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Trial Shows Vaccine Protects Against Stem Cell Complications

Drip infusion

(Stux, Pixabay)

24 December 2015. An early-stage clinical trial indicates a vaccine protects against complications from stem cell transplants used to treat blood-related cancers. Results of the trial conducted by City of Hope medical center in Duarte, California that developed the vaccine appear online in the journal The Lancet Haematology (paid subscription required), and were discussed earlier this month at a meeting of American Society of Hematology.

The study reports on a treatment to prevent infections from cytomegalovirus that occur when patients for blood-related cancers, such as leukemia or lymphoma, receive bone marrow transplants from closely-matched donors as a therapy. Bone marrow contains immature blood-forming stem cells that restore the natural stem cells often destroyed from high doses of radiation or chemotherapy.

But because people with blood-related cancers often have weakened immune systems, they are susceptible to cytomegalovirus infections that can occur when stem cells are transplanted. Many, if not most, healthy people carry the cytomegalovirus, but it rarely causes symptoms. Individuals with compromised immune systems, however, such as those receiving bone marrow transplants, can experience fever, diarrhea, pneumonia, or hepatitis, among other conditions from the virus’s infections.

Researchers at City of Hope in the lab of virologist Don Diamond developed the CMVPepVax vaccine as an alternative to standard anti-viral drugs that the authors say can be expensive or toxic to some patients. CMVPepVax is an engineered peptide containing a protein from cytomegalovirus and a synthetic protein resembling tetanus bacteria designed to activate the immune system of individuals with the cytomegalovirus. The vaccine is given as a preventive measure against infection by generating more T-cells that fight the invading virus.

The clinical trial tested CMVPepVax with 36 people receiving donor bone-marrow transplants for a range of blood-related cancers, with participants randomly receiving either CMVPepVax at 28 and 56 days after the transplant or standard levels of care. The trial looked primarily at the vaccine’s safety, watching for evidence of graft-versus-host disease, an adverse immune response to donor stem cells, as well as other adverse reactions. The study also measured T-cell production in participants.

The results show the vaccine was safe for participants, with no serious adverse effects resulting from graft-versus-host disease among CMVPepVax recipients. One serious adverse event was reported from the vaccine that the authors say was resolved in 48 hours. About equal numbers in both groups experienced mild immune reactions from their transplants. After 100 days, recipients of the vaccine had more protective T-cells generated, and less reactivation of cytomegalovirus — thus less need for antiviral drugs — than patients receiving standard levels of care.

The findings revealed another and unexpected result: participants receiving CMVPepVax had fewer relapses of their cancer and a lower risk of mortality from non-relapse related conditions. “If some of these benefits are substantiated in future studies,” says Diamond in a City of Hope statement, “perhaps the vaccine might be of greater value to other populations.”

City of Hope is recruiting participants for a larger intermediate-stage trial of CMVPepVax, conducted with University of Minnesota.

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