DNA Damage-Response Pathway in Lymphoma Determines Interactions with Macrophages By Altered PD-L1 Expression and Exosome Formation

The tumor microenvironment is characterized by multiple interactions of transformed malignant cells with non-transformed stroma or immune cells. Particularly macrophages play a pivotal role in this network determining disease progression and therapeutic response. In previous work we could show that macrophages are an essential mediator of therapeutic response in the synergistic response to the administration of the chemoimmunotherapy. The combination treatment strongly increases tumor clearance by repolarization of tumor-associated macrophages from a suppressive to an activated phenotypic state. Here, se analyzed the functional implications of the DNA damage response pathway for the generation of the ASAP and synergy in chemoimmunotherapy.

We attempted to disrupt DNA damage response pathway in lymphoma cells generated from the hMB humanized Double-Hit-Lymphoma model by knock-down of key elements like ATM, DNA-PK or p53. We could prevent the formation of the stimulatory cytokine release effect on macrophage phagocytic capacity. Here, p53 status displays a key regulatory role on macrophage mediated malignant cell depletion. TP53 activation via Nutlin-3A treatment of lymphoma cell enhances ADCP in in p53 wild-type cells, while not displaying enhancement in p53-deficient lymphoma cells. Addressing the treatment in vivo using the hMB model for modeling of Double-Hit Lymphoma bearing mice we could demonstrate diminished ASAP and ADCP for p53-deficient lymphoma treated with cyclophosphamide in vivo.

Using primary human CLL patient cells comparing both wild-type and p53-deficient status, the p53-deficient CLL cells failed to induce the stimulatory, cytokine-mediated effect on macrophage phagocytosis in response to combination treatment as seen with the p53 proficient CLL cells. Using a CLL mouse model by treating Eµ-TCL1/p53^wt/wt as well as Eµ-TCL1p53^-/- mice we could show that low-dose cyclophosphamide treated Eµ-TCL1p53^-/- mice failed to induce an antibody mediated stimulatory effect on macrophage phagocytosis capacity as seen with Eµ-TCL1/p53^wt/wt mice. A similar effect was seen for primary multiple myeloma cells in response to daratumumab displaying significantly less ADCP of p53-deficient multiple myeloma cells.

As for the mechanism of p53-defined interaction within the tumor microenvironment we subjected p53-wild-type and p53-deficient lymphoma cells for proteomic analysis. Here we could identify a significantly deregulated protein expression profile for exosome release in p53 deficient lymphoma cells. Verifying this finding by assessing size and frequency exosomes released by respective cell populations we reveal profound changes induced by p53 loss.

Furthermore we could identify up-regulation of PD-L1 in p53-deficient cells. Blocking this checkpoint in the ADCP assay could significantly restore phagocytic capacity of macrophages and overall therapeutic response.

In this work, we indicate that p53 functional status determines phagocytic function and therapeutic response to monoclonal antibodies. We can verify this finding in independent models in vitro and in vivo as in primary CLL and myeloma patient cells. We furthermore identify altered exosome profiles and checkpoint inhibitor expression in lymphoma cells as underlying mechanism of macrophage modulation.

Finally our ongoing research offers possibility to reveal and tailor new combinatorial treatment approaches for chemo-refractory patients.