Chinese Journal of Cancer
`
`Immune checkpoints in cancerclinicaltrials
`
`Elad Sharon’, Howard Streicher’, Priscila Goncalves” and Helen X. Chen’
`
`Abstract
`
`Immunology-based therapyis rapidly developing into an effective treatment option for a surprising
`range of cancers. We have learned over the last decade that powerful immunologic effector cells may
`be blocked by inhibitory regulatory pathways controlled by specific molecules often called “immune
`checkpoints.” These checkpoints serve to control or turn off the immune response whenit is no longer
`needed to prevent tissue injury and autoimmunity. Cancer cells have learned or evolved to use these
`mechanisms to evade immune control and elimination. The development of a new therapeutic class
`of drugs that inhibit these inhibitory pathways has recently emerged as a potent strategy in oncology.
`Three sets of agents have emergedin clinical trials exploiting this strategy. These agents are antibody-
`based therapies targeting cytotoxic T-lymphocyte antigen 4 (CTLA4), programmedcell death 1 (PD-1),
`and programmedcell death ligand 1 (PD-L1). These inhibitors of immune inhibition have demonstrated
`extensive activity as single agents and in combinations. Clinical responses have been seen in melanoma,
`renal cell carcinoma, non-small cell lung cancer, and several other tumor types. Despite the autoimmune
`or inflammatory immune-mediated adverse effects which have been seen, the responses and overall
`survival benefits exhibited thus far warrant further clinical development.
`
`Key words Immunecheckpoints, PD-1, PD-L1, CTLA4, immunotherapy, immune modulators
`
`Immune checkpoints refer to regulatory pathways in the
`immunomethat inhibit a portion of an active immune response
`against a specific target or set of targets'. Immune checkpoints
`are therefore seen as a normal part of the immune system’s
`regulatory cascade and necessary to modulate and maintain immune
`homeostasis. These regulatory pathways are redundant, multi-
`faceted, and complex (Figure 1). Their presence and evolutionary
`developmentare thoughtto reflect the fact that a normal immune
`response can also be potentially deadly to a host if not properly
`regulated, as evidenced by autoimmunedisease.
`As immunotherapy has gained a foothold in the anticancer
`armamentarium, there is a commonly held belief among
`oncologists that cancers thwart these regulatory mechanisms to
`evade immunedetection and continue their growth and spread.
`However, the whole picture is more complex.
`In many chronic
`infections, immune checkpoints are exploited by parasitic and viral
`
`Authors’ Affiliations: ‘Cancer Therapy Evaluation Program,Division of
`Cancer Treatment and Diagnosis, National CancerInstitute, Bethesda,
`MD 20892, USA; *Medical Oncology Service, Center for Cancer
`Research, National CancerInstitute, Bethesda, MD 20892, USA.
`Corresponding Author: Elad Sharon, 9609 Medical Center Drive,
`5W502, Bethesda, MD 20892, USA. Tel: +1-240-276-6565; Fax: +1-
`240-276-7894; Email: sharone @ mail.nih.gov.
`dol: 10.5732/cjc.014.10122
`
`pathogens as evidenced by T-cell exhaustion in these conditions”.
`Cancer, however, arises from within the host. While some immune
`checkpoints are engaged to avoid immune-mediated eradication,
`others are merely a part of the normal immuneresponseto stimuli.
`Weare only beginning to understand these pathways.
`As a therapeutic class, drugs that inhibit these co-inhibitory
`signaling pathways, also known as immune checkpointinhibitors,
`have emerged as a mainstay in melanoma therapy, with potential
`roles in the treatment of renal cell carcinoma (RCC), non-small cell
`lung cancer (NSCLC), urothelial cancer, head and neck cancer,
`ovarian cancer, and various lymphomas®""!,
`In fact, ClinicalTrials.
`gov nowlists dozensoftrials with immune checkpointinhibitors in a
`broad range ofindications. As the targets of therapy are components
`of the immune system, there is currently no theoretical reason
`to exclude any potential histologies or tumor types from clinical
`evaluation. However, from a drug development perspective, this can
`be a challenge, as the resources are constantly constrained. It will
`be important to optimize the developmentof strategies to efficiently
`explore the therapeutic potentials.
`While a variety of agents could be deemedto interact with
`immune checkpoint inhibitors, the focus of this review are limited
`to the most advanced agentsin clinical trials, those targeting the
`cytotoxic T-lymphocyte antigen 4 (CTLA4), programmedcell death 1
`
`434 www.cjcsysu.com
`
`CACA Chinese Anti-Cancer Association
`GenomeEx. 1016
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`

`

`Elad Sharonetal.
