Inhibition of murine prostate tumor growth and activation of immunoregulatory cells with recombinant canarypox viruses.
BACKGROUND
Immunization with modified tumor cells carrying recombinant immunomodulatory genes is being explored as cancer immunotherapy. In this study, we examine whether canarypox ALVAC viruses carrying immunostimulatory cytokine genes (granulocyte-macrophage colony-stimulating factor, interleukin 2, interleukin 12, and tumor necrosis factor-alpha) can induce antitumor immunity (to rechallenge) in the RM-1 model of a highly aggressive, weakly immunogenic murine prostate cancer.


METHODS
For antitumor activity studies, RM-1 murine prostate cancer cells were infected with the parental ALVAC virus or one or two recombinant ALVAC-cytokine viruses and then injected into male C57BL/6 mice. For rechallenge studies, other mice were first given an injection subcutaneously with irradiated (nonproliferating) recombinant ALVAC-infected RM-1 cells and then (10 days later) with untreated RM-1 cells. For the determination of which immune cells were required for antitumor activity, mice were immunodepleted of CD4, CD8, or natural killer (NK) NK1.1 cells with the corresponding monoclonal antibodies and were then given an injection of ALVAC-cytokine-infected RM-1 cells. For all experiments, tumor outgrowth and animal survival were monitored.


RESULTS
After subcutaneous injection into mice, RM-1 cells infected with one (except ALVAC-interleukin 2) or two ALVAC-cytokine recombinants had statistically significantly greater antitumor activity than RM-1 cells infected with parental ALVAC (P<.001 for all; two-sided test). The antitumor activity of RM-1 cells infected with any two ALVAC-cytokine recombinants was greater than, but not statistically significantly different from, that of RM-1 cells infected with any one ALVAC-cytokine recombinant. NK1.1 cells were necessary for antitumor activity, but tumor-specific CD4(+) regulatory T cells were also induced that inhibited CD8(+) RM-1-specific cytotoxic T cells, resulting in the lack of immunity to a rechallenge by RM-1 cells.


CONCLUSIONS
Canarypox viruses can transfer immunostimulatory cytokine genes into RM-1 prostate cancer cells. When such cells were injected into mice, the cytokines induced an antitumor response against this highly aggressive, weakly immunogenic tumor. This response, however, did not protect the mouse against a rechallenge with RM-1 cells because suppressor CD4(+) T cells were induced that inhibited tumor-specific CD8(+) cytotoxic T cells.
Griffith
T S
TS
Department of Urology, University of Iowa, Iowa City 52242-1089, USA. thomas-griffith@uiowa.edu
Kawakita
M
M
Tian
J
J
Ritchey
J
J
Tartaglia
J
J
Sehgal
I
I
Thompson
T C
TC
Zhao
W
W
Ratliff
T L
TL
D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D000941:Antigens / Q000096:biosynthesis; D000950:Antigens, Ly; D000954:Antigens, Surface; D018150:Avipoxvirus / Q000235:genetics*; D015704:CD4 Antigens / Q000096:biosynthesis; D016827:CD8 Antigens / Q000096:biosynthesis; D005434:Flow Cytometry; D018014:Gene Transfer Techniques; D015316:Genetic Therapy; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000235:genetics; D018664:Interleukin-12 / Q000235:genetics; D007376:Interleukin-2 / Q000235:genetics; D037181:Lectins, C-Type; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D055651:NK Cell Lectin-Like Receptor Subfamily B; D009368:Neoplasm Transplantation; D011471:Prostatic Neoplasms / Q000276:immunology / Q000628:therapy*; D014176:Protein Biosynthesis; D011506:Proteins; D011994:Recombinant Proteins / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000378:metabolism; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics
D000911:Antibodies, Monoclonal; D000941:Antigens; D000950:Antigens, Ly; D000954:Antigens, Surface; D015704:CD4 Antigens; D016827:CD8 Antigens; D007376:Interleukin-2; C527211:Klrb1c protein, mouse; D037181:Lectins, C-Type; D055651:NK Cell Lectin-Like Receptor Subfamily B; D011506:Proteins; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D018664:Interleukin-12; D016178:Granulocyte-Macrophage Colony-Stimulating Factor