CD4 and neoplasm: Mouse A20 B-cell lymphoma modified with influenza hemagglutinin (HA) gene to express HA antigen (A20HA) was developed as an experimental system allowing the quantitative determination of systemic tumor progression effects on population of naive TCR clonotypic CD4+ Th cells that is specific for HA antigen in terms of their proliferation versus depletion and state of activation versus anergy [4, 20, 21, 23].