Shaheen R. Alanee, MD, MPH, MBA, FACS
Disclosures: Merck & Co.: Funding for research on anti-PD1 in bladder cancer

Senior Staff Physician

Department of Urology

Henry Ford Health System

Detroit, Michigan

Matthew J. O’Shaughnessy, MD, PhD
Disclosures: Nothing to Disclose

Urology Service, Department of Surgery

Memorial Sloan Kettering Cancer Center

New Yorker, New York

* This AUA Update addresses the Core Curriculum topic of Oncology – Adult: Bladder Neoplasms

2017 vol-36-lessons-31.pdf
dPub

Learning Objective:At the conclusion of this continuing medical education activity, the participant will be familiar with the role of the immune system in localized and metastatic bladder cancer, and have a working knowledge of current and emerging immune based therapies for bladder cancer.

Key Words
urinary bladder neoplasms; carcinoma, transitional cell; immunotherapy; programmed cell death 1 receptor; BCG vaccine

INTRODUCTION

Immunotherapy has developed into one the most active areas of investigation in oncology, and applications for urothelial carcinoma are among the most promising. Not only has bacillus Calmette-Guérin treatment of non-muscle invasive bladder cancer been one of the most successful cancer immunotherapies to date, recent FDA approval of a programmed cell death 1 checkpoint inhibitor has been one of the most signifi cant advances in bladder cancer therapy in the last 30 years. We review the immunobiology of bladder cancer including the role of the immune system in localized and advanced bladder cancer, describe the indications for current immune based therapies for bladder cancer, and discuss areas of active investigation and emerging therapies.

Bladder cancer is an ideal target for immunotherapy because several features of the disease make it uniquely suitable for treatment with immune agents. It is easy to deliver therapeutic agents directly to the primary tumor intravesically while limiting systemic toxicity. Response to treatment can be assessed directly by cystoscopy, and it is possible to measure immune responses by analyzing cytokines and immune cell populations in urine. Furthermore, bladder cancer is known to have a high mutation rate, which increases antigenicity and susceptibility to an activated immune response.{{5003}} These features have led to the development of successful immunotherapies that are currently used for localized and advanced bladder cancer, with more in development. 

Components of an antitumor immune response. Effective antitumor immune responses require complex and coordinated action by the host immune system. Several key elements are
necessary for successful cell mediated tumor rejection, which underlies the therapeutic immune response against cancers. First, tumor associated antigens require processing and uptake by host antigen presenting cells such as dendritic cells or macrophages, which in turn become activated and display the antigens in major histocompatibility complex molecules. Next, the activated antigen presenting cells transition to lymph nodes where they function to either activate or suppress effector cells of the immune system. Finally, effector cells transition to the tumor microenvironment where they mediate the antitumor response. The major effectors of the antitumor immune response are Th1 CD4+ T lymphocytes, Th1 cytokines, cytotoxic CD8+ T lymphocytes and natural killer cells (Figure 1).

At each step of the antitumor response, complex regulation and feedback from the tumor and the tumor microenvironment can either enhance or impair tumor rejection. The antitumor response can be negatively regulated by production of immunosuppressive cytokines that inhibit effector cell recruitment and activation. Antitumor responses are also regulated through the effects of immunosuppressive cell populations (including T regulatory cells) and cells of the innate immune system (including myeloid derived suppressor cells, tumor associated macrophages and natural killer cells). Finally, tumor cells may impair cytotoxic effector cells of the immune system through direct cell contact. A key regulatory pathway that modulates the antitumor immune response is the immune checkpoint family of cell surface molecules. Ligand activation of these immune checkpoint molecules, which include cytotoxic T lymphocyte associated antigen 4 (CTLA-4) and PD-1, inhibits T cell function.

Recent insights into the mechanisms of tumor immunology have fueled interest in the development of new strategies for immune therapy of cancer. Currently, the 2 approaches to generate effective antitumor responses are 1) positive feedback to stimulate the immune response and 2) blocking negative regulatory pathways such as checkpoint molecules to prevent downregulation of the antitumor response. Strategies to promote the antitumor immune response by both approaches are used and currently under investigation in various stages of bladder cancer (Figure 2).

