Long considered an immunogenic tumour, immunotherapy has been the cornerstone of systemic treatment in renal cell carcinoma (RCC) for decades. Since the introduction of interleukin 2 and interferon-alfa in the 80s to the more recently approved nivolumab (anti-PD-1) in second line setting. Moreover, on the basis that anti-CTLA-4 and anti-PD-1/PD-L1 intrinsic mechanisms are different, double checkpoint inhibition was proposed to further improve anti-tumor immune response. The first trial to assess double checkpoint inhibition was the Checkmate 016 (nivolumab and ipilimumab), showing acceptable safety and promising antitumor activity that led to the first phase III trial with combination immunotherapy in RCC, the Checkmate 214. This trial showed superior overall survival and response rate of the combination immunotherapy (nivolumab and ipilimumab) versus sunitinib in intermediate- and poor- risk advanced RCC, leading to its approval in this setting. Despite these advances, there is still room for improvement. In this sense, cytokines and T-cell costimulatory molecules are currently under investigation. This review summarizes the principles of immunotherapy and its role in RCC, provides an update on double checkpoint blockade and finally discusses the major challenges with double checkpoint blockade.
RATIONAL FOR IMMUNOTHERAPY
Three steps need to be achieved in order to yield antitumor immunity: 1) immunization which implies antigen presentation and dendritic cell maturation, 2) T-cell response which requires interaction between stimulatory and inhibitory molecules and surface proteins, and 3) immunosuppression that implicates the tumor microenvironment strategies that alter T cell effects through suppressive ligands (such as PD-L1,PD-L2) or molecules (indoleamine 2,3-dyoxigenase-IDO) among others [1, 2].
T-cell response regulation has revolutionized the targets in cancer. By removing known inhibitory pathways, T-cell response can be let freely to act. One of the effectors of this carefully delineated balance are the cytotoxic T-cells surface proteins that allow for immune response restrain, known as checkpoint proteins . On nature they display a wide variety, but so far only two have been well described in literature. Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and Programmed cell death protein (PD-1) are surface proteins that undergo upregulation after T-cells are activated [4, 5]. These inhibitory checkpoint proteins exemplify different mechanisms and pathways but ultimately own the same objective: lighten and improve antitumor immune response [6, 7].
T-cell activation requires interaction between CD28 on the T-cell surface and B7 on the antigen-presenting cell surface. CTLA-4 displaces CD28 from B7 which ensues T-cell suppression and at the same time enhances T regulatory cells activation and suppresses helper T-cells [4, 8]. Mellman et al. suggests that the explanation for therapy at this point needs previous tumor-protective T-cells that would become activated after CTLA-4 blocking . In contrast, PD-1 and its ligands (PD-L1 and PD-L2), members of the B7 gene family, operate through a different inhibitory pathway . These transmembrane proteins, found in T- and B-cells, are responsible for activation of T regulatory cells through de novo conversion of CD4+ T-cells and inhibition of interferon-γ, tumor necrosis factor-α and IL-2 production allowing for immunosuppressive function. Furthermore, if PD-1 is expressed persistently on T-cells an exhaustive phenotype emerges depicting diminished immune function . PD-1 ligands (PD-L1 and PD-L2) are not only expressed by antigen presenting cells but many non-immune cells and even tumor cells [5, 11]. Thus, they present a diversity of ligands different in nature, function and implications on the therapeutic approach.
The well-balanced immune structure can be hijacked by the tumor microenvironment so it can develop, progress and prevail in the organism. This understanding introduced the concepts of immunoevasion and tumor-promoting inflammation among cancer hallmarks [12, 13]. Immune checkpoint blockade with an anti-CTLA-4 and anti-PD-1/PD-L1 represent part of these advances in several immunogenic cancer types such as melanoma, non-small-cell lung cancer (NSCLC) and renal cell carcinoma (RCC), among others .
Immunotherapy has been used in kidney cancer for decades [15, 16]. RCC has been considered as an immunogenic tumor because of the increased infiltration of immune cells including T-cells, dendritic cells, natural killer T-cells, macrophages and memory cells, and also increased cytokine secretion. In the 80s and 90s, advanced RCC immunotherapy was based on high-dose interleukin-2 (IL-2) and interferon-alfa (IFNa) which elicited a high burden of toxicities and yield low efficacy. More recently, Nivolumab, an anti-PD-1 monocloncal antibody, was the first immune checkpoint inhibitor approved by the FDA in 2015 based on results of the CheckMate 025 study [16–18].
