Adjuvant effect of a Flt3 ligand (FL) gene-transduced xenogeneic cell line in a murine colon cancer model.
BACKGROUND
Flt3 Ligand (FL) has been shown to elicit antitumor responses induced by tumor antigen stimulation. Allogeneic and xenogeneic cell lines transduced with cytokine genes may be used to augment the antitumor efficacy of tumor antigens.


OBJECTIVE
The objective was to evaluate the augmentation of tumor lysate-induced immunity by a more clinically applicable FL gene-transduced xenogeneic cell line in combination with interleukin-2 (IL-2) in a CC-36 murine colon cancer model.


METHODS
Human 143B osteosarcoma tumor cells were transduced with full-length FL cDNA (143B-FL). Secretion of FL from 143B-FL was analyzed in vivo in normal BALB/c mice transplanted with 143B-FL, and expansion of dendritic cells (DC) was also analyzed in the same mice by flow cytometry. Eight-week-old, male BALB/c mice were used in a prophylactic vaccination protocol utilizing tumor lysate (CLy), 143B-FL, and soluble IL-2. Prophylactic group designations (n = 10/group) were as follows: ten million 143B-FL cells (alone, with tumor lysate, or with tumor lysate and IL-2), IL-2 with tumor lysate, IL-2 alone, or a no treatment control. The tumor lysate (200 microg of protein) and IL-2 (100,000 IU) injections were administered intraperitoneally. Mice were challenged subcutaneously with 10(3) CC-36 tumor cells. Tumor protection and tumor burden (TB), as mean tumor diameter, were determined. Peripheral blood lymphocytes (PBLs) from the 143B-FL + IL-2 + tumor lysate vaccinated group were analyzed for cytolytic activity in 4-h chromium release assays. In addition, plasma cytokine concentrations of interleukin-12 (IL-12) and interferon gamma (IFN-gamma) were assessed by ELISA. Student's t tests were used for all statistical comparisons.


RESULTS
In vivo expression of FL was observed 24 h following the inoculation of 143B-FL, and a four fold increase in DCs was observed in the peripheral blood of these mice. Mice immunized with a combination of 143B-FL, tumor lysate and IL-2 showed statistically significant protection against tumor development (10%) for 100 days after tumor challenge; incidences in other groups ranged from 40 to 100% (P < 0.05). Moreover, this immunization protocol produced the lowest TB at 3- and 6-week time points (0, 1.6 mm) when compared to all other groups (TB between 7.2 and 15.9 mm) (P < 0.05). In addition, PBLs from vaccinated mice showed increased cytolytic activity against CC-36 target cells. This corresponded to increased levels of IL-12 and IFN-g in the plasma of mice following vaccination.


CONCLUSIONS
These data suggest that FL gene-transduced xenogeneic tumor cells may augment the immunity induced by tumor antigens and systemic IL-2 through the activation of dendritic cells and T-cell-mediated mechanisms.
Kim
Eugene M
EM
Department of Surgery, Saint Vincents Hospital & Medical Center of New York, New York Medical College, 10011, USA.
Sivanandham
Muthukumaran
M
Stavropoulos
Christos I
CI
Wallack
Marc K
MK
D000230:Adenocarcinoma; D000818:Animals; D015478:Antigens, Heterophile / Q000235:genetics; D003110:Colonic Neoplasms; D003601:Cytotoxicity Tests, Immunologic; D003713:Dendritic Cells / Q000166:cytology / Q000276:immunology; D005434:Flow Cytometry; D066298:In Vitro Techniques; D007371:Interferon-gamma / Q000097:blood; D007376:Interleukin-2 / Q000097:blood; D008214:Lymphocytes / Q000166:cytology / Q000276:immunology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D012516:Osteosarcoma; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured
D015478:Antigens, Heterophile; D007376:Interleukin-2; D008565:Membrane Proteins; C084881:flt3 ligand protein; D007371:Interferon-gamma