C57BL/6 mice, were used. The expression of foreign gene products in vitro in infected RM-1 cells was measured by immunoprecipitation, bioassay, or flow cytometry. The effects of foreign gene product expression on RM-1 tumor cell growth in C57BL/6 mice were measured after subcutaneous injection (in the back) of 5 x 10(5) uninfected or infected cells; measurements included determinations of time to a measurable tumor size, tumor size as a function of time, and survival. The induction of protective immunity by uninfected and infected RM-1 cells was tested by injection of lethally irradiated (70 Gy) cells and subsequent challenge with uninfected cells. The generation of cytotoxic T cells was monitored by use of a 51Cr release assay. Severe combined immunodeficient (SCID) mice were used to determine whether T or B lymphocytes were involved in ALVAC vector-mediated antitumor responses. Data were analyzed by use of Pearson's modification of the chi-squared test and Kaplan-Meier survival methods. Reported P values are two-sided. RESULTS The level of foreign gene product expression in ALVAC-infected RM-1 cells was dependent on the multiplicity of virus infection used; a multiplicity of five viruses per infected cell was chosen for subsequent experiments. RM-1 tumor growth in C57BL/6 mice was not affected by tumor cell expression of IL-2 alone, IFN gamma alone, or B7-1 alone; however, expression of TNF-alpha alone significantly delayed tumor growth at early time points (compared with parental ALVAC-infected tumors, P = .0001 at day 21 and P = .037 at day 28). Tumor cell expression of both TNF-alpha and IL-2 completely inhibited tumor growth in 60%-100% of treated mice. No protection against subsequent tumor challenge was detected in mice previously exposed to RM-1 cells expressing both TNF-alpha and IL-2. Cytotoxic T-lymphocyte activity toward RM-1 cells was not observed in C57BL/6 mice that rejected tumors. Tumor cell expression of TNF-alpha and IL-2 also resulted in tumor growth inhibition in SCID mice. CONCLUSIONS RM-1 mouse prostate cancer cells are readily infected by ALVAC vectors, and foreign gene products are efficiently expressed. Inhibition of RM-1 tumor growth by tumor cell expression of TNF-alpha and IL-2 appears to involve nonspecific antitumor activity.

Poxvirus vectors for gene transfer

Abstract: A promising approach to cancer immunotherapy is immunization with modified tumor cells carrying cytokine or immunomodulatory genes. Cytokine genes (tumor necrosis factor-alpha, interleukin 2, interferon gamma) and costimulatory molecule, B7-1, were incorporated into canarypox virus, ALVAC, which does not replicate in infected mammalian cells, and highly attenuated vaccinia virus, NYVAC. We examined the effect of local cytokine production on the growth of the mouse prostate tumor, RM-1, and the mouse bladder tumor, MBT-2. The vectors expressed the high levels of cytokines and B7-1 and the tumor growth of infected cells was significantly inhibited. The mice immunized with irradiated MBT-2 cells infected with ALVAC-interleukin 2 were protected against the subsequent challenge of parental tumor cells. We conclude that poxvirus vectors are useful for gene delivery in immunotherapy studies because of their infection efficiency, their capability of high gene product expression, their safety, and their case of handling.