In addition, based on the core concept that anti-CTLA-4 and anti-PD-1/PD-L1 intrinsic mechanisms are different, double checkpoint inhibition was proposed to further improve anti-tumor immune response. Anti-CTLA-4 acts in lymphoid organs in early steps of immune response. In contrast, anti-PD-1/PD-L1 acts in the tumor microenvironment later in the response. In this review we will summarize the current evidence of double immune checkpoint blockade in renal-cell carcinoma (RCC).
Double immune checkpoint blockade
Simultaneous pathway blockade and sequential blockade are the backbone of combination therapy in kidney cancer. The association of both immune checkpoint inhibitors in a preclinical setting is more effective disrupting the tumor microenvironment . In RCC, the concept has been proven to be clinically effective within the Checkmate-016 and Checkmate-214 trials.
|Efficacy||Checkmate 016 (N3I1)||Checkmate 214|
|ORR||40% (95% CI 26.4 to 55.7)||42% (95% CI, 37 to 47)|
|Overall Survival||not reached (95% CI, 26.7 months to not reached)||not reached (95% CI, 28.2 months to not estimable|
|12 -month OS||81%||80% (95CI, 76 to 84)|
|PFS||7 months (95% CI, 3.7 to 14.3 months)||11.6 months (95% CI, 8.7 to 15.5)|
IPILIMUMAB-NIVOLUMAB COMBINATION IN ADVANCED RENAL CELL CARCINOMA
The first study to assess the combination of immune checkpoint inhibitors (ICI) in mRCC was the Checkmate-016 study (NCT01472081) . This phase I trial was based on previous results on patients with melanoma and lung cancer where double immune checkpoint blockade was more effective than monotherapy and also on efficacy evidence of anti-CTLA-4 antibodies in mRCC [14, 21]. Its primary endpoint was the overall safety and tolerability of nivolumab plus ipilimumab. Eligible patients were divided in 3 groups that received nivolumab 3mg/kg plus ipilimumab 1mg/kg (N3I1), nivolumab 1mg/kg plus ipilimumab 3mg/kg (N1I3) or nivolumab 3mg/kg plus ipilimumab 3mg/kg (N3I3) every 3 weeks for four cycles and then only nivolumab 3mg/kg every 2 weeks until progression or toxicity. Accrual on N3I3 group was discontinued due to the observed high-grade 3 or 4 adverse effects (AEs) (83.3%). On the other hand, high-grade AEs in N3I1 and N1I3 treatment groups were 38.3% and 61.7%, respectively. N3I1 treatment group had also lower treatment-related AEs, lower treatment discontinuation rates and less patients requiring immune modulating medications (61.7% vs 83.0%). After a median follow-up of 22.3 months, the objective response rate (ORR) for both treatment-naive arms was 40% and the progressive disease (PD) rate as best response was 17%. Complete response (CR) and partial response (PR) rates in N3I1 treated patients were 10.6% and 29.8%, respectively. In comparison, there were no CR in N1I3 treated patients and the PR rate was 40.4%. Safety profile favoured N3I1 treatment group, therefore it was selected for further development in a phase III trial.
