Battle of Thermopylae: 300 Spartans (natural killer cells plus obinutuzumab) versus the immortal warriors (chronic lymphocytic leukemia cells) of Xerxes' army.

Aim: To analyze the effects of subcutaneous or intravenous rituximab + lymphokine-activated killer cells, obinutuzumab or ibrutinib on natural killer (NK) cell levels in chronic lymphocytic leukemia and follicular lymphoma patients. Patients & methods: The distribution of peripheral blood NK cells of 31 patients was analyzed by flow cytometry. Results: We detected a decrease of NK cells in peripheral blood below normal range after obinutuzumab treatment. During maintenance treatment with subcutaneous rituximab, an NK cell reduction was less pronounced than after intravenous rituximab treatment, despite lymphokine-activated killer cell infusions. Conclusion: After one dose of obinutuzumab, each NK cell in peripheral blood destroys 25 leukemic cells. Lay abstract: The standard treatment of chronic lymphocytic leukemia and follicular lymphoma is chemotherapy in combination with anti-CD20 monoclonal antibodies, resulting in the destruction of the immune system, or a Kamikaze effect'. Unfortunately, immunotherapy with rituximab or obinutuzumab may be of limited efficacy when the immunological system is overwhelmed by abundant tumor cells or is diminished by chemotherapy, which eliminates effector immune cells such as natural killer cells before they would be able to kill the whole tumor. Hence, it is important to measure the number of immune cells to ensure that during the encounter of effector cells with tumor cells, sufficient `warriors' can win the battle against the tumor. Otherwise, something akin to the Battle of Thermopylae can happen where a limited number of Spartan warriors faced a huge army and were defeated in the end.