Herpes virus ICP47 and US11 suppression of CTL activity adapted for use in gene therapy

A major stumbling block encountered in gene therapy clinical trials has been the rapid destruction of the therapeutic product by the host's immune response. The goal of this work is to diminish the host Cytotoxic T Lymphocyte (CTL) response to gene therapy transgenes and transduced cells by incorporating immunosuppression genes into gene therapy vectors. The processing and presentation of antigens through the class I Major Histocompatibility Complex (class I MHC) pathway is known to be an early response to viral infection. Disruption of the class I MHC pathway results in a decrease of the CD8+ CTL response and prolongs viral survival in the host. Two viral immune suppression genes that interfere with the class I MHC pathway, the herpes virus ICP47 encoding gene and the human cytomegalovirus US11 gene, were cloned and each incorporated into an LXSN retroviral vector. The vectors were used to transduce multiple cell lines including human, rat, and dog. The US11 gene effectively decreases the class I MHC cell surface expression in all cell lines tested whereas the ICP47 gene functions in all but the rat cells. In vitro cytotoxicity experiments show the level of class I MHC reduction correlates with a reduction of specific lysis by anti-tumor primed CTL populations. Three separate applications of ICP47 and US11 suppression of CTL activity are reported. First, the reduction of class I MHC expression in target cells was used to characterize the ability of a clinically relevant anti-tumor cell line to select tumor targets. Second, class I MHC cell surface expression was reduced in two promising anti-tumor cell lines which are currently being used for allogeneic transplant in cancer treatments. Third, US11 class I MHC down regulation in murine cells was used in an attempt to prolong the survival of a chemically generated tumor model cell line in vivo.