Open Access

ARTICLE

BCG Induces PD-1 Upregulation on Circulating CD8⁺ T Cells and IL-6 and IL-8 Secretion In Vitro

Gabriela R. Barbosa^1,2, Luciana S. B. Dal Col^3,4, Caroline C. Bighetto¹, Maria Carolina X. de Godoy¹, Marina D. B. P. Campioni⁴, Marcus V. Sadi^2,3, Alessandra Gambero^1,2, Leonardo O. Reis^1,2,4,*

1 Immuno-Oncology, Pontifical Catholic University of Campinas (PUC-Campinas), Campinas, SP, Brazil
2 INCT UroGen, National Institute of Science, Technology and Innovation in Genitourinary Cancer (INCT), Campinas, SP, Brazil
3 Paulista School of Medicine, Federal University of São Paulo, São Paulo, SP, Brazil
4 UroScience, State University of Campinas (Unicamp), Campinas, SP, Brazil

* Corresponding Author: Leonardo O. Reis. Email:

Oncology Research 2026, 34(7), 20 https://doi.org/10.32604/or.2026.075738

Received 07 November 2025; Accepted 02 May 2026; Issue published 16 June 2026

Abstract

Backgrounds: Bacillus Calmette-Guérin (BCG) remains the most effective adjuvant therapy for non-muscle-invasive bladder cancer (NMIBC); however, the immunological underpinnings of its efficacy remain incompletely understood. This study aims to elucidate the dual immunomodulatory roles of BCG by integrating systemic and tumor-intrinsic analyses, through determining the systemic effects of BCG instillation on immune checkpoint expression and direct inflammatory response in a previously established in vitro tumor model. Methods: We investigated systemic and tumor-intrinsic immune responses to BCG. Flow cytometry was used to evaluate immune checkpoint expression on circulating lymphocyte subsets in NMIBC patients (n = 7) at various stages of BCG therapy. In parallel, an in vitro model of PD-L1 modulation using breast cancer cell lines (MDA-MB-231 and MCF-7) was stimulated with BCG and TLR agonists, and the secretion of IL-6 and IL-8 was assessed using an ELISA. Results: Peripheral immune profiling revealed stable lymphocyte frequencies, but a significant increase in PD-1 expression on CD8⁺ T cells following BCG exposure (p = 0.0068), with no significant modulation in CTLA-4 levels. In vitro, MDA-MB-231 cells exhibited robust IL-6 secretion upon high-dose BCG stimulation (p = 0.0277), whereas MCF-7 cells showed increased IL-8 release (p < 0.0001). Other TLR agonists had limited effects. Conclusions: BCG induces dual immunomodulation, characterized by PD-1 upregulation in systemic CD8⁺ T cells and the release of pro-inflammatory cytokines from epithelial tumor cells. These findings support the potential of combining BCG with immune checkpoint inhibitors and underscore IL-6 and IL-8 as candidate biomarkers of tumor-intrinsic responsiveness.

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Supplementary Material

Supplementary Material File

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