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Background Immune cell alterations in active neoplasms are established by cancer cells and result from a complex crosstalk between cancer, immune, vascular, and stromal cells, referred to as tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSC) are a myeloid subpopulation, integral to immunosuppression in the TME. In diffuse large B cell lymphoma (DLBCL), high MDSCs correlate with stage and are associated with poor outcome. Despite increasing understanding of the TME in active disease, the status of the immune system in complete remission (CR) and practical consequences thereof have not been studied. Materials and Methods We established a flow cytometry-based immunophenotype analysis of fresh blood samples to compare patients at first diagnosis of DLBCL, cured from DLBCL, and healthy donors. Inhibitory MDSCs were shown by T cell suppression assays and intracellular staining of Arg1 and COX2. Functional characterization was done by T cell vaccine recall response following in vitro stimulation with SARS-CoV2 peptide. Serum cytokines were measured by ELISA and correlated with immunophenotypic data. Results Patients cured from DLBCL have persistent immune dysfunction. Specifically, rate and number of MDSCs are significantly elevated in cured patients even years after remission has been achieved. These findings are not affected by age, stage, R-IPI, therapy lines, or time elapsed since end of therapy. The suppressive capacity of MDSC is confirmed by inhibition of T cells proliferation in co-culture assay and by high intracellular expression of Arg1 and COX2. The persistence of inhibitory myeloid cells in the cured patients is accompanied by additional changes in immune cells and cytokines. The CD4 and CD8 T cell compartments are substantially activated, with a consistent increase of activated CD4 T cells (HLA-DR and CD69+) and of terminally differentiated T cells such as CD8 TEMRA (CD45RA+/CD27-). The antigen specific response to SARS-CoV2 peptide in the cured cohort is lower than that of the age-matched controls. Further supporting chronic inflammation, several cytokines including IL6 or β2-microglobulin remain elevated in the cured, while B NHL-derived CXCL9 or CXCL10 are back to levels of healthy controls. In line with chronic inflammation, the number of MDSCs positively correlates with levels of serum IL-6. This is further linked through the demonstration that monocytes of healthy individuals shift towards MDSC phenotype when stimulated with IL-6 in vitro. Conclusions Altogether, the presence of inhibitory myeloid cells and hyperactivated senescent T cells, supports a persisting systemic immune dysfunction in DLBCL survivors, which show functional relevance and can impact the patients' management. Whether these changes predict relapse or long-term responses is under ongoing investigation. G. Benintende: B. Research Grant (principal investigator, collaborator or consultant and pending grants as well as grants already received); Modest; Kite/Gilead. R. Pelzl: B. Research Grant (principal investigator, collaborator or consultant and pending grants as well as grants already received); Modest; Kite/Gilead. K. Wendland: None. F. Gsottberger: None. S. Petkovic: None. L. Mellenthin: None. S. Völkl: None. A. Mackensen: None. F. Müller: B. Research Grant (principal investigator, collaborator or consultant and pending grants as well as grants already received); Modest; Kite/Gilead.
Benintende et al. (Fri,) studied this question.