CD28 and B-cell non-Hodgkin lymphoma: Therefore, we co-incubated murine A20 B cell lymphoma cells that were uninfected or infected overnight with CPXV (Brighton Red (BR) strain) or VACV (MOI = 5) (Western Reserve) with splenocytes from BALB/c mice together with plate bound α-CD3 and α-CD28 antibodies.