Below, we would like to give you an understanding of our active area of research, which is based on the previous research activity of Dr. Guenter Schwamberger at the Max-Planck-Institute for Immunobiology in Freiburg and the University of Salzburg. As on the page Fundamentals, we have attempted to present the partially highly complex context in a rather simplified popular science form. Here as well, we have added, as far as possible, links to external sources of information like Wikipedia (marked as [W]) and other data open to the public. Furthermore, as appropriate, the text also contains references to selected original scientific papers. A list of these references can be found right after the text, as far as possible also with links to the respective websites (access in part unfortunately liable to pay costs). Back navigation is possible via <.
1. Cancer Defense by the Innate Immune System
- New Light to an Old Story -
1.4. A New Role for TNF
1. Cancer Defense by the Innate Immune System
- New Light to an Old Story -
1.1. History <
About 150 years ago, the German surgeon Wilhelm Busch rather incidentally observed the dramatic shrinking of an inoperable tumor as a consequence of a severe postoperative bacterial infection, a so-called erysipelas [W] . This discovery subsequently stimulated various attempts for treating cancer with intentionally induced infections. Despite singular cases of success, this therapeutic approach in practice however proved unfeasible, due to the incalculable risks of infections in a time without antibiotics. This rapidly led to attempts to replace the infections by administration of killed bacteria. Yet, this in principle highly successful treatment modality, pioneered by the American surgeon William Coley [W] [2, 3], also turned out not very practicable, due to partially life-threatening side effects, which today are known as symptoms of septic shock [W]. Subsequent attempts to separate the antitumor-active components of bacterial extracts from the supposed toxic contaminants met with no success, but in the forties of the last century led to the isolation and chemical characterisation of the so-called bacterial endotoxins [W], components of the cell wall of Gram-negative bacteria [W], which, due to their chemical composition, today are termed lipopolysaccharides, shortly LPS [W].
In contrast to the original expectations however, these substances did not show any direct effects on isolated cancer cells, suggesting that LPS only functions as a trigger for an endogenous cancer defense reaction. Proof to this notion was provided in the early sixties of the last century by transmission of the antitumor effects of LPS by a factor in the serum [W] of LPS-treated animals . Shortly thereafter, another remarkable discovery was made, namely that certain cells of the immune system termed macrophages, after stimulation with LPS are able to specifically destroy a broad spectrum of unrelated tumor cells (see Fundamentals, Chapter 3.1), and that this antitumor activity, at least in part, is mediated by an antitumor factor released by macrophages (see historical overview in Fig. 1).
Fig. 1. Historical overview on the most important milestones of spontaneous cancer cure by infections.
1.2. Tumor Necrosis Factor A Momentous Scientific Mistake <
These findings however initially went unnoticed within the scientific community, but then, with the remarkable delay of more than 10 years, triggered a dramatic race between three American research groups for the identification of this factor. Thus consecutively, an endogenous antitumor substance termed Tumor Necrosis Factor, shortly TNF, [W] was isolated from the culture fluid of activated macrophages and shortly thereafter also from the serum of LPS-treated animals, characterized biochemically and produced by biotechnological means already in the early eighties of the last century . As turned out quickly however, the same molecule had already independently been isolated by another research group in conjunction with the induction of the septic shock and metabolic wasting by LPS and thus termed Cachectin .
Although this molecule for a long time was regarded as the sought-after antitumor factor, by and by, unexpected discrepancies between the original biologic findings and the observed effects of isolated TNF emerged, particularly concerning the totally unexpected life-threatening effects of this factor , which today is considered a proinflammatory cytokine and one of the key mediators of septic shock, i.e. the acute toxic effects of LPS. Furthermore TNF, in contrast to activated macrophages and the sera of LPS-treated animals, showed only rather limited activity against a few cancer cell types under cell culture conditions. Finally, it turned out that the observed restricted antitumor activity of TNF is typically not based on the direct destruction of cancer cells, but on the destruction of blood vessels in the center of the tumor. This results in a so-called haemorrhagic necrosis, transiently depriving the cancer cells of their blood supply and causing the center of the tumor to collapse. However typically, the tumor gets destroyed in its center only and within a short period of time resumes unimpeded growth .
Had TNF to this point been regarded as a biological miracle cure and magic bullet against cancer cells, these disappointing findings led to a rapid loss of interest in natural cancer defense by macrophages. Meanwhile, due to demonstration of the central role of TNF in carcinogenesis and metastasis, the picture of the supposed tumor necrosis factor has finally turned into that of a tumor-promoting factor . Yet, the key question, how the antitumor effects of bacterial infections or LPS come about, remained unsolved.
