Iowa postdoctoral research scholar testing a prime-boost vaccine for prostate cancer

When you get treated for measles, you receive multiple doses of a vaccination in order to generate more immunological memory. So, if you happen to acquire a virus that causes the measles later in life, your body will remember the benefits of the vaccine and protect you from the illness.

This is how a prime-boost vaccination works.

These prime-boost vaccinations are the focus of Caitlin Lemke's research as a postdoctoral scholar in the College of Pharmacy at the University of Iowa. Lemke has spent the last year-and-a-half testing a prime-boost vaccine for prostate cancer that targets Prostate Specific Antigen (PSA)-a protein produced by cells of the prostate gland. The PSA test measures the level of PSA in the blood. The higher a man's PSA level, the more likely it is that cancer is present.

Lemke has worked in Aliasger Salem's laboratory since 2008. Salem is an associate professor in the Department of Pharmaceutical Sciences and Experimental Therapeutics in the College of Pharmacy.

“Prime-boost vaccinations are really good at generating memory in our body's cells,” Lemke said. “With cancer, if you have a vaccine that can kill the existing tumors now, you want memory if there is a recurrence down the line.”

Lemke, an Iowa City native who earned her Ph.D. in immunology at the UI in 2006, is working with a heterologous prime-boost model, meaning the first vaccination is different than the second. In contrast, when treated for measles, you receive the same vaccination each time.

Lemke's prime vaccination is a particle-based formulation made from a biodegradable polymer that breaks down into normal by-products of your metabolism upon entering the body. Lemke said these by-products are FDA approved.

“Cells acquire these by-products, become stimulated, and present the cancer-related antigen to T cells and other cells that will mount the anti-tumor response,” Lemke said.

Her boost is an adenovirus, which expresses PSA or any other desired model antigen.

“When you receive the boost, a week after the prime vaccination, the stage has already been set; the cells are geared up and ready to go,” Lemke said. “When you hit them with the boost, you get a really strong immune response. You not only get a strong initial response, but you get really good memory.

“That's what I am seeing and what other labs are seeing.”

Lemke, who was awarded a prestigious 2009 Pharmaceutical Research and Manufacturers of America (PhRMA) Foundation Postdoctoral Research Award, is testing these novel vaccines in mice. She is immunizing the mice weekly, drawing blood and analyzing the different immune cells present in the white blood cells. Lemke plans to tumor challenge the mice and see how well the different treatment groups are protected 60 days after receiving the immunization.

She is waiting 60 days as a test of cell memory.

“I have other models where the mice are tumor challenged first,” Lemke said. “You give the mice a tumor and then you come in with your vaccine and see its effectiveness. I've gotten some interesting results, which have to be repeated to see how they hold up.”

If these results are found to be reproducible, they will have significant implications in the design of vaccine dosage schemes for clinical trials.

The Salem Laboratory is collaborating with UI Urology Professor David Lubaroff, whose research group currently has a prostate cancer vaccine in clinical trials. Lemke said Lubaroff's one-dose adenovirus model is being used in her studies.

Lemke admits that cancer is cured in mice all the time. But curing cancer in humans is a completely different story.