Early variations in lymphocytes and T lymphocyte subsets are associated with radiation pneumonitis in lung cancer patients and experimental mice received thoracic irradiation

Diagnosis and treatment of radiation induced pneumonitis in patients with lung cancer: An ESTRO clinical practice guideline

The incidence of radiation pneumonitis (RP) has decreased significantly compared to historical series, mainly due to improved radiotherapy techniques and patient selection. Nevertheless, some patients still develop RP. This guideline provides user-friendly flowcharts to address common clinical practice questions regarding RP. We summarize the current state of the art regarding the mechanisms, risk factors, diagnosis and treatment of RP. Dosimetric constraints to minimize the incidence of RP, as well as risk factors for developing RP, such as idiopathic pulmonary fibrosis (IPF) were identified. The combination of radiotherapy and medication as a risk factor for the development of RP was reviewed. RP remains a diagnosis of exclusion, but an algorithm for reaching the diagnosis has been proposed. Finally, practical approaches to the treatment of RP are outlined.

Predicting Severe Radiation Pneumonitis in Patients With Locally-Advanced Non-Small-Cell Lung Cancer After Thoracic Radiotherapy: Development and Validation of a Nomogram Based on the Clinical, Hematological, and Dose-Volume Histogram Parameters

PURPOSE

This study aimed to investigate the risk factors for severe radiation pneumonitis (RP) after thoracic radiotherapy (RT) in patients with locally advanced non-small cell lung cancer (NSCLC), develop a prediction model to identify high-risk groups, and investigate the impact of severe RP on overall survival (OS).

METHODS

We retrospectively collected clinical, dosimetric, and hematological factors of patients with stage III NSCLC receiving thoracic RT without immunotherapy. The primary and secondary end points were severe RP and OS, respectively. Fine-Gray competing risk regression analyses were used to identify the risk factors for severe RP. The patients were randomly divided into training and validation cohorts at a ratio of 6:4. The model was evaluated using receiver operating characteristic (ROC) and calibration curves, and decision curve analysis (DCA). The OS of patients in the RP vs. non-RP and mild RP vs. severe RP groups was analyzed using the Kaplan-Meier method.

RESULTS

A total of 305 patients were enrolled in the analysis, and 32 (10.5%) developed severe RP. Interstitial lung disease (ILD) (P = .013), percentage of ipsilateral lung volume receiving ≥ 20 Gy (ipsilateral V20) (P = .029), pre-RT derived neutrophil lymphocyte ratio (dNLR) (P = .026), and post-RT systemic inflammation response index (SIRI) (P = .010) were independent predictors of severe RP, and were used to establish the nomogram based on a training cohort. The ROC area under the curve (AUC) of the nomogram was 0.804. Calibration curves and DCA showed favorable consistency and positive net benefits in both training and validation cohorts. Cases who developed severe RP had a shorter OS than those who developed mild RP (P = .027).

CONCLUSION

ILD, ipsilateral V20, pre-RT dNLR, and post-RT SIRI could predict severe RP in patients with locally advanced NSCLC receiving thoracic RT. By combining these indicators, a nomogram was constructed and validated, demonstrating its potential value in clinical practice.

C-C motif chemokine ligand 5 contributes to radon exposure-induced lung injury by recruiting dendritic cells to activate effector T helper cells

Radon (222Rn) is a naturally occurring radioactive gas, ionizing radiation emitted by the radon induces oxidative stress and the up-regulation of inflammatory proteins, which may cause lung damage or cancer. However, the underlying pathogenesis remains to be determined. Effector T helper cells are key in mediating the host's protection and immune homeostasis. In this study we revealed that, accompanied by the activation of effector T helper cells, there is a significant increase in C-C motif chemokine ligand 5 (Ccl5) in the lung of mice after cumulative inhalation of radon at 3, 9, 21, 45, 90, and 180 working level months (WLM). In vitro experiments showed that Ccl5 attracts DC migration and promotes the activation of effector T helper cells in the Ccl5-DC and T cells co-culture model. Of particular interest, Ccl5 neutralization in vivo inhibited the migration of DC cells and the subsequent activation of effector T helper cells, which finally protected mice from radon-induced lung damage and inflammatory response. Ultimately, transcriptome sequencing and western blot analysis showed that Ccl5 activates the CCR5/PI3K/AKT/Nr4a1 pathway to increase the secretion of IL-12 and IFN-γ by DC cells, which then promotes the activation of effector T helper cells. Overall, these results indicate that Ccl5 significantly contributes to the progression of radon-induced lung damage by modulating DC to activate effector T helper cells.

