Immunotherapy in combination with suicide gene therapy for
breast cancer was tested using a metastatic animal model.
Subcutaneous injection of the nonimmunogenic
breast cancer cell line 4T1 in BALB/C mice gave rise to
tumors in 100% of mice with both
micrometastases and macrometastases in the lung. We used the herpes simplex virus
thymidine kinase (HSV-TK) gene along with the
cytokine genes
granulocyte-macrophage colony-stimulating factor (
GM-CSF) and
interleukin-2 (IL-2) to determine their effect on
tumor regression and inhibition of lung
metastasis. Adenoviral (AV) vectors carrying these transgenes, in separate constructs, were used in this study. Intratumoral administration of AV-TK followed by 10 days of
ganciclovir treatment resulted in a delay in
tumor growth and, in some cases, in a low to moderate reduction in
tumor volume. Inclusion of either
GM-CSF or
IL-2 gene with HSV-TK resulted in a slightly greater reduction in
tumor volume, although these data were not significantly different from those obtained for TK treatment alone. However, when both
cytokine genes were combined with TK, a substantial reduction in
tumor growth was observed compared with HSV-TK alone (P < .02).
Tumor weight data also exhibited superior efficacy of TK/
GM-CSF/IL-2 treatment when compared with animals treated with TK gene only (P < .01). More importantly, TK/
GM-CSF/IL-2 combination gene therapy induced a significant reduction in lung
metastasis compared with any other treatment groups in the 4T1 model (P < .001 between TK
GM-CSF/IL-2 versus TK only). Surgical excision of primary
tumors after TK/
GM-CSF/IL-2 plus
ganciclovir treatment resulted in anti-metastatic activity that was similar to that observed for animals in which no surgery was performed. Survival analysis showed a significant difference between animals treated with AV-TK/
GM-CSF/IL-2 and animals treated with TK only at 35 days after virus injection (P < .01). Immunophenotypic data suggest infiltration of lymphocytes within the tumor microenvironment in TK- and
cytokine gene-treated animals. Thus, the overall data presented here demonstrate that TK gene therapy in combination with
GM-CSF and
IL-2 gene-mediated
immunotherapy strategies have important implications in the treatment of
breast cancer.