Blood cancers or lymphomas occur when the bone marrow of the patient produces faulty blood cells. A potentially live saving procedure for blood cancers is a transplantation of bone marrow from a healthy donor, also known as allogeneic hematopoietic stem cell transplantation (allo-HSCT).
Before the donor stem cells can be introduced, the patient undergoes a course of high dose chemo and/or radiation therapy. The aim is to eliminate or weaken the patient’s existing immune system and create the right conditions for the donor stem cells to function normally and reproduce.
Once the new stem cells have been introduced, they can become the foundation of a new healthy immune system.
Risks of viral infection
After the treatment is complete, it can take up to a year for the patient’s immune system to fully recover. During this time patients are highly susceptible to viral infections.
Which viruses present the biggest problem?
In the months following an allo-HSCT, the patient will be susceptible to infection by any virus present in the transplanted donor cells. However, the biggest risk comes from dormant or latent viruses that can be present either in the patient’s bloodstream before treatment even begins or can be transplanted together with the allo-HSCT from the donor. Some of the most problematic of these latent viruses are cytomegalovirus (CMV) and adenovirus (ADV).
Why are latent viruses such an issue?
These types of viruses present a particularly high risk to people who have undergone HSCT, because they are very common in adult populations throughout the world. As a result, many patients are already infected by one or more of them prior to treatment.
Once infected, some viruses can remain in the body, but in most cases are rendered harmless by a healthy immune system. However, an HSCT patient’s severely compromised immune system can allow these viruses to go unchecked. If this happens, it can lead to prolonged periods of illness, a range of post-treatment complications and even death.
Virus-Specific Immune Reconstitution
To accelerate recovery of their immune system, the patient can be given T cells that target CMV or ADV. This procedure is generally referred to as virus-specific immune reconstitution (VSIR). The treatment aims to generate an immediate immunity to the targeted virus.
In effect, this is a second transplant, except it consists of mature virus-specific immune cells and not hematopoietic (blood generating) stem cells. Cell Medica derives these T cells from a healthy donor who most often also provided the original stem cells.