`
`Immune checkpoints in cancerclinical trials
`
`(PD-1), and programmed cell death ligand 1 (PD-L1) pathway. The
`early trials involving CTLA4- and PD-1/PD-L1—targeting agents have
`shown howthe addition of just one blocking antibody can reveal
`a hidden immune response, with potentially massive therapeutic
`benefit for patients. Immune modulators targeting other mechanisms
`(Table 1), such as indoleamine 2,3-dioxigenase (IDO)!"?")
`
`lymphocyte-activation gene 3 (LAG3)"!, T-cell membraneprotein 3
`(TIM3)'"*,, signaltransducer and activatorof transcription 3 (STAT3)"",
`glucocorticoid-induced tumornecrosis factor receptor (TNFR) family-
`related protein (GITR)”, and agents against the humaninhibitory
`killer lgG-like receptor (anti-KIR) targeting natural killer (NK) cells
`havealso entered the clinical trials arena?"
`
`Lymph node
`
`Peripheral tissue
`
`
`Heme, hematologic tumors; ATL, acute T-cell leukemia; CTCL, cutaneous T-cell lymphoma; AML, acute myeloid leukemia.
`
`anti-CTLAd
`
`\
`
`anti-PD-1
`
`( anki-PD-L1
`
`ootanti-KaR
`a
`
`NK i®
`
`Figure 1. Regulatory pathways In Immuno-oncology. The immune system has multiple levels of co-stimulatory (shown
`in green) and co-inhibitory (shownin red) pathways, helping to maintain immune homeostasis in the midst of responding
`to antigenic stimulation. Antibodies blocking cytotoxic T-lymphocyte antigen 4 (CTLA4), programmedcell death 1 (PD-1),
`and programmedcell death ligand 1 (PD-L1) have shown remarkable clinical activity and further development is underway.
`Agonist antibodies, which directly interact with co-stimulatory pathways such as 41BB and CD40,are also in clinical
`development. Other meansofaffecting the immune responsesare being explored,including direct actionon regulatory T (Treg)
`cells and naturalkiller (NK) cells. MHC, major histocompatibility complex; TCR, T-cell receptor.
`
`Table 1. Other immunotherapeutic agents in development
`
`Target
`
`Name
`
`Indication(s)
`
`Company
`
`Phase
`
`Clinical Trials.govidentifier (selected trials)
`
`B7.1
`B7H3
`LAG3
`
`CD137
`
`KIR
`
`CCR4
`CD27
`0x40
`
`CD40
`
`Galiximab
`MGA271
`IMP321
`BMS-986016
`BMS-663513
`PF-05082566
`IPH2101
`
`Lymphoma
`Solid tumors
`Solid tumors
`Solid tumors
`Solid tumors
`Lymphoma
`Myeloma, AML
`
`Biogen Idec
`Macrogenics
`Immuntep
`Bristol-Myers Squibb
`Bristol-Myers Squibb
`Pfizer
`Innate Pharma (BMS)
`
`KW-0761
`CDX-1127
`MEDI-6469
`
`Kyowa Kirin
`ATL, CTCL
`Solid tumors & Heme CellDex Therapeutics
`Solid tumors
`MedImmune/AZ
`
`CP-870,893
`
`Pancreatic
`
`Genentech
`
`PhaseII
`Phase|
`Phase1/II
`Phase|
`Phase I/II
`Phase|
`PhaseII
`
`Phase I/II
`Phase|
`Phase|
`
`Phase|
`
`NCT00516217
`NCT01391143
`NCT00349934
`NCT01968109
`NCT00309023
`NCT01307267
`NCT01248455
`NCT01256073
`
`NCT00920790
`NCT01460134
`NCT02205333
`
`NCT01456585
`
`www.cjcsysu.com
`
`Chin J Cancer; 2014; Vol. 33 Issue 9 435
`GenomeEx. 1016
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`

`

`Elad Sharonet al.
`
`Immune checkpoints in cancer clinical trials
`
`CTLA4Inhibition and Human Cancers
`
`CTLA4background
`
`(FDA) and the European Medicines Agencyfor the treatment
`of metastatic melanoma following research showing improved
`survival™!, Ipilimumabis a fully humanized immunoglobulin (Ig) G1
`kappa monoclonal antibody that antagonizes CTLA4 and prevents
`ligand binding™.
