BACKGROUND

Chemotherapy with Docetaxel (Doc) is efficient in a subset of prostate cancer (PCa) cases; however, most patients ultimately develop resistance to Docetaxel. The tumor immune microenvironment and secreted cytokines play a substantial role in development of resistance to chemotherapy. Our previous study has demonstrated that CD4+ T cells in prostate tumor microenvironment contribute to PCa progression; meanwhile, we found increased CD4+ T-cell infiltration in tumor area after Doc treatment; however, their effects on PCa chemosensitivity remain unclear. Here, we aim to explore the role and mechanisms of CD4+ T cells in PCa chemotherapy sensitivity.

METHODS

CD4+ T-cell infiltration in Doc-treated paraffin-embedded specimens from transurethral resection of prostate, radical prostatectomy, or bone metastasis was detected by immunohistochemistry. The castration-resistant PCa cell lines-C4-2 and CWR22RV1, and CD4+ T-cell lines-HH and Molt-3 were used in the coculture system. After coculture with the lymphocytes, PCa cell chemosensitivity was detected by cell counting kit-8, terminal deoxynucleotidyl transferase dUTP nick-end labeling assays, and Western blot analysis. Various cell cytokines were determined by cytokine arrays and reverse-transcription polymerase chain reaction. The recombinant human C-C motif chemokine ligand 5 (CCL5) was added to PCa cells for further confirming its effects and anti-CCL5 antibody was used for neutralization. S3I-201, a signal transducer and activator of transcription 3 (STAT3) inhibitor, was added to the coculture system to detect STAT3 role in chemosensitivity. Tumor xenografts in nude mice were used for confirming effects of CD4+ T cells in vivo study.

RESULTS

We found more infiltrated CD4+ T cells in human PCa lesions than in the adjacent noncancerous tissues after Doc treatment. In vitro cell line study confirmed that CD4+ T cells increase the PCa Doc resistance. Quantative polymerase chain reaction and cytokine arrays indicated that after coculture with PCa, CD4+ T cells could secrete large amounts of CCL5. Moreover, CCL5 stimulation enhanced PCa resistance to Doc, and anti-CCL5 antibody could partly reverse this process. We found that CD4+ T cells could activate P-STAT3 signaling via secreting CCL5 and adding a STAT3 inhibitor can reverse the chemoresistance. In vivo mouse model with xenografted 22RV1 cells and CD4+ T cells also confirmed the in vitro results.

CONCLUSIONS

Together, our results indicate that infiltrating CD4+ T cells could promote PCa chemotherapy resistance via modulation of the CCL5/STAT3 signaling pathway.