Immuno-oncology Combinations: A Review of ClinicalExperience and Future Prospects
Scott J. Antonia1, James Larkin2, and Paolo A. Ascierto3
AbstractImmuno-oncology is an evolving treatment modality that includes immunotherapies designed to
harness the patient’s own immune system. This approach is being studied for its potential to improve
long-term survival across multiple tumor types. It is now important to determine how immunotherapies
may be most effectively used to achieve the best possible patient outcomes. Combining or sequencing
immunotherapies that target distinct immune pathways is a logical approach, with the potential to
further enhance the magnitude of the antitumor immune response over single agents. Early clinical data
in patients with melanoma treated with two immune checkpoint inhibitors, ipilimumab and nivolu-
mab, suggest support for this combination approach. Numerous other combination approaches are
being evaluated in early-phase clinical trials; however, their clinical activity remains unknown. Clinical
experience to date has shown that when combining an immuno-oncology agent with an existing
therapeutic modality, it is important to determine the optimal dose, schedule, and sequence. Clin Cancer
Res; 20(24); 6258–68. �2014 AACR.
IntroductionTumors avoid immune destruction by a range of complex
and often overlappingmechanisms that disrupt key compo-nents of the immune system involved in mounting aneffective antitumor response (1–4). Tumors can avoid rec-ognition and elimination by the immune system by disrupt-ing antigen presentationmechanisms, either through down-regulation ofMHC class Imolecules or by disabling antigen-processingmachinery. Alternatively, or additionally, tumorsmay suppress the immune system by disrupting pathwaysinvolved in controlling T-cell inhibition (checkpoint) andactivation (3, 5), or by recruiting immunosuppressive celltypes, such as regulatory T cells (Treg) and myeloid-derivedsuppressor cells (MDSC). The release of factors, includingadenosine and prostaglandin E2, and the enzyme indolea-mine 2,3-dioxygenase (IDO) is another mechanism thattumors may use to suppress immune activity (3).
The idea of targeting the immune system as a therapeuticapproach in cancer is not new.Cytokines [interleukin-2 (IL2)and interferon-a (IFNa)] have been used for decades, pre-dominantly in patients with renal cell carcinoma (RCC) andmelanoma. However, these cytokines are not target specific,
andhavebeen associatedwith significant toxicity and limitedefficacy; these factors restrict use to healthy patients and onlya select group of these patients will derive benefit (6, 7).
Immuno-oncology is an evolving treatment modalitythat includes immunotherapies designed to target andharness the patient’s immune system directly to kill tumorcells (8, 9). Numerous strategies for overcoming tumorimmune evasion are under evaluation (Table 1). Becausethese approaches directly target the patient’s immune sys-tem, they have the potential for activity across multipletypes of cancer. Examples of immunotherapeutic appro-aches under clinical investigation include T-cell checkpointinhibitors or agonists for T-cell–activating pathways, novelcytokines such as IL12 and IL15, therapeutic vaccines,elimination of immunosuppressive cells, and other agentsand approaches designed to enhance immune cell function(Table 1; refs. 10–12).
Since the approval of IL2, sipuleucel-T (a therapeuticvaccine composedof recombinant antigenproteindesignedto stimulate T-cell responses) and ipilimumab [a cytotoxicT-lymphocyte antigen 4 (CTLA-4) immune checkpointinhibitor] were the first immunotherapies to be approvedfor patients with cancer. Sipuleucel-T was approved in 2010for asymptomatic or minimally symptomatic metastaticcastrate–resistant prostate cancer (CRPC) and ipilimumabin 2011 for unresectable or metastatic melanoma. Bothagents were shown to significantly improve overall survival(OS) in phase III clinical trials (Fig. 1; refs. 13–16).
Monoclonal antibodies targeting programmed death-1(PD-1) ligand (PD-L1) interaction, another immune check-point pathway, are the most advanced in clinical develop-ment after ipilimumab and sipuleucel-T, and various agentsarebeing tested in clinical trials across a rangeof tumor types.
1Moffitt Cancer Center and Research Institute, Tampa, Florida. 2The RoyalMarsden, London, United Kingdom. 3IstitutoNazionale Tumori FondazioneG. Pascale, Naples, Italy.
Note: S.J. Antonia and P.A. Ascierto share senior authorship.
