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Cervical Cancer and the Future of Stem Cell treatment

Cervical Cancer and the Future of Stem Cell treatment

May 24, 2023
Dr. Lana du Plessis
May 24, 2023
Dr. Lana du Plessis

Cervical cancer is the second most frequent cancer among women in South Africa and the first most frequent cancer among women between 15 and 44 years of age. It is the 14th most frequent cancer among women in the United States of America and the fourth most frequent cancer among women between 15 and 44 years of age in the USA. Cervical cancer proceeds slowly from the neoplasia stage to invasive cancer, and it is curable if diagnosed and treated early. However, in developing countries, although preventable; poor access to prevention, screening, and treatment contributes to 90% of deaths.

The fact that it is one of the most common cancers in women living with HIV, worsens the picture. Sexually active people will become infected with HPV at some point in their lives. However, the only harmful strains are types – 16 and 18, which cause 70% of cervical cancers and precancerous cervical lesions. About 3.9% of women in the general population are estimated to harbour cervical HPV16/18 infection at a given time, and 71.2% of invasive cervical cancers are attributed to HPVs 16 or 18 (1).

Insistent infection of the cervical epithelium by high-risk HPV can lead to cervical intraepithelial neoplasia which may progress to invasive cervical cancer, such as squamous cell carcinoma, adenosquamous cell carcinoma, or adenocarcinoma. The most conventional treatment for earlystage cervical cancers is radical hysterectomy (surgical removal of the cervix, uterus, and surrounding tissues called the parametrium) (2).

The alternative is radiation therapy (RT), which is usually given in combination with chemotherapy. In advanced (metastatic) diseases, targeted therapies are widely explored. Regrettably, limited success has been achieved using targeted intervention strategies with small molecules, angiogenesis inhibitors, and monoclonal antibodies directed against specific tumour antigens and proliferation pathways. For example, overexpression of EGFR has been linked with poor prognosis in cervical cancer, thus EGFR is an ideal candidate for therapeutic targeting. However, even limited success has been achieved with monoclonal therapy using cetuximab (CET) (chimeric IgG1, anti-EGFR mAb) as monotherapy or CET in combination with chemotherapy.

An alternative therapy has been the use of immunotherapy for cervical cancer. Even this has shown limited success. The focus of this has been vaccination approaches against HPV-derived oncogenes (E6 and E7) to trigger an efficient antitumor T cell response. These failed responses have been contributed to the extensive HLA down-regulation commonly observed in cervical cancer. Thus, it is believed that natural killer (NK) cell-based therapies may prove more effective than T cellbased approaches in the treatment of cervical cancer. The role of the innate immune response in host defense and viral clearance during (early) infection is well recognised. NK cells are potent in exerting rapid cytotoxicity by releasing cytotoxic granzyme B and perforin to lyse virus-infected cells and tumour cell targets. The efficient activity of NK cells is regulated by an equilibrium between inhibitory (e.g., CD94/NKG2A) and activating (e.g., CD16, DNAM-1, CD94/NKG2C, CD94/NKG2D) receptors. Various strategies have been adopted to cure cancer, such as adoptive cellular immunotherapy, including chimeric antigen receptors (CARs)-T cells-based and natural killer (NK) cell-based therapies. These therapies have made substantial improvements in the prognosis of patients.

NK cells are the core cells of the innate immune system and are the first line of defense against cancer cells and virus infection. NK cells can kill tumour cells without antigen sensitisation and antibody involvement. In recent years they have been used in the immunotherapy of malignant tumours. NK cells use unique mechanisms that depend on a set of stimulatory and inhibitory receptors, such as NKp30, NKp46, NKG2D, and NKG2A, and these receptors, function as switches, to determine whether NK cells are activated to kill target cells. Once activated, NK cells release perforin and granzyme; perforin perforates the surface of target cells, facilitating granzyme B to induce the apoptosis of target cells. In addition, NK cells can also secrete amounts of cytokines, including IFN-γ and TNF-α, which act on the target cells directly or further activate other types of immune cells. Another activation mechanism of NK cells is to enable target cells to be programmed for apoptosis through Fas/FasL or TRAIL (3).

NK cells can be derived from various sources, including umbilical cord blood (UCB), induced pluripotent stem cells, peripheral blood (PB), and embryonic stem cells. Unlike PB, UCBs are easy, quick, and pain-free to collect at birth and cryopreserved, making them readily obtainable. Of note, UCB has also been regarded as an allogeneic and off-the-shelf source of NK cells. Various expansion methods have been exploited to elevate the number and activity of NK cells to satisfy clinical use. Given that preclinical and clinical results of UCB-derived NK cells-based therapies have shown positive outcomes, it is reasonable to conclude that this form of immunotherapy is attractive and promising.