CD73/adenosine dynamics in treatment-induced pneumonitis: balancing efficacy with risks of adverse events in combined radio-immunotherapies

Consolidation with PD-1/PD-L1-based immune checkpoint blockade after concurrent platinum-based chemo-radiotherapy has become the new standard of care for advanced stage III unresectable non-small cell lung cancer (NSCLC) patients. In order to further improve therapy outcomes, innovative combinatorial treatment strategies aim to target additional immunosuppressive barriers in the tumor microenvironment such as the CD73/adenosine pathway. CD73 and adenosine are known as crucial endogenous regulators of lung homeostasis and inflammation, but also contribute to an immunosuppressive tumor microenvironment. Furthermore, the CD73/adenosine pathway can also limit the immune-activating effects of cytotoxic therapies by degrading the pro-inflammatory danger molecule ATP, which is released into the tumor microenvironment and normal lung tissue upon therapy-induced cell damage. Thus, while targeting CD73 may enhance the efficacy of radio-immunotherapies in cancer treatment by mitigating tumor immune escape and improving immune-mediated tumor killing, it also raises concerns about increased immune-related adverse events (irAEs) in the normal tissue. In fact, combined radio-immunotherapies bear an increased risk of irAEs in the lungs, and additional pharmacologic inhibition of CD73 may further enhance the risk of overwhelming or overlapping pulmonary toxicity and thereby limit therapy outcome. This review explores how therapeutic interventions targeting CD73/adenosine dynamics could enhance radiation-induced immune activation in combined radio-immunotherapies, whilst potentially driving irAEs in the lung. We specifically investigate the interactions between radiotherapy and the CD73/adenosine pathway in radiation pneumonitis. Additionally, we compare the incidence of (radiation) pneumonitis reported in relevant trials to determine if there is an increased risk of irAEs in the clinical setting. By understanding these dynamics, we aim to inform future strategies for optimizing radio-immunotherapy regimens, ensuring effective cancer control while preserving pulmonary integrity and patient quality of life.

Mechanisms of radiation-induced tissue damage and response

Radiation-induced tissue injury (RITI) is the most common complication in clinical tumor radiotherapy. Due to the heterogeneity in the response of different tissues to radiation (IR), radiotherapy will cause different types and degrees of RITI, which greatly limits the clinical application of radiotherapy. Efforts are continuously ongoing to elucidate the molecular mechanism of RITI and develop corresponding prevention and treatment drugs for RITI. Single-cell sequencing (Sc-seq) has emerged as a powerful tool in uncovering the molecular mechanisms of RITI and for identifying potential prevention targets by enhancing our understanding of the complex intercellular relationships, facilitating the identification of novel cell phenotypes, and allowing for the assessment of cell heterogeneity and spatiotemporal developmental trajectories. Based on a comprehensive review of the molecular mechanisms of RITI, we analyzed the molecular mechanisms and regulatory networks of different types of RITI in combination with Sc-seq and summarized the targeted intervention pathways and therapeutic drugs for RITI. Deciphering the diverse mechanisms underlying RITI can shed light on its pathogenesis and unveil new therapeutic avenues to potentially facilitate the repair or regeneration of currently irreversible RITI. Furthermore, we discuss how personalized therapeutic strategies based on Sc-seq offer clinical promise in mitigating RITI.

A multiomics approach-based prediction of radiation pneumonia in lung cancer patients: impact on survival outcome

PURPOSE

To predict the risk of radiation pneumonitis (RP), a multiomics model was built to stratify lung cancer patients. Our study also investigated the impact of RP on survival.

METHODS

This study retrospectively collected 100 RP and 99 matched non-RP lung cancer patients treated with radiotherapy from two independent centres. They were divided into training (n = 175) and validation cohorts (n = 24). The radiomics, dosiomics and clinical features were extracted from planning CT and electronic medical records and were analysed by LASSO Cox regression. A multiomics prediction model was developed by the optimal algorithm. Overall survival (OS) between the RP, non-RP, mild RP, and severe RP groups was analysed by the Kaplan‒Meier method.