Corresponding Author: Scott J. Antonia, Moffitt Cancer Center andResearch Institute, Tampa, FL 33612. Phone: 813-745-8470; E-mail:[email protected]
Table 1. Potential strategies for overcoming tumor immune evasion mechanisms and examples of agentsin clinical development (12)
Treatment strategy Examples of agents in clinical development
Reversing the inhibition of adaptive immunity (blocking T-cell checkpoint pathways)
* Inhibiting the CTLA-4 checkpointmoleculea
Ipilimumab: approved for melanomaTremelimumab: phase II for malignant mesothelioma, HCC, melanoma
* Inhibiting the interaction between PD-1checkpoint and its ligandsa
Nivolumab (anti–PD-1): phase III for melanoma, NSCLC, RCC
Pembrolizumab (MK-3475; anti–PD-1): phase III for NSCLC, melanomaMPDL3280A (RG7446; anti–PD-L1): phase III for NSCLCPidilizumab (CT-011; anti–PD-1): phase II for FL, prostate, pancreatic, melanomaAMP-514 (MEDI0680; anti–PD-1): phase I for solid tumorsMEDI4736 (anti–PD-L1): phase I for solid tumorsAMP-224 (recombinant PD-L-Fc fusion protein): phase I for solid tumorsrHIgM12B7 (anti–PD-L2): phase I for melanoma
* Inhibiting the LAG-3 checkpointmolecule
IMP321: phase I for breast, RCC; phase II for melanomaBMS-986016: phase I for solid tumors
* Inhibiting the TIM-3 checkpoint No agent undergoing clinical evaluation
* Inhibiting the adenosine A2A receptor No agent undergoing clinical evaluation
Switching on adaptive immunity (promoting T-cell costimulatory receptor signaling using agonist antibodies)* Promoting CD137 signaling Urelumab: phase I for B-cell NHL, CLL, solid tumors
PF-05082566: phase I for NHL
* Enhancing OX-40 signaling MEDI6469: phase II for breast, prostate, solid tumors
* Promoting GITR signaling TRX518: phase I for melanoma, solid tumors
* Enhancing CD27 signaling CDX-1127: phase I for CD27-expressing hematologic malignancies and solid tumors* CD40 Activation CP-870,893: phase I for pancreatic, melanoma
Chi Lob 7/4: phase I for advanced malignancies* Systemic recombinant IL21administration (range of effects thatenhance immune cell function)
Denenicokin: phase II for melanoma, ovarian and phase I for RCC, NHL
rhIL 15: phase I for melanoma, kidney, NSCLC, SCHN
* Systemic recombinant IL7administration (range of effects,including on T-cell development)
rhIL 7: phase II for various solid tumors
Improving the function of innate immune cells* Manipulating the activation of NK-cellinhibitory receptors (KIR)
Lirilumab: phase II for AML (maintenance); phase I for solid tumors
* Stimulating macrophages and DCs Toll-like receptor agonists:Bacillus Calmette-Gu�erin (TLR 2/4 agonist): approved for bladder carcinoma
Hiltonol (TLR7 agonist): phase II various solid and hematologic malignanciesImiquimod (TLR7 agonist): approved basal cell carcinomaResiquimod (TRL7/8 agonist): phase I/II various solid and hematologic malignanciesCpG 7909 (TLR 9 agonist): phase II various solid tumors
Activating the immune system (potentiating immune-cell effector function)* IDO inhibition INCB024360: phase II for melanoma, EOC, PPC, FTC
Indoximod: phase II for breast, prostate
(Continued on the following page)
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One of the more exciting aspects of immunotherapies isdemonstrated with data from clinical trials for ipilimu-mab, nivolumab, and pembrolizumab that show thepotential for long-term survival. In a phase III study ofipilimumab in previously treated patients with metastaticmelanoma (study MDX010-020), the survival rate at 2and 3 years was 25% for each (17). In addition, in apooled analysis of data from 12 ipilimumab clinicalstudies with follow-up of up to 10 years in some patients,an OS plateau started at approximately 3 years and the 3-year survival rate was 22% (18). The PD-1 immunecheckpoint inhibitors nivolumab and pembrolizumabhave also shown durable responses in phase I studies(19–21).
Although targeting the immune systemhas emerged as aneffective treatment approach for patients with CRPC andmetastatic melanoma (17, 18), for the development of thistreatmentmodality to progress, it is important to determinehow agents should be used to achieve the best possiblepatient outcomes.Combining immunotherapieswithotherestablished and investigational cancer therapies is a field ofactive investigation, with a multitude of approaches underconsideration. This review focuses on (i) combining orsequencing immunotherapies that target distinct immunepathways, particularly T-cell checkpoints, and (ii) combin-ing immunotherapies with existing therapeutic modalities,specifically BRAF-targeted therapies, chemotherapies, andradiotherapy.
