On Sept. 14, 2021, City of Hope announced that it had begun enrolling patients in a Phase 2 clinical trial of its COH04S1 vaccine that is the first to study the safety and effectiveness of an investigational vaccine in blood cancer patients who have received a bone marrow transplant or chimeric antigen receptor (CAR) T therapy.

The trial was also the first to compare an investigational COVID-19 vaccine to the current FDA-approved COVID-19 vaccine, the Pfizer vaccine, in people who are immunocompromised and receiving immunosuppressive therapy.