The future of immunotherapy in advanced renal cell carcinoma: beyond PD-1/PD-L1 inhibitors

The advent of immunotherapy has revolutionized the landscape of treatment in several cancers, with renal cell carcinoma (RCC) being one of the most responsive to this therapy [1]. This therapeutic approach is based on the complex interaction between the cancer and the immune system. It begins with cancer cells activating the innate and adaptive immune systems, resulting in tumor cell death. However, the same process leads to a natural selection of resistant clones, capable of resisting and eluding the immune response. One of the most recognized mechanisms of immune resistance is the upregulation of programmed death ligand 1 (PD-L1) on tumor cells. PD-L1 binds programmed cell death 1 (PD-1) on T cells. The PD-1 axis is usually activated as an immune tolerance mechanism. By activating this path, resistant clones suppress the immune activity and escape T-cell recognition [2].

In RCC, immunotherapy with PD-1 inhibitors emerged initially as a subsequent treatment option after tyrosine kinase inhibitor (TKI) failure [3]. In recent years, several combinations between TKIs and PD-1/PD-L1 inhibitors have been studied as first-line treatment and compared with sunitinib monotherapy. In addition to their primary anticancer effects, TKIs can increase T-cell infiltration and decrease immune suppression in the tumor microenvironment. Different TKI anti-PD-1 combinations pembrolizumab plus axitinib (KEYNOTE-426 trial), pembrolizumab plus lenvatinib (CLEAR trial) and nivolumab plus cabozantinib (CHECKMATE 9ER trial) showed an improved overall response rate (ORR) and general better survival outcomes in terms of progression-free survival (PFS) and overall survival (OS) [4–6]. Moreover, in the phase III trial KEYNOTE-564, pembrolizumab was also found to improve disease-free survival as adjuvant therapy compared with placebo in high-risk RCC after surgery [7].

However, because the majority of patients eventually develop resistance to PD-(L)1 inhibition in one of several ways, long-term outcomes for RCC require further improvement. For example, tumor cells can activate alternative inhibitory pathways or create an ‘immune cold’ microenvironment [8,9]. Thus, there is a great interest and important clinical need of exploring other possible immune targets and finding predictive biomarkers. At this time, oncologists are helped in clinical practice by prognostic factors that are mainly laboratoristic or clinical. The discovery of novel molecular or genomic predictive factors could further help understanding and aid in selecting which patients could benefit from a specific treatment [10,11].

Cytotoxic T lymphocyte antigen 4

Cytotoxic T lymphocyte antigen 4 (CTLA-4) is a protein receptor constitutively expressed on regulatory and activated T cells. It binds with CD80 and CD86 proteins on antigen-presenting cells, thus causing the inhibition of T-cell activation and migration. CTLA-4 acts as an immune checkpoint between two types of immune cells and does not directly affect the interaction between T cells and cancer cells as does PD-1. Therefore, acting on a different phase than the PD-1/PD-L1 axis, targeting both pathways has been studied in different neoplasms to avoid possible resistance [11].

Ipilimumab is a fully human monoclonal antibody (mAb) that targets CTLA-4 and was first approved as monotherapy in metastatic melanoma [12]. Subsequently, ipilimumab showed positive results in combination with anti-PD-1 mAb nivolumab in other malignancies, such as non-small-cell lung cancer (NSCLC), malignant pleural mesothelioma and esophageal cancer [13]. In metastatic RCC, ipilimumab was also initially studied as monotherapy in a phase II study including treatment-naive and IL-2-pretreated patients. With 3 mg/kg dose, 13% of patients had an objective response, and 33% experienced grade 3–4 toxicity [14]. Due to the significant toxicity, ipilimumab monotherapy was not further investigated. Ipilimumab was successively studied with nivolumab in phase I study Checkmate-016, in different dosage depending on treatment arm. The schedule with nivolumab 3 mg/kg and ipilimumab 1 mg/kg was the combination that showed the best balance of efficacy and toxicity with ~40% of ORR, 2 years OS of 67.3% and grade 3–4 adverse events of 38.3% [15].

These results lead to Checkmate-214, a phase III randomized trial that compared nivolumab and ipilimumab versus sunitinib, the standard of care at the time. In patients with intermediate and poor-risk disease as for IMDC criteria, in two of three co-primary end points, the combination showed improved efficacy with better ORR compared to sunitinib alone, 42 versus 27% and higher survival rates at 18 months with 75 versus 60% of patients alive. The benefit in OS was maintained at 5-year follow-up, with 43% of patients alive in the experimental arm versus 31%. Conversely, PFS was longer with the combination, 11.6 versus 8.4 months but did not meet the prespecified statistical significance criteria. Interestingly, in the 23% of patients with good-risk disease, ORR and PFS was better with sunitinib, but with no difference in OS. Grade 3–4 adverse events were inferior with nivolumab and ipilimumab than with sunitinib, 46 versus 63% [16]. Following these results, the combination of nivolumab and ipilimumab is widely approved and used for intermediate- and poor-risk patients.