RESULTS

Sixteen radiomics features, two dosiomics features, and one clinical feature were selected to build the best multiomics model. The optimal performance for predicting RP was the area under the receiver operating characteristic curve (AUC) of the testing set (0.94) and validation set (0.92). The RP patients were divided into mild (≤ 2 grade) and severe (> 2 grade) RP groups. The median OS was 31 months for the non-RP group compared with 49 months for the RP group (HR = 0.53, p = 0.0022). Among the RP subgroup, the median OS was 57 months for the mild RP group and 25 months for the severe RP group (HR = 3.72, p < 0.0001).

CONCLUSIONS

The multiomics model contributed to improving the accuracy of RP prediction. Compared with the non-RP patients, the RP patients displayed longer OS, especially the mild RP patients.

Association of T Cell Senescence with Radiation Pneumonitis in Patients with Non-small Cell Lung Cancer

PURPOSE

Associations between immunosenescence and radiation pneumonitis (RP) are largely unknown. We aimed to identify a peripheral blood T cell senescence biomarker to predict RP in patients with non-small cell lung cancer (NSCLC).

METHODS AND MATERIALS

Patients with locally advanced NSCLC who received definitive concurrent chemoradiotherapy (dCRT) were prospectively registered (cohort 1, n=23; cohort 2, n=31). Peripheral blood was collected at baseline, during dCRT, and at 1 month post-dCRT. Patients were dichotomized to grade ≥2 (G2+) RP and grade 0-1 (G0-1) RP. Flow cytometry was performed to assess phenotypes and functional properties of T cell subsets. RP incidence was estimated via competing risk analysis.

RESULTS

Five and six patients exhibited G2+ RP following dCRT in cohorts 1 and 2, respectively. Patients with G2+ RP exhibited a more aged T cell pool and higher frequencies of senescent CD57⁺CD28^-CD8⁺ T cells than patients with G0-1 RP at baseline, during dCRT, and at 1 month post-dCRT. These senescent cells exhibited increased granzyme B, IFN-γ, and TNF-α production. Higher baseline frequency of CD57⁺CD28^-CD8⁺ T cells was an independent predictor of G2+ RP (hazard ratio, 8.42; 95% confidence interval, 2.58-27.45; P<0.001). Recursive partitioning analysis revealed three distinct risk groups stratified by baseline CD57⁺CD28^-CD8⁺ T cell frequency and lung V_{20 Gy}, with 1-year cumulative G2+ RP incidences of 50.0%, 16.7%, and 0% for high-, intermediate-, and low-risk groups, respectively (P=0.002).

CONCLUSIONS

Higher baseline frequencies of CD57⁺CD28^-CD8⁺ T cells correlated with increased G2+ RP risks. Our results suggest the need for further investigation of the role of T cell senescence on radiation-induced organ damage.

Clinical and Dosimetric Predictors for Postoperative Cardiopulmonary Complications in Esophageal Squamous Cell Carcinoma Patients Receiving Neoadjuvant Chemoradiotherapy and Surgery

BACKGROUND

Neoadjuvant chemoradiotherapy followed by esophagectomy is the standard treatment for patients with locally advanced esophageal squamous cell carcinoma (ESCC). This study explored correlations of clinical factors and dose-volume histogram (DVH) parameters with postoperative cardiopulmonary complications and predicted their risk by establishing a nomogram model.

METHODS

Clinical and DVH parameters of ESCC patients who underwent trimodality treatment from 2002 to 2020 were collected. Postoperative cardiopulmonary complications were recorded. Logistic regression analysis was applied, and a nomogram model was constructed. Area under the receiver operating characteristic (AUC) curve, calibration curve, and decision curve analyses were performed to evaluate the performance of the nomogram.

RESULTS

Of the 307 ESCC patients enrolled in this study, 65 (21.2%) experienced pulmonary complications and 57 (18.6%) experienced cardiac complications. The following six risk factors were identified as independent risk factors for pulmonary complications by multivariate logistic regression analyses in the integrated model: male sex (odds ratio [OR], 3.26; 95% confidence interval [CI], 1.27-9.70; P = 0.021), post-radiation therapy (RT) forced expiratory volume in 1 s (FEV1) (OR, 0.51; 95% CI 0.28-0.90; P = 0.023), mean lung dose (MLD) (OR, 1.13; 95% CI 1.01-1.28; P = 0.041), and pre-RT monocyte (OR, 8.36; 95% CI 1.23-11.7; P = 0.03). The AUC of this integrated model was 0.705 (95% CI 0.64-0.77). The paclitaxel and cisplatin (TP) concurrent chemotherapy regimen was the independent predictor of cardiac complication (OR, 2.50; 95% CI 1.22-5.55; P = 0.016).

