Exposure to acute psychological and physiological stressors is associated with impairments in immune function including reduced exercise-induced mobilization of naïve (NA) T-cells and increased mobilization of antigen-specific, highly differentiated T-cells following maximal exercise. However, the impact of sustained stressors on the immune response to maximal exercise is unknown. PURPOSE: Characterize the impact of self-reported stress and well-being on lymphocyte responses to acute bouts of exercise in collegiate swimmers over six months. METHODS: Blood samples were collected from fifteen NCAA D1 swimmers (7 M, 6 F: 19.8 ± 0.7 y) before and after maximal swims at two timepoints (V1: immediately post-season 1 and V3: early season 2). An additional mid-off season timepoint (V2) was collected in a subset of nine swimmers. T-cells were quantified by flow cytometry, and self-reported measures of sleep quality (PSQI), symptoms of upper respiratory tract infection (URTI, WURRS-21), and overtraining (DALDA) were collected. Linear mixed models were used to determine the effects of exercise, season timepoint, and their interaction on lymphocyte percentages (α=0.05). Pearson’s correlation coefficients were used to assess correlations between lymphocyte percentages and stress measures. RESULTS: Lower sleep quality was correlated with greater resting and post-exercise senescent CD4+ T-cell percentages (r= 0.44, p= 0.01; r= 0.47, p = 0.004, respectively). Low sleep quality was also correlated with lower post-exercise NA CD4+ T-cells (r= -0.35, p= 0.04). Higher ratings of self-reported symptoms of URTI (r= 0.38, p= 0.02) and overtraining (r= 0.38, p= 0.02) were correlated with greater post-exercise senescent CD4+ T-cell percentages. Compared to pre-exercise, post-exercise NA CD8+ T-cell percentages were lower at V1 and V2, while CD8+ T-cell percentages were higher post-exercise (p < 0.01). CONCLUSION: Elevations in stress and well-being at rest adversely impacted immune response to maximal exercise in collegiate swimmers. Impaired sleep quality and higher URTI and overtraining symptoms were associated with an exacerbated exercise-induced mobilization of senescent CD8+ T-cells, highlighting the importance of monitoring athlete stress level and overall well-being throughout the competitive season.