More recently, the same combination, with the addition of cabozantinib 40 mg, met its primary end point of improved PFS (hazard ratio 0.73, 95% CI: 0.57–0.94; p = 0.013). However, OS data are immature, complete response with the triplet therapy was surprisingly low at 3% and toxicity was also important with the triplet combination with 73 versus 41% of grade 3–4 toxicity and discontinuation of 12 versus 5% [17].

In advanced RCC, other combinations of anti-PD-(L)1 and anti-CTLA-4 are currently being studied. MK-3475-03A (NCT04626479) and MK-3475-03B (NCT04626518) are phase Ib/II umbrella studies ongoing in first-line and pretreated RCC. One arm in both studies involve a co-formulated antibody of pembrolizumab and a novel anti-CTLA-4 agent, Quavonlimab (MK-1308), alone (03B) or in combination with lenvatinib (03A). Another coformulation, MEDI5752 is also being evaluated, in combination with axitinib (NCT04522323). Nivolumab and ipilimumab were also tested in adjuvant setting, a more challenging setting in RCC due to discordant results in immunotherapy trials [18]. However, the combination did not improve disease-free survival (DFS) compared with placebo, and the OS data are currently too immature. Another combination of anti PD-L1 agent durvalumab with anti-CTLA-4 agent tremelimumab is under investigation in this setting (NCT03288532). Further data from triple combination and longer follow-up for COSMIC-313 trial are awaited. The main concern regarding triplets is the management of important toxicities in the face of limited survival gainings. Therefore, results from a higher number of studies will determine whether triplets will be considered a standard-of-care for first-line treatment. Similarly, results from durvalumab plus tremelimumab combination in adjuvant setting will help clarify which patients could benefit from an adjuvant treatment.

Lymphocyte activation gene-3

Lymphocyte activation gene-3 (LAG-3) is an inhibitor receptor that binds the MHC class II. It is expressed on various immune cells, such as activated T, B and NK cells. The activation of LAG-3 induces the inhibition of T-cell proliferation and diminishes the production of inflammatory mediators such as IL-2, IFN- γ and TNF. Furthermore, in the tumor microenvironment, LAG-3 is also expressed on tumor-infiltrating lymphocytes, where it seems to be associated with increased activity in suppressive T cells and reduced activity in cytotoxic T cells with decreased proliferation and production of cytokines. All these functions help create an immune microenvironment with a depletion of immune response. The role of LAG-3 as an immune checkpoint makes it a potential target for immunotherapy. Moreover, LAG-3 seems to be highly expressed in the RCC microenvironment [19].

Relatlimab is the first anti-LAG-3 agent approved in solid tumors, with positive results in metastatic melanoma in combination with nivolumab [20]. Favezelimab (MK-4280) is a humanized IgG4 monoclonal antibody against LAG-3. It is currently being studied in combination with pembrolizumab in various malignancies such as lung cancer (NCT03516981) and colorectal cancer (NCT05064059). The combination of pembrolizumab and favezelimab is being studied in advanced RCC in the umbrella phase Ib/II studies MK-3475-03A (NCT04626479) and MK-3475-03B (NCT04626518), and results are highly anticipated. Given the positive outcomes in melanoma, results from trials with anti-LAG3 agents are the most expected in advanced RCC. This would expand the range of immune pathways targetable and further vary the treatments to avoid immune resistance.

T-cell immunoglobulin & ITIM domain

T-cell immunoglobulin and ITIM domain (TIGIT) is a receptor expressed by a variety of immune cells such as CD4+ and CD8+ T and NK cells, and it is often hyperexpressed in the tumor microenvironment. TIGIT binds to CD155, CD112 and CD113, which are generally overexpressed in cells. RCC is one type of cancer in which the TIGIT pathway seems to be more upregulated. The mechanism of action is not fully clear but it seems that the binding decreases the function of immune cells by direct inhibition, by reducing the production of cytokines and shifting to an inhibitory phenotype. Moreover, TIGIT can intervene in the phosphoinositide 3-kinase cascade pathway and nuclear factor kappa B, suppressing the activation of NK and T cells [21]. For these reasons, also TIGIT is seen as a promising target.

Agents targeting TIGIT in combination with anti-PD-(L)1 agents are being studied in various types of cancer. Egitilimab (NCT04761198) and tiragolumab are two agents in the final phases of development. The latter, in combination with atezolizumab, showed some promising results in NSCLC [22], but the phase III trial (NCT04294810) did not met the primary PFS end point. Vibostolimab is another anti-TIGIT agent that has demonstrated antitumor activity in monotherapy and in combination with pembrolizumab in advanced solid tumors [23]. In advanced RCC, vibostolimab is currently being studied in an arm of in the umbrella phase Ib/II studies MK-3475-03A (NCT04626479).