CONCLUSIONS

For ESCC patients who underwent trimodality treatment, male sex, post-RT FEV1, MLD, and pre-RT monocyte were confirmed as significant predictors of postoperative pulmonary complications. A nomogram model including six risk factors was further established. The independent predictor of cardiac complication was TP concurrent chemotherapy.

Effect of intensity modulated radiotherapy on lymphocytes in patients with esophageal squamous cell carcinoma and its clinical significance

Background

Radiotherapy usually leads to a decrease in the total number of lymphocytes in patients with esophageal cancer. The factors that causing lymphopenia and the clinical significance of lymphopenia are studied in this article.

Patients and methods

110 patients with esophageal squamous cell carcinoma who had undergo intensity-modulated radiation therapy were enrolled. Statistical methods were used to analyze the correlation between lymphopenia and total survival in patients with esophageal cancer during radiotherapy, and analyze the correlations between nutritional factors and lymphopenia.

Results

There were 11 patients with the lowest lymphocyte value with level 1-2 during radiotherapy, accounting for 10% of all the patients, and 110 patients with level 3-4, accounting for 90% of all the patient. In all the enrolled patients, the incidence of lymphocyte nadir G1, G2, G3 and G4 MinALC during radiotherapy accounted for 0.91%, 9.09%, 62.73% and 27.27%, respectively.KM survival analysis showed that the overall survival of patients in the group (MinALC ≤ 0.41×10⁹/L) was significantly lower than that of the patients in the other group (MinALC>0.43×10⁹/L). Nutritional indicators were positively correlated with the decline degree of lymphocytes. The minimal value of lymphocyte can predict the occurrence of grade 3-4 radiation pneumonitis.

Conclusion

Lymphopenia induced by radiotherapy can predict survival and radiation pneumonitis. Nutritional factors such as hemoglobin and albumin were positively correlated with total lymphocytes numbers induced by radiotherapy.

Nomogram based on circulating lymphocyte subsets for predicting radiation pneumonia in esophageal squamous cell carcinoma

Purpose

Currently, the relationship between radiation pneumonia (RP) and circulating immune cell in patients with esophageal squamous cell carcinoma (ESCC) remains unclear. This study aimed to explore the relationship between RP and circulating lymphocyte subsets in patients with ESCC receiving chemoradiotherapy (CRT), and develop a nomogram model to predict RP. Since we should implement clinical intervention to ≥ grade 2 RP, a nomogram model for ≥ grade 2 RP was also established to provide an early warning.

Patients and methods

This study retrospectively included 121 patients with ESCC receiving CRT from Guangxi Medical University Cancer Hospital from 2013 to 2021. Independent factors associated with occurrence of RP and ≥ grade 2 RP were identified by univariate and multivariate logistic regression analysis in the training cohort, and incorporated into nomograms. The predictive accuracy and discrimination of the model was assessed using Concordance Index (C-index), calibration curve and decision curve analysis (DCA). And each model was internally validated. Additionally, to verify the optimized predictive performance of the nomograms, the area under the ROC curve (AUC) of each nomogram was compared to that of single independent risk factors, lung V10 and lung V20, respectively. Moreover, each model was further evaluated for risk stratification to identify populations at high risk of RP and ≥ grade 2 RP.

Results

Multivariate analysis suggested that TNM stage, post-RT percentage of CD8+ T cell, and lung V15 were independent predictive factors of RP. Besides, pre- and post-RT percentage of CD8+ T cell, and V15 were independent factors of ≥ grade 2 RP. The C-indexes of RP and ≥ grade 2 RP nomograms were 0.809 (95% CI: 0.715-0.903) and 0.787 (95% CI: 0.685-0.889) in the training cohort, respectively. And the C-indexes of RP and ≥ grade 2 RP nomograms were 0.718 (95% CI: 0.544-0.892) and 0.621 (95% CI: 0.404-0.837) in the validation cohort, respectively. The calibration curves showed that the predicted values of model agreed well with actual observations. Moreover, DCA results indicated the applicability and accuracy of the models to predict RP and ≥ grade 2 RP. After stratification, the incidence of the high-risk group was significantly higher than that of the low-risk group with respect to either RP or ≥ grade 2 RP.

