receiving chemotherapy
Photo by Rhoda Baer
Researchers say they have discovered a type of macrophage that may protect against lung infections during chemotherapy.
These macrophages, found in the lungs of mice, were able to survive chemotherapy.
The macrophages could remove bacteria when activated by a vaccine, which improved survival in mice with lethal bacterial pneumonia that had received chemotherapy and were therefore depleted of neutrophils.
The researchers said these results suggest the cells—known as vaccine-induced macrophages (ViMs)— might be able to protect cancer patients from life-threatening infections.
“We have identified a new form of housekeeping macrophage in mice that may, in future, be harnessed to protect against lung infections—like bacterial pneumonia—that remain one of the greatest threats to survival of cancer patients during chemotherapy,” said Peter Murray, PhD, of St. Jude Children’s Research Hospital in Memphis, Tennessee.
Dr Murray and his colleagues detailed this discovery in PNAS.
Working in a mouse model that mimics infection in chemotherapy-treated patients, the researchers found that vaccination protected mice from Pseudomonas aeruginosa pneumonia.
The quest to understand how such protection was possible in the absence of neutrophils led the team to discover ViMs.
The researchers found that ViMs were produced in the lungs following vaccination, proliferated locally, and could persist for at least a month.
Analyses suggested ViMs are closely related to alveolar macrophages, which originate in the embryo, reside in the air-exposed surfaces of alveoli, and are self-maintained in adults.
“All lines of cellular and molecular evidence in this study point to alveolar macrophages as the source of ViMs,” Dr Murray said.
However, unlike alveolar macrophages, the population of ViMs remained stable during chemotherapy and exhibited enhanced phagocytic activity.
When ViMs were transferred to unvaccinated mice depleted of neutrophils via chemotherapy, the animals were protected from lethal Pseudomonas infections.
“We now know that increasing the number of ViMs in the tissue can compensate for the immune deficit caused by chemotherapy,” said study author Akinobu Kamei, MD, of St. Jude Children’s Research Hospital.
“In this study, we relied on vaccination prior to chemotherapy. Going forward, we will explore other, more practical methods for use at the bedside to effectively induce tissue-resident macrophages like ViMs.”
The possible approaches include using drugs or cytokines to induce protection in the immune-compromised host.