Table 1. Potential strategies for overcoming tumor immune evasion mechanisms and examples of agentsin clinical development (12) (Cont'd )
Treatment strategy Examples of agents in clinical development
* Inhibition of TGF-b signaling GC1008; phase I for melanoma, RCCLY2157299: phase I/II various solid tumors
TEW 7197: phase I solid tumorsIMC-TR1 (LY3022859): phase I solid tumors
* Systemic IL2 or IFNa administrationa Agents approved
* Various vaccine-based strategiesa Various approaches under clinical evaluation
Abbreviations: ADCC, antibody-dependent cell-mediated cytotoxicity; AML, acute myeloid leukemia; CLL, chronic lymphocyticleukemia; EOC, epithelial ovarian cancer; FL, follicular lymphoma; FTC, fallopian tube cancer; GITR, glucocorticoid-induced tumornecrosis factor related gene; HCC, hepatocellular carcinoma; NHL, non-Hodgkin lymphoma; PPC, primary peritoneal cancer; SCHN,squamous cell head and neck cancer; TIM, T-cell immunoglobulin mucin; TLR, Toll-like receptor.aApproaches in which approved compounds or investigational compounds are being studied in phase III trials.
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Figure 1. Targeting two distinctimmune checkpoint pathways:interim data from a phase I study ofconcurrent ipilimumab andnivolumab. Patients with advancedmelanoma treated with ipilimumabin combination with nivolumab hada preliminary 1-year OS rate of82%. These data provided therationale for initiation of a phase IIItrial of the ipilimumab/nivolumabcombination in previouslyuntreated patients with metastaticmelanoma. Reprinted withpermission fromWolchok et al. (16).
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Combining immunotherapies that target distinctimmune pathwaysCombining or sequencing immunotherapies that
target distinct immune pathways is a rational strategy todetermine whether the magnitude of the antitumorimmune response may be improved over that generatedwith a single agent. Potential combination approachesundergoing clinical evaluation include dual T-cell check-point inhibition, T-cell checkpoint inhibition combinedwith immunomodulatory antibodies designed to enhanceT-cell activity through agonistic interaction with costimu-latory receptors (aiming to switch on adaptive immunity),T-cell checkpoint inhibition combined with approaches toimprove the function of innate immune cells, and T-cellcheckpoint inhibition combined with other approaches toenhance the immune response (Table 2; refs. 3, 5, 12).
Dual T-cell checkpoint inhibitionGiven that T-cell checkpoint inhibitors (e.g., ipilimu-
mab, nivolumab, pembrolizumab) have shown single-agent clinical activity in several tumor types (5, 13),and preclinical data suggest checkpoint molecules mayact synergistically to regulate T-cell function and pro-mote tumor immune escape, it is rational to evaluatewhether combining checkpoint inhibitors improvesactivity, achieving an OS benefit in a greater proportionof patients compared with either agent alone (Fig. 2;refs. (16, 22–24). Initial support for dual T-cell check-point inhibition has come from a phase I study inwhich patients with advanced stage III or IV melanomawere treated with both ipilimumab (1 or 3 mg/kg) andnivolumab (0.3 mg/kg, 1 mg/kg, or 3 mg/kg) in aconcurrent or sequenced regimen (16, 25). An objectiveresponse rate (ORR) rate of 40% was achieved inpatients treated with the concurrent regimen (ORR was53% at the maximum tolerated dose, nivolumab 1 mg/kg, ipilimumab 3 mg/kg). The preliminary 1-year OSrate with the concurrent regimen was 82% [95% con-fidence interval (CI) 69.0–94.4; Fig. 1; ref. 16]. Thesepromising results prompted the initiation of a phase IIIstudy (CheckMate 067) to further evaluate concurrenttreatment with ipilimumab and nivolumab (12).Phase I studies are in progress to evaluate ipilimumab
plus nivolumab in patients with a range of solid tumors[including RCC, non–small cell lung cancer (NSCLC),colon cancer, triple-negative breast cancer, gastric cancer,pancreatic cancer, and small-cell lung cancer (SCLC); ipi-limumab plus pembrolizumab (anti–PD-1) in patientswith melanoma, RCC, and NSCLC; tremelimumab (ananti–CTLA-4 agent) plus MEDI 4736 (anti–PD-L1 agent)in NSCLC; and an anti-lymphocyte activation gene 3 (LAG-3) monoclonal antibody BMS-986016 plusnivolumab(anti–PD-1) in patients with solid tumors (Table 2;ref. 12)]. The latter combination is supported by preclinicaldata that showed strong synergistic antitumor activity whenboth the PD-1 and LAG-3 immune checkpoint pathwayswere blocked (23). Dual anti–LAG-3/anti–PD-1 antibodytreatment curedmost mice of established fibrosarcoma and
colon adenocarcinoma tumors that were largely resistant tosingle antibody treatment (22).
