Interferon‐activated tumor inhibition in vivo. Small amounts of interferon‐gamma inhibit tumor growth by eliciting host systemic immunoreactivity

Abstract

Ten international units (IU) of recombinant (r) or natural (n) murine interferon (MuIFN)-gamma were used for the in vivo immunotherapy of a chemically induced fibrosarcoma (CE-2) of BALB/c mice. In vitro, doses of r-IFN-gamma below 100 units have a marginal antiproliferative effect on CE-2 cells and do not induce expression of H-2d class-II antigens, whereas they do increase that of class-I antigens. In vivo, 10 daily injections of 10 IU of r- or n-MuIFN-gamma at the challenge site provide significant protection against increasing doses of CE-2 tumor cells. This protection was enhanced when non-reactive T-lymphocytes from CE-2 tumor-bearing mice were admixed at a 10:1 ratio with the CE-2 tumor cells. Combined lymphocyte and r-MuIFN-gamma treatment also inhibited the growth of already established tumors when it was started before these reached a mean diameter of 5 mm. Tumor inhibition depends upon activation of the host immune system. The antitumor activity of r-MuIFN-gamma and T-lymphocytes was null when mice were first irradiated with 450 rads. Moreover, host leukocytes massively infiltrated the area of tumor growth and the small r-MuIFN-gamma doses injected daily activated various host immunoreactivity mechanisms.

Inhibition of tumor growth and enhancement of metastasis after transfection of the γ‐interferon gene

“…While macrophages and eosinophils apparently bind and kill tumor cells, the role of T-lymphocytes is intriguing, since they are a significant component of the reactive infiltrate and display a few characteristics of activated lymphocytes, but there is no evidence of their lytic activity. These morphological findings confirm the functional results obtained in immunodepressed mice and are in line with previous data obtained from local administration of IFN-y (Giovarelli et al, 1986). It is well established that IFN-y potentiates several mechanisms of macrophage lytic potential and enhances surface expression of TNF; however, the scarcity of apoptotic figures, as found morphologically, is not suggestive of a major involvement of membrane TNF in the inhibition of IFN-y clones.…”

Interferon‐γ is not an antiviral, but a growth‐promoting factor for t lymphocytes

“…[3H]dThd in TCA-precipitable material was measured as previously described [27]. The significance of differences in [3H]dThd uptake was determined by a one-tailed Student's t-test.…”

“…[3H]dThd in trichloroacetic acid (TCA)-precipitable material was measured as previously described [27]. Splenic T lymphocytes were enriched on a nylon wool column.…”

“…(d) T lymphocytes from normal 6-8-week-old BALB/c mice were obtained by passing spleen cells on nylon wool columns, as described by Julius et al [28]. The column-emerging cells were used immediately after purification or stimulated in vitro with Con A for 72 h as previously described [27]. They were then extensively washed and cultured in fresh RPMI 1640 medium supplemented with 10 U of rIL2 and 5% FBS.…”

“…The monolayers were washed three times with RPMI 1640 medium without serum to remove nonadherent cells and cultured in vitro for a further 3 days before use to allow the decay of the endogenous antiviral resistance [26]. (c) Thymocytes from normal 6-8-week-old BALB/c mice were used immediately after in vivo removal or stimulated in vitro with Con A, as previously described [27]. After 72 h the cells were extensively washed to remove Con A and cultured in fresh RPMI 1640 medium supplemented with 5% FBS and 10 U recombinant interleukin 2 (rIL2), kindly provided by Dr. A. Galazka (Glaxo, Geneva, Switzerland).…”