P53 Prevents TCR-Dependent Peripheral T-Cell Lymphomagenesis From Chronically Stimulated T Cells.

Compelling evidence suggests that chronic infections by various pathogens are linked to lymphoma development. The transformation process is supposed to be either direct (eg for EBV) or indirect. The association between Helicobacter pylori chronic infection and gastric marginal zone lymphoma (MZL) is the best characterized example for an indirect transformation. Several other pathogens such as hepatitis C virus, Campylobacter jejuni or Streptococcus Pneumoniae (Spn) are also suspected to promote B-cell lymphoma development through repeated stimulations of the BCR and/or inflammation. However, except for gastric MZL, animal models are lacking to study potential correlations between chronic infections and lymphoma development.

To amplify and precipitate lymphomagenesis by precluding repair of DNA lesions potentially generated during chronic immune response, p53-deficient mice were used as a permissive model. Given the suspected role of carbohydrates from encapsulated bacteria such as Spn in promoting chronic lymphocytic leukemia, p53^−/− (n=15) and p53^+/− (n=53) mice were chronically injected with heat-killed Spn until disease development. P53-deficient mice chronically injected with PBS were used as control.

Unexpectedly, chronic injections of Spn promoted T-cell rather than B-cell lymphomagenesis in both p53^−/− and p53^+/− mice and shortened survival in p53^+/− mice (P=.004). Whereas mostly thymic CD4⁺CD8⁺ double positive T-cell lymphomas have been described in p53-deficient mice, a vast majority of lymphomas observed following chronic Spn injections were of peripheral origin (TdT⁻) and exhibited an effector memory phenotype (CD44^hiCD62L^loCCR7⁻CD25⁻). Clonality and transferability of those peripheral T-cell lymphomas (PTCL) were established. Furthermore, lymphoma cells showed features of chronically stimulated T cells such as TCR, CD3 or CD4/CD8 co-receptor down-regulations along with PD-1 up-regulation. Several lines of evidence suggested a contribution of the TCR to the development of these PTCL: 1/all PTCL following Spn injections exhibited a Vß repertoire usage bias (Vß8 in 100%) consistent with a transformation process originating from a chronically-stimulated T cell by a pathogen-specific immunodominant peptide; 2/cyclosporin A, a strong TCR signaling inhibitor, decreased cell survival in vitro, and prolonged mice survival following transfer of lymphoma cells into recipient mice; 3/engraftment of CD8⁺ PTCL in MHC class I KO mice was significantly reduced compared to wild type mice (P<.0001). Finally in vitro survival of PTCL was strongly dependent on the addition of γ_c cytokines (IL-7 and IL-15) in agreement with the expression of CD122 and CD127 and their potential memory origin.

The absence of B-cell lymphoma development in p53^−/− mice and its very late onset in p53^+/− mice (ie >450 days) compared to T-cell lymphoma prompted us to dissect the potential role of p53 in mature T-cell response in a context of chronic stimulation. WT and p53^−/− negatively selected CD4⁺ and CD8⁺ T cells were repeatedly (ie every 7–10 days) stimulated in vitro using anti-CD3/anti-CD28-coated beads. In agreement with previous reports, no significant difference of cell viability was observed after the first or the second stimulation confirming the minor role of p53 in initial activation and proliferation as well as in activation-induced cell death. Nonetheless, a dramatic increase in cell viability was observed 48h after the third stimulation of p53^−/− T cells, indicating a crucial function of p53 in deletion of chronically activated T cells.

Chronic stimulations with heat-killed Spn unexpectedly increased peripheral T-cell lymphoma development in p53-deficient mice. Phenotypic characterization was consistent with a transformation process occurring in a pathogen-specific chronically-stimulated T cell. The incidence of p53 mutations is higher in T-cell than in B-cell mature malignancies in humans and the p53 pathway is functionally impaired in virtually all enteropathy-associated T-cell lymphomas, which are supposed to be a key model for an antigen-driven process. Therefore, aside from its known role in immature T-cell lymphoma development and in progression of B-cell malignancies, our work sheds light on a previously unsuspected physiopathological role of the p53 pathway in peripheral T-cell lymphomagenesis.

No relevant conflicts of interest to declare.