PDCD1 and hepatitis B virus infection: As part of our immunotherapy development programs, we have been putting in efforts to generate an anti-PD-1 antibody that can be used in combination with our other drug candidates for the treatment of cancer and viral hepatitis B. A promising, novel, recombinant anti-human PD-1 IgG4 humanized monoclonal antibody against PD-1, P1801, was derived from library screening and produced in a cell expression system.