Based on: Paper published in the journal Cell by a research team at Innate Pharma
The development of cancer treatments that target the human body’s own immune system, such as blocking immune inhibitory receptors, have been revolutionary in the fight against cancer. Immune inhibitory receptors are proteins on the surface of cells that send a signal to suppress immune cells. Significant efforts are now being made to develop therapies that target these inhibitory receptors to improve the body’s immune response against tumors (Ravetch & Lanier, 2000). In particular, the programmed cell death protein 1 (PD-1) is an inhibitory receptor that has been successfully targeted in cancer treatments. However, only some patients treated with PD-1-targeted therapies show a strong response and some cancers show resistance to such therapies (Seidel et al., 2018). Therefore, it is critical that new therapeutic targets, such as those that block other inhibitory pathways, are found. One possibility is the NKG2A receptor present on natural killer (NK) cells (a type of cell that can attach to some tumor cells without needing to be stimulated first) and CD8+ T cells (a type of white blood cell that can bind and kill cells infected by cancer or intracellular bacteria and viruses). NKG2A binds to the protein HLA-E in humans and inhibits the function of T and NK cells.
To further investigate this possibility, the authors examined the impact NK2GA had on the activity of cytotoxic lymphocytes (a type of white blood cell that kills cancer cells). Andre et al (2018) injected cell lymphoma A20 cells (tumor cells that express Qa-1b, a molecule in mice that is very similar to the human HLA-E molecule) or Qa-1b deficient A20 cells into syngeneic mice (genetically identical mice). The normal A20 cells progressively grew in mice whereas 70% of the mice injected with the Qa-1b deficient A20 cells did not show any tumor growth (Andre et al., 2018). This result indicated to the authors that Qa-1b may be a practical target to study in mice.
The authors’ next step was to investigate the immune response to the A20 tumor cells. Andre et al (2018) injected mice with A20 cells and used FACS analysis to examine the immune cells that infiltrated the tumors. They found that the tumors were infiltrated by NK and CD8+ cells. Around 60% of the NK cells that infiltrated the tumors expressed the NKG2A receptor (Andre et al., 2018). In addition, Sagiv-Barfi et al (2015) reported that efficient control of A20 tumors was partially dependent on PD-1 (a molecule on cell surfaces that down-regulates the immune system). The authors examined whether PD-1 was expressed and saw that around 45% of the CD8+ cells that infiltrated the tumor also expressed PD-1. Furthermore, about half of those CD8+ cells that expressed PD-1 also expressed the NKG2A receptor (Andre et al., 2018). These results suggested to the author that blocking the NKG2A receptor could promote antitumor activity.
To determine whether NKG2A blockade could promote antitumor activity, the authors generated a recombinant (generated without animals using synthetic genes) mouse version of the anti-mouse NKG2A antibody (a protein that is produced in response to and binds to a specific molecule). They treated mice with A20 tumors with the anti-NKG2A antibody, a PD-L1 (the molecule that binds to the PD-1 receptor) antibody, or a combination of both. The authors observed that the combination of both antibodies had a combined greater effect in rescuing mice from death (around 75%) than either antibody on its own (Andre et al., 2018). The authors sought to explore whether the antitumor effect demonstrated by the combination of antibodies was dependent on NK cells or CD8+ cells. To investigate this, they treated mice with anti-asialo-GM1 (an antibody that depletes NK cells) or anti-CD8+ antibodies (an antibody that depletes CD8+ cells). They observed that without NK cells or CD8+ cells, the enhanced antitumor effect from combining anti-NKG2A and anti-PD-L1 antibodies significantly diminishes (Andre et al., 2018). This result indicated to the authors that the antitumor effect of combining both antibodies is dependent on both NK and CD8+ T cells.
In the previous experiment, the authors demonstrated the antitumor properties of the anti-NKG2A antibody and sought to further investigate the antitumor properties by using the antibody to treat another tumor, RMA-Rae 1β T lymphoma. Similar to A20 cells, RMA-Rae 1β cells also express Qa-1b and PD-L1. Andre et al. (2018) injected RMA-Rae 1β tumor cells into mice and used FACS analysis to examine the amount of NK and CD8+ cells that infiltrated the tumor. They observed neither the anti-NKG2A or anti-PD-L1 antibody were effective in controlling RMA-Rae 1β tumor growth (Andre et al., 2018). In contrast, they found that a combination of the anti-NKG2A and anti-PD-L1 antibodies reduced tumor growth in 45% of the mice. Furthermore, they observed CD62L_ CD44+ effector memory CD8+ T cells (a subset of T cells that have previously encountered the antigen and mount a faster and stronger immune response in following encounters ) in the spleens of mice infected with RMA-Rae 1β but not in the spleens of untreated mice. The next step was to determine whether treatment with a combination of anti-NKG2A and anti-PD-L1 antibodies results in the formation of memory T cells that can mount more effective response. Andre et al (2018) tackled this question by injecting RMA-Rae 1β tumor cells into mice that were previously injected and cured with anti-NKG2A and anti-PD-L1 antibodies treatment. They found that mice who were previously exposed and cured completely rejected the RMA-Rae 1β tumor cells, whereas the RMA-Rae 1β tumor cells grew in untreated mice. These results collectively indicated that blocking the NKG2A receptor can generate memory CD8+ cells capable of initiating stronger and faster responses against cancerous cells.