`CTLA4is one of several co-inhibitory molecules that aid in
`A phaseIII combination study of ipilimumab at 3 mg/kg with a
`modifying the T-cell response to antigen activation. The primary role
`glycoprotein 100 (gp100) peptide vaccine was conducted with 676
`of CTLA4 is to modify T-lymphocyte response to stimuli. CTLA4
`patients with stageIII or IV unresectable melanoma, randomized in
`regulates the clonal burst size during priming and secondary
`a 3:1:1 ratio. The results showed the median overall survival (OS) in
`expansion, which is thought to be proportional to the activation
`the ipilimumab plus gp100 group was 10.0 months [95% confidence
`strength of the complex formed by the T-cell receptor—major
`interval (Cl), 8.5 to 11.5 months], as compared with 6.4 months
`histocompatibility complex (TCR-MHC complex), both in terms of
`(95% Cl, 5.5 to 8.7 months) in the gp100 alone group [hazard ratio
`binding affinity and co-stimulation by accessory signals. CTLA4,
`also knownasclusterof differentiation (CD) 152, is an inhibitory
`(HR) for death, 0.68; P < 0.001]. The median OSin theipilimumab
`alone group was 10.1 months (95% Cl, 8.0 to 13.8 months; HR for
`molecule found onTcells, and its counterpart is CD28. CD28is a co-
`stimulatory signal, but it is important to note that CTLA4 has higher
`death with ipilimumab alone as compared with gp100 alone, 0.66;
`P = 0.003). Grade 3 or 4 immune-related adverse events occurred
`avidity for its ligands than CD28, which suggests a dominance of
`in 10% to 15% of patients treated with ipilimumab and in 3% of
`inhibitory signals in immune activation. The ligands for both CD28
`and CTLA4 are known as B7 proteins, which are found on antigen-
`patients treated with gp100 alone. The investigators concludedthat
`presenting cells (APCs). There are two typesof B7 proteins: B7-1 (also
`ipilimumab, with or without a gp100 peptide vaccine, as compared
`known as CD80) and B7-2 (also known as CD86)"'”,
`with gp100 alone, improved OSin patients with previously treated
`In normalcircumstances, T lymphocytes are thought to express
`metastatic melanoma. Adverse events can be severe, long-lasting, or
`CTLA4 on their surface immediately upon response to antigenic
`both, but most are reversible with appropriate treatment, particularly
`corticosteroids”.
`stimulation of TCR. Because a blocking antibody would attenuate
`the inhibitory signal, an anti-CTLA4 antibody would appearto have a
`Another supportive study in metastatic melanomainvolved 502
`clear role in enhancing antitumor immunity, as the interaction of B7
`patients in a 1:1 randomizedtrial of ipilimumab at a dose of 10 mg/kg
`plus dacarbazine at a dose of 850 mg/m”of body surface area versus
`with CD28 would thereby be enhanced. Indeed, in preclinical models,
`this is exactly what was seen”, However, B7is rarely presentin the
`dacarbazine and placebo. The OS waslongerin the group receiving
`tumor microenvironment, leading to a second hypothesis for how anti-
`ipilimumab-dacarbazine therapy than in the dacarbazine-placebo
`CTLA4antibodies may enhance immune-mediated tumorrejection”
`arm (11.2 months vs. 9.1 months). Survival rates were also higher
`CTLA4is differentially expressed among separate T-lymphocyte
`for the ipilimumab-dacarbazine arm at 1 year (47.3% vs. 36.3%),
`subsets. Indeed, higherlevels of surface expression of CTLA4 are
`2 years (28.5% vs. 17.9%), and 3 years (20.8% vs. 12.2%), with
`seen in regulatory T cells (Treg cells) as compared with effector
`an HR for death at 0.72 (P < 0.001). Grade 3 or 4 adverse events
`T cells (Teff cells). Researchers have established that higher Teff/
`were recorded in 56.3% of patients in the experimental arm and only
`27.5% in the control arm""!. Thesefindings further support the use of
`Treg ratios in both CD4-positive and CD8-positive tumor-infiltrating
`lymphocytes are associated with enhanced tumoreradication when
`ipilimumab in metastatic melanoma.