Conclusion

TNM stage, post-RT percentage of CD8+ T cell, and lung V15 were the independent predictors of RP toxicity. Pre- and post-RT percentage of CD8+ T cell, and lung V15 were the independent factors of ≥ grade 2 RP toxicity. The nomograms based on circulating lymphocyte subsets can robustly predict RP and ≥ grade 2 RP, guiding clinicians in risk stratification and early intervention.

Aberrant Alteration of Circulating Lymphocyte Subsets in Small Cell Lung Cancer Patients Treated with Radiotherapy

Purpose: The role of different circulating lymphocyte subsets, as well as their correlation with clinical characteristics of small cell lung cancer patients have not yet been fully understood. This study aims to evaluate the influence of the fluctuating absolute numbers of lymphocyte subpopulations in peripheral blood of patients with small cell lung cancer. Methods: The absolute counts and percentages of lymphocyte subsets in peripheral blood of 329 patients with small cell lung cancer were retrospectively analyzed. The numbers of CD3⁺, CD3⁺CD4⁺, and CD3⁺CD8⁺ T lymphocytes, CD3^-CD19⁺ B lymphocytes, and CD3^-CD16⁺CD56⁺ NK cells were evaluated by flow cytometry. Their relationship with the patients' clinical characteristics were statistically evaluated. Results: The CD4/CD8 values derived from the absolute number and percentage of CD3⁺CD4⁺ cells divided by CD3⁺CD8⁺ cells were identical (1.86  ±  0.99). There was no association between any of the lymphocyte subsets levels and age/sex of the 329 patients with small cell lung cancer. The patients with advanced stage had a reduction in CD3⁺ and CD3⁺CD4⁺ T cell counts and a decreased CD4/CD8 ratio. The levels of CD3⁺CD4⁺ T cells, CD3^-CD19⁺ B cells, CD3^-CD16⁺CD56⁺ NK cells, and CD4/CD8 ratio were associated with advanced tumor-node-metastasis stage. Patients who had undergone radiotherapy were characterized by lymphopenia with lower numbers of CD3⁺, CD3⁺CD4⁺, CD3⁺CD8⁺ T lymphocyte, B lymphocyte, NK cell, and CD4/CD8 ratio. The evaluation of individual CD4/CD8 ratio should be combined with other clinical parameters. Conclusions: Patients with small cell lung cancer have altered lymphocyte homeostasis. Lymphopenia was a long-lasting feature of the enrolled patients who were treated with radiotherapy. The available lymphocyte subsets levels might be used to manage the clinical treatment scheme.

Promising Biomarkers of Radiation-Induced Lung Injury: A Review

Radiation-induced lung injury (RILI) is one of the main dose-limiting side effects in patients with thoracic cancer during radiotherapy. No reliable predictors or accurate risk models are currently available in clinical practice. Severe radiation pneumonitis (RP) or pulmonary fibrosis (PF) will reduce the quality of life, even when the anti-tumor treatment is effective for patients. Thus, precise prediction and early diagnosis of lung toxicity are critical to overcome this longstanding problem. This review summarizes the primary mechanisms and preclinical animal models of RILI reported in recent decades, and analyzes the most promising biomarkers for the early detection of lung complications. In general, ideal integrated models considering individual genetic susceptibility, clinical background parameters, and biological variations are encouraged to be built up, and more prospective investigations are still required to disclose the molecular mechanisms of RILI as well as to discover valuable intervention strategies.

Comparison of Radiation Pneumonitis in Lung Cancer Patients Treated with HT versus IMRT and Circulating Lymphocyte Subsets as Predicting Risk Factors

Purpose

We sought to compare the symptomatic radiation pneumonitis (RP) in lung cancer patients treated with helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT), and examine the predictive value of circulating lymphocyte subsets affecting the occurrence of RP.

Patients and Methods

Circulating lymphocyte subsets, clinical characteristics, dosimetric parameters and pulmonary function were collected from 130 lung cancer patients treated with HT (n = 53) or IMRT (n = 77) from 2016 through 2020. Symptomatic RP was compared between groups. Binary logistic regression was used to identify predictors of RP.