Immunobiology of intravesical BCG treatment. The anticancer effect of BCG has been under investigation for more than 50 years.{{5004}} A role for BCG immunotherapy in bladder cancer was established in the seminal work of Morales et al in 1976 when they reported the effects of BCG in 9 patients with NMIBC.{{5005}} Subsequent randomized controlled trials in patients with medium and high risk NMIBC showed that BCG signifi - cantly reduced tumor recurrence and progression (defined as requiring cystectomy) compared to transurethral resection of the bladder tumor.{{5006}},{{5007}}BCG is now the standard of care for high risk non-muscle invasive disease, including carcinoma in situ, high grade (Ta) papillary tumors and tumors invasive to the lamina propria (T1). Although immunotherapy in the form of intravesical BCG has been used in the management of localized bladder cancer for 40 years, the mechanism of action is still under investigation. What appears clear, however, is that BCG effi cacy requires an intact immune system, live BCG bacteria and contact with bladder cancer cells.{{5008}},{{5009}}

BCG attachment to urothelial cells via the fi bronectin containing extracellular matrix is required for initiation of the antitumor response.{{5010}} The live BCG mycobacterium is internalized by bladder cells through macropinocytosis (a form of endocytosis), a process promoted by the presence of certain mutations such as PTEN loss or oncogenic RAS.{{5011}} Despite response rates of up to 70% with BCG treatment, some patients do not respond and it is possible that mutations in these genes are a mechanism that may predict susceptibility to BCG treatment. Following macropinocytosis, BCG uptake leads to interleukin 6 secretion{{5012}},{{5013}} and can also result in increased antigen presentation by bladder cells,12 triggering the immune response to BCG. 

Within hours of BCG treatment, the host immune system is activated and a local immune response is evident in activated immune cell populations in the urine and bladder wall.{{5015}},{{5016}}CD4+ and CD8+ T lymphocytes, natural killer cells and granulocytes are key to the cellular immune response.{{5017}} In addition, numerous cytokines and chemokines are released into the urine. The response is not strictly a Th1-type response, but cytokines that define the Th1 response are present in urine and systemically after bCG treatment. Th1 cytokines include interleukin 2, interleukin 12 and interferon-γ. Other cytokines that play a role in the local antitumor response with BCG include interleukin 6, interleukin 8, interleukin 18, tumor necrosis factor and tumor necrosis factor related apoptosis inducing ligand.{{5018}},{{5019}},{{5020}} In addition to the local immune response, there is evidence that BCG therapy induces a systemic immune response. For example, serum interleukin 2 and interferon-γ levels increase in patients treated with intravesical BCG . Furthermore, in up to 40% of patients treated with intravesical BCG a previously negative tuberculin skin test is converted which is predictive of durable response.{{5021}},{{5022}}

Immunobiology of checkpoint blockade. Checkpoint blockade is an area of growing interest across many areas of oncology, including urological oncology. The first “checkpoint inhibitor” approved for patients with cancer (previously treated metastatic melanoma), ipilimumab, is a monoclonal antibody that prevents the interaction of CTLA-4 with the costimulatory ligands B7-1 and B7-2.{{5023}} CTLA-4 is normally present on activated T cells and when ligated, it antagonizes the interaction between CD28 on T cells and B7 on antigen presenting cells. This ligation of CTLA-4 inhibits the secondary costimulatory signal that antigen presenting cells provide to T cells, effectively downregulating the effector T cell response.{{5024}},{{5025}} As a consequence of widespread B7-1 and B7-2 expression, CTLA-4 has a broad role in modulating activation of T cells. In addition to blocking the downregulation of effector function of tumor infiltrating lymphocytes,24 ipilimumab may also deplete T regulatory cells, creating a powerful antitumor immune response.{{5027}},{{5028}} However, although ipilimumab elicits strong antitumor responses, the broad immune activation can lead to significant immune related toxicity. 

