In vitro immune blastogenesis during contact sensitivity in tumor-bearing mice. I. Description of progressive impairment and demonstration of splenic suppressor cells

Cells as vehicles for cancer gene therapy: the missing link between targeted vectors and systemic delivery?

Systemic administration of currently manufactured viral stocks has not so far achieved sufficient circulating titers to allow therapeutic targeting of metastatic disease. This is due to low initial viral titers, immune inactivation, nonspecific adhesion, and loss of particles. One way to exploit the elegant molecular manipulations that have been made to increase vector targeting is to protect these vectors until they reach the local sites of tumor growth. Various cell types home preferentially to tumors and can be loaded with the constructs required to produce targeted vectors. Here we discuss the potential of using such cell carriers to chaperone precious vectors directly to the tumors. The vectors can incorporate mechanisms to achieve tumor site-inducible expression, along with tumor cell-specific expression of the therapeutic gene and/or replicating viral genomes that would be released at the tumor. In this way, the great advances that have so far been made with the engineering of vector tropisms might be genuinely exploited and converted into clinical benefit.

Suppression of the delayed type hypersensitivity response by tumor facilitating factor of B16 melanoma. A tumor factor suppresses immune responses

BACKGROUND

Tumor facilitating factor is a cell surface glycoprotein produced by B16 melanoma that has been found to reduce the lethal inoculum for B16. Tumor facilitating factor induces macrophage spreading in vitro, reduces macrophage chemotaxis in vivo, and depresses lymphocyte mitogenesis in vitro.

OBJECTIVE

It is assumed that the immune modifying effects are responsible for tumor facilitation. As tumors may be poor immunogens or inducers of inflammation, studies were conducted to determine whether tumor facilitating factor alters the inflammatory cascade of cells found in infiltrates of delayed type hypersensitivity.

RESULTS

Freeze-thawed B16 cells, used as the source of TFF, caused a suppression of delayed type hypersensitivity measured as ear swelling in the mouse. When culture supernatant was substituted for freeze-thawed cells as a source of TFF and injected at different time points of the delayed type hypersensitivity response, the greater suppression was with tumor facilitating factor injections at 24 hours pre-elicitation only (82%), and 24 hours both presensitization and pre-elicitation (89%). Immunohistological staining demonstrated that tumor facilitating factor decreases ear thickness and cellular infiltrates, specifically Mac-1 staining cells, to a site of delayed hypersensitivity. Peritoneal cell analysis confirmed these findings.

CONCLUSION

These data are consistent with the hypothesis that tumor facilitating factor alters immune functions including macrophage and lymphocyte mobility and recruitment to a target site, thereby allowing for facilitation of tumor growth.

Interferon-gamma reduces tumor-induced Ia- macrophage-mediated suppression: role of prostaglandin E2, Ia, and tumor necrosis factor-alpha

Tumor growth enhances macrophage (M phi) suppressor activity by causing M phi to increase synthesis of inhibitory molecules such as prostaglandin E2 (PGE2) or decreasing their expression of up-regulatory molecules such as the class II MHC protein Ia. Although these tumor-induced changes are correlated, it is unknown whether tumor-bearing host (TBH) Ia- M phi become more suppressive by increasing their PGE2 synthesis. To assess the role of PGE2 in tumor-induced Ia- M phi-mediated suppression of CD4+ T-cell alloreactivity, unseparated (Ia(+)-enriched) or Ia(+)-depleted (Ia-) populations of murine normal host (NH) or TBH splenic M phi were added to mixed lymphocyte reaction (MLR) cultures. NH or TBH Ia- M phi were significantly more suppressive than their respective unseparated populations, and TBH Ia- M phi were more suppressive than their NH counterparts. When PGE2 production was blocked with indomethacin, TBH Ia- M phi-mediated suppression was reduced more than suppression mediated by all other M phi populations. A PGE2-specific ELISA showed more PGE2 in Ia- M phi-containing cultures than in those with whole M phi and more in cultures containing TBH Ia- M phi than in their NH counterparts. Because interferon-gamma (IFN-gamma) is a potent M phi activation molecule that regulates both Ia expression and PGE2 production, the effects of IFN-gamma on tumor-induced Ia- M phi-mediated suppression were investigated. Exogenous IFN-gamma reduced suppression mediated by all M phi populations except NH unseparated M phi. IFN-gamma suppressed alloreactivity without M phi or with NH unseparated M phi. Suppression mediated by NH or TBH Ia-, and TBH unseparated M phi was also reduced when M phi were pre-incubated with IFN-gamma before their addition to MLR cultures. IFN-gamma addition did not block Ia- M phi-mediated suppression by decreasing M phi PGE2 production. In fact, IFN-gamma addition increased PGE2 production two-fold in MLR cultures. However, IFN-gamma partly reduced suppression mediated by exogenous PGE2 added to M phi-depleted cultures. Cytofluorometric analysis showed that IFN-gamma increased the percentage of Ia+ M phi in NH and TBH Ia- M phi populations. Blocking TNF-alpha activity with anti-TNF-alpha antibodies caused IFN-gamma to suppress alloreactivity in all M phi-added cultures. Collectively, these data show that tumor-induced suppression mediated by Ia- M phi is caused by increased PGE2 synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Suppression of interleukin-2 production by macrophages in genetically susceptible mice infected with Leishmania major