Ipilimumab plus nivolumab combination has not been compared with either nivolumab or ipilimumab alone in mRCC. However, results from Chackmate-016 led to the conduct of a phase III trial with the combination. In the Checkmate 214, 1096 patients with previously untreated mRCC were randomized 1:1 to receive nivolumab 3mg/kg plus ipilimumab 1mg/kg every 3 weeks for four doses, then only nivolumab 3 mg/kg every 2 weeks or sunitinib 50mg orally daily for 4 weeks on followed by 2 weeks off. Primary endpoints were overall survival (OS), ORR and progression-free survival (PFS) in the intermediate and poor IMDC risk-groups. After a median of 25.2 months, there was a significant improvement in 18-month OS (75% with the combination versus 60% with sunitinib) and ORR (42% vs 27%, respectively, P < 0.001), favouring nivolumab plus ipilimumab combination . The median OS was not reached (NR) and 26 months for immunotherapy combination and sunitinib, respectively. Of note, the CR rate was 9% and 1%, respectively, and the median PFS was 11.6 and 8.4 months, respectively (HR 0.82, p = 0.03). Similar benefit was seen when evaluating the whole cohort including all IMDC risk-groups (good, intermediate and poor) (secondary endpoint). The safety profile showed any-grade and high-grade AEs of 93% and 46%, respectively, in the immunotherapy combination arm, and 97% and 63%, respectively, in the sunitinib arm. Interestingly, although the AE-related treatment discontinuation rate was superior in the ICI combination arm (22%) versus the sunitinib arm (12%), patients who discontinued in the experimental arm due to drug-related AEs experienced long-term benefit, with durable responses after the last dose of treatment. Moreover, the recently reported PROs (patient reported outcomes) as an exploratory endpoint, showed an improve of the health-related quality of life (HRQOL) across all instruments (Assessment of Cancer Therapy Kidney Sympton Index-19, Functional Assessment of Cancer Therapy-General, and EuroQol five dimensional three level) for the immunotherapy combination arm in patients with intermediate or poor risk mRCC . Efficacy in the good IMDC risk-group only was evaluated as an exploratory outcome. In this good-risk group, sunitinib treated patients had higher 18-month OS, ORR and PF. However, it should be mentioned that the CR rate in good-risk patients treated was higher with the immunotherapy combination (11% versus 5%). Also as an exploratory analysis, among intermediate and high risk patients who had quantifiable PD-L1 expression (<or ≥1%) the combination immunotherapy arm showed superiority in both OS and ORR irrespective of PD-L1 expression versus the control arm. However, mPFS among patients with < 1% PD-L1 expression was similar in both arms of treatment (HR 1.00; 95% CI, 0.80 to 1.26), whereas among patients with ≥1% PD-L1 expression mPFS was superior with the immunotherapy combination (HR 0.46; 95% CI, 0.31–0.67) . On April 16, 2018, the FDA approved the double immune checkpoint blockade, nivolumab plus ipilimumab, for the treatment of intermediate or poor risk, previously untreated advanced RCC patients.
|Treatment related adverse effects.||Checkmate 016||Checkmate 214|
|Median Age (range)||54(26–68)||62(26–85)|
|MSKCC/ IMDC prognosis risk intermediate-poor||55.30%||77.70%|
|Treatment Arm||Nivo 3mg/kg+Ipi 1mg/kg||Nivo 3mg/kg+Ipi 1mg/kg|
|Grade 3-4 toxicity||38.30%||46%|
|Discontinuation rate for toxicity||10.60%||22%|
Despite the remarkable progress that has been achieved with ipilimumab and nivolumab combination, there is still room for improvement in efficacy and safety profile. It remains unclear whether the enhanced efficacy of combined anti PD-1 and anti-CTLA4 therapy is mediated by additive engagement or through independent mechanisms from each drug . T-cell costimulatory molecules represent a vast number of proteins under investigations such as LAG3, TIM3 or TIGIT, VISTA from the immunoglobulin superfamily (IgSF) or OX40, GITR, 4-1BB, CD40 from the tumor necrosis factor receptor superfamily (TNFRSF) and others. Better understanding of each specific protein and its stimulatory role are required for an enhanced development of novel immune checkpoint blockade combinations . Table 3 shows selected combinations in early clinical development phase.