`CTLA4 blockadeis employed in tumor models”*”",
`Thepreliminary results of the first adjuvant trial were reported
`Other mechanismsof action involving Treg cells have been
`at the 2014 Annual Meeting of the American Society of Clinical
`hypothesized. For example, Treg cells are known to reduce B7
`Oncology (ASCO). The European Organization for Research and
`expression on both human and animal APCs”. While B7 is thought
`Treatment of Cancer (EORTC) conductedatrial with 951 patients
`to directly signal CTLA4, leadingtoits co-inhibitory effect, the reverse,
`with stage Ill melanomafollowing complete resection (EORTC 18071,
`or CTLA4 signaling to APCs via B7, also occurs. CTLA4 reverse
`NCT00636168). Patients were randomizedto receive ipilimumab at
`signaling via B7 canlead to increased expression of IDO. IDO leads
`a dose of 10 mg/kg versus placebo every 3 weeks for 4 doses. The
`to a reducedlevelof localtryptophanstoresin the microenvironment,
`medianrelapse-free survival was 26.1 monthsforthe ipilimumab arm
`which inhibits T-lymphocyte activation and proliferation””. Lastly,
`and 17.1 monthsfor the placebo arm, with an HR of 0.75 (95% Cl,
`0.64 to 0.90; P = 0.001). The adverse event profile was thought to
`recently discovered alternatively spliced mRNA molecules encode
`soluble CTLA4 molecules lacking transmembrane domains. These
`be generally consistent with that seen in advanced melanoma, but a
`higherincidence of endocrinopathies were reported”.
`soluble inhibitors could also mediate immune suppression, either by
`down-regulating B7 expression as noted above or by blocking the
`While the results were largely seen as positive, there arestill
`potential interaction of B7 and the co-stimulatory molecule CD28”,
`unresolved issues that maylimit the ability of regulatory agencies
`to approveipilimumab in the adjuvantsetting. In particular, patients
`with stage III melanoma have the option of high-doseinterferon,
`which is the standard of care in the United States™!. In addition, as
`noted above, the dose chosen in EORTC 18071 trial was 10 mg/kg
`ofipilimumab, higher than the dose used in the metastatic setting.
`
`Ipilimumab
`
`The first anti-CTLA4 agentin clinical development, ipilimumab,
`was approved by the United States Food and Drug Administration
`
`436 Chin J Cancer; 2014; Vol. 33 Issue 9
`
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`GenomeEx. 1016
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`

`Elad Sharonetal.
`
`Immune checkpoints in cancerclinicaltrials
`
`Anotherlarge adjuvanttrial, E1609 (NCT01274338), addresses the
`questions of the optimal dose of ipilumumab and its comparative
`effectiveness to high-doseinterferon. In this trial, conducted by the
`Eastern Cooperative Oncology Group (ECOG)under the sponsorship
`of the United States National CancerInstitute (NCI), 1,500 patients
`with stage III or IV melanoma that has been fully resected are
`randomized to three arms: high-dose interferon, ipilimumab at 3 mg/
`kg, and ipilimumab at 10 mg/kg". Thetrial is close to completing
`accrual and the outcome data are eagerly awaited.
`Other indications with ipilimumab are still under clinical
`development. On ClinicalTrials.Gov, a search with the term
`“ipilimumab’returns 191 trials, over 100 of which remain open. Much
`of the attention in ipilimumabclinical development has moved to
`combination therapy, particularly with the anti-PD-1 agent nivolumab.
`The developmentof ipilumumab brought up interesting ques-
`tions about the best endpoints of efficacy assessmentfor this class
`of agents. In the phaseIII melanomatrials with ipilimumab described
`above, improvements in OS seen in the metastatic setting were not
`accompanied bysignificant radiographic responses to therapy. This
`has complicated efficient drug development, as responserate is
`lesslikely to serve as a readoutof efficacy, at least when ipilimumab
`is used as a monotherapy. Monotherapyisstill being explored in
`various settings, however.
`In one example, in a single institution
`case series, 5 patients with recurrent glioblastoma multiforme (GBM)
`who weretreated with ipilimumab were followed. Patients had time
`to progression ranging from 1 to 6 months, and 1 patient remains
`recurrence-free 19 months after therapy, suggesting penetration of
`this drug across the blood-brain barrier™!,
`Currently, there are no biomarkers to predict which patients or
`tumor types are more likely to respond to anti-CTLA4 therapies.
`Some analysis suggested that a high mutational load may be
`associated with a clinical benefit from ipilimumab.
