Alterations of Immune Cells By Large B Cell Lymphoma Persist Years after Achieving Complete Remission and Correlate with Impaired Adaptive Immunity

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Background: The tumor microenvironment (TME) has recently emerged as one of the key players in the understanding of cancer biology and treatment resistance. Cells central to immune inhibition in the TME are myeloid derived suppressor cells (MDSCs). They represent a heterogenous immature myeloid subset which physiologically mediates the termination of inflammatory processes. However, in diffuse large B cell lymphoma (DLBCL), MDSCs are believed to be recruited by the malignant cells which installs a tumor-associated immunosuppression possibly further supporting disease progression. Number and rate of MDSCs correlate with disease stage and represent an independent prognostic factor for poor outcome. Whereas the treatment of DLBCL patients has evolved profoundly the functional consequences of changes in the TME during treatment and, even more so, once patients are cured remain unclear. Hypothesis: With the objective of understanding functional relevance towards adaptive immunity, we aimed to characterize the immune phenotype of patients at different time points during their disease. Method: We established a flow cytometry-based-TruCount analysis of whole blood samples to compare the immune phenotype of newly diagnosed DLBCL patients, of cured patients and of healthy donors. To functionally examine the immune status within the cured cohort after SARS-CoV2-vaccination, T cell vaccine response following in vitro stimulation, anti-spike antibody titers in the serum and serum levels of lineage specific cytokines were measured. To prove the inhibitory properties of MDSCs, we performed T cell suppression assays in co-culture. Results: Patients with active disease at first diagnosis which were treatment naïve displayed increased numbers of monocytic MDSCs (CD14(+) CD15(-) CD11b(+) CD33(+) HLA-DR(-) Lin(-)) compared with healthy donors. In patients at relapse before salvage treatment, average rate and numbers of MDSCs was higher than at first diagnosis. In patients cured from DLBCL the high rate of MDSCs persisted compared to healthy donors or patients with active disease. The increased rate of MDSCs was independent of number of undergone therapy lines, initial Ann Arbor stage or revised international prognostic index (R-IPI). For patients that were SARS-CoV2-vaccinated after the cure from DLBCL, the amount of MDSCs correlated negatively with serum levels of Anti-Spike IgG (p=0.01). With today only 16 samples measured, there was a trend towards a negative correlation between rate of MDSCs and SARS-CoV2-specific activation of T cells as measured by IFN-γ secretion. The correlation between sCD14 and T cell responses, however, reached significance (p=0.0005). Just as MDSCs from patients with active disease, MDSCs derived from cured patients were able to suppress the proliferation of unspecifically stimulated T cells. Furthermore, T cells in the peripheral blood of patients in complete remission after DLBCL showed significant activation and a substantially higher rate of senescence suggesting patterns of chronic inflammation. In line, the possibly cured people showed higher rates of Teffector cells compared with healthy controls. Conclusions: Our results indicate that cured DLBCL patients continue to be in an immunocompromised state even beyond two years after achieving complete remission. The presence of inhibitory myeloid cells with proven ability to suppress immune reactions together with hyperactivated and senescent T cells and an increase of effector T cells supports the conclusion of a systemic immune dysfunction long after the treatment finished. Functionally impaired immune responses compared with healthy people towards SARS-CoV2 indicates that patients cured from DLBCL are a vulnerable group to infection due to reduced vaccine response or virus reactivation. In summary, we show for the first time that patients cured from DLBCL show persisting alterations of immune cells which functionally impair adaptive immunity.