|Phase IIIb/IV||NCT02982954 Checkmate 920||January 2023||Nivolumab plus Ipilimumab||Safety Trial of Nivolumab Combined With Ipilimumab in Subjects With Previously Untreated, Advanced or Metastatic RCC|
|Phase III||NCT03138512 Checkmate 914||July 2023||Nivolumab plus Ipilimumab||A Phase 3 Randomized Study Comparing Nivolumab and Ipilimumab Combination vs Placebo in Participants with Localized Renal Cell Carcinoma Who Underwent Radical or Partial Nephrectomy and Who Are at High Risk of Relapse|
|NCT03288532 RAMPART||December 2037||Active Monitoring or Durvalumab or Durvalumab plus Tremelimumab||An International Investigator-led Phase III Multi Arm Multi Stage Multi-centre Randomised Controlled Platform Trial of Adjuvant Therapy in Patients With Resected Primary Renal Cell Carcinoma (RCC) at High or Intermediate Risk of Relapse|
|NCT03260894 Keynote- 679/Echo-302||June 2020||Pembrolizumab plus Epacadostat or Sunitinib or Pazopanib||A Randomized, Open-Label, Phase 3 Study to Evaluate Efficacy and Safety of Pembrolizumab (MK-3475) Plus Epacadostat vs Standard of Care (Sunitinib or Pazopanib) as First-Line Treatment for Locally Advanced or Metastatic Renal Cell Carcinoma (mRCC)|
|Phase II||NCT03203473 OMNIVORE Study||November 2014||Nivolumab or Nivolumab plus Ipilimumab||Phase II Study of Optimized Management of Nivolumab Based on REsponse in Patients With Advanced Renal Cell Carcinoma|
|Phase I/II||NCT02335918||January 2020||Nivolumab plus Varlilumab||A Phase l/ll Dose Escalation and Cohort Expansion Study of the Safety, Tolerability and Efficacy of Anti-CD27 Antibody (Varlilumab) Administered in Combination With Anti-PD-1 (Nivolumab) in Advanced Refractory Solid Tumors|
|NCT02089685 KEYNOTE-029||June 2020||Pembrolizumab plus Pegylated Interferon alfa-2b or Pembrolizumab plus Ipilimumab||Pembrolizumab Plus Pegylated Interferon alfa- 2b or Ipilimumab for Advanced Melanoma or Renal Cell Carcinoma: Dose-Finding Results from the Phase Ib Study|
|NCT02983045 PIVOT-02||June 2021||Phase I: NKTR-214 + nivolumab Phase II: NKTR- 214 + nivolumab+ipilimu mab||A Dose Escalation and Cohort Expansion Study of CD122-Biased Cytokine (NKTR-214) in Combination With Anti-PD-1 Antibody (Nivolumab) or in Combination With Nivolumab and Anti-CTLA4 Antibody (Ipilimumab) in Patients With Select Advanced or Metastatic Solid Tumors|
|Phase I||NCT02496208||September 2019||Cabozantinib plus Nivolumab or Cabozantinib plus Nivolumab plus Ipilimumab||A Phase 1 Study of Cabozantinib Plus Nivolumab (CaboNivo) Alone or in Combination With Ipilimumab (CaboNivoIpi) in Patients With Advanced/Metastatic Urothelial Carcinoma and Other Genitourinary Tumors|
|NCT01975831||December 2019||Durvalumab plus Tremelimumab||Phase 1 study to evaluate the safety and tolerability of MEDI4736 (durvalumab, DUR)+tremelimumab (TRE) in patients with advanced solid tumors.|
|NCT02210117||November 2020||Arm A: Nivolumab or Arm B: Nivolumab plus Bevacizumab or Arm C: Nivolumab plus Ipilimumab||A Pilot Randomized Tissue-Based Study Evaluating Anti-PD1 Antibody or Anti-PD1 + Bevacizumab or Anti-PD1 + Anti-CTLA-4 in Patients With Metastatic Renal Cell Carcinoma Who Are Eligible for Cytoreductive Nephrectomy, Metastasectomy or Post-Treatment Biopsy|
|NCT02614456||December 2021||Nivolumab plus Interferon-gamma||Combination Immunotherapy With Interferon- gamma and Nivolumab for Patients With Advanced Solid Tumors: A Phase 1 Study|
Cytokines were the main treatment for mRCC during decades; however the rate of response was low. A novel C122-biased cytokine (NTRK-214) is currently under development in combination with nivolumab and ipilimumab in the phase I/II PIVOT-02 trial. It is expected that NKTR-214 may unleash T cell proliferation and disrupt the tumor microenvironment. The combination of NKTR-214 and nivolumab assures a potentially non-overlapping effective synergistic mechanism. This study was conceived as a 4 part study (NCT02983045). Study part 1 determined doses and scheduling according to safety and efficacy profile of the combination. The selected dose and schedule was NKTR-214 0.006 mg/kg and nivolumab 360 mg every 3 weeks per intravenous infusion. In study Part 2, the combination was given to patients with metastatic melanoma, RCC, urothelial carcinoma, non-small cell lung cancer or triple negative breast cancer. The RCC cohort enrolled 48 patients of which PD-L1 status was unknown for 4 patients, 30 had a negative status, and 14 had a positive status. Preliminary results showed in previously untreated RCC patients an overall ORR of 46%. The median time on study was 5.6 months. The PD-L1 negative patients ORR was 53% (9/17), while it was 29% (2/7) for PD-L1 positive patients . In the study part 3, a triple combination will be attempted in order to assess safety, tolerability and efficacy (ORR): NKTR-214 0.006 mg/kg plus nivolumab 360mg, every 3 weeks, and ipilimumab 1mg/kg every 6 weeks. Study part 4 will plan to enrol more patients to further evaluate the triplet combination.