`In particular,
`one group of researchers has focused onidentifying a “neoantigen
`signature” that correlates with benefit. Findings are preliminary,
`but this suggests that tumor genetics might explain the divergent
`outcomes amongpatients treated with ipilimumab™,
`
`Tremelimumab
`
`Tremelimumab (formerly CP-675,206) is a human IgG2
`monoclonalantibody specific for CTLA4.In a large, single-arm phase
`Il trial, 241 response-evaluable patients with advancedrefractory or
`relapsed melanomaweretreated at a dose of 15 mg/kg intravenously
`every 3 months. Objective responses were observedin 6.6% of those
`patients, which led to a phaseIII trial in a similar patient population”.
`In the phaseIII trial in advanced melanoma, 655 patients were
`enrolled and randomly assigned to treatment with tremelimumab or
`chemotherapy. Median OSbyintentto treat was 12.6 months (95%
`Cl, 10.8 to 14.3 months) for tremelimumab and 10.7 months (95%
`Cl, 9.36 to 11.96 months) for chemotherapy (HR, 0.88; P = 0.127).
`Of note, while objective response rates weresimilar in the two arms
`(10.7% in the tremelimumab arm and 9.8% in the chemotherapy
`arm), duration of response wassignificantly longer among patients
`treated with tremelimumab (35.8 months vs. 13.7 months, P =
`
`www.cjcsysu.com
`
`0.0011)"". Regardless, the study failed to demonstrate a statistically
`significant survival advantage of treatment with the investigational
`drug overstandard-of-care chemotherapy.
`While the results were disappointing, there was a possibility that
`the dosing schedule of tremelimumab (once every 3 months) was
`insufficient to achieve results similar to thatofipilimumab. As a result,
`ongoing efforts with tremelimumab as a monotherapy have used more
`frequent dosing. The preferred dose and schedule for tremelimumab
`for ongoing trials has generally been 10 mg/kg intravenously, every
`4 weeks for 6 months. A phaseIl, single-arm study of tremelimumab
`as a second-line treatment was conducted with 29 patients with
`malignant mesothelioma. Results showed a partial response in 4
`patients (13.8%) and stable disease in 11 patients (37.9%), with OS
`of 11.5 months™"!. As a result, a phaseIII, double-blinded, randomized
`trial is currently underway using tremelimumab in mesothelioma”.
`Tremelimumab is also being tested in various combinations in a
`variety of other tumortypes.
`
`PD-1/PD-L1 Inhibition and Human
`Cancers
`
`PD-1/PD-L1 background
`
`Comparedto the limited development with CTLA4, there is
`an immenselevel of interest and investment by pharmaceutical
`companiesin the PD-1/PD-L1 pathway (Table 2). Seven major
`companies have entered the fray, with multiple phaseIII registration
`trials already underwayin a variety of malignancies, most notably
`melanoma, RCC, and NSCLC(Table 3). This enthusiasm is justified,
`as Clinical trial results thus far confirm that targeting the PD-1/PD-
`L1 pathway represents the most exciting opportunity for advancing
`cancer immunotherapyto date.
`Whereas CTLA4is involved in central tolerance and control, the
`PD-1 receptoris critical in peripheral tolerance. PD-1 is expressed on
`T lymphocytes during thymic development. Similar to CTLA4, PD-1
`becomes expressed on CD4- and CD8-positive T lymphocytes during
`antigenic stimulation, serving as a co-inhibitory signal. In addition,
`PD-1 is expressed on numerousother immune cells, including
`naturalkiller T cells, B cells, monocytes, and certain dendritic cell
`subsets“**", PD-1 has two main ligands, namely PD-L1 (also known
`as B7-H1) and PD-L2 (also known as B7-DC). While PD-L2 has a
`muchhigheraffinity for PD-1,
`it is expressed chiefly on activated
`dendritic cells, macrophages, certain B-cell subsets, and other
`immunecells. PD-L1 is more widely expressed on hematologic and
`non-hematologic tissues".
`As a co-inhibitory signal, PD-1 engagementresults in reduced
`cytokine production, cytolytic activity, and lymphocyteproliferation””.
`PD-1 is up-regulated in T lymphocytes following viral infections and
`down-regulated following viral clearance. In chronic viral infections,
`however, CD8-positive T lymphocytes express PD-1 constitutively,
`likely through gene demethylation, contributing to what has been
`termed a T-cell exhaustion phenotype. In human immunodeficiency
`virus (HIV) infection, for example, high levels of PD-1 expression
`allow for persistent interaction between PD-L1 expressed by APCs
`
`Chin J Cancer; 2014; Vol. 33 Issue 9 437
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`

`Elad Sharonetal.