T-cell checkpoint inhibition combined with agonisticantibodies against T-cell costimulatory receptors
In theory, if agents designed to release the checkpoint-mediated inhibition of T cells were combined with agonistantibodies designed to enhance costimulatory T-cell signal-ing, a more effective immune response may be generated(5). To date, no data are available from clinical trialsevaluating these combinations, but studies are in progress.CD40 plays a key role in the development of T-cell–depen-dent antitumor immunity, and is essential in enablingantigen-presenting cells to process and present antigeneffectively to T cells (26–28). Combining T-cell checkpointblockade (using anti–CTLA-4 agent tremelimumab) withan agent that targets the costimulatory molecule CD40(CP-870,893) is being investigated in a phase I trial inpatients with melanoma (12).
Other agonist antibodies designed to target receptors,including OX-40, CD27, GITR, and CD137, are in devel-opment. The clinical evaluation of these agents as mono-therapy is at an early stage, although the limited dataavailable suggest they canbe safety administered topatients.Data from a large phase I trial with urelumab (anti-CD137)in more than 100 patients did show liver toxicity, with2 deaths reported at higher doses. Clinical evaluation ofurelumab is continuing at lower doses in advanced solidtumors and hematologic malignancies (29). Evaluatingcombinations of these antibodies with checkpoint inhibi-tors and other immunotherapies is an exciting possibility,but one that should be evaluated with caution.
Another agonistic therapeutic approach that was evalu-ated with catastrophic effects was the CD28 agonistTGN1412. In a first-in-human phase I trial, TGN1412administration resulted in a cytokine storm that causedsevere adverse events in the six volunteers (30). As explainedbyCurran and colleagues (31), CD28 iswidely expressed onall mature T-cell populations; therefore, an agonistic CD28antibody may be expected to have a polyclonal "superagonist" effect—this is in contrast to other costimulatorymodules, such as CD137 or OX-40, which are onlyexpressed on a proportion of T cells, so agonist antibodiesare likely to have a more selective effect.
T-cell checkpoint inhibition combined withapproaches to improve the function of innate immunecells
Adaptive immune responses to cancer involve variouscomponents of innate immunity. In viewof this, combiningtherapies designed to enhance T-cell function with agentsdesigned to improve innate immune cell function areworthy of evaluation. Natural killer (NK) cells are innateeffector cells that maintain tolerance to self-tissue via theexpression of killer cell immunoglobulin-like receptors(KIR), which negatively regulate NK-cell activity by bindingto the MHC class I molecules expressed on most "normal"cells (32–35). Tumor cells may appear like normal cells by
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retaining or upregulating MHC class I to escape immuno-surveillance by NK cells (33). Lirilumab is an anti-KIRantibody that blocks the inhibitory KIR signal, therebypotentiating NK-cell killing of tumor cells, despite expres-sion of MHC I. A regimen designed to enhance innate andadaptive immunity, respectively, could theoreticallyachieve more favorable biologic and clinical activity com-pared with either agent alone (36, 37). This could beachieved in a variety ways, such as by using an anti-KIRagent (lirilumab) in combination with PD-1 or CTLA-4immune checkpoint inhibitors. Clinical trials are underway evaluating such combinations (Table 2; ref. 12).
