City of Hope, a biomedical research and cancer treatment centre, has started participant enrolment for Phase II clinical trial of its Covid-19 vaccine candidate, COH04S1, in immunocompromised individuals on immunosuppressive therapy.

The trial will involve 240 blood cancer patients who are immunocompromised and received a bone marrow transplant or chimeric antigen receptor (CAR) T treatment.

It is said to be the first to assess a Covid-19 vaccine candidate in this patient population.

The trial is also the first to compare a Covid-19 vaccine candidate versus Pfizer’s US Food and Drug Administration (FDA)-approved Covid-19 vaccine in these patients.

Participants will be administered two vaccinations 28 days apart and will be monitored for any possible complications.

As COH04S1 does not replicate or grow in quantity inside the body, it is expected to be safe for use in stem cell transplant or CAR T patients.

The biological response is the primary objective of the Phase II trial while secondary outcomes include moderate adverse events, non-relapse mortality and unacceptable adverse events among others.

COH04S1, which comprises SARS-CoV-2 spike as well as nucleocapsid proteins, was found to be safe and well-tolerated in a previous Phase I trial in healthy volunteers.

Immunocompromised patients have frequently had a weak antibody response with Emergency Use Authorization (EUA) and FDA-approved Covid-19 vaccines compared to healthy vaccinated people, City of Hope noted.

City of Hope Department of Hematology & Hematopoietic Cell Transplantation professor Don Diamond said: “Current EUA and FDA-approved vaccines are not working as well for those with weakened immune systems.

“Our vaccine is built on an FDA-approved and widely used platform known as modified vaccinia ankara (MVA) that has been used safely and effectively in cancer and transplant patients by the City of Hope.

“MVA vaccines also tend to produce an immune response quickly — in less than 14 days — with only mild side effects.”

In preclinical research, COH04S1 was able to generate robust neutralising antibodies that can identify SARS-COV-2 variants, along with T cell responses against the spike and nucleocapsid proteins.