Role of the Immune System in Mediating the Antitumor Effect of Benzophenothiazine Photodynamic Therapy

Abstract

The role of the host immune system in contributing to tumor regression following benzophenothiazine photodynamic therapy (PDT) was examined. Photodynamic therapy with 2-iodo-5-ethylamino-9-diethylaminobenzo[a]-phenothiazinium chloride (2I-EtNBS) eradicated EMT-6 mammary fibrosarcomas in 75-100% of treated mice. In contrast, PDT failed to inhibit tumor growth in T-cell-deficient nude mice. Furthermore, T-cell depletion studies with anti-CD8 antibody revealed that the CD8+ T-cell population was critical for an effective PDT response (tumor volume 14 days post-PDT: 262 mm3 vs 59 mm3 in controls; P < 0.01). Because anti-CD4 antibody inhibited tumor growth in the absence of PDT, the role of CD4+ T cells remains unclear. Depletion of natural killer (NK) cells in vivo with anti-asialo-GM1 antibody significantly reduced a suboptimal PDT effect relative to vehicle controls (tumor volume 13 days post-PDT: 513 mm3 vs 85 mm3, respectively; P < 0.001). However, splenic NK cells obtained from PDT-treated tumor-bearing mice were not cytotoxic in vitro against EMT-6 cells, suggesting that NK cells contribute to the PDT effect in vivo by an indirect mechanism. In addition, when mice with complete tumor regression following PDT were rechallenged 28 days later with 5 x 10(5) EMT-6 cells, tumor growth was significantly inhibited as compared to controls (tumor volume 40 days postrechallenge: 137 mm3 vs 833 mm3 in controls; P < 0.03; percent animals without tumor in five experiments: 67% vs 8% in controls). Collectively, these results demonstrate that CD8+ T cells are required to prevent tumor regrowth after 2I-EtNBS-PDT, NK cells contribute to this response and such PDT can elicit protective antitumor immunity.

5-Aza-2′-deoxycytidine potentiates antitumour immune response induced by photodynamic therapy

“…Many reports support the role for CD8 + T cells in antitumour efficacy of this treatment [23,24,25]. CD8 + T cells are described as the key players in PDT mediated long-term control of tumours, while CD4 + helper T cells seem to play a supportive role [1,26].…”

Boosting Tumor-Specific Immunity Using PDT

“…This group used an EMT6 mammary carcinoma model in which depletion of CD8 + T cells led to a 50% decrease in cures after PDT compared to unmanipulated mice [47]. Similar results were obtained by different groups using 2-iodo-5-ethylamino-9-diethylaminobenzo-phenotiazinium chloride or Photofrin ® as photosensitizers, albeit Photofrin® was used in a combination approach with 5-aza-2’-deoxycytidine to induce the tumor antigen P1A [53,54]. However, presence of P1A was not necessary to sustain long-term immunity.…”

Heat-shock protein 70-dependent dendritic cell activation by 5-aminolevulinic acid-mediated photodynamic treatment of human glioblastoma spheroids in vitro

“…Immediately after PDT, there is immigration of neutrophils into the tumour (Krosl et al , 1995), and depletion of neutrophils before treatment abrogates the curative effect (de Vree et al , 1996; Korbelik and Cecic, 1999), suggesting an important contribution of innate immunity to the efficacy of PDT. However, results from immunodeficient NOD/SCID mice, lacking B and T cells, and nude mice, lacking T cells only (Canti et al , 1994; Korbelik et al , 1996; Hendrzak-Henion et al , 1999; Preise et al , 2009), indicate an essential role of adaptive T-cell immunity as well, with CD8 + cytotoxic T cells as main effectors and a supportive role for CD4 + T-helper cells (Hendrzak-Henion et al , 1999; Korbelik and Cecic, 1999; Korbelik and Dougherty, 1999; Preise et al , 2009). Moreover, Mroz et al (2010) identified antigen-specific cytotoxic T cells after benzoporphyrin-derivative/PDT treatment in a CT26.CL25 colon carcinoma model.…”

“…Reduced efficacy of PDT in immunodeficient mice lacking T cells (Korbelik et al , 1996; Hendrzak-Henion et al , 1999; Preise et al , 2009) indicates a pivotal role of T cells. This is further supported by adoptive transfer experiments (Korbelik and Dougherty, 1999; Preise et al , 2009) and lymphocyte-depletion studies (Hendrzak-Henion et al , 1999; Korbelik and Cecic, 1999; Korbelik and Dougherty, 1999), identifying CD8 + cytotoxic T cells as main effectors.…”

“…Reduced efficacy of PDT in immunodeficient mice lacking T cells (Korbelik et al , 1996; Hendrzak-Henion et al , 1999; Preise et al , 2009) indicates a pivotal role of T cells. This is further supported by adoptive transfer experiments (Korbelik and Dougherty, 1999; Preise et al , 2009) and lymphocyte-depletion studies (Hendrzak-Henion et al , 1999; Korbelik and Cecic, 1999; Korbelik and Dougherty, 1999), identifying CD8 + cytotoxic T cells as main effectors. However, for such T-cell responses to occur, tumour antigens have first to be taken up by immature dendritic cells (DCs), danger signals have to induce DC maturation, associated with migration of DCs to local lymph nodes and mature DCs in the lymph nodes have to present the tumour antigens to the specific T cells in the context of adhesion, co-stimulatory and other accessory molecules, either directly or after antigen transfer to other DCs (Ueno et al , 2010).…”