During the cancer-development process, host immunity can become disrupted, which allows cancer cells to proliferate and grow unchecked. This is often a result of cancer cells directly releasing into the environment of the patient chemical signals called cytokines, which act to dampen-down immune response. Similarly, cancer cells can alter its outward appearance, effectively disguising itself from immune sentinel cells. More specifically, cancer cells as part of their development become invisible to the immune system. This often forms part of the oncogenic process resulting in cells that are less responsive to the activity of the immune system. Consequently, patients with an already perfect-working immune system would not be able to utilise it to target cancer cells. Furthermore, using other treatments as a way of enhancing the immune system would be inefficient as the tumour cells would simply remain “hidden” from it.
Taking these together, I embarked on a 24-month study that that was part funded by the ICVI, which sought to explore the effect of chemotherapy on immunity. In particular, this approach considered ways of modifying the immune system by re-educating immune cells, causing them to be more active against tumour cells.
There are a number of ways of restoring full immune function: 1) specific immune cells can be refined and enhanced to make them more “cancer targeting”; 2) brakes that are by default engaged in certain immune cells can be released leading to more activity; and 3) the baseline level of immune activity can be raised, analogous to pressing down further the throttle. Some of these approaches that are typically used individually, have led to improvements in the immune system, making it more unfriendly to cancer.
Papers published and described
- Liu WM, et al. Pre-treatment with chemotherapy can enhance the antigenicity and immunogenicity of tumours by promoting adaptive immune responses. Br J Cancer. 2010 Jan 5;102(1):115-23.
- Liu WM, et al. Supernatants derived from chemotherapy-treated cancer cell lines can modify angiogenesis. Br J Cancer. 2012 Feb 28;106(5):896-903.
- Liu WM, et al. Supernatants from lymphocytes stimulated with Bacillus Calmette-Guerin can modify the antigenicity of tumours and stimulate allogeneic T-cell responses. Br J Cancer. 2011 Aug 23;105(5):687-93.
- Liu WM and Dalgleish AG. Cancer cell-derived supernatants that support the carcinogenic process: a future cancer therapy target. Future Oncol. 2012 Jul;8(7):767-9.
- Liu WM and Dalgleish AG. The potential beneficial effects of drugs on the immune response to vaccination. Semin Oncol. 2012 Jun;39(3):340-7.
- Liu WM, et al. The gene expression profile of unstimulated dendritic cells can be used as a predictor of function. Int J Cancer. 2012 Feb 15;130(4):979-90.
- Liu WM, et al. Dendritic cell phenotype can be improved by certain chemotherapies and is associated with alterations to p21(waf1/cip1.). Cancer Immunol Immunother. 2013 Oct;62(10):1553-61.
- Liu WM, et al. Supernatants of tumours treated with chemotherapy can alter tumour growth and development in vivo. Anticancer Res. 2015 Mar;35(3):1499-508.
Summary of findings
The first part of my work explored the way that certain chemotherapy drugs were able to enhance and/or restore the visibility of cancer cells to the immune system by driving up key markers such as HLA-1, which is a protein on the surface of cancer cells that immune cells use. Without this, it is often thought cancer cells can proliferate unimpeded. This first paper was published in 2010 [a]. In it, we had assessed the expression of HLA1 on a variety of tumour cells before and after chemotherapy agents (cyclophosphamide, oxaliplatin or gemcitabine). In addition, we also examined the effect that these drugs may have on the chemicals released by tumour cells. These were important as these chemicals called cytokines can influence the interactions between dendritic cells (DCs) and T cells, which determines the ultimate responses between cancer cells and immune cells. Our results showed that some chemotherapy agents can increase HLA1 expression in tumour cells, even when expression is low. Increases were associated with killing by cytotoxic T cells, which were negated by HLA1-blockade. Furthermore, T-cell function, as indicated by increased proliferation, was enhanced as supernatants derived from tumours treated with chemotherapy augmented DC-maturation and function. We concluded there is evidence that a facet of immune surveillance can be restored by appropriate chemotherapy agents. Also, tumours exposed to some chemotherapy may secrete cytokines that can mature DCs, which ultimately enhances T-cell responses.
This initial finding confirmed the concept that drugs could influence the chemicals released by tumours. We termed these chemicals “supernatants”. We explored further the possible role of these supernatants exuded by cancer cells and quickly realised that they could serve as primitive communication network used by tumour cells to influence the host. Indeed, we quickly identified a way that supernatants could influence a process called angiogenesis, which meant tumours could hijack the blood supply in patients to divert nutrients to feed growth. These findings were published in a follow-up paper [b]. Specifically, we showed that supernatants contain a rich cocktail of cytokines, a number of which are potent modulators of angiogenesis. They also contained microvesicular bodies containing RNA transcripts that code for proteins involved in transcription, immune modulation and angiogenesis. These supernatants altered intracellular signalling molecules in endothelial cells and significantly enhanced their tubulogenic character; however, this was severely compromised when supernatants from tumours treated with chemotherapy was used instead. We concluded, tumour exudates and bioactive material from tumours could influence cellular functions, and that treatment with some chemotherapy could serve to negate these pro-tumourigenic processes. We were aware that there would be cross-talk between tumour cells and immune cells, and also were able to show that immune cells also produced supernatants that could influence cellular interactions and ultimately tumour growth and the response by the immune system [c].
With these data, we highlighted the potential of targeting their function as a new way of treatment in an editorial [d]. Of particular note, we described how tumour-derived supernatants could modify immune responses and alter the host microenvironment to support cancer growth; however, certain chemotherapy could work to negate this pro-cancerous feature of these supernatants. This presented an exciting way into tackling cancer progression. Indeed, we produced a review article to highlight further the central idea of using chemotherapy drugs more generally to enhance immunity as a way of supporting cancer vaccines [e].
Another avenue of work emanating from the original 2010 paper was the effect that chemotherapy may also have on a group of cells called dendritic cells (DCs). These cells serve as “wanted ads”, teaching immune cells that act as tumour killers to target cancer cells more effectively. I therefore focused part of the research into understanding the nature of the effects of chemotherapy on DCs. First, I showed how DCs were changed at a gene level after treatments with chemotherapy [f], and second, how we could use this information to identifying ways of enhancing DCs to render them more anticancer in nature [g]. In particular, we showed DCs separated into two groups based on their ability to respond to a maturation stimulus. This quality correlated with a particular receptor profile of granulocyte-macrophage colony-stimulating factor and interleukin 4 expressed on the monocytes from which they were derived. DC quality was also associated with p21 expression, and artificially increasing their levels in DCs by using some chemotherapy improved function. Overall, these studies highlighted a role for common chemotherapy in activating p21 in DCs, which is a prerequisite for good DC function and anticancer action.
Our final research publication took everything we had discovered from the papers listed above, and examined the effects in a mouse study [h]. In short, we explored the effects that vaccination with supernatants derived from tumours may have on tumour growth in a BALB/c model, and showed a number of cytokines were detected in the supernatants capable of increasing B-cell lymphoma 2 (BCL2) protein expression in cancer cells; of note, significantly higher levels of granulocyte-macrophage colony stimulating factor (GM-CSF) were detected in chemotherapy-treated supernatants compared to controls. Vaccinating mice with supernatants from untreated tumours significantly impeded the growth of sub-cutaneous-implanted tumours. However, this anticancer effect was significantly diminished if the supernatants used were from cancer cells treated with gemcitabine. The study lends in vivo support to the idea that tumours produce bioactive components that can influence host biology and that certain chemotherapies can negate these, and the results takes us one step closer to clinical trials in patients with cancer.