In-Depth: A potential vaccine substitute for people with compromised immune systems? Scientists test new role for monoclonal antibodies Dr. Christian Ramers, Family Health Centers of San Diego A doctor in San Diego prepares a monoclonal antibody cocktail for COVID-19 made by Eli Lilly and Company. and last updated 2021-04-27 14:53:26-04 SAN DIEGO (KGTV) -- Shortly after Jay Heydt got the COVID-19 vaccine, he signed up for a clinical trial to measure his immune response. He knew his odds of producing antibodies were low. Heydt has leukemia. Heâs one of the millions of Americans with a compromised immune system who may not be protected by vaccination.