Other immunotherapy combination partnersCytokine therapy. Cytokines have the capacity to stim-
ulate an immune response, although arguably less specif-ically comparedwithother immunotherapeutic approaches(3). IL21 has a role inNK and T-cell activation, and systemicadministration of a recombinant IL21 (rIL21) has demon-strated antitumor activity in tumors, including metastaticmelanoma (38). On the basis of preclinical studies inmouse tumor models which showed enhanced antitumoractivity when rIL21 was combined with either anti–CTLA-4or anti–PD-1 agents (39), phase I dose-escalation studiesare evaluating these combinations in patients withadvanced or metastatic melanoma (ipilimumab; ref. 40)or solid tumors (nivolumab; ref. 41).Other cytokines are under evaluation asmonotherapy for
cancer therapy, but a phase II trial is ongoing with IL7,which has a wide range of biologic activities, including arole in T-cell development, after standard therapy withsipuleucel-T for patients with asymptomatic or minimallysymptomatic metastatic CRPC (12).IDO inhibition. IDO is an immunosuppressive enzyme
that is involved in maintaining peripheral immune toler-ance by suppressing the function of both innate and adap-
tive immune cells. Data frompreclinical studies suggest thatinhibiting IDO can promote the proliferation, survival, andfunction of various immune cells [e.g., T cells, NK cells, anddendritic cells (DC)], reduce the generation of Tregs, andsignificantly inhibit tumor growth (42, 43). Furthermore,studies in murine models showed that host-derived IDOcan suppress the antitumor activity of an anti–CTLA-4antibody. However, inhibition or absence of IDO com-bined with therapies targeting immune checkpoints, suchas CTLA-4, PD-1/PD-L1, and GITR, acts synergistically tocontrol tumor growth and improve OS (44). Thus, com-bining an agent that inhibits IDO with another immuno-therapywould appear to be a rational approach and is beingevaluated in several clinical trials (Table 2). A phase II trial isevaluating the IDO inhibitor indoximod in combinationwith the therapeutic vaccine sipuleucel-T in patients withprostate cancer (Table 2; ref. 12).
Adoptive cell transfer and T-cell engineering. Adoptivecell transfer (ACT) involves the collection of tumor-infil-trating lymphocytes (TIL) from patients, the in vitro expan-sion of autologous lymphocytes with reactivity to tumorantigens, and the subsequent transfer back to the patient,with the expectation that the tumor-specific lymphocyteswill attack the tumor (11, 45). ACT has demonstrateddurable complete responses in patients with melanoma(45). In a phase II study, 20 of 93 patients with metastaticmelanoma (22%) had durable, complete remissions(>3–7 years) after treatment with IL2 and ACT of TILs.
In addition to the expansion and transfer of TILs,approaches to modify the patient’s T cells are underevaluation. These include engineering T cells using chi-meric antigen receptors (CAR) to redirect them to specifictumor-antigen targets before reinfusion. T-cell receptor(TCR) gene therapy is another strategy in development;the objective is to induce immune reactivity againsttumors by introducing genes encoding a tumor-reactiveTCR into patients’ T cells, improving immune reactivity.Combining these types of approaches with other immu-notherapies may further improve clinical efficacy. Trialsof ACT, CARs, and TCR gene therapy in combination withimmune checkpoint inhibitors or other approaches areongoing or under consideration.
Therapeutic vaccines. Although the variousmechanismsof actionof therapeutic vaccines are beyond the scopeof thisreview (46, 47), most vaccines are designed to (i) presenttumor antigens to the immune system and (ii) provideimmune modulation. Because of their differing mechan-isms of action, vaccines and other immunotherapies arepotential combination partners. Clinical data have shownpromising results with some combinations, for example,gp100 peptide vaccine and IL2 in melanoma, and ipilimu-mab combined with granulocyte macrophage-colony stim-ulating factor cell-based vaccine in pancreatic cancer (48,49). However, no survival advantage was seen in patientswithmelanoma treated with gp100 plus ipilimumab versusthose given ipilimumab alone in a phase III trial (13, 17).
Various phase I and II clinical trials combining a vaccinewith a checkpoint inhibitor are ongoing in patients with
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melanoma or prostate cancer (Table 2; ref. 12). However, aclear demonstration of the vaccine’s ability to induce clin-ically relevant antitumor responses in patients is required,as historically, the clinical translation of cancer vaccinesinto efficacious therapies has been challenging (with theexception of sipuleucel-T, the only approved therapeuticcancer vaccine; ref. 47). Data suggest that T cells activated atthe vaccine site are "shut down" when they enter the tumormicroenvironment, most likely due to tumor-mediated T-cell–suppressive mechanisms (50, 51). With tools such asPD-1 immune checkpoint inhibitors that are designed toblock tumor-mediated T-cell suppression in the tumormicroenvironment, it is worth evaluating whether vaccinesmay improve clinical efficacy when combined with a check-point inhibitor. However, data from the only publishedvaccine/PD-1 checkpoint inhibitor study showed the addi-tion of a vaccine did not improve the efficacy of PD-1inhibition (52).
Integrating immunotherapies with existingtherapeutic modalities
Existing treatment modalities, (e.g., chemotherapy, radio-therapy, and molecularly targeted therapies) cause tumorreduction, not only through cytotoxic/cytostatic effects, butalso through mechanisms that may potentiate immuneactivity, including modification of the tumor microenviron-ment and release of tumor antigens. This activity may becomplementary, even synergistic, to the immunotherapiesdesigned to support an antitumor immune response.
