A possible vaccine for breast cancer
In our current BIO230 discussion about viruses, we introduced the link between certain types of cancers and infection by a variety of different viruses. The first to be characterized by Francis Rous was a cancer of chickens, which had been infected with a virus that now bears his name, Rous Sarcoma Virus. The mechanisms by which viruses can induce cancer are rather complex, but the presence of an infectious agent as the causative agent allows the possibility of preventing the cancer by preventing the infection. Indeed, this is the premise behind the vaccine Gardasil which offers protection against infection by Human Papilloma Virus–a virus highly correlated with cancers in both genders. Of course, many cancers have no association with an infectious agent, which led me to be very surprised by this news alert pointed to me by Summer 2013 Micro student Dominique S. This was surprising because there was no indication that any infectious agent was involved with the cancer, so the mechanism of how a vaccine might protect was unclear.
The news alert references a primary research article by scientists at the Cleveland Clinic. The scientists used a model in mice to study the metastasis of tumors. A cancer cell line grown in tissue culture was injected into healthy mice, and the mice were observed to develop mammary tumors that resembled human breast tumors. The researchers noted that the tumors strip only expressed a protein called α-lactalbumin, a protein normally found only in breast tissue during milk production. Since the tumors cells in a non-lactating mouse would be the only cells to be making α-lactalbumin, the felt that this protein would make an attractive anti-cancer target. Consequently, they immunized mice with α-lactalbumin antigen, so that the mouse’s own immune system would start to produce an immune response against the protein, and hopefully against the tumor cells should they be present. This is essentially an induced autoimmune response (the body attacks an antigen that belongs to its own cells, in this case in lactating breast tissue), with the hope that the immune response would essentially be specific for the tumors. What they found was that the mice produced a strong T cell response against the tumor antigen, and it offered significant protective effect.
The work is currently progressing into clinical trials, and the Cleveland Clinic hopes to enroll human subjects into a pilot study in the near future. Phase 1 trials will be with women who have survived breast cancer using standard treatments but are at risk for recurrence, to determine the necessary vaccine dose to promote an effective immune response. Later trials will be with healthy, but at risk women, to see if the vaccine offers protection in humans as it seems to in mice. Some significant issues can still arise. First, the immune response of the mouse is not the same as the immune response of the human, and what works well in one animal may not work at all in the other. Second, the approach promotes an autoimmune response in the host. While α-lactalbumin expression in healthy women is only during active lactation, this likely means that it would be highly inadvisable for anyone receiving this vaccine to become pregnant.