1.3. MTC 170 A Novel, Old TNF? <
on these findings, the research group of Dr. Guenter Schwamberger at the Max-Planck-Institute for Immunobiology in
This factor, which to this point has been characterized as a high molecular mass protein and hence has been tentatively termed MTC 170 (for Macrophage-Tumor-Cytotoxin, molecular mass 170 KiloDalton), in contrast to TNF, exhibits selective cell-toxic activity against a large variety of animal as well as human tumor cell types, with no obvious impairment of normal, non-transformed cells (Fig. 3 and Fig. 4).
Fig. 2. Biochemical characterization of the tumor-cytotoxic activity in the culture fluid of activated mouse macrophages (a) or human macrophagens (b), respectively, by separation according to molecular size (Mr = molecular mass in KiloDalton (kDa); Void = exclusion limit of the carrier material, here over 1000 kDa; A 280 = photometrical detection of protein distribution)
(© G. Schwamberger)
Fig. 3. Microscopic picture of the destruction of cancer cells by MTC 170.
Left: Untreated, live cancer cells (stained dark blue). Right: Remnants of cancer cells destroyed by MTC 170 (unstained).
(© G. Schwamberger)
Fig. 4. Sensitivity of normal cells and various cancer cells of mouse and human origin, respectively, towards the cytotoxic effects of MTC 170 or TNF.
(© G. Schwamberger)
Surprisingly however, the initial functional and biochemical characterization of this activity turned out highly reminiscent of the original findings on TNF activity, in particular the antitumor activity that had been described in sera of LPS-treated mice [14, 15] (see also Fig. 6). Thus, the assumption was close at hand that MTC 170 might in fact represent the originally sought-after antitumor factor.
Based on this hypothesis, and in close collaboration with the research group of Dr. Marina Freudenberg and Dr. Chris Galanos, MTC 170 activity was finally also demonstrated in the serum of LPS-treated mice. Interestingly, the release of this factor into the serum occurs with quite some delay, compared to the very rapid, but transient release of TNF. Thus, serum samples collected several hours after LPS injection, accordingly termed late tumor necrosis sera, do contain MTC 170 activity, but no detectable TNF activity [16, 17]. These sera, besides the already mentioned cell-toxic effects on various cultivated tumor cells, also exhibit marked activity against experimental tumors in an animal model. Thus, in the experiments performed so far, complete and permanent cure of advanced tumors was achieved by a single application of these sera or partially purified MTC 170 in about 90% of the treated animals, without obvious toxic side effects  (Fig. 5).
Fig. 5. Destruction of an experimental mouse tumor by a single intravenous injection of MTC 170-containing late tumor necrosis serum, on day 7 (d7) after tumor initiation. The picture series shows the complete cure of the tumor in MTC 170-treated animals within 2 weeks (d21), in contrast to the progressive tumor growth in untreated animals.
(© G. Schwamberger)
These findings, and the direct comparison between the original data on TNF activity and the molecule later isolated as TNF (see Fig. 6), strongly suggest that MTC 170, in contrast to TNF, in fact constitutes the originally sought-after tumor necrotizing factor, and ultimately pivotal factor of macrophage-mediated, natural cancer defense.
in vitro: in cell culture; in vivo: in experimental animals; regression: shrinkage of the tumor mass; systemic toxicity: severe, disseminated side effects to the point of septic shock.
(© G. Schwamberger)
1.4. A New Role for TNF <
Based on this notion, obviously the question arose, whether TNF is relevant for this reaction at all, and if so, in which way. Starting on the observation that TNF activity can be detected in the serum of LPS-treated animals about 7 to 8 hours prior to MTC 170, and the meanwhile also established activating effect of this proinflammatory cytokine on macrophages, it was tempting to speculate that TNF might constitute an endogenous trigger for the release of MTC 170 by macrophages. Indeed, the subsequent experiments demonstrated the key role of this cytokine as an endogenous signal for the release of MTC 170, albeit requiring help by a second key cytokine of the immune system, interferon-gamma, [W] [18, 19]. Thus, in contrast to the previous notion, TNF may primarily have an indirect function as an intermediate signal in natural cancer defense, thus also providing a rather simple resolution of the so far conflicting findings of the respective role of TNF.