The immune effects of chemotherapy and radiotherapyare widely recognized and reviewed elsewhere (53–62).Immune potentiatingmechanisms include release of tumorantigens for immune presentation, depletion of immuno-suppressive cells (e.g., MDSCs, Tregs), activation ofimmune effectors (NK cells, DCs, B cells, conventionaleffector T cells), and sensitization of tumor cells to lysis.
Targeted therapies may also sensitize tumor cells toimmune-mediated killing by a variety of mechanisms.These have been reviewed by Vanneman and colleagues(58), and includepromoting effectiveDCmaturation, T-cellpriming, activation, and differentiation into long-livedmemory T cells, increasing expression of death receptorsor "distress" ligands, reducing expression of prosurvivalsignals, abrogating the production of tumorigenic inflam-mation, and inhibiting immunosuppressive cell types (63).BRAF inhibitorsmay also increase TILs and enhance antigenpresentation (64, 65). Interestingly, while the BRAF inhi-bitors have a potentiating effect on the immune system,MEK inhibitors have a possible reverse effect, reducing thesecretion of cytokines (66) and reducing the activity ofT lymphocytes (65) and DCs (67).
Clinical experience and considerations in combiningnovel immunotherapies with existing treatmentmodalities
Ipilimumab is the most widely studied combinationpartner for existing treatmentmodalities, anddata highlightthe need for careful consideration in the choice of combi-
nation partner and approach to treatment. Preliminary datafor ipilimumab in combination with chemotherapy, radio-therapy, and targeted therapy with BRAF inhibitors, arediscussed below, alongside data with other immuno-therapies. Table 2 provides a summary of ongoing clinicaltrials with immunotherapies (excluding ipilimumab) incombination studies with chemotherapy, radiotherapy,and targeted therapies (12).
Chemotherapy combinations. Ipilimumab has shownpromising results when combined with chemotherapy inpatients with melanoma and lung cancer; however, dataindicate that careful consideration of the combinationapproach is going to be important in regard to tolerabilityand optimizing patient outcomes.
Patients with previously untreated melanoma whoreceived ipilimumab (10mg/kg) plus chemotherapy (dacar-bazine) had significantly improvedOS comparedwith thosewho received chemotherapy alone (11.2 months vs. 9.1months; ref. 15). However, the benefit of the combinationrelative to ipilimumab alone remains unclear, as there wasnot an ipilimumab-alone arm in the trial. The combinationwas also less well tolerated compared with dacarbazinealone. Grade 3 or 4 adverse events occurred in 56.3% ofpatients treated with ipilimumab/dacarbazine comparedwith 27.5% treated with dacarbazine/placebo (P < 0.001;ref. 15). Similarly, data from a three-arm, phase I studyshowed that ipilimumab could be safety combined witheither dacarbazine or carboplatin/paclitaxel in patients withmelanoma (68).
Combining ipilimumab with paclitaxel and carbopla-tin significantly improved immune-related progression-free survival (irPFS) compared with chemotherapy alonein a phase II study in patients with NSCLC and extensive-disease SCLC (69, 70). However, the improvement inirPFS was only evident when the drugs were given on aphased schedule (e.g., two doses of placebo plus pacli-taxel/carboplatin followed by four doses of ipilimumabplus paclitaxel/carboplatin), not when they were givenconcurrently. Phased ipilimumab, concurrent ipilimu-mab, and control, respectively, were associated withmedian irPFS of 5.7, 5.5, and 4.6 months in patientswith NSCLC, and 6.4, 5.7, and 5.3 months in patientswith SCLC. The overall incidence of treatment-relatedgrade 3/4 adverse events was similar across the arms, andipilimumab did not appear to exacerbate the adverseevents associated with chemotherapy (69, 70). Ongoingtrials are further evaluating ipilimumab/chemotherapycombinations in melanoma and lung cancer, as well asin various other solid tumors, and will hopefully provideinformation about how best to combine these treatmentmodalities.
