Study explains how early childhood vaccination reduces leukemia risk

http://www.eurekalert.org/pub_releases/2015-05/uoc--use051515.php

Public Release: 18-May-2015
University of California - San Francisco

A team led by UCSF researchers has discovered how a commonly administered vaccine protects against acute lymphoblastic leukemia (ALL), the most common type of childhood cancer.

The Haemophilus influenzae Type b (Hib) vaccine not only prevents ear infections and meningitis caused by the Hib bacterium, but also protects against ALL, which accounts for approximately 25 percent of cancer diagnoses among children younger than 15 years, according to the National Cancer Society. The Hib vaccine is part of the standard vaccination schedule recommended by the Centers for Disease Control and is routinely given to children in four doses before 15 months of age.

Though the cancer protection offered by the Hib vaccine has been well established in epidemiological studies, it is not well-known among the public at large, and the mechanism underlying this effect has been poorly understood. Now, in work to be reported on Monday, May 18, 2015 in Nature Immunology, an international team led by UCSF researchers has shown that recurrent Hib infections can put certain immune-system genes into overdrive, converting "pre-leukemia" blood cells -- which are present in a surprisingly large number of newborns -- into full-blown cancer.

"These experiments help explain why the incidence of leukemia has been dramatically reduced since the advent of regular vaccinations during infancy," said Markus Müschen, MD, PhD, professor of laboratory medicine at UCSF and senior author of the study. "Hib and other childhood infections can cause recurrent and vehement immune responses, which we have found could lead to leukemia, but infants that have received vaccines are largely protected and acquire long-term immunity through very mild immune reactions."

•••••

Though the researchers focused on Hib, a bacterial infection, they believe that the same mechanisms may be at work in viral infections. The team is currently conducting experiments to determine if protection against leukemia is also provided by vaccines against viral infections, such as the well known MMR vaccine at the center of recent anti-vaccination controversies.

•••••