Mechanisms of Antigen Dependent and Independent Rejection of High Grade B-Cell Lymphoma in a Murine Model.

Abstract 4091

Poster Board III-1026

The rejection of Non Hodgkin Lymphomas expressing foreign, for example viral, antigens is compromised despite the presence of specific T-cells. The underlying immunosuppressive mechanisms are poorly understood. Using a transgenic mouse lymphoma model, where the proto-oncogene c-myc is driven by parts of the immunoglobulin lambda locus representing a t(8;22) translocation as found in Burkitt's lymphoma, we investigated the anti-lymphoma activity of specific T-cells. By retroviral transduction of a specific foreign antigen (chicken Ovalbumin-IRES-GFP, OVA) into cell lines from primary c-myc transgenic lymphomas we established a syngeneic model that would allow us to address the role of interferon gamma signalling in rejection of high grade lymphomas. All primary lymphoma cells displayed normal MHC class I and II levels on the surface when compared to wildtype splenic B-cells. This expression could be enhanced by treatment with interferon gamma (IFNg,100U/ml) up to 10 fold. When retrovirally OVA-transduced lymphoma cells were injected into either wildtype or GFP transgenic recipients, animals displayed a significant delay in lymphoma growth compared to non transduced or IRES-GFP transduced control cell lines. 80% of the recipient mice rejected OVA expressing lymphomas. By contrast, we observed 100% mortality when GFP expressing control lymphomas were injected in GFP transgenic recipients, which are tolerant for GFP. Developing OVA expressing lymphomas (20%) displayed a loss of GFP expression indicating a selection for antigen negative cells (p=0.001). In spleens from mice rejecting OVA-expressing lymphomas we found up to 1.8% SIINFEKL specific T-cells. To gain more mechanistic insights, we transferred OVA expressing lymphoma cells into IFNg, Stat1-/- or IFNg-/-receptor deficient recipients. Lack of STAT1-/- or IFNg-receptor on the recipient side or inability to secrete IFNg was associated with fast lymphoma progression and growth was not different when compared to non transduced, antigen negative cell lines. When IFNg-receptor or STAT1 deficient OVA expressing cell lines were transferred into wildytpe mice, rejection was not influenced. Outgrowing OVA expressing lymphomas in wildtype mice displayed a high MHC class I and II expression compared to the cell line prior to injection. MHC induction was absent in lymphomas transferred to Stat1 or IFNg deficient recipients. Depletion of NK cells by anti AsialoGM antibody in wildtype recipients resulted in a significant reduction of disease free survival (80% vs. 50%, p=0.002) and animals developed larger tumors which were eventually rejected resulting in a comparable overall survival. In peripheral blood of NK depleted mice significantly more OVA specific T-cells were detectable through pentamer staining. When lymphoma cell lines were injected into Rag1-/- mice, NK cell mediated rejection was also significantly impaired upon depletion. Our results suggest that T-cell mediated rejection of high grade B-cell lymphomas is strongly dependent on host IFNg secretion and that NK cells substantially contribute to T-cell mediated rejection.