At the same time, further experiments demonstrated that both cytokines are primarily responsible for sensitizing the animals to LPS, whereas especially TNF is obviously not essentially required for release of MTC 170 after LPS-treatment [Schwamberger et al., unpublished results]. This may in the future open up new strategies for selective induction of MTC 170 by LPS, while at the same time blocking TNF, the mediator of the endotoxic effects of LPS. Thus, the data at hand for the first time provide a chance for a therapeutic application of the antitumor effects of LPS, while at the same time avoiding the TNF-mediated endotoxic effects, i.e. virtually without side effects, which moves the great dream of William Coley and several generations of scientists after him within close reach.
1.5. Immunological Consequences of Tumor Destruction by MTC 170 <
In view of the high therapeutic
efficacy in the animal model, the research group of Dr. Schwamberger, now at the
We are thus convinced that the further elucidation of this natural tumor defense principle will pave the way for novel, highly effective alternatives to conventional therapeutic approaches in cancer medicine.
1.6. Visions <
What is the relevance of these experimental findings derived from an animal model for understanding this natural cancer defense reaction, which originally has been observed for the first time in man, and its potential application in human medicine?
The nearly complete accordance of the experimental data on MTC 170 in the animal model and in man suggests that the findings derived from animal experimentation may be largely transferrable to the mechanisms of natural cancer defense in man. Albeit, as we believe, this provides legitimate reason to hope that these insights may be employed for therapeutic applications in cancer medicine, the latter, without doubt, will require further intensive research efforts. Thus, the aim of our future experimental work primarily is the isolation and further biochemical characterization of the molecule(s) responsible for this activity, as a prerequisite for the anticipated therapeutic application in cancer medicine. In addition, by this we also hope to gain insights into the molecular and cellular mechanisms that provide the basis for the tumor-specific way of action, for potential utilization of these mechanisms for therapeutic purposes. Last not least, we are also interested in the further elucidation of the biological regulatory circuits that control the production and release of MTC 170 by macrophages, to allow for a selective activation of this natural tumor defense principle as cancer prevention and as a biological cancer therapy.
2. References <
06. Beutler, B., Greenwald, D., Hulmes, J. D., Chang, M., Pan, Y. C., Mathison, J., Ulevitch, R., Cerami, A. 1985. Identity of tumour necrosis factor and the macrophage-secreted factor cachectin. Nature 316:552-554. [full text] <
08. Watanabe, N., Niitsu, Y., Umeno,
H., Kuriyama, H., Neda, H., Yamauchi, N., Maeda, M., Urushizaki,
11. Schwamberger, G., Flesch,
12. Harwix, S., Andreesen, R., Ferber, E., and Schwamberger, G. 1992. Human macrophages secrete a tumoricidal activity distinct from tumor necrosis factor-alpha and reactive nitrogen intermediates. Res. Immunol. 143:89-94. [full text] <
13. Schwamberger, G., Harwix, S., Ferber, E., and Andreesen, R. 1993. Human macrophages secrete a novel tumoricidal activity distinct from but synergizing with tumor necrosis factor (TNF) alpha. J. Leukocyte Biol. 53:A 582 [abstract] <
14. Carswell, E. A., Old, L. J.,
15. Green, S., Dobrjansky, A., Carswell, E. A.,
16. Schwamberger, G., Ferber, E., Freudenberg, M., and Galanos, C. 1994. Induction and preliminary characterization of a TNF-independent tumoricidal activity in sera of mice treated with P. acnes and challenged with LPS. Eur. Cytokine Netw. 5:220. [abstract] <
17. Schwamberger, G., Hammerl, P., Ferber, E., Freudenberg, M., and Galanos, C. 2003. TNF revisited: TNF-independent antitumor activity in sera of mice sensitized with Propionibacterium acnes and challenged with lipopolysaccharide. J. Leukoc. Biol.74:1056-1063. [free full text] <
18. Schwamberger, G., Hammerl, P., Ferber, E., Freudenberg, M., and Galanos, C. 1996. TNF-alpha induces secretion of a high molecular weight tumoricidal activity (MTC 170) in murine bone marrow-derived macrophages. Eur. Cytokine Netw. 7:307. [abstract] <
19. Schwamberger, G., Hammerl, P., Freudenberg, M., and Galanos, C. 1996. TNF-alpha mediates induction of a high molecular weight tumoricidal activity (MTC 170) in sera of mice pretreated with P. acnes or interferon-gamma. Eur. Cytokine Netw. 7:291. [abstract] <