Group 2: Ibrutinib treated patients Patients who are receiving ibrutinib as 1st or 2nd line treatment. After at least 12 months of ibrutinib, patients will be assessed for MRD. MRD-positive patients will be treated with ibrutinib + INVAC-1 for 6 months and at the end of the combined treatment period, MRD will be assessed. MRD-negative patients (defined as <0.01% of CLL cells in total cells analyzed) will have the option to stop or continue ibrutinib. Then, they will be followed-up regularly for two years. Patients who become MRD-positive after being MRD-negative will resume ibrutinib single agent.