Silicon Microparticles Dramatically Boost Efficacy of Breast Cancer Vaccines

Particles protected antigen from premature destruction and prompted the immune system to attack cancer cells.

The efficacy of cancer vaccines could be significantly enhanced by loading antigens into silicon microparticles, according to a recent study.

Published online in Cell Reports, the study showed microparticles loaded with the HER2 antigen protected it from premature destruction and caused the immune system to recognize and relentlessly attack breast cancer cells that overexpress the HER2 antigen.

"We could completely inhibit tumor growth after just one dose of the cancer vaccine in the animal model," principal investigator Haifa Shen, MD, PhD, said in a press release. "This is the most amazing result we have ever seen in a tumor treatment study."

The efficacy of the treatment was apparently due to porous silicon microparticles (PSMs), which produced a strong, sustained immune response at local sites of tumor activity and growth, with or without any antigen loaded.

"We have shown for the first time that a microparticle can serve as a carrier for sustained release and processing of tumor antigens," Dr. Shen said. "But just as importantly, we learned the microparticles themselves appear to be enough to stimulate a type I interferon response, and were even transferred from one antigen-presenting cell to another to maintain a long-lasting antigen-releasing effect."

There are currently no FDA-approved vaccines for breast cancer, however any approved vaccine for the disease may target HER2, which is overexpressed in the tumor cells of 15 to 30% of breast cancer patients. A vaccine targeting HER2 could prompt more destructive immune system agents to identify cancer cells that overproduce HER2 and destroy them while leaving healthy cells alone.

Thus far, vaccines that target HER2 have only experienced moderate success.

"Vaccines targeting the HER2 oncoprotein have been tried," Dr. Shen said. "But these vaccines have mostly not been very potent because of inefficient vaccine delivery, a poor immune response at the site of the tumor, and other factors. We have shown that the PSM-mediated vaccine is not only potent enough to trigger tumor cell killing, but also modifies the tumor microenvironment in a way that favors tumor treatment."

A vital characteristic of the PSM function is stimulating the immune system to fight cancer, the study noted.

"PSMs persistently challenge the antigen-presenting cells to activate the T cells and the PSMs modify the tumor microenvironment so that the cytotoxic T cells maintain their activity,” Dr. Shen noted.

Dr. Shen added that PSMs could work for any number of cancer antigens and cancer types, as the PSMs could be loaded with multiple antigens for a single vaccine target or multiple antigens for several targets, which could potentially further enhance the efficacy.

Prior to human clinical trials, the researchers must determine the toxicity of antigen-loaded PSMs.

"Besides developing a highly potent breast cancer vaccine, we have also demonstrated that PSMs are versatile," Dr. Shen said. "This is a technology platform that can be applied by other scientists to develop vaccines for other types of cancers, ultimately helping, we hope, more types of cancer patients."