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The advent of novel immunotherapy (CAR-T cell therapy, bispecific CD20×CD3 antibodies) have highlighted the importance of T-cells in the treatment of lymphoma. However, overall T-cell characteristics have not been properly examined in patients receiving conventional chemotherapy. Next-generation sequencing (NGS) of the T-cell receptor (TCR) has enabled the possibility of identifying hundred thousands of unique T-cell clones in a single patient sample. Here we analyzed the impact of systemic TCR diversity and T-cell clonotypes in patients with Non-Hodgkin lymphoma (NHL) and Hodgkin-lymphoma (HL) receiving high-dose chemotherapy with stem cell support (HDT/ASCT). Autologous peripheral blood stem cell harvest samples from patients with lymphoma (predominantly B-cell NHL) were collected as part of a national population-based study (Husby et al. - Leukemia 2020). We performed high-throughput RNA-based sequencing of the V, D and J segment of the TCR β-chain to identify unique clonal rearrangements. To ensure supreme quality for TCR repertoire calculations, samples with less than 100.000 aligned reads to the TCR β chain were omitted from further analysis. By using the MiXCR bioinformatic pipeline we analyzed the number of unique clonotypes and TCR repertoire diversity, as calculated by the Simpson index. T-cell clonotype and diversity were for categorical analyses split in two groups by the median, respectively. A total of 96 patients with lymphoma who were intended for HDT/ASCT were included and analyzed for TCR characteristics. In brief, median age was 56 years, 64% were male and major subtypes were diffuse large B-cell lymphoma (37%), follicular lymphoma (24%), Hodgkin lymphoma (16%), and mantle cell lymphoma (14%). Median follow-up time was 6.7 years. Number of unique T-cell clonotypes was not associated with age (Fig. 1A), but low levels were highly associated with inferior survival (Fig. 1B, p=0.008), especially in the first year of follow-up. In contrast, elderly patients had a trend toward lower TCR diversity (Fig. 1C, p=0.08), but this did not impact overall survival (Fig. 1D). Low T-cell clonotype levels was also significantly associated with presence of clonal hematopoiesis (Fig. 1E, p=0.033). No association with clonal hematopoiesis was found with regard to TCR diversity (Fig. 1F). Furthermore, we investigated TCR repertoire in relation to subsequent severe infections (defined as sepsis, pneumonia, or invasive fungal infection). Number of unique T-cell clonotypes did not have an impact (Fig. 1F), but remarkably patients with a high T-cell diversity had significant increased incidence of severe infections in the first 500 days after sampling (Fig. 1G, p=0.029). This implies that patients who have a high T-cell diversity before high-dose chemotherapy, are more capable of mounting an immune response against infectious pathogens. These findings should be validated in larger homogenous cohorts. However, they imply the importance of inherent immune characteristics in patients with lymphoma. Although the immune response is exceedingly complex, we have identified systemic T-cell characteristics that associate with several important clinical variables. Assessment of systemic immunological parameters in patients with aggressive lymphoma may in the future inform on choice of optimal personalized therapy. Figure 1 Figure 1. Disclosures El-Galaly: ROCHE Ltd: Ended employment in the past 24 months; Abbvie: Other: Speakers fee. Larsen: Odense University Hospital, Denmark: Current Employment; Celgene: Consultancy; BMS: Consultancy; Novartis: Consultancy; Gilead: Consultancy.