This study is open to individuals who contracted an infection with adenovirus after receiving an allogeneic hematopoietic cell transplant (HCT). Adenoviruses (AdV) are a group of common viruses that infect the lining of the eyes, airways, intestines, urinary tract, and nervous system, and can cause mild to severe illness.

In healthy people, T-cells defend the body against viruses. When someone receives a HCT, they get immune suppressing therapy, and their T-cell numbers become low. This makes it more difficult for the body to control viruses that are already in the body but might not be active yet. One of these viruses, called an adenovirus, can cause infection leading to symptoms such as common cold or flu-like symptoms, bronchitis, pneumonia, pink eye, inflammation of the stomach, intestines, and less commonly bladder infection or neurologic disease. 

There are currently no specific medications for the treatment of adenovirus infections, and it may be treated by reducing the dose of medications that weaken the immune system or by giving other medications that may help with AdV infections.
   
Posoleucel (ALVR105) is an investigational medicine that contains T-cells made from healthy donors to potentially help defend the body against specific viruses. Investigational means that it has not yet been approved by the United States Food and Drug Administration (FDA).

This study will compare ALVR105 to placebo to see if it helps reduce AdV infection symptoms. It will also look at if the amount of specific viruses in the blood and urine are lowered.

Participants will be randomized to receive either ALVR105 or placebo. Randomization is like flipping a coin and there is a 50/50 chance of being assigned to either group. The placebo looks like ALVR105 but does not have any T-cells in it.

All participants will also receive standard of care therapy throughout the duration of the study. Total study participation will last approximately 6 months.