`
`Immune checkpoints in cancer clinical trials
`
`Table 2. Agents targeting PD-1/PD-L1in clinical development
`
`Company
`
`Agent targeting PD-1
`
`Agent targeting PD-L1
`
`CureTech
`
`CT-011
`
`Pidilizumab (humanized IgG1 mAb)
`
`MedImmune/AZ
`
`AMP-514
`
`MED14736(fully human mAb)
`
`EMD Serono
`
`N/A
`
`MSB0010718C
`
`PD-1, programmed death 1 receptor; PD-L1, programmedcell death ligand 1;
`available.
`
`lgG4, immunoglobulin G4; mAb, monoclonal antibody; N/A, not
`
`Table 3. Selected ongoing PD-1/PD-L1trials in melanoma, renal cell cancer (RCC), and non-small cell lung cancer
`(NSCLC)
`
`Sponsor
`
`Setting
`
`Phase
`
`Comparison
`
`Primary
`endpoint
`
`Clinicaltrials.
`Sample Primary
`completion date govidentifier
`size
`
`Bristol-Myers Squibb NSCLC
`
`3rd-line squamouscell
`
`Il
`
`Nivolumab vs. docetaxel
`
`OS
`
`264
`
`Jan 2016
`
`NCT01642004
`
`Pembrolizumabvs. OS & PFS 645~—-Feb 2015 NCT01866319
`
`
`
`Merck
`Melanoma
`‘st-/2nd-line {ipi-naive)
`III
`ipilimumab
`
`Bristol-Myers Squibb Melanoma 2nd-line post-ipi
`
`Bristol-Myers Squibb Melanoma 1st-/2nd-line
`
`Ill
`
`Ill
`
`Nivolumabvs.
`chemotherapy
`
`Nivolumabvs.
`chemotherapy
`
`os
`
`405
`
`May 2015
`
`NCT01721746
`
`os
`
`410
`
`Sept 2015
`
`NCT01721772
`
`
`
`Genentech 287=Mar 2016NSCLG 2nd-line MPDL3280A vs. docetaxel 0S NCT01903993
`
`NCT02008227 ORR,overall responserate; OS, overall survival; PFS, progression-free survival; ipi, ipilumumab. Other footnotesas in Table 2.
`
`
`
`
`
`
`
`
`
`Genentech
`
`NSCLC
`
`2nd-line
`
`Ill
`
`MPDL3280Avs. docetaxel OS
`
`850
`
`Jun 2017
`
`using the anti-PD-L1 antibody, BMS-936559 (NCT02028403).
`and subsequent T-cell dysfunction. T-lymphocyte activation is
`Similarly, tumors use the same pathway, meant to induce
`essentially blocked in this setting. In an experimentusing B cells from
`HIV-infected individuals, researchers were able to show increased
`peripheral immune tolerance, to evade T-lymphocyte—mediated
`immune eradication. Tumors evading an active immune response
`responses to HIV antigens in the presence of PD-1 blocking
`antibodiesin vitro” This suggests that an active immune response
`are thought to express PD-L1 following T lymphocyteinfiltration
`can be induced if effective blockade of the PD-1/PD-L1 pathway
`and expression of interferon-gamma. Expression of PD-L1 has
`
`can be implemented.Aclinical trial sponsored by the US National been associated with a poor prognosis in a wide variety of human
`tumors'**"!_ Interestingly, in one analysis of glioma cases,a better
`Institutes of Health is currently planned to investigate that possibility
`
`438 Chin J Cancer; 2014; Vol. 33 Issue 9
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`

`Elad Sharonetal.
`
`Immune checkpoints in cancerclinicaltrials
`
`prognosis was seen in patients whose tumor-adjacentbrain tissue
`expressed PD-L1 and whose tumors did not express PD-L1. This
`suggests a general role for PD-L1 in protecting normal tissue from
`immuneattack, though it would be important to see these findings
`replicated elsewhere andin other tumor types”.
`In general, the results of PD-1/PD-L1 blockade have been
`encouraging. Higher response rates and durable responses were
`seen with PD-1/PD-L1 blocking antibodies than with CTLA4 blockade
`in melanoma, RCC, and unexpectedly, NSCLC.In addition, although
`similar immune-mediated adverse events were seen with both CTLA4
`
`and PD-1/PD-L1 agents, the severity of adverse events has generally
`beenlower, with the caveat that fatal pneumonitis was seen in 1% of
`the patients on the nivolumab phase| trial described below”.