Spleen cells from BALB/c mice infected with 2 X 10(7) L. major promastigotes and developing progressive disease produced significantly lower levels of interleukin-2 (IL-2) in response to concanavalin A stimulation than did spleen cells from uninfected mice. In contrast, spleen cells from sublethally irradiated and infected mice, which were able to contain lesion development, produced significantly higher levels of IL-2. The increase in IL-2 production closely paralleled lesion regression. Mice protectively immunized by four intravenous injections with lethally irradiated promastigotes also produced enhanced levels of IL-2, which were sustained after challenge infection. In contrast, spleen cells from BALB/c mice given four s.c. injections of irradiated promastigotes produced high levels of IL-2 before but not after infection. These mice eventually produced levels of IL-2 indistinguishable from those of unimmunized mice with progressive disease. There is thus an inverse relation between disease progression and the ability of spleen cells to produce IL-2. Spleen cells from mice with uncontrolled disease not only produced lower levels of IL-2 but also impaired IL-2 production by normal spleen cells. The ability to inhibit IL-2 was abrogated by passing the cells through a Sephadex G-10 column, removal of plastic adherent cells, and removal of carbonyl iron-ingesting cells. Furthermore, Sephadex G-10 column-treated and plastic adherent, nonspecific esterase-positive spleen cells from mice with progressive disease were able to suppress IL-2 production by normal splenic T cells. The suppressive activity of the adherent cells was not affected by treatment with anti-Thy-1.2 antibody and complement. In contrast, adherent spleen cells from uninfected mice were devoid of such suppressor activity. The depressed IL-2 production by spleen cells from progressively infected mice could be restored to that of normal spleen cells by the addition of indomethacin to the culture. There was however, no correlation between IL-2 production and IL-1 activity in infected or immunized BALB/c mice. Thus, it appears that the suppression of IL-2 production is mediated by prostaglandins elaborated by macrophages from chronically infected mice.

Induction of suppressor cells by a tumor-derived suppressor factor

Murine fibrosarcomas produce a factor that activates suppressor cells to inhibit expression of delayed-type hypersensitivity (DTH) responses to dinitrochlorobenzene (DNCB). This tumor-derived suppressor factor (TDSF) was partially purified by preparative isoelectric focusing of spent medium and 3 M KCl extracts of cultured methylcholanthrene-induced and spontaneous fibrosarcomas of C3H/He mice. Incubation of 1 micrograms/ml of a fraction, isoelectric pH less than 2.9, with normal syngeneic spleen cells for 1-6 hr at 37 degrees C induced suppressor cells that inhibited the primary DTH response to DNCB upon intraperitoneal transfer to normal C3H/HeJ mice. TDSF was not present in extracts of either syngeneic embryonic fibroblasts or normal spleen cells or in medium conditioned by normal peritoneal exudate cells but was present in 3 M KCl extracts of and the spent medium from four different cultured murine fibrosarcomas. TDSF activity was not restricted at the major histocompatibility complex. The suppressor cells inhibited the efferent limb of the DTH response because (1) hyporesponsive recipients of TDSF-treated spleen cells had splenic effector T cells capable of transferring DTH to DNCB into naive secondary recipients and (2) the ability of Lyt 1+,2- effector Tdth cells to transfer a secondary DTH response to DNCB was inhibited by co-incubation with macrophages or Lyt 1-,2+ T cells treated with TDSF. Preliminary biochemical analysis suggested that TDSF was an RNA- protein complex. Thus, several murine fibrosarcomas produced a soluble factor that activated splenic suppressor cells to depress the immune response to nonneoplastic antigens. These suppressor factors represent a novel group of regulatory molecules which may be ribonucleoprotein complexes.