Nivolumab is being investigated in combination with avariety of agents in a large phase I trial (CheckMate 012,NCT01454102) in chemotherapy-na€�ve patients withNSCLC. Treatment arms include nivolumab monotherapyand nivolumab in combination with three, platinum-baseddoublet chemotherapy regimens, bevacizumab given afterat least four cycles of platinum doublet chemotherapy, and
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erlotinib (EGFR-mutation positive nonsquamous NSCLCpatients). Preliminary data indicate that nivolumab plusplatinum-based chemotherapy has a manageable safetyprofile with no drug-related deaths reported so far. Objec-tive responses have been observed in each arm, and 1-yearOS rates ranged from 50% to 87% (71).Radiotherapy combinations. Ipilimumab has been eval-
uated in combination with radiotherapy in patients withmetastatic CRPC and melanoma. Promising activity withmanageable tolerability was observed in a phase I/II trialin patients with CRPC who had progressed after antian-drogen therapy (72); however, results from a phase IIItrial showed no significant improvement in OS with theaddition of ipilimumab to radiotherapy in post-docetaxelCRPC. A subgroup analysis did suggest benefit forpatients with less advanced disease (73). An analysis ofclinical data from 21 patients with advanced melanomawho had received radiotherapy after ipilimumab progres-sion on the Italian Expanded Access Program indicatedthat radiotherapy after ipilimumab treatment may furtherpotentiate its effect (74). A local response to radiotherapywas detected in 13 patients (62%), while 8 patients (38%)did not show any local regression. The median OS for all21 patients was 13 months (range 6–26). Eleven (85%) of13 patients with local response showed an abscopaleffect, suggesting that local response to radiotherapy maybe predictive for the abscopal response and outcome. Themedian OS for patients with and without abscopalresponses was, respectively, of 22.4 months (range 2.5–50.3) and 8.3 months (range 7.6–9.0). There are nowover 15 clinical trials alone in progress to evaluate ipili-mumab plus radiotherapy.Initial data from a phase I trial of MPDL3280A, an anti–
PD-L1 monoclonal antibody, in combination with localradiotherapy showed evidence of activity in the five patientstreated (75). Overall, case reports and data from severalsmall clinical studies showing successful, sometimes dra-matic, outcomes with radiotherapy/immunotherapy com-binations in patients with melanoma provide additionalsupport for further evaluation; these are comprehensivelydiscussed by Barker and Postow (76).Targeted therapy combinations. Clinical data are lim-
ited on the efficacy of combining ipilimumab with tar-geted agents, although numerous trials are ongoing,particularly in melanoma, where three targeted therapiesare now approved in the United States for patients withmelanoma and mutated BRAF (dabrafenib, vemurafenib,and trametinib).Immunotherapy and BRAF inhibitor combinations are
extensively reviewed by Hu-Lieskovan and colleagues (77).Some data indicate that the sequencing of BRAF inhibitorsand ipilimumab has a marked effect on the efficacy andtolerability of the combination in patients with BRAF-mutant melanoma, and indicate that the drugs should besequenced (78–80). Data from a recent retrospective anal-ysis of a cohort of patients treatedwith immunotherapy andthen a BRAF inhibitor (with or without a MEK inhibitor)showed prior immunotherapy did not appear to have an
adverse effect on response to a BRAF inhibitor. However,outcomes were poor when ipilimumab was given afterBRAF inhibitor discontinuation (81).More data are needed,but there is some rationale to use either agent first in asequencing approach, depending on the disease kinetics. Inmore rapid progressors, a BRAF inhibitor may be used firstto reduce tumor load followed by ipilimumab tomaintain aresponse; in patients with more indolent disease, ipilimu-mab may be given first followed by vemurafenib to reducetumor burden (78).
In a phase I trial, concurrent administration of vemur-afenib and ipilimumab at the approved monotherapydoses or with a lower dose of vemurafenib resulted inhepatotoxicity that was greater than expected for eitheragent alone (80). These safety analyses demonstrate therisk of using vemurafenib and ipilimumab concurrently,and these drugs should not be used in combinationoutside of a clinical trial. Ongoing studies are evaluatingthe optimal sequence of these agents in patients withBRAF-mutant metastatic melanoma. Severe cutaneousand neurologic toxicity has also been reported in twopatients with melanoma during therapy with vemurafe-nib after receiving treatment with a PD-1 immune check-point inhibitor (nivolumab or pembrolizumab; ref. 82).It is also noteworthy that dose-limiting toxicities havebeen observed in patients with RCC treated with thetargeted agent sunitinib and either rhIL21 (hematologictoxicity) or the anti–CTLA-4 agent tremelimumab (renalfailure), further emphasizing the need for caution whenevaluating combinations (83, 84).
RCC is a tumor for which combining immunotherapyand targeted therapy is of substantial interest. Preliminarydata from aphase II trial of nivolumab in combinationwithpazopanib or sunitinib in patients with metastatic RCCshowed evidence of activity with ORRs of 45% and 52%,respectively, and amanageable safety profile (85). This trialand others evaluating various combinations in RCCcontinue.