PD-1 is another important immune checkpoint expressed on T cells after activation via the T-cell receptor. PD-1 is thought to play a dominant role in the suppression of T-cell responses in the setting of constitutive antigen expression such as the tumor microenvironment.{{5029}} PD-1 is expressed on tumor infiltrating lymphocytes in multiple different cancers{{5030}},{{5031}},{{5032}} but it can also be expressed on B cells, natural killer T cells, dendritic cells and activated monocytes.{{5033}} The ligands for PD-1, PD-L1 and PD-L2 are expressed in a variety of normal tissues{{5034}},{{5035}} but also on human cancers including bladder and kidney cancer.{{5036}},{{5037}}PD-L1 can be expressed on tumor infiltrating immune cell populations. Expression of PD-L1 is induced by inflammatory cytokines including interferon-γ, and it is a critical regulator of mechanisms of tumor escape from immune recognition as a response to the inflammatory immune infiltrate.{{5036}} Because PD-L1 is not constitutively expressed in normal tissues but is expressed in response to inflammatory conditions, it is believed to negatively regulate ongoing immune responses rather than systemic regulation of autoreactive T-cell responses like CTLA-4.{{5038}} For this reason, targeting the PD-1 pathway is a rational target for cancer immune therapy (Figure 3). 

Immunotherapy for non-muscle invasive bladder cancer

BCG. BCG has been widely used for many years as an immunotherapy for high risk NMIBC and is currently the standard of care for the treatment of moderate and high risk superficial bladder cancer after endoscopic resection.{{5039}},{{5040}}BCG has been shown to reduce the risk of recurrence and delay disease progression in patients with high risk NMIBC.{{5041}},{{5042}} Its maximum benefit is attained through an initial treatment followed by maintenance therapy stratified in its intensity by the level of risk of the tumor recurring after an induction course. Although consideration of maintenance BCG is recommended by the AUA guidelines, there is a lack of consensus about the benefit of maintenance since a survival benefit has not been established, and there is a high rate of treatment discontinuation because of side effects and patient intolerance.{{5043}} To reduce BCG treatment failures and improve therapy, recombinant BCG has been developed with strains that express various cytokines, although the effectiveness of these modifications has not been established.{{5044}} Intravesical Mycobacterium phlei cell wall nucleic acid complex is a BCG related treatment that has shown modest activity in patients with high risk NMIBC after failure of BCG.{{5045}} Despite some evidence of activity in these cases, no modifications to the original BCG therapy have yet achieved FDA approval. 

Cytokine therapy. Cytokines are proteins produced by normal and cancer cells in response to pathogens that have a wide array of immunomodulatory effects. The cytokine with the most demonstrated potential in bladder cancer therapy is interferon α-2b, which was examined as an intravesical monotherapy and in combination with BCG in patients with NMIBC who are BCG naïve. However, interferon-α-2b has been consistently less effective than BCG and did not add benefit to BCG in the primary treatment setting.{{5046}} Interferon α-2b has also been evaluated for use after BCG failure. In a large single arm study of combination therapy in 1007 patients the recurrence free rate was 45% for those in whom BCG failed, although it was much less effective in patients who had received 2 prior courses of BCG. Based on these data, BCG plus interferon α-2b could be used as a treatment alternative for patients after BCG fails.{{5047}},{{5048}}

Oncolytic viruses. Oncolytic viruses selectively replicate in tumor cells causing their death and releasing tumor antigens that stimulate the immune system against other uninfected cancer cells. Two viruses are currently in advanced stages of development and testing. The first is CG0070, an oncolytic adenovirus that selectively replicates in and destroys retinoblastoma pathway deficient cells, and carries the gene for granulocyte-monocyte colony-stimulating factor, an immunomodulatory cytokine. In a phase I study 35 subjects received intravesical treatments and 49% had complete response.{{5049}} The response rate was even higher (>80%) in patients with high retinoblastoma status. A phase III study using this virus is ongoing at multiple centers in the United States (NCT02365818).

The second virus is rAd-IFN/Syn3, which is a non-replicating recombinant adenovirus vector encoding the interferon α-2b gene combined with Syn 3, a clinical surfactant excipient that enhances the adenoviral mediated transduction of urothelial cancer cells (the process by which foreign DNA is introduced into the tumor cells via the viral vector). The response rate to this virus was 43% in patients with detectable interferon α-2b in a phase I trial.{{5050}} A phase II study evaluating intravesical administration of rAd-IFN/Syn3 in patients with BCG refractory or relapsed bladder cancer recently completed accrual but has not yet been reported (NCT01687244). 

Vaccine therapy. Cancer vaccines are designed to elicit immune responses to antigens consistently expressed in tumors cells. Antigen targets under investigation include human epidermal growth factor receptor 2 (HER2), cancer-testis antigens, carcinoembryonic antigen and MUC1. 

