Cyclophosphamide chemotherapy sensitizes tumor cells to TRAIL-dependent CD8 T cell-mediated immune attack resulting in suppression of tumor growth

Our plain-English summary of Cyclophosphamide chemotherapy sensitizes tumor cells to TRAIL-dependent CD8 T cell-mediated immune attack resulting in suppression of tumor growth, by R.G. van der Most, A.J. Currie, A.L. Cleaver, et al (PloS One, 2009).

The study

• Authors: R.G. van der Most, A.J. Currie, A.L. Cleaver, J. Salmons, A.K. Nowak, S. Mahendran, I. Larma, A. Prosser, B.W. Robinson, M.J. Smyth, A.A. Scalzo, M.A. Degli-Esposti, R.A. Lake
• Journal: PloS One
• Published: 2009;4(9):e6982
• Cited by: 78 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Anti-cancer chemotherapy can be simultaneously lymphodepleting and immunostimulatory. Pre-clinical models clearly demonstrate that chemotherapy can synergize with immunotherapy, raising the question how the immune system can be mobilized to generate anti-tumor immune responses in the context of chemotherapy.

Methods And Findings: We used a mouse model of malignant mesothelioma, AB1-HA, to investigate T cell-dependent tumor resolution after chemotherapy. Established AB1-HA tumors were cured by a single dose of cyclophosphamide in a CD8 T cell- and NK cell-dependent manner. This treatment was associated with an IFN-alpha/beta response and a profound negative impact on the anti-tumor and total CD8 T cell responses. Despite this negative effect, CD8 T cells were essential for curative responses. The important effector molecules used by the anti-tumor immune response included IFN-gamma and TRAIL. The importance of TRAIL was supported by experiments in nude mice where the lack of functional T cells could be compensated by agonistic anti-TRAIL-receptor (DR5) antibodies.

Conclusion: The data support a model in which chemotherapy sensitizes tumor cells for T cell-, and possibly NK cell-, mediated apoptosis. A key role of tumor cell sensitization to immune attack is supported by the role of TRAIL in tumor resolution and explains the paradox of successful CD8 T cell-dependent anti-tumor responses in the absence of CD8 T cell expansion.

In plain English

This was a laboratory study in mice and cultured cells. The authors used AB1-HA, a mouse mesothelioma cell line derived from an asbestos-induced tumor line, to study how the chemotherapy drug cyclophosphamide interacts with immunity. A single dose routinely cured 75–100% of small tumors, and this effect depended on CD8 T cells, a type of immune cell. In culture, the drug's active form killed tumor cells by programmed cell death (apoptosis). The drug also sharply reduced CD8 T cell multiplication, including that of tumor-specific cells. The treatment failed in 7 of 10 mice lacking interferon-gamma and in 9 of 9 lacking both interferon-gamma and perforin. Mice lacking TRAIL, a death-triggering molecule, responded less well. In T cell-deficient mice, adding a TRAIL-mimicking antibody prolonged tumor control. That combination was associated with liver toxicity, which prevented long-term study. The authors concluded that the data support a model in which chemotherapy makes tumor cells more vulnerable to killing by T cells, and possibly NK cells, without T cells needing to multiply. Direct tests of this were left for further studies.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment (mouse tumor model) with supporting cell-culture experiments
• Who was studied: Female BALB/c mice aged 6–8 weeks, including normal (wild-type) and athymic nude mice, plus gene-deficient mice (TRAIL-deficient, perforin-deficient, and perforin/IFN-gamma double-deficient) bred in Australia. AB1-HA mesothelioma cells were injected under the skin of the right flank. Groups were typically 5 mice per experiment. No humans were studied.
• Exposure: The exposure studied was the chemotherapy drug cyclophosphamide, given as a single dose of 150 mg/kg. Its active metabolite maphosphamide was used in culture. Asbestos exposure was not studied; the AB1 tumor cell line used was originally asbestos-induced.
• Main results:
  • In normal mice, cyclophosphamide cured 75–100% of small (just palpable) tumors, and the anti-tumor effect depended on CD8 T cells.
  • In cultured AB1-HA cells, maphosphamide increased the proportion of cells showing signs of apoptosis, and the increase grew with the dose.
  • Treatment was linked with a type-I interferon (IFN-alpha/beta) response. Blocking type-I interferon only marginally affected how well cyclophosphamide worked.
  • In treated mice, the recovery and multiplication of transferred tumor-specific CD8 T cells were significantly reduced. Frequencies of the mice's own tumor-specific CD8 T cells did not differ significantly from those in untreated mice, with a trend toward lower frequencies (P = 0.06).
  • Mice cured by cyclophosphamide all resisted a second injection of AB1-HA tumor cells (n = 20; data not shown).
  • In IFN-gamma-deficient mice, the anti-tumor response was prevented in 7 of 10 mice. Perforin deficiency did not abolish the drug's effect. Combined IFN-gamma and perforin deficiency completely abolished it in 9 of 9 mice.
  • In TRAIL-deficient mice, cyclophosphamide was less effective than in normal mice (n = 10, two combined experiments).
  • In nude mice, which lack functional T cells, the anti-DR5 antibody alone was ineffective and cyclophosphamide alone had a very short-lived effect. The combination gave prolonged control of tumor growth and was associated with liver toxicity.
• The authors' conclusion: The authors concluded that their data support a model in which chemotherapy sensitizes tumor cells to apoptosis mediated by T cells, and possibly NK cells. In their view, this model explains how CD8 T cells worked against the tumor without expanding in number.
• Limitations the authors state:
  • The perforin-deficient experiments treated larger tumors (4–6 mm2 instead of 1 mm2), which the authors note reduces the drug's efficacy.
  • Liver toxicity associated with the cyclophosphamide plus anti-DR5 combination prevented study of long-term tumor control.
  • The relative roles of NK cells and CD8 T cells and the source of TRAIL were not determined. Measuring whether drug-treated tumor cells become more sensitive to DR5 ligation was left for further studies.

Topics

Medical terms in this study, explained in our Lexicon: Chemotherapy, Immunotherapy, Malignant Mesothelioma, Apoptosis.

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