To further investigate if NKG2A is a good therapeutic target for human cancers, the authors used immunohistochemistry to monitor how much HLA-E and NGK2A was expressed on a variety of tumors. They stained the cancerous tissue with antibodies that bind to HLA-E and NGK2A then added a second antibody that reacts with the first antibody and measured the amount of activity that took place. They observed that HLA-E and NKG2A was strongly expressed by squamous cell carcinoma of head and neck (SCCHN) (Andre et al., 2018). Since SCCHN strongly expressed HLA-E and NGK2A, the authors’ next step was to investigate SCCHN more closely to see if it could be a viable target for NGK2A blockade. They used FACS analysis to look at the cells that infiltrated the SCCHN tumors and found a high number of CD8+ and NK cells that expressed PD-1 and NKG2A (Andre et al., 2018). This result suggested that a NGK2A blockade in combination with another checkpoint inhibitor (such as anti-PD-1/PD-L1 antibodies) could work well against SCCHN tumors.
After determining SCCHN could be an effective target for a NGK2A blockade and demonstrating that the NGK2A blockade has strong antitumor effects in mice, the authors sought to examine if it would be effective in humans. They generated a human version of the anti-NGK2A antibody (named monalizumab) and combined it with K562 tumor cells (human leukemia cells) forced to express HLA-E. Normal tumor cells activate NK cells because they don’t express HLA-E but tumor cells that do express HLA-E activate NK cells at a much lower frequency (Andre et al., 2018). The authors observed that HLA-E-expressing tumor cells activated normal levels of NK cells after the monalizumab was added. Andre et al (2018) had previously demonstrated that anti-NGK2A and anti-PD-L1 antibodies had an enhanced antitumor effect in mice so the authors tested whether this was true in humans as well. To determine this, they added monalizumab with or without durvalumab (an antibody that binds PD-L1 and allows T cells to function) to tumor cells that expressed HLA-E and PD-L1 and do not effectively activate NK cells. The authors observed that monalizumab increased the frequency of active NK cells but noted that the two antibodies had additive effects when combined. In addition, the authors also investigated the effect of combining monalizumab and durvalumab on CD8+ activity since their previous results demonstrated that about half of the CD8+ cells that infiltrated the tumor expressed the inhibitory receptor NGK2A. They found that the combination of the two drugs improved production of the cytokine IFN-ℽ (a signalling molecule) and the killing ability of CD8+ cells (Andre et al., 2018). These results collectively indicated that monalizumab promotes the antitumor activity of NK cells and CD8+ T cells in humans.
Finally, the authors established a clinical trial to evaluate the effectiveness of monalizumab in cancer patients. They found that treatment with monalizumab and cetuximab (the standard drug used to treat SCCHN) reduced tumors in 8 of 26 patients while 14 of 26 exhibited stable disease (Andre et al., 2018). This result was a significant improvement upon the outcomes when only cetuximab is used on its own and indicated combination therapy of monalizumab with cetuximab has promise for SCCHN patients.
This paper demonstrates several key conclusions regarding the antitumor effects of anti-NGK2A antibodies. The authors show that blocking NKG2A promotes antitumor activity in mice by activating NK and T cells functions. In addition, they also show that combined blocking of NKG2A and PD-1/PD-L1 enhances the antitumor effect. Finally, they show that a human anti-NGK2A antibody (termed monalizumab) promotes an antitumor effect in human NK and CD8+ T cells and is more effective in treating SCCHN than the standard drug when monalizumab used in combination with the standard drug. Future directions could involve an investigation into whether other forms of disease are affected by NKG2A expression and if they may benefit from a NKG2A blockade.
References
André, P., Denis, C., Soulas, C., Bourbon-Caillet, C., Lopez, J., Arnoux, T., ... & Rossi, B. (2018). Anti-NKG2A mAb is a checkpoint inhibitor that promotes anti-tumor immunity by unleashing both T and NK cells. Cell.
Sagiv-Barfi, I., Kohrt, H. E., Czerwinski, D. K., Ng, P. P., Chang, B. Y., & Levy, R. (2015). Therapeutic antitumor immunity by checkpoint blockade is enhanced by ibrutinib, an inhibitor of both BTK and ITK. Proceedings of the National Academy of Sciences, 201500712.
Ravetch, J. V., & Lanier, L. L. (2000). Immune inhibitory receptors. Science, 290(5489), 84-89.
Seidel, J. A., Otsuka, A., & Kabashima, K. (2018). Anti-PD-1 and Anti-CTLA-4 Therapies in Cancer: Mechanisms of Action, Efficacy, and Limitations. Frontiers in oncology, 8, 86.
No comments:
Post a Comment