DN24-02 is an autologous cellular immunotherapy vaccine designed to target the HER2 receptor, and results from a randomized phase II study of patients with high risk HER2+ invasive urothelial carcinoma are pending (NCT01353222). This vaccine consists of autologous peripheral blood mononuclear cells, including antigen presenting cells that are activated ex vivo with a recombinant fusion protein consisting of HER2 linked to granulocyte-monocyte colony-stimulating factor and then subsequently infused back into the patient. Another vaccine against HER2, AdHER2/neu, is being evaluated at the National Institutes of Health Clinical Center as part of a phase I trial (NCT01730118) in patients with HER2+ metastatic solid tumors including bladder cancer.

Cancer-testis antigens are highly expressed in urothelial cancers but absent from normal tissue, making them a potential target for vaccine development.{{5051}} Vaccines with the cancertestis antigen MAGE-A3 are under development for NMIBC as well as muscle invasive bladder cancer, and have been tested in phase I and phase II trials that have completed recruitment with results pending (NCT01498172, NCT01435356).

Finally, MUC1 and carcinoembryonic antigen are being investigated as potential targets for poxviral based vaccine therapy. PANVAC, a cancer vaccine therapy that contains transgenes for the tumor associated antigens MUC1 and carcinoembryonic antigen (which are overexpressed in urothelial carcinoma) as well as 3 human T-cell costimulatory molecules (B7-1, intracellular adhesion molecule 1 and leukocyte function associated antigen), is in a phase II study determining efficacy with BCG therapy vs BCG alone in patients with high grade NMIBC that did not respond to prior BCG therapy (NCT02015104).

Checkpoint inhibitors for NMIBC. No checkpoint inhibitors are currently approved for NMIBC but this is an area of active investigation. Immune checkpoint receptors, including PD-1, are upregulated on activated T cells and function to negatively regulate immune responses. PD-L1, the ligand for PD-1, is highly expressed in BCG induced granulomas in patients who do not respond to BCG, suggesting that this immune checkpoint may be a key factor for BCG treatment failure.35 Studies with PD-1 checkpoint inhibition are under way, including a phase 1 study using pembrolizumab, a PD-1 checkpoint inhibitor, alone or in combination with BCG for patients with high risk NMIBC after failure of BCG induction therapy. The preliminary results of the trial were anticipated in early 2017 (NCT02324582). A phase II trial currently recruiting participants will evaluate the response to pembrolizumab monotherapy in patients with NMIBC that has not responded to BCG therapy (NCT02625961). A phase IB/II trial, also recruiting participants, will study atezolizumab, an anti-PD-L1 antibody, alone and in combination with BCG in patients with high risk NMIBC (NCT02792192).

immunotherapy for advanced bladder canceR

The objective responses to checkpoint inhibition by atezolizumab led to FDA approval in 2016, which was considered a major breakthrough, as there had been no new approved agents for advanced urothelial cancer in nearly 30 years.

Checkpoint inhibition for bladder cancer was first studied in a phase I trial that included 12 patients with invasive urothelial cancer who received 2 doses of ipilimumab before cystectomy.{{5052}} The study demonstrated tolerability of the regimen with the majority of adverse events consisting of grade 1-2 toxicities, although surgery had to be delayed in 2 cases. The investigators also reported an increased presence of CD4+ T cells in the tumor and systemic circulation. A phase II trial evaluating ipilimumab in combination with gemcitabine + cisplatin (the current standard of care) for advanced or metastatic urothelial carcinoma is under way (NCT01524991). Based on data showing efficacy of ipilimumab with anti-PD-1 agents in other advanced cancers, further trials with this combination are opening or currently recruiting participants. Anti-CTLA-4 therapy is still under investigation and not currently approved for treatment of advanced urothelial cancer. 

