## 3 Discussion  
We demonstrated that MYC mitigates the efficacy of clinically available conventional and T cell-redirecting antibodies targeting different surface antigens (CD20, CD38 and CD19) using pharmacological and genetic approaches of MYC targeting in vitro and ex vivo in various B-cell malignancies. We revealed that MYC can blunt the efficacy of immunotherapeutic antibodies via target antigen downregulation in the case of CD20, but also via induction of tumor intrinsic resistance towards NK cell- and T cell-mediated cytotoxicity by upregulating anti-apoptotic pathways and suppressing T-cell activation. To investigate a broad range of cell lines and primary cells derived from B-cell malignancies, we used the synthetic MYC inhibitor 10058-F4. To date, the use of various other agents has been studied to target MYC-driven tumors [30,31]. Many of these agents also modulate other pathways and cellular processes, inducing off-target effects, making it difficult to specifically study the effect on MYC. We selected 10058-F4 over alternatives, such as BET bromodomain inhibitors or kinase inhibitors, because 10058-F4 specifically inactivates MYC by binding directly to MYC's basic-helix-loop-helix-leucine-zipper domain [20], specifically at the Helix 2-ZIP junction (residues 402-412) [32]. Subsequently, MYC's directed transcription is disabled, and MYC mRNA and protein levels are down-regulated, either due to a loss of acetylation or due to a let-7-mediated negative feedback loop [33]. Hence, the effects observed here after treatment with 10058-F4 can be directly attributed to MYC. To avoid the negative side effects of MYC inhibition on peripheral blood immune effector cells and to explore the mechanisms behind the increased susceptibility to therapeutic antibodies, we additionally targeted MYC using CRISPR-Cas9 gene-editing technology. CRISPR-Cas9 efficiently causes stable short frameshift insertion-deletions into protein coding target genes that allow for a reduced risk of off-target effects [34] whilst specifically examining the effect of \(MYC\) modulation. The standard approach herein is to obtain single cell-derived clones, which may originally display subtle genetic or phenotypic differences. To outbalance any bias introduced by genetic heterogeneity, we analyzed 10 _MYC-targeted_ clones. We observed limited and nonspecific genetic heterogeneities. Nine out of ten clones exhibited similar results that were reversed after the successful repair of \(MYC\) in a number of subclones. These results convincingly demonstrated that specific \(MYC\) targeting, but not off-target effects or inter-clonal genetic heterogeneity, was responsible for the observed results. Among the mechanisms that we observed by which MYC mitigates the efficacy of rituximab, daratumumab and blinatumab, only the MYC-mediated downregulation of CD20 was described earlier [21; 35]. It was previously suggested that MYC directly represses the promotor of the _MS4A1_ gene, encoding CD20 [21; 35], and via induction of the MS4A1/CD20-targeting miR-222 [21]. The upregulation of CD20, but not CD38 or CD19, expression in MYC downregulated clones points to the relative importance of MYC-mediated intracellular escape mechanisms against NK-cells and T-cells beyond target antigen modulation. Interestingly, the efficacy of all immunotherapeutic approaches was similarly increased in the nine clones, indicating converging escape mechanisms against NK-cells and T-cells. To our knowledge, the MYC-mediated apoptosis deregulation and direct suppression of T-cell activation as escape mechanisms from immunotherapeutic approaches have not been demonstrated before. Apoptosis induction is a key mechanism of NK cell- and T cell-mediated tumor cytotoxicity. Our results indicate that MYC can effectively modulate apoptotic proteins to induce immune escape from NK cell- and T cell-mediated cytotoxic machinery.