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Tumor immunotherapy based on the use of Chimeric Receptor Modified T cells (CAR T cells) is a promising approach for the treatment of a refractory hematological cancer. However, a robust response mediated by CAR T cells is observed only in a minority of patients and the expansion and persistence of CAR T cells in vivo is mostly unpredictable. In order to enhance the effectiveness of CAR-based immunotherapy we tested the immunoadjuvant properities of lenalidomide in combination with CAR19 T cells in a mouse model of B cell lymphoma. CAR19 construct which was used is composed of anti-CD19scFv joined with signaling domain of 4-1BB and TCR zeta and was delivered into T cell via lentiviral transduction. Lenalidomide is an immunomodulatory drug used for the treatment of multiple myeloma and selected B-cell malignancies, e.g. mantle cell lymphoma (MCL) or activated B-cell subtype of diffuse large B-cell lymphoma (ABC-DLBCL). However, the precise mechanism of action is not very well understood and it is believed that is mediated by a modulation of activity of E3 ubiquitin ligase cereblon which leads to increased ubiquitinylation of Ikaros and Aiolos transcription factors resulting in changes of expression of various receptors on the surface of tumor cells. To test our hypothesis, immunodeficient NSG mice (NOD-SCID-gamma chain null mice) were s.c. transplanted with various human B cells lymphoma cells (MCL or ABC-DLBCL) followed by i.v treatment with CAR19 T cells with or without daily i.p. lenalidomide. First, when we measured the growth of tumors following treatment with CAR19 T cells plus lenalidomide we found that this combination more effectively suppressed growth of s.c. B-NHL tumors than treatment with only CAR19 T cells or only lenalidomide (Figure 1, 1x10e7 Nemo tumor cell s.c., followed with 2 doses of 1x10(7) CAR19 T cells + Lenalidomide daily, tumor weight was measured 14 days after treatment). Additionally, in this experiment lenalidomide significantly enhanced infiltration of residual tumors by CD8+CAR19 T cells (not shown). Next, we tested the response of CAR19 T cells in vitro to B-NHL cells in the presence or, absence of lenalidomide to determine the costimulatory effect of lenalidomide on signaling via CAR, our data show that lenalidomide significantly enhanced functional response of CAR19 T cells following recognition of B cells in vitro which is demonstrated by enhanced production of IFN-gamma and by increased expression of CD69 by CAR19 T cells, interestingly, this effect was seen only if CAR19 T cells but not B-NHL cells were pre-treated with lenalidomide or, when we activated CAR19 T cell with antibody to CAR but not with antibody to CD3. Thus, our data indicate that lenalidomide might work through direct effects on T cells and specifically enhance signaling via CAR. The biochemical events underlying this costimulatory effect of lenalidomide on signaling by CAR are currently being investigated. In summary, our data support the use of lenalidomide for augmentation CAR-based immunotherapy in clinical settings. Figure 1 Figure 1. Disclosures Klener: Cellgene: Research Funding.