PD-1 checkpoint inhibitors have significant activity in advanced bladder cancer and a favorable side effect profile compared to ipilimumab. The first phase I study of a PD-1 checkpoint inhibitor was a successful multicenter open label trial of atezolizumab (an engineered anti-PD-L1 antibody made by Genentech) which demonstrated a 25% objective response rate in 67 heavily pretreated patients with metastatic bladder cancer who had limited treatment options.{{5053}} Responses were rapid and ongoing at the data cutoff. Treatment was well tolerated with no grade 4-5 treatment related adverse events, and only 4% of patients experienced grade 3 adverse events. These impressive results in a group of patients with refractory disease earned atezolizumab an FDA Breakthrough Therapy designation in 2014, representing a first for bladder cancer.{{5054}}

The follow-up phase II trial, IMvigor 210, looked at the effect of atezolizumab in patients with locally advanced or metastatic urothelial carcinoma that progressed during or following platinum based chemotherapy. Analysis of IMvigor 210 revealed an overall objective response rate of 15%, with ongoing responses in 84% of responders at the time of data cutoff.{{5055}} Grade 3-4 immune related adverse events occurred in 5% of patients. Atezolizumab is currently approved for the treatment of locally advanced or metastatic urothelial carcinoma that has worsened during or following platinum containing chemotherapy, or within 12 months of receiving platinum containing chemotherapy either before (neoadjuvant) or after (adjuvant) surgical treatment. A phase III trial, IMvigor 010, will evaluate adjuvant atezolizumab vs observation after cystectomy in patients with high risk muscle invasive bladder cancer (NCT02450331). The combination of atezolizumab plus gemcitabine/carboplatin vs gemcitabine/carboplatin alone is being tested in cisplatin ineligible patients with metastatic or locally advanced urothelial cancer in IMvigor 130, a phase III trial (NCT 02807636).

Pembrolizumab (an anti-PD-1 antibody made by Merck) is another PD-1 checkpoint inhibitor with demonstrated activity in advanced bladder cancer and an overall response rate of 25% in a phase I study (NCT01848834). Grade 3-4 immune related adverse events occurred in 15% of patients.{{5056}} This same drug is currently being tested in combination with neoadjuvant gemcitabine + cisplatin chemotherapy for patients with muscle invasive bladder cancer (NCT02690558) and for locally advanced or metastatic bladder cancer or as a second line treatment in multiple clinical trials (NCT02443324, NCT02335424, NCT02452424, NCT02500121). KEYNOTE-045, a pivotal phase III trial with pembrolizumab in patients with metastatic or locally advanced urothelial cancer who experienced disease progression after platinum based chemotherapy, is ongoing (NCT022566436).

A third checkpoint inhibitor, nivolumab (an anti-PD-1 antibody made by Bristol-Myers Squibb), had activity in a phase I/II trial in which 24% of patients with recurrent metastatic urothelial carcinoma achieved an objective response. Grade 3-4 immune related adverse events affected 22% of patients.{{5057}} Combination therapy with nivolumab and ipilimumab for advanced or metastatic genitourinary or other solid tumors is under investigation (NCT01928394 and NCT02496208).

Finally, durvalumab, (MEDI4736), an investigational human monoclonal antibody directed against PD-L1, was recently granted breakthrough therapy designation by the FDA for the treatment of patients with PD-L1 positive inoperable or metastatic urothelial bladder cancer whose tumor progressed during or after 1 standard platinum based regimen.

Predicting response to PD-1 inhibitors. Expression of PD-L1 on tumor cells has been proposed as a biomarker of response to PD-1 inhibition. Although in some studies there is a higher rate of response in patients with high PD-L1 expression on tumor infiltrating immune cells, a proportion of patients without PD-L1 expression still respond to inhibition. For example, in the phase 1 atezolizumab study objective responses were seen in 43% of patients with high PD-L1 expression on tumor infiltrating immune cells assessed by immunohistochemistry compared to 11% of patients with low PD-L1 expression.{{5053}} No correlation was found between response and tumor PD-L1 expression. Similarly, in the IMvigor 210 study response rates were 26% for high PD-L1 expression on tumor infiltrating immune cells compared to 15% overall. 

PD-L1 is an imperfect predictor of response to checkpoint blockade because of the effects of prior therapy, and expression is variable and modulated by inflammatory cytokines.{{5058}} Characterization of PD-L1 expression is also challenging due to variability in antibodies used for assessment, differences in the definition of PD-L1 positivity and use of proprietary detection techniques, as most protocols were developed for diagnostic purposes and remain proprietary. Finally, recent research shows PD-L1 expression on infiltrating myeloid and T cells but not on tumor cells to be a better predictor of response to anti-PD-1 agents in patients with cancer.{{5059}} Currently, no biomarker for anti-PD1 response is widely validated or available for use in clinical practice.