`
`PD-1-targeting agents
`
`Nivolumab
`Nivolumab (BMS-936558) is a fully human IgG4 monoclonal
`antibody targeting PD-1. A phase I/II study was reported in 2012
`in the New England Journal of Medicine in parallel with a plenary
`session at the 2012 ASCO Annual Meeting™., Patients onthe trial had
`advanced melanoma, NSCLC,castration-resistant prostate cancer,
`RCC, or colorectal cancer (CRC). Patients received nivolumab at
`doses of 0.1 to 10.0 mg/kg of body weight every 2 weeks for up to 12
`cycles until disease progression or a complete response occurred.
`Of the 296 patients enrolled, only 14% experienced grade 3 or 4
`drug-related adverseevents, but there were 3 deaths from pulmonary
`toxicity. No maximum tolerated dose (MTD) was defined. Cumulative
`responserates (all doses) were 18.4% (14/76) among patients with
`NSCLC, 27.6% (26/94) among patients with melanoma, and 27.3%
`(9/33) among patients with RCC™) A subsequent analysis of the
`104 patients in thattrial with metastatic melanoma was performed.
`The investigators reported that the median OS in nivolumab-treated
`metastatic melanoma patients was 16.8 months, and 1- and 2-year
`survival rates were 62% and 43%, respectively. Among the 33
`patients (30.8%) with objective tumor regressions, the Kaplan-Meier
`estimated median response duration was 2 years. Of note, responses
`were not observed in prostate cancer and colon cancerpatients on
`the trial.
`While preliminary results from the phase I/II trial suggested
`that PD-L1 could be an appropriate biomarkerfor patient selection,
`subsequent analyses have shown numerous PD-L1—negative
`patients had respondedto treatment with nivolumab, although lower
`rates are seen. Given the variability and limitation of the available
`PD-L1 assays,a true absence of PD-L1 expression in those patients
`cannot be confirmed. Atthis time it remains to be determined whether
`
`PD-L1 is a predictive markerof response for PD-1 pathwayinhibitors.
`At the 2014 ASCO Annual Meeting, preliminary results of other
`nivolumabclinicaltrials were reported. In a small dose-escalationtrial
`in Japan, 3 of 13 patients with platinum-resistant ovarian cancer had
`objective responses to nivolumab. Theinitial 10 patients were treated
`at a dose of 1 mg/kg, and 2 responders were from that cohort. The
`subsequent cohort that received 3 mg/kg had only 3 patients, but 1
`was a responder. Theseresults, though preliminary, were promising”.
`
`www.cjcsysu.com
`
`In addition, investigators reported early results using nivolumab at
`a dose of 3 mg/kg every 2 weeksin patients with treatment-naive
`advanced NSCLC. The initial results on 20 patients revealed an
`objective response rate of 30%. Two patients had a greater than
`80% target lesion reduction at 18 weeks, Of the 15 evaluable tumor
`samples, 9 were PD-L1—positive (defined as greater than 5% PD-
`L1 expression using a Dakokit), and the response rate was 67% in
`PD-L1-positive patients; whereas no responses were observedin
`the 6 PD-L1—negative patients"!, Combinations of nivolumab with
`conventional chemotherapy or epidermal growth factor receptor
`(EGFR)inhibitors were also reported, but results are difficult to
`interpret in the absence of randomized comparisons***”.
`
`Pembrolizumab
`Pembrolizumab (MK-3475, formerly lembrolizumab) is a
`humanized IgG4 monoclonal antibody targeting PD-1. Pembro-
`lizumab has been very successfulin treating melanoma and NSCLC,
`similar to nivolumab. Significant differences cannot be assessed
`in the absence of a randomizedtrial comparing the two agents.
`However, binding affinities of the agents are different. Nivolumabis a
`fully human IgG4, and pembrolizumab is humanized. In phase| trials,
`neither agent has been found to have a maximally tolerated dose.
`That said, more time and energy has been spent on searching for an
`appropriate dose for pembrolizumab.
`In the first major publication involving pembrolizumab, Hamid ef
`al." reported that patients with advanced melanoma were analyzed
`after being treated with three separate dosing strategies: 10 mg/
`kg of body weight every 2 or 3 weeks or 2 mg/kg every 3 weeks.
`Ultimately, 135 patients with advanced melanomaweretreated.
`Adverse events were similar to those found in patients treated with
`nivolumab,including fatigue, rash, pruritus, and diarrhea. Response
`rates across all dose levels were 38% (95% Cl, 25% to 44%).