Results

The IMRT group had larger planning target volume (319.9 vs 240.8 cc, P = 0.041); more ECOG performance status 0–1 (96.1% vs 79.2%, P = 0.002); more stage III–IV disease (94.8% vs 37.6%, P = 0.028); and more combined systemic therapy (85.7% vs 69.8%, P = 0.022). Grade ≥2 RP were comparable between IMRT and HT groups (16.9% vs 15.1%, P = 0.785). For stage III–IV disease, IMRT was associated with lower lung V10 (31.9% vs 35.8%, P = 0.047) and lower incidence of grade 5 RP (0% vs 9.1%, P = 0.018). All lymphocyte subsets reduced after radiotherapy. The decrease degree of total T cell count and CD4⁺ T cell count were larger after IMRT than HT (P = 0.043, P = 0.021). In univariate analysis, the smoking status, lower baseline FEV1, and higher total T cell count, higher CD8⁺ T cell count, lower total B cell count, lower CD4⁺/CD8⁺ ratio after radiotherapy were associated with the development of grade ≥2 RP. The higher CD8⁺T cell count after radiotherapy was the only risk factor associated with grade ≥2 RP in multivariable analysis (OR 1.003; 95% CI: 1.000–1.005; P = 0.044).

Conclusion

IMRT was associated with lower lung V10 and less grade 5 RP than HT for stage III–IV lung cancer. Higher CD8⁺ T cell count after radiotherapy was associated with an increased risk of RP. HT may better preserve total T cell and CD4⁺ T cell than IMRT.

The Predictive Value of MLR for Radiation Pneumonia During Radiotherapy of Thoracic Tumor Patients

Purpose

To evaluate the predictive value of blood lymphocyte, monocyte to lymphocyte ratio (MLR), and neutrophil to lymphocyte ratio (NLR) for radiation pneumonia (RP) in patients with thoracic tumors receiving radiotherapy.

Patients and Methods

The clinical data of 65 patients with thoracic tumor (esophageal cancer, lung cancer) treated by radiotherapy in our hospital were retrospectively analyzed. Patients were divided into the RP group and the non-RP group according to the Common Terminology Criteria for Adverse Events (CTCAE 5.0). Data on blood cell counts, including lymphocytes, monocytes, and neutrophils, were collected before (0 weeks) and after 1, 2, and 4 weeks of radiotherapy.

Results

Of the 65 patients enrolled, 27 developed radiation pneumonia and 38 did not. Patients’ clinical factors, including age, TNM stage, tumor type, underlying lung disease, and history of smoking, had no correlation with RP. ANOVA of repeated measurement data showed that the changes of MLR in the group with RP during radiotherapy were significantly different from those in the non-RP group (P<0.05). The RP prediction model based on the identified risk factors was established using receiver operator characteristic curves. The results showed that the area under the curve for the monocyte to lymphocyte ratio was 0.755 (95% CI, 0.63–0.87, P=0.000), and the best cutoff point for MLR was 0.426.

Conclusion

MLR could predict radiation pneumonia in patients with thoracic tumor radiotherapy and achieve early monitoring, early prevention, and treatment.

Early variations in lymphocytes and T lymphocyte subsets are associated with radiation pneumonitis in lung cancer patients and experimental mice received thoracic irradiation

There were no ideal markers to predict the development of radiation pneumonitis (RP). We want to investigate the value of variations of lymphocytes and T lymphocyte subsets in predicting RP after radiotherapy (RT) of lung cancer based on previous clinical findings. A total of 182 lung cancer patients who received RT were retrospectively analyzed. Circulating lymphocytes and T lymphocyte subsets were measured before, during, and after RT. Patients were evaluated from the start of RT to 6 months post‐RT. A mice model with acute radiation‐induced lung injury was established and circulating lymphocytes were measured weekly until 8 weeks after irradiation. Univariate and multivariate analyses were adopted to identify risk factors of RP. Lymphocyte levels significantly decreased (P < .001) in patients before RP symptoms developed that also was able to be seen in the mice model and the values recovered during remission of symptoms. The decrease in lymphocyte count reflected the severity of RP. Meanwhile, CD4⁺ T lymphocyte count was significantly lower during the occurrence of symptoms in patients with RP than in those without RP (P < .001), and it improved along with RP recovery. Levels of lymphocytes and CD4⁺ T lymphocyte subsets proved as independent predictors of RP. Here we showed that lower peripheral blood levels of lymphocytes and CD4⁺ T lymphocyte were associated with an increased risk of RP, which was validated by this mice model, and thus are associated with differences in radiation‐induced lung toxicity among individuals and help identify those who are susceptible to developing RP after RT.