Side effects of immune checkpoint inhibitors and their managementCheckpoint inhibitors are associated with a unique spectrum of side effects, called immune related adverse events, with which clinicians should be familiar. These side effects are due to the immune mechanism of action and may be related to cross-reactivity between tumor neoantigens and normal tissue antigens. Early recognition and initiation of treatment are key to reducing the risk of serious complications from immune related adverse events. The organ systems most frequently affected are skin (34%), gastrointestinal tract (13%), endocrine glands (8%) and liver (4%) but they can occur in other organ systems.{{5055}},{{5060}} Although immune related adverse events with single agent administration of anti-PD-1 or anti-PD-L1 antibodies are frequent (affecting 60% of patients), only 10% of these side effects are grade 3-4 and in only 3% of patients are the side effects severe enough to require discontinuation of treatment. Most immune related adverse events develop within 16 weeks of starting therapy and resolve within a few weeks after cessation of the drug. The incidence of grade 3-4 immune related adverse events is significantly higher with CTLA-4 inhibition alone (33%) or in combination with PD-1 inhibition (29% to 61%).{{5061}}

Systemic: Fatigue is common in patients treated with immune checkpoint inhibitors but grade 3 fatigue occurs in only 2% of patients and most can tolerate it with no interruption in therapy.{{5062}} Fever, chills, flushing, alterations in blood pressure, pruritus, urticaria and dyspnea have been observed in up to 6% of patients during infusion, and these can be treated with acetaminophen or nonsteroidal anti-inflammatory drugs. Patients with a history of infusion reaction may benefit from premedication with antihistamines.

Dermatologic: Dermatologic toxicities associated with PD-1 pathway blockade include various types of rash, pruritus, alopecia, urticaria, vitiligo, exfoliation and exacerbation of prior skin illnesses like psoriasis. These side effects occur in up to 20% of patients within 3 to 4 months after initiation of therapy. Treatment may include topical steroids with antihistamine if pruritus
is prominent.{{5063}}

Gastrointestinal: Gastrointestinal toxicities secondary to checkpoint inhibition can range from mild diarrhea to severe colitis that requires intensive therapy and discontinuation of treatment. Although gastrointestinal side effects can affect up to 25% of patients treated with anti-PD-1 therapies, only 1% of these events amounts to grade 3-4 toxicity, and they are much less common compared to the gastrointestinal side effects of the anti-CTLA-4 antibody ipilimumab. When diarrhea occurs within the first few months after initiation of immune checkpoint inhibitor therapy, infectious causes need to be ruled out and colonoscopy should be performed to investigate inflammatory changes in the colon. Grade 1-2 bowel toxicity can be managed with rehydration. Patients with grade 2 events that are worsening or persist for >5 days should stop treatment and receive oral corticosteroids. Intravenous corticosteroids may be required in patients with grade 3-4 gastrointestinal toxicity.{{5064}}

Hepatotoxicity: Hepatotoxicity in patients treated with checkpoint inhibitors most often manifests as elevation in liver enzymes, with grade 3-4 abdominal pain, nausea and vomiting in just 1%. Treatment includes supportive measures and corticosteroids. Serial liver function testing is recommended at baseline and every few months during follow-up.{{5064}}

Immune Mediated Pneumonitis: Severe grade 3-4 pneumonitis after anti-PD-1 therapy is rare (3% to 4%) but it can be fatal in 0.5% of cases. This side effect develops within 2 to 3 months after treatment initiation in patients with urothelial carcinoma. Patients present with shortness of breath, cough and radiographic changes that range from the appearance of ground glass to bronchiectasis and pleural effusion.{{5065}} Pulmonology should be consulted and treatment withheld for grade 2 events and discontinued for grade 3 or higher. Supportive measures and corticosteroids are the mainstay of treatment, with some patients requiring more aggressive immunosuppressive therapy with infliximab or mycophenolate mofetil.

Endocrine: The most commonly reported endocrine related side effects of treatment with anti-PD-1 drugs include type I diabetes mellitus (9%), hypothyroidism (8%), hyperthyroidism (2.5%), adrenal insufficiency (2%) and hypophysitis (0.5%). Severe endocrinopathy has been observed in less than 2% of patients. It is recommended that endocrinology be consulted to manage these cases. Treatment includes discontinuation of checkpoint inhibitors for patients with grade 2 or higher events, hormonal replacement and corticosteroid therapy as appropriate.{{5066}}

Neurological: Although rare (<1%), aseptic encephalitis, Guillain-Barré syndrome, limbic encephalitis, posterior reversible encephalopathy syndrome and transverse myelitis have been reported with immune checkpoint inhibitor therapy.{{5067}},{{5068}} Neurology should be consulted and treatment stopped for any grade of neurological side effects. Imaging to rule out brain metastasis from the primary malignancy as a cause of neurological changes should also be considered.