`Investigators found no difference among those with and without
`prior ipilimumab therapy. Responses were durable, and the median
`progression-free survival (PFS) among the 135 patients was longer
`than 7 months”.
`A subsequentprospective, randomized analysis was performed
`using both the 2 mg/kg and the 10 mg/kg doses, given every 3 weeks
`to patients with ipilimumab-refractory advanced melanoma. There
`were 89 patients in the 2 mg/kg cohort and 84 patients in the 10
`mg/kg cohort. The response rate was 26% at both doses. Safety
`profiles were similar and there were no deaths reported. Other
`attempts to analyze patients with melanoma have beenreported,
`including an analysis of 411 melanoma patients treated across
`multiple dose levels and multiple trials, which was reported at the
`2014 ASCO Annual Meeting. Median OS data wasnotavailable, but
`1-year OSrate overall dose cohorts was 71%. Response rates were
`encouraging as well, ranging from 26% to 57%, varying based on
`ipilimumabpriortreatment, dose, and schedule™.
`Investigators also reported preliminary results of a phase| trial
`of previously treated patients with locally advanced or metastatic
`NSCLC. Enrolled patients with PD-L1 detected in their tumors
`by a preliminary immunohistochemical assay were randomized
`to pembrolizumab at a dose of 10 mg/kg every 2 weeks or every
`
`Chin J Cancer; 2014; Vol. 33 Issue 9 439
`GenomeEx. 1016
`Page 6 of 11
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`Genome Ex. 1016
`Page 6 of 11
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`Elad Sharonet al.
`
`Immune checkpoints in cancer clinical trials
`
`3 weeks. In addition, some patients with tumors without PD-L1
`expression who had receivedat least twopriorlines of therapy were
`treated at a dose of 10 mg/kg every 2 weeks. Ultimately, 102 patients
`comprised the every-2-week cohort (including 43 whose tumors did
`not express PD-L‘1), and 119 patients comprised the every-3-week
`cohort. Investigators reported that 48% of patients experienced drug-
`related adverse events, with 6% experiencing grade 3/4 adverse
`events. As in the nivolumab trial reported above, pneumonitis was
`a concern, with 3 cases of drug-related grade 3/4 pneumonitis. The
`Response Evaluation Criteria in Solid Tumors (RECIST) response
`rate in all patients was 21%. The response rate wasslightly higher
`(24%) for patients with PD-L1—positive tumors (more specifically,
`31% on the every-2-week cohort and 22% on the every-3-week
`cohort). RECIST responserates were 8% for patients without PD-L1
`expression”
`
`Pidilizumab
`Pidilizumab is a humanized IgG‘ antibody targeting PD-1. The
`agent wasinitially evaluated in a phase| trial targeting hematologic
`malignancies. Presently, there are a number ofclinical trials
`underwayin both hematologic andsolid tumors™.
`The results of two pidilizumabclinical trials were recently
`published in peer-reviewed journals. In a single-center, single-arm,
`phaseII trial, 32 patients with relapsed follicular lymphoma received
`pidilizumab at a dose of 3 mg/kg every 4 weeksfor4 infusions with
`up to 8 additionalinfusions administered. In addition, rituximab was
`given at a dose of 375 mg/m’ of body surface area every week for
`4 weeks. Investigators reported that 19 of 29 evaluable patients
`achieved an objective response, with complete responses in 15
`patients (51.7%)®.
`An additional phaseII trial involved patients with diffuse large
`B-cell lymphoma (DLBCL)following autologous hematologic stem cell
`transplantation (AHSCT). Sixty-six patients were treated with 3 doses
`of pidilizumabin thefirst 1 to 3 months after AHSCT. The PFSrate
`was 72% at 6 months after AHSCT (90% Cl, 60% to 82%), meeting
`the primary endpoint. Thirty-five patients had measurable disease
`following AHSCT,and the responserate in those patients was 51%”.
`Investigators also presented results on the use of pidilizumab
`in metastatic melanoma at the 2014 ASCO Annual Meeting. In this
`trial, 103 patients were randomizedin a 1:1 ratio to receive either
`1.5 mg/kg or 6 mg/kg every 2 weeks for 27 doses. Response rates
`were lower than those observedin patients treated with other PD-
`1—targeting agents, but the OS rate at 12 months was 64.5% (90%
`Cl, 55.6% to 72.0%). No significant differences were seen between
`different strata or dose groups™!.
`
`PD-L1-targeting agents
`
`MPDL3280A
`MPDL3280Ais an engineered human IgG1 monoclonalantibody
`that targets PD