BCL2 and lymphoma: Several groups have therefore attempted to investigate the role of hemizygous vs. homozygous Crebbp inactivation on mature B cell differentiation and lymphoma development in vivo using different strategies from early inactivation in all hematopoietic cells, early B-cell specific deletion or GC-specific deletion [Cγ1-Cre (92)], in combination or not with BCL2 transgenic models.