The anti-CD137 agents urelumab and PF-05082566 areboth in phase I trials in combination with rituximab inpatients with non-Hodgkin lymphoma (Table 2). Clinicalstudy of these agents with rituximab is based on preclin-ical data that have shown enhanced tumor regressionwhen an anti-CD137 agent was used after a therapeuticmonoclonal antibody (86, 87). The anti-CD137 antibodyis proposed to enhance rituximab-dependent cytotoxicitythrough antigen-dependent cell-mediated cytotoxicity(86). Recent preclinical data showing enhanced antilym-phoma activity with rituximab combined with KIR block-ade (lirilumab) also support clinical investigation of thiscombination (34).
ConclusionsImmuno-oncology is an evolving treatment modality,
with agents being studied for their potential to providelong-term survival across a broad range of tumor types,and for their synergistic activity when combined with othertreatmentmodalities. It is important now to determine how
www.aacrjournals.org Clin Cancer Res; 20(24) December 15, 2014 6265
to advance this field and how to use these new immu-notherapies most effectively to achieve the best patientoutcomes. Areas of investigation are broad, and includecombining or sequencing immunotherapies that targetdistinct immune pathways, combining or sequencing animmunotherapeutic agent with existing treatment modal-ities, and determining the optimal schedule of therapies incombination regimens. At present, it is difficult to identifythe best combination approaches to pursue given the lim-ited data and the somewhat unexpected occurrence oftoxicity with some combinations (e.g., ipilimumab andvemurafenib). Future data from preliminary clinical studieswill help to direct research.
Combining immunotherapies has the potential to over-comemore than one of the barriers that tumor cells developto evade the immune system, and may provide an OSbenefit in a greater portion of patients comparedwith eitheragent alone (Fig. 1). However, the ideal sequence, schedule,and combination of immunotherapies need to be deter-mined. Likewise, it is important to determine optimal dose,schedule, and sequence when combining an immunother-apywith radiotherapy, chemotherapy, or targeted agents, asthese therapies all have different mechanisms of action. Afinal consideration for combining immunotherapieswill beto identify the regimens with the best risk–benefit profile.We can expect improvements in overall clinical efficacy asnew agents targeting alternative or overlapping tumor-asso-ciated immunosuppressive mechanisms are developed andused in combination or sequentially.
Disclosure of Potential Conflicts of InterestS.J. Antonia is a consultant/advisory board member for Bristol-Myers
Squibb and MedImmune/AstraZeneca. J. Larkin reports receiving com-mercial research grants from Bristol-Myers Squibb, Novartis, and Pfizer,and is a consultant/advisory board member for Bristol-Myers Squibb,GlaxoSmithKline, Merck, Novartis, Pfizer, and Roche/Genentech. (Note:all consultancy/advisory board membership was uncompensated after2012.) P.A. Ascierto reports receiving commercial research grants fromBristol-Myers Squibb, Merck, Roche/Genentech, and Ventana; speakersbureau honoraria from Bristol-Myers Squibb, GlaxoSmithKline, andRoche/Genentech; and is a consultant/advisory board member for Bris-tol-Myers Squibb, GlaxoSmithKline, Merck, Novartis, Roche/Genentech,and Ventana. No other potential conflicts of interest were disclosed.
Authors' ContributionsConception and design: J. Larkin, P.A. AsciertoDevelopment of methodology: J. Larkin, P.A. AsciertoAcquisitionofdata (provided animals, acquired andmanagedpatients,provided facilities, etc.): P.A. AsciertoAnalysis and interpretation of data (e.g., statistical analysis, biosta-tistics, computational analysis): J. Larkin, P.A. AsciertoWriting, review, and/or revision of the manuscript: S.J. Antonia,J. Larkin, P.A. AsciertoAdministrative, technical, or material support (i.e., reporting or orga-nizing data, constructing databases): P.A. AsciertoStudy supervision: P.A. Ascierto
AcknowledgmentsThe authors thank Rebecca Turner of StemScientific, a health care com-
munications firm funded by Bristol–Myers Squibb, for providingwriting andeditorial support.
Grant SupportJ. Larkin is supported by the NIH Research Royal Marsden Hospital/
Institute of Cancer Research Biomedical Research Centre for Cancer.
Received July 2, 2014; revised September 17, 2014; accepted October 4,2014; published OnlineFirst October 23, 2014.
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