You can go to the most prestigious medical center in the world and ask “How is my immune system?” and, after a short period of eye rolling and looks of amused incomprehension, you might (if they don’t just throw you out) be offered a white blood cell count (which you should probably decline). … How did we arrive at this state of affairs? A good case can be made that the mouse has been so successful at uncovering basic immunologic mechanisms that now many immunologists rely on it to answer every question. … Well, except that mice are lousy models for clinical studies. This is readily apparent in autoimmunity (von Herrath and Nepom, 2005) and in cancer immunotherapy (Ostrand-Rosenberg, 2004), where of dozens (if not hundreds) of protocols that work well in mice, very few have been successful in humans. 1
|Cytotoxic T lymphocyte attacking a tumor cell|
The above (emphasis added) is from a recent manifesto from immunology giant Mark Davis.1 (He isn’t the first to make this point, of course, but when Mark Davis speaks, immunologists listen.) Davis’s suggested solution was, among other things, to start using humans as their own models, taking advantage of the large numbers of humans who are routinely screened and overcoming the lack of experimental control by taking a “systems” approach, including large-scale data collection from healthy and ill people and large-scale informatics as part of the analysis.2 (He also comments on the “humanized” mouse approach that I mentioned briefly the other day.)
Here’s an example of the power of human models, though it’s not exactly what Davis is describing.3 I’ve mentioned before the evidence that cancers in mice are controlled by the immune system (for example, here and links therein). In those experiments, mutant mice, lacking one or more components of the immune response, were shown to be predisposed to cancer. There are also a couple of human studies that indicate the same thing; people on long-term immunosuppression (as in transplant recipients) are somewhat more likely to get certain kinds of cancer, for example.
|CTL attacking a tumor cell|
One advantage of using humans as models of their own diseases is that there are an amazing number of well-documented mutations and disease-associated genes in humans. Human disease is taken very seriously, it’s well funded (at least in comparison to, say, dog and cat disease); even diseases that are very rare can be identified in humans and the gene variant identified. One such disease is Type II familial hemophagocytic lymphohistiocytosis (FHL), a rare, rapidly fatal disease caused by mutations in the perforin gene. 4 Perforin is important in cytotoxic T lymphocyte function, and it’s one of the immune genes that has been shown to be important in preventing cancers in mice.5
Are patients with Type II FHL at risk of developing cancer, like mice with targeted perforin mutations? It’s not an easy question to ask, because most patients die relatively young. But because these are humans, this very rare disease is nevertheless well documented, and the authors were able to search the literature for a suitable subset of patients:
… we identified a subgroup of individuals from nonconsanguineous families who possessed 2 mutated PRF1 alleles but whose onset of FHL was markedly delayed (the age at onset of 10 years or older) or even abolished. A total of only 23 such cases could be identified in the entire literature … Ten of the individuals (Patients 14–23 inTable 1) developed manifestations of FHL without any other significant infectious or neoplastic sequelae reported. … Remarkably, in 11 of these 13 individuals (or 48% of the entire cohort of 23), the primary clinical presentation was with either B or T cell lymphoma or acute or chronic leukemia of lymphoid origin. … The very high frequency of hematological cancers in this 23-patient cohort … is vastly in excess of that in the general population.3
There’s a lot of other interesting stuff in the paper, but this is enough to make the point: Just as in mice, perforin in humans (and therefore, the immune system) is important in preventing cancer.
I’ll leave with this now-familiar observation from the paper:
It is clearly problematic to extrapolate experimental data from inbred mouse strains to an outbred human setting where such evidence is far more difficult to gather.3
- DAVIS, M. (2008). A Prescription for Human Immunology Immunity, 29 (6), 835-838 DOI: 10.1016/j.immuni.2008.12.003[↩][↩]
- Again, of course, Davis isn’t the first to advocate this approach.[↩]
- Chia, J., Yeo, K., Whisstock, J., Dunstone, M., Trapani, J., & Voskoboinik, I. (2009). Temperature sensitivity of human perforin mutants unmasks subtotal loss of cytotoxicity, delayed FHL, and a predisposition to cancer Proceedings of the National Academy of Sciences, 106 (24), 9809-9814 DOI: 10.1073/pnas.0903815106[↩][↩][↩]
- Familial hemophagocytic lymphohistiocytosis. Primary hemophagocytic lymphohistiocytosis.
Henter JI, Aricò M, Elinder G, Imashuku S, Janka G.
Hematol Oncol Clin North Am. 1998 Apr;12(2):417-33[↩]
- Perforin-mediated Cytotoxicity Is Critical for Surveillance of Spontaneous Lymphoma.
Mark J. Smyth, Kevin Y.T. Thia, Shayna E.A. Street, Duncan MacGregor, Dale I. Godfrey, and Joseph A. Trapani.
The Journal of Experimental Medicine, Volume 192, Number 5, September 5, 2000 755-760[↩]