KEY POINTS AND CHALLENGES WITH DOUBLE IMMUNE CHECKPOINT BLOCKADE
Why double and not single-agent?
Double immune checkpoint blockade has been shown to be more powerful than single-agent immunotherapy across different tumour types, but also more toxic . However, the superiority of immunotherapy doublets versus single agents has not yet been demonstrated for mRCC. It is known that nivolumab alone benefits previously treated metastatic renal cell carcinoma patients [22, 28], but we do not know the magnitude of the benefit with the addition of ipilimumab. Recent data with pembrolizumab monotherapy in untreated mRCC patients has shown encouraging activity , with a confirmed ORR of 38.2% (n = 42; 95% CI 29.1–47.9), with 3 complete responses (2.7%) and 39 (35.5%) partial responses. The durable clinical response rate was 59.1 with a favourable safety profile. It seems clear that the addition of ipilimumab is more toxic and some patients may not need the combinations . Further research to better understand which patients do really benefit the combination is required to avoid toxicities (financial and non-financial). Clinical trials with adaptive design such as TITAN (NCT02917772) or OMNIVORE (NCT03203473) will help to understand this issue.
What is the optimal duration of treatment?
There is evidence showing that patients who respond to immunotherapy and combination immunotherapy achieve durable responses and long-term survival . Although immune checkpoint blockade is already a standard of care across different tumour types, there is no clear evidence about the duration of treatment on responders. In recent data from the Keynote-006 4-year survival and outcomes after cessation of pembrolizumab showed that 86% of the patients who completed pembrolizumab 2 years remained progression-free 20 months after the last dose of treatment . Also, it has been shown that nearly 70% of the melanoma patients who discontinued single-agent nivolumab due to toxicity and that obtained a complete or partial response maintained their responses despite the stop of treatment [30, 32]. Moreover, this may be even more complex when it comes to patients who achieve a complete response. The clinical trial Keynote-001 showed that a high proportion of patients who achieved a complete response are able to maintain the response for a long time after the end of treatment, with an estimated 24 month disease-free survival of 89% . Altogether, these results suggest stopping immune checkpoint blockade after a certain period of time on treatment could be a reasonable approach. However, further research on this topic is warranted.
How should we assess atypical responses?
Although there is lack of evidence, we are now familiar with the so known “pseudoprogression” which usually appears as a radiological progression with target lesion increase but without clinical deterioration. There are data suggesting that treatment beyond progression may be an option for some patients [33, 34]. However, there is also evidence supporting that some patients may have hyperprogressive disease, but little is known about the mechanisms involved . It has been speculated to be a result of immunotherapy but it has also been suggested to be the consequence of aggressive natural tumour behaviour. Nonetheless, knowledge on this field is scarce and further studies are needed to better understand and define which patients are more likely to rapidly progress and which ones will instead experience pseudoprogression and therefore benefit of treatment beyond radiological progression .
Several trials will be conducted in the next years that will elucidate future combination’s impact on RCC. In a near future, the patient’s signature tumor biology should be matched with the best corresponding first line option among a handful of options: either monotherapy or combinations. Double immune checkpoint blockade has shown favourable results but adverse effects should be taken into consideration. The most definitive evidence of double checkpoint inhibitor therapy on intermediate-poor risk patients with previously untreated advanced RCC are the results from Checkmate trial 214 with a remarkable 9% complete response rate.
Although we are now familiar with immune checkpoint blockade therapies, there are still some open questions such as optimal duration of treatment or unexpected radiological responses, including primary progressions, that require further study.
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