Background: Radiation therapy (RT) is an important step in the treatment of primary breast cancer as it is one of the leading contributors to cancer incidence among women. Most patients with this disease acquire radiation-induced lymphopenia in the early post-radiation period; however, little is known about the effect of RT on the composition of lymphocyte populations in such patients. This study was aimed at investigating the effect of adjuvant remote RT—performed in the classical mode for patients with primary breast cancer—on the main components of cell-mediated immunity (major lymphocyte populations), including those in patients receiving chemotherapy. Methods: Between 2020 and 2022, 96 patients with stage I–III breast cancer were included in this study. All patients in the final stage of complex treatment received RT via a 3D conformal technique (3DCRT). The clinical target volume of this RT included the breast or chest wall and locoregional lymphatics. Flow cytometry was used to assess the levels and phenotypes of circulating lymphocytes before and after RT (no more than 7 days before and after RT). The evaluation of the impact of polychemotherapy (PCT) was conducted to determine whether it was a risk factor for the onset of radio-induced lymphopenia (RIL) in the context of RT. Results: When assessing the immune status in the general group of patients (n = 96), before the start of adjuvant external beam radiotherapy (EBRT), the average number of lymphocytes was 1.68 ± 0.064 × 10⁹/L; after the course of adjuvant EBRT, it decreased to 1.01 ± 0.044 × 10⁹/L (p < 0.001). When assessing the absolute indicators of cellular immunity in the general group of patients with BC after a course of adjuvant EBRT, significant dynamics were revealed by the changes in all cell populations of lymphocytes (paired t-test, p < 0.05). Conclusion: The adaptive immune system in breast cancer patients changed in the early post-radiation period. The absolute levels of B-, T- and natural killer cells significantly reduced after RT regardless of whether the patients previously underwent chemotherapy courses. RT for patients with primary breast cancer should be considered in clinical management because it significantly alters lymphocyte levels and should be considered when assessing antitumor immunity, as significant changes in T-cell immunity have been observed. In addition, the identified changes are critical if specific targeted therapy or immunotherapy is needed.

Each person is inevitably exposed to low doses of ionizing radiation (LDIR) throughout their life. The research results of LDIR effects are ambiguous and an accurate assessment of the risks associated with the influence of LDIR is an important task. Mesenchymal stromal cells (MSCs) are the regenerative reserve of an adult organism; because of this, they are a promising model for studying the effects of LDIR. The qualitative and quantitative changes in their characteristics can also be considered promising criteria for assessing the risks of LDIR exposure. The MSCs from human connective gingiva tissue (hG-MSCs) were irradiated at doses of 50, 100, 250, and 1000 mGy by the X-ray unit RUST-M1 (Russia). The cells were cultured continuously for 64 days after irradiation. During the study, we evaluated the secretory profile of hG-MSCs (IL-10, IDO, IL-6, IL-8, VEGF-A) using an ELISA test, the immunophenotype (CD45, CD34, CD90, CD105, CD73, HLA-DR, CD44) using flow cytometry, and the proliferative activity using the xCelligence RTCA cell analyzer at the chosen time points. The results of study have indicated the development of stimulating effects in the early stages of cultivation after irradiation using low doses of X-ray radiation. On the contrary, the effects of the low doses were comparable with the effects of medium doses of X-ray radiation in the long-term periods of cultivation after irradiation and have indicated the inhibition of the functional activity of MSCs.

Neuroplasticity and inflammation play important part in the body’s adaptive reactions in response to prolonged physical activity. These processes are associated with the cross-interaction of the nervous and immune systems, which is realized through the transmission of signals from neurotransmitters and cytokines. Using the methods of flow cytometry and advanced biochemical analysis of blood humoral parameters, we showed that intense and prolonged physical activity at the anaerobic threshold, without nutritional and metabolic support, contributes to the development of exercise-induced immunosuppression in sportsmen. These athletes illustrate the following signs of a decreased immune status: fewer absolute indicators of the content of leukocytes, lowered values in the immunoregulatory index (CD4⁺/CD8⁺), and diminished indicators of humoral immunity (immunoglobulins A, M, and G, and IFN-γ). These factors characterize the functional state of cellular and humoral immunity and their reduction affects the prenosological risk criteria, indicative of the athletes’ susceptibility to develop exercise-induced immunosuppression.