Immunoglobulin-like transcript 4

Immunoglobulin-like transcript 4 (ILT4) receptor is generally expressed by various cells of the myeloid lineage, such as granulocytes, macrophages, monocytes and dendritic cells. Its main ligands are MHC class I, HLA-G and other HLAs. Expression of these molecule are correlated with poor prognosis and immunosuppressive tumor microenvironment. Moreover, new data indicate that targeting ILT-4 in tumor microenvironment may induce a pro-inflammatory surrounding [24]. Therefore, anti-ILT-4 agents, in combination with anti-PD-(L)1 agents, could improve the immune response against cancer cells. MK-4830 is an anti-ILT-4 agent that showed antitumor activity and a good safety profile alone and in combination with pembrolizumab in solid tumors [25]. The combination of pembrolizumab and MK-4830 is currently being studied in advanced RCC in pretreated patients in the umbrella study MK-3475-03B (NCT04626518). The same combination is also being evaluated in NSCLC (NCT04165083), ovarian cancer (NCT05446870) and melanoma (NCT04303169). Another anti-ILT-4 agent, CDX-585, is being evaluated in earlier phase in several neoplasm, including RCC (NCT05788484).

Alternative immune strategies (vaccines, T-cell agonists, CAR-T)

The intestinal microbiota has recently draw attention for its primary role in cancer and especially as an immune modulator. With the increasing use of immune agents in oncology, interest in the gut microbiota has increased even more with preclinical data that suggest a possible involvement in predicting poor or good response, especially when altered by antibiotics [26]. In a study of patients with kidney cancer, a more diversified microbiota was related to a better response to checkpoint inhibitors [27]. CBM588 is a live bacterial product containing Clostridium butyricum. A retrospective study in lung cancer evidenced the impact of CBM588 on PFS and OS in patients treated with checkpoint inhibitors [28]. An interesting phase I trial investigated the combination of nivolumab and ipilimumab with or without CBM588 in first-line RCC in 30 patients randomized 2:1. Despite the small numbers, PFS was significantly improved with the combination (12.7 vs 2.5 months, hazard ratio 0.15, 95% CI: 0.05–0.47; p = 0.001). Response Rate was also higher but not statistically significant (58 vs 20%; p = 0.06) [29]. CBM588 is currently being studied in RCC in combination with nivolumab and cabozantinib in a phase I trial (NCT05122546). Another strategy to trigger the immune system into the fight against cancer cells are vaccines. Being an immunogenic cancer, RCC is ideal for the development of vaccines. Several trials in RCC have been conducted in the past decade, mainly early phase trials, with different compounds such as autologous tumor cell vaccines, peptide vaccines and dendritic cell vaccines. Preliminary results were generally good in ORR and PFS, but data are limited by the overall small number of patients in these studies [30]. One of the major and most recent vaccine trials, IMPRINT, was a phase III study investigating IMA 901, a multipeptide vaccine, in combination with sunitinib versus sunitinib alone in first-line metastatic RCC. Primary end point of OS was not met [31]. Currently several vaccines are being investigated in RCC in combination with various agents both in early phase (NCT05127824) or in metastatic setting (NCT05641545, NCT05329532).

Chimeric antigen receptor (CAR)-T cells are engineered to recognize and bind to a specific antigen. CAR-T cell therapies are also a promising field in cancer immunology. In the past three decades, the role of T cells in RCC have been widely evidenced, particularly for IL-2 [32]. Several phase I and II trials with CAR-T cells are ongoing in RCC with different targets such as VEGF (NCT01218867), CCT-301 (NCT03393936) and CD70 (NCT02830724). These last strategies have yet to be demonstrated to be widely effective in solid tumors. However, there is an high interest in exploring the microbioma as a possible future ally in immunotherapy. Further results from trial with bacterial product will help define subsequent landscapes.

Take home message

Immunotherapy with anti-PD-(L)1 agents in combination with TKI or ipilimumab is now the cornerstone of treatment in advanced RCC. Pembrolizumab also revealed its role in adjuvant setting. However, despite progress in the outcomes, some patients show primary resistance, and the majority of patients will develop eventual resistance to such agents [2].

Therefore, there is an unmet need to find further combinations or agents that will help overcome primary and secondary resistance. Anti-CTLA-4 agent ipilimumab has already an established role in combination with nivolumab. However, the most eagerly anticipated results from the ongoing trials are those from combinations of three agents: anti PD-(L)1, anti CTLA-4 and TKI, particularly with regard to whether toxicity will be a limiting issue. Other targets, such as TIGIT, LAG-3 and ILT-4 have promising results in early trials, and results from bigger studies are awaited. Finally, the use of bacterial products seems to have an interesting perspective and further results from phase II and III trials will help clarify its efficacy.