Although unexpanded UCB-derived NK cells have some limitations, including availability in low numbers due to the small volume of the UCB unit and immature function. These shortcomings have been overcome by a diverse range of approaches to expand UCB-derived NK cells in vitro.

To achieve this goal, large-scale expansion in their numbers and enhancing the activity of UCBderived NK cells in vitro were done through a variety of methods. IL-2-alone was previously used to expand NK cell, but this approach did not show significant results and needed further improvement. Subsequently, multiple cytokines-only approaches, including IL-2, IL-12, IL-15, and IL-18, were, therefore, used to satisfactorily expand NK cells. Thus, artificial antigen-presenting cells combined with cytokines have been used to expand NK cells in vitro, with satisfactory purity and number of NK cells (4).

UCB-derived NK cells have demonstrated utility in various clinical applications. Using non-modified UCB-derived NK cells has also shown that UCB CD34+-derived NK cells were more cytotoxic to cervical tumour cells, which were not restricted by HLA-ABC expression, and the levels of degranulation of NK cells were higher, compared to PB-derived-NK cells (5).

Approaches that strengthen the expression of activating receptors or diminish the inhibitory receptors of NK cells have been explored to enhance their activity. For UCB-derived NK cells, the expression of NKG2D in expanded NK cells was elevated in vitro, and NKG2D mediated the cytotoxicity of them against tumour cells. Therefore, the belief is that UCB-derived NK cells can also be genetically modified using CAR (NKG2D-DAP10-CD34), and their cytotoxicity against tumour cells will be enhanced significantly.

Besides, NK cells can also be activated by reducing the expression of inhibitory receptors, such as NKG2A, which can serve as a potential checkpoint for NK cell-based therapy. It is a known fact that the expression of NKG2A is relatively higher in UCB-derived NK cells than in PB-NK cells. Therefore, it would be fascinating to know which of PB or UCB would fare better if antibodies or PEBLs were also used to block the expression of NKG2A. If we speculate; combining UCB-derived NK cells with anti-NKG2A molecules or modifying them with CAR-NKG2A would present much more potent anti-tumour activity than using UCB-derived NK cells only. This aspect has not been studied yet and would provide interesting results in the future.

Only a few studies have investigated UCB-derived NK cells modified via CARs, the results are striking and promising. For instance, NK cells derived from the CD34+ hematopoietic progenitor stem cells of UCB units could be successfully engineered to express CAR-CD19 using co-culture with a feeder stroma of murine OP9-DL1 cells in the presence of human recombinant cytokines. UCB-derived CARCD19-NK cells generated by transducing CAR-CD19 plasmids to UCB-derived NK cells under IL-2 and IL-15 stimulation were more capable of degranulation when co-cultured with CD19 positive cells, compared to non-modified. In the future, except for targeted CD19 antigens, more types of CARs should be gradually engineered into UCB-derived NK cells (6-9).

Thus UCB-derived NK cell-based immunotherapy has boundless therapeutic potential for cancer patients. UCB-derived NK cells’ number and function are typically substantially improved after expansion in vitro. They have the added advantage of possessing high anti-tumour effects both in vivo and in vitro. Therefore, UCB-derived NK cells are a promising allogeneic “off-the-shelf” anti-cancer cellular immunotherapeutic.

Apart from the above-mentioned applications of umbilical cord-derived stem cells, in other studies, umbilical cord mesenchymal stem cells have shown inhibition of cervical cancer. Even exosomal miR-15a-5p from umbilical cord mesenchymal stem cells (UCMSCs) inhibited epithelial-to-mesenchymal transition (EMT) and metastasis of cervical cancer. In other studies, conditioned medium and cellular extract of the human umbilical cord showed inhibition of cervical cancer cells (10-12).

Current pre-clinical and clinical studies have indicated that stem cell-based therapies hold massive potential for the treatment of human disease. Mesenchymal stem cells (MSC) and umbilical cord mesenchymal stem cells in particular are promising anti-cancer agents to treat a number of different cancer types. MSC has inherent “homing” and “tumour-trophic” migratory properties, allowing them to be loaded and to deliver effective, targeted therapy to isolated tumours and metastatic disease. MSC have been readily engineered to express anti-proliferative, pro-apoptotic, anti-angiogenic agents that precisely target different cancer types. Many of these strategies have been validated in a wide range of studies evaluating treatment feasibility or efficacy, as well as establishing methods for real-time monitoring of stem cell migration in vivo for optimal therapy surveillance and accelerated development. Current clinical trials using these stem cells as agents for delivery to various tumour types are underway and hold great promise for novel therapeutic interventions in the future.


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