Renal Dysfunction: Acute interstitial nephritis has been reported with anti-PD-1 drug use in 2% to 3% of patients. Management includes nephrology consultation, corticosteroid therapy and treatment cessation for high grade events.{{5069}}

Contraindications to immune checkpoint inhibitors. While no absolute contraindications to immune checkpoint inhibitors have been identified, it is important to monitor patients for signs of severe side effects and discontinue treatment when appropriate as discussed previously. These drugs may cause embryofetal toxicity based on their mechanism of action and, therefore, women of reproductive potential are required to use highly effective contraception during treatment and for at least 4 months after the last dose.

Cost. Checkpoint inhibitors are generally very expensive drugs. Wholesale prices per milligram are estimated to be $28.78 for nivolumab, $51.79 for pembrolizumab and $157.46 for ipilimumab putting a typical course of treatment with nivolumab at about $100,000 per patient. For responders, checkpoint inhibitors are often continued indefinitely or until toxicity requires discontinuation. For these patients, costs may be even higher (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4570079/ Accessed 1/19/2017).

Future directions

Immunotherapy has a clear role in the treatment of NMIBC and advanced bladder cancer. For high risk NMIBC there is a measurable benefit to intravesical BCG immunotherapy. However, there is a need to develop new strategies to treat high risk NMIBC due to the possibility of future limitations in BCG availability and because in some patients disease fails to respond or recurs despite BCG treatment. Much work is under way to improve upon this situation. Identification of immune biomarkers that predict BCG response might include variability in host immune cell phenotype and/or cytokines, or features of BCG uptake by urothelial cells that favor a response. The identification of antigens presented to T cells during BCG immunotherapy could also improve delivery of BCG therapy. Currently, what is not well defined is whether target antigens include either BCG specific antigens, tumor associated antigens or a combination of both. Finally, it may be possible to augment the immune response to BCG in combination with cytokines or checkpoint inhibitors, and these are areas of ongoing investigation.

PD-1 checkpoint blockade is a major breakthrough in the treatment of advanced stage urothelial cancer and as work in this field continues, it is likely that the indications for checkpoint blockade will expand. Checkpoint blockade may even become the preferred treatment modality for advanced stage urothelial cancer. PD-1 blockade combined with blockade of other immune checkpoints is a strategy being explored. Potential checkpoints include lymphocyte-activation gene 3, T-cell immunoglobulin mucin-3 and B7-H3. Lymphocyte-activation gene 3, which is structurally similar to CD4 and binds Class II major histocompatibility complex molecules with high affinity, is upregulated on activated CD4+ and CD8+ T cells, and serves as a negative regulator of T-cell homeostasis.{{5070}},{{5071}} PD-1 blockade combined with lymphocyte-activation gene 3 blockade may synergize to be more effective than either agent alone, and this is an area of ongoing investigation (NCT01968109).{{5072}}

T-cell immunoglobulin mucin-3 is expressed on bladder cancer cells and tumor infiltrating lymphocytes from patients with bladder cancer, correlates with PD-1 expression and may be associated with adverse clinical outcomes.{{5073}} B7-H3, a member of the B7 super family, is a costimulatory molecule that has inducible expression on T cells, monocytes and dendritic cells. B7-H3 can upregulate or downregulate immune responses.{{5074}},{{5075}} In urothelial cancer B7-H3 is expressed across tumor stage and is increased in BCG recipients.{{5076}},{{5077}} It is speculated that combination blockade of these checkpoints may further enhance the antitumor responses of PD-1 blockade.

Finally, it may be possible to modulate the tumor microenvironment to enhance the antitumor immune response. A strategy being considered is combining radiation to the primary tumor with checkpoint blockade. Several clinical trials are under way which have been designed to evaluate this combination in muscle invasive or metastatic bladder cancer (NCT02560636, NCT02621151, NCT02662062).