Immuno-oncology is a rapidly growing therapeutic field that embraces the concept of modulating the immune system to recognize tumor cells and target them for destruction—by either harnessing the effects of the immune system or preventing the evasion of tumor cells from therapeutic targeting.
The cancer immunity cycle consists of a complex interplay between tumors and immune cells that culminates in an immune response that kills cancererous cells (Figure 1).1 Tumors can prevent this interplay if they maintain a suppressive microenvironment. This microenvironment can also thwart anticancer drugs.2 Consequently, overcoming or remodeling the immunosuppressive microenvironment that is found in many solid tumors is a significant task.
Over the past several years, several immuno-oncology modalities have emerged. These modalities, which include checkpoint inhibition, adoptive T-cell therapy (ACT), and cancer vaccines, are often designed to account for the many proteins that are expressed on cell surfaces. Such proteins may allow malignant cells and lymphocytes to evade immune responses.
Proteins of interest include the cytotoxic T lymphocyte antigen 4 (CTLA-4) receptor and the programmed cell death-1 (PD-1) receptor along with its ligand (PD-L1). CTLA-4 was the first immune checkpoint receptor to be identified and validated as a drug target, and it has progressed into clinical trials for a variety of cancers.
Ipilimumab—an antibody targeting CTLA-4 and approved by the FDA for use in patients with melanoma—works by inhibiting the process of immune suppression in tumors and facilitating T-cell activation against tumor cells. Clinical response rates have been remarkable in some tumor types, and the number of indications susceptible to the therapy is increasing rapidly.
Antibodies targeting PD-1 and PD-L1 (nivolumab and pembrolizumab) have also been approved to treat several types of tumors including melanoma, lung cancer, and bladder cancer. Utilizing a combination of checkpoint inhibitors could improve long-term survival rates, increasing them to levels approaching 60% in some cancers. The hope is that novel and appropriately scheduled immune checkpoint inhibitor combinations, along with appropriate tumor sequencing strategies and patient stratification, could increase survival rates in the future, bringing them closer to 80%, or pushing them even higher.3
Adoptive T-Cell Therapy
In ACT, T cells activated against tumor-specific antigens are isolated from the patient, expanded ex vivo, and then reintroduced to the patient. This form of treatment marks the beginning of a new era in cancer therapy, providing a transformative way to combat complex diseases. In recent years, clinical trials using chimeric antigen receptor (CAR) T cells engineered to recognize B-cell cancers (via a specificity for the B-cell antigen CD19 therapy) have shown high rates of response (70–90%), along response times of unprecedented durability in acute and chronic leukemia.4
Cancer vaccines are aimed at triggering an immune response. Unlike traditional vaccines, cancer vaccines do not aim to prevent the development of the cancer. These therapies are designed to stimulate the body’s immune system to mount a more robust and effective attack against cancer cells that are already established or circulating in the body—ultimately increasing the specificity of the immune response. This approach generates specific vaccines for certain types of cancers; that is, cancer vaccines are designed to heighten the response to the relevant antigens on surfaces of cancer cells.
Therapeutic cancer vaccines may act via dendritic cells, which are specialized immune cells that can “teach” T cells by identifying neoantigens. For example, immune cells may be removed from the patient and developed into dendritic cells that are specific to the type of cancer present in the patient, then returned into the patient with the goal of inducing a better T-cell response.
In 2010, the FDA approved the first cancer vaccine, Provenge (sipuleucel-T). This vaccine, for castration-resistant prostate cancer, extends overall survival in patients, but it does not have any effect on the time to disease progression, thus highlighting the scope for development of more efficacious therapies.5
Comprehensive characterization of compounds in the early stages of the drug discovery process can provide insights to improve efficacy downstream and improve the likelihood of successful compounds in the clinic. The scientists at Charles River Laboratories have established a powerful translational immuno-oncology platform with the capability of progressing biologics or small-molecule modulators of the immune response from in vitro to in vivo assays using primary human immune cells and mouse variants of current checkpoint inhibitors and small molecules of in vivo research models.
The platform is supported by an internal blood donor panel which ensures highly reproducible data and high-quality immune cells that are prepared immediately once sampled. The assays currently available capturing the main phases of the cancer immune cycle can be found on Charles River’s immuno-oncology website.
Charles River’s translationally focused immuno-oncology platform enables oncology researchers to rapidly assess the immune modulatory function of therapeutic modalities in high-throughput development. The platform has been expanded to determine the effects of activated immune cell populations on tumor cell spheroid cultures (Figure 2a). Moreover, the platform can be used to assess T-cell activation (Figure 2b), proliferation, and cytokine release, as well as T-cell exhaustion, T-cell migration, and macrophage phagocytosis (Figure 2c). It can also help define diverse aspects of microenvironmental control for immune responses—allowing the high-bar assessment of therapeutics in complex biological assays.
The platform has been validated with standard-of-care chemotherapeutics, including anti-CTLA-4, anti-PD-1, and a selection of small-molecule inhibitors of targets known to modulate immune responses, including indoleamine-pyrrole 2,3-dioxygenase (IDO) inhibitors.
Ex vivo analysis of activated mouse splenocyte response to checkpoint inhibitors, measured as cytokine release, and modulation of immune cell populations, as measured by flow cytometry, supports the translation of important compounds from the bench to preclinical models.
Syngeneic mouse tumor models have frequently been used to profile immune responses in tumors; the scientists at Charles River have optimized and profiled existing checkpoint inhibitors to support immuno-oncology drug discovery using mouse and rat antibody variants of anti-CTLA-4 and anti-PD-1.
To confirm the translational development of our platform, we have refined and optimized humanized mouse models using subcutaneous implanted patient-derived xenografts (PDXs) with human engraftment via CD34+ hematopoietic stem cells in NOG mice—which have been profiled with the current standard-of-care immunotherapies including anti-CTLA-4 and anti-PD-1.
Charles River’s screening platform as illustrated in Figure 3 will support the translation of compounds from in vitro primary immune cell assays to modulation of mouse immune cell populations in ex vivo splenocytes and tumors. We anticipate that this platform will support the identification and development of the next generation of checkpoint inhibitors or small-molecule inhibitors of tractable kinase, phosphatase, and chemokine targets.
Shilina Roman (email@example.com) is group leader, integrated biology, discovery services and Martin O’Rourke, Ph.D., is senior director, oncology in vitro biosciences, integrated drug discovery at Charles River Laboratories.
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5. Kantoff PW, Higano CS, Shore ND, et al. Sipuleucel-T immunotherapy for castration-resistant prostate cancer. N. Engl. J. Med. 2010; 363(5): 411–422.