To investigate the changes of CD4⁺ and CD8⁺ T lymphocyte subsets and tumor-infiltrating lymphocyte (TIL) density in tumor tissue before and after neoadjuvant treatment for rectal cancer, and to find immune markers for sensitivity to preoperative neoadjuvant chemoradiotherapy.

The stage changes and efficacy evaluation after neoadjuvant therapy were assessed by magnetic resonance imaging and pathology. The number of CD4⁺ and CD8⁺ T cells in tumor tissue before and after neoadjuvant radiotherapy and chemotherapy was assessed by immunohistochemistry.

After radiotherapy, there were two more cases of CD4⁺ TIL grade 1, one more case of CD4⁺ TIL grade 2, and three less cases of CD4⁺ TIL grade 3. There was no statistically significant difference in the CD4⁺ TIL grade distribution between before and after radiotherapy (P＞0.05). After radiotherapy, there were ten less cases of CD8⁺ TIL grade 1, six more cases of CD8⁺ TIL grade 2, and four more cases of CD8⁺ TIL grade 3. There was a statistically significant difference in the CD8⁺ TIL grade distribution between before and after radiotherapy (P＜0.05). The higher the CD8⁺ TIL density in rectal cancer tumor tissue before radiotherapy, the more the proportion of patients achieving complete remission and partial remission, and the less the number of cases with stable disease and progressive disease (P＜0.05). There was no significant correlation between CD4⁺ TIL density and the local efficacy (P＞0.05).

After neoadjuvant radiotherapy and chemotherapy for rectal cancer, the reduction rate of T stage cases is 46.2%, and that of N stage is 40.4%. CD8⁺ T cells significantly increase in tumor tissue after chemoradiotherapy for rectal cancer, but there are no significant changes in CD4⁺ T cells. Higher CD8⁺ TIL grade is associated with a higher postoperative tumor regression rate. CD8⁺ TIL grade may be a predictive indicator for radiation sensitivity.