Age 18-80 years

Histologically confirmed chronic lymphocytic leukemia

Leucocyte count more than 20 x 10 9/L

No other simultaneous treatment for lymphoma

No treatment indicated for chronic lymphocytic leukemia

WHO performance status 0-2

HIV negativity

Negativity for hepatitis C virus , HBsAG, anti-hepatitis B core antigen, or other active infection uncontrolled by treatment

Agree to abstain from donating blood while taking study drug therapy and for one week following discontinuation of study drug therapy

Agree not to share study medication with another person and to return all unused study drug to the investigator

Written informed concent

Pretreatment With Valproate Prior to Immunotherapy Targeting Cluster of Differentiation Antigen 20 in Chronic Lymphocytic Leukemia