Phase II Study of IL-2 and Rituximab Maintenance in High Risk B Cell Non-Hodgkin's Lymphoma

Interleukin 2 (IL-2) is a naturally circulating cytokine produced by immune cells including T cells, dendritic cells and thymic cells. IL-2 is an integral part of T cell proliferation, autoimmunity and self-tolerance. Low dose IL-2 has been studied as maintenance therapy following autologous stem cell transplantation in Non-Hodgkin's Lymphoma. One early study showed that low dose IL-2 at dose of 3 million units per m2 twice a week for one year increased the activity and absolute number of natural killer (NK) cells which are a type of cytotoxic lymphocyte that is a major component of our innate immune system. More importantly, this dose of IL-2 prolonged time to progression in 9 patients with residual disease after autologous transplant and induced sustained complete remissions in two more patients. NK cells are involved in tumor killing via antibody dependent cell cytotoxicity, release of cytotoxic granules causing direct tumor killing and expression of ligands that trigger apoptosis or programmed cell death. In that study, no changes were seen in regulatory T cells which have been recently found to exert an inhibitory effect on NK cell function and hence limit the NK cell's ability to exert an anti-tumor effect.2,5 Because both regulatory T cells and NK cells express the IL-2 receptor, higher doses of IL-2 administration (14MIU SQ thrice weekly) would expand both populations of cells which may explain the lack of benefit seen in other clinical studies. At lower doses of 3MIU SQ twice weekly used in the earlier study, we anticipate selective upregulation of NK cells without effecting regulatory T cells.

Rituximab is a monoclonal antibody against CD20 antigen that is expressed in most B cell lymphomas. It is commonly used in the treatment of B cell lymphomas either alone or in combination with other therapy. It has been used as part of initial treatment after diagnosis as well as re-treatment if lymphoma recurred. It has also been studied as maintenance therapy in relapsed or resistant follicular lymphoma showing that rituximab delayed disease progression compared to the group who did not receive maintenance rituximab.11 The mechanism of action of rituximab includes complement mediated cytotoxicity, antibody dependent cellular cytotoxicity, induction of apoptosis and sensitization of cancer cells to cytotoxic chemotherapy. Antibody dependent cellular cytotoxicity is mediated by NK cells, macrophages and monocytes.13 The purpose of this study is to determine if the combination of low dose IL-2 plus rituximab is more effective than low dose IL-2 alone after primary or salvage therapy.