Advances in immunotherapy in cervical cancer

INTRODUCTION AND BIOLOGICAL RATIONALE OF IMMUNOTHERAPY IN CERVICAL CANCER

Cervical cancer is the fourth most frequently diagnosed cancer and the fourth leading cause of cancer death in women, with an estimated 606 000 new cases and 342 000 deaths worldwide in 2020. The highest incidence and mortality rates are generally observed in countries with the lowest values on the Human Development Index. This striking geographic variation is due, among other factors, to unequal access to prophylactic vaccination and early detection of pre-invasive disease via screening programs. Therefore, cervical cancer is considered a largely preventable disease.1

Human papillomavirus (HPV) is a necessary but not sufficient cause of cervical cancer, with 12 oncogenic or high-risk subtypes classified as group 1 carcinogens by the International Agency for Research on Cancer monographs. In that respect, HPV types 16 (HPV-16) and 18 (HPV-18) are responsible for approximately 70% of cervical cancer cases. Other important cofactors include sexually transmittable infections (human immunodeficiency virus (HIV) and Chlamydia trachomatis), smoking, a higher number of childbirths, and long-term use of oral contraceptives.1

The natural history of cervical cancer is well understood. A multistep carcinogenesis model is widely accepted, starting with HPV infection followed by progression to precancerous lesions, and invasion to cancer, in a long process that may last for up to 15 years. Infection with high-risk subtypes of HPV leads to the production of E6 and E7 oncoproteins, which inhibit tumor suppressor genes p53 and Rb, respectively, crucial for malignant transformation of cells.2 3

Carcinogenesis is greatly influenced by the dynamics and composition of the immune microenvironment, in a process known as ‘immunoediting’. As a virally driven tumor, cervical cancer shows particularly higher lymphocyte infiltration compared with HPV-negative malignancies. Additionally, the increased presence of CD8+ tumor-infiltrating lymphocytes has been linked to improved survival rates4 5 and better efficacy outcomes from standard therapy6 7 in patients with cervical cancer. Intriguingly, despite the presence of tumor-reactive immune infiltrates, tumor growth may persist, since HPV-infected cancer cells can modulate the immune microenvironment to create a pro-tumorigenic state of immune suppression and evasion, through multiple mechanisms: (1) E7 oncoprotein has been shown to downregulate the cyclic GMP–AMP synthase (cGAS) stimulator of interferon gene (STING) pathway, an important innate response pathway to viral DNA that induces the expression of type I interferon genes by directly inhibiting STING. (2) HPV E6 can also dampen type I interferon gene expression by inhibiting the interferon regulatory factor IRF3. (3) Downregulation of antigen presentation on major histocompatibility complex by HPV E5 or mutations in antigen presentation pathway genes lead to decreased recognition by effector T cells. (4) Overexpression of E7 in a pre-clinical cervical cancer model has been shown to upregulate the programmed death-ligand 1 (PD-L1) immune checkpoint on infected tumor cells, inhibiting cytolytic T cell activity. (5) HPV modulates human leukocyte antigen (HLA) expression to engage NK cell inhibitory receptors—for example, through the interaction of HLA-E molecules with NKG2A. (6) Evidence of HPV antigen-specific FOXP3+ T regulatory cells, which function to suppress both CD8+ and CD4+ cells in the tumor microenvironment. (7) CD4+ T cells are typically skewed toward a TH2 response which potentiates a humoral response.8

PD-L1 expression seems to have a major role in creating this ‘immune-privileged’ site for the initiation and persistence of HPV infection by downregulating T cell activity and generating an adaptive immune resistance. Its expression has not been demonstrated in normal cervical tissue, but it is detectable in 95% of cervical intra-epithelial neoplasia, and cervical cancer T cells, antigen-presenting cells, and tumor cells. PD-L1 expression in cervical squamous cell carcinoma varies widely from 19% to 88%, and it is less prevalent in cervical adenocarcinoma (14%).9 The prognostic significance of PD-L1 expression in cervical cancer has been reported in a few studies, with contradictory results.10 Interestingly, a study showed that both the extent and the pattern of PD-L1 expression is an important prognostic factor, since marginal PD-L1 expression, most probably induced by interferon-γ signaling, was associated with a favorable prognosis in comparison with diffuse PD-L1 expression or lack of PD-L1.11

All these findings mentioned above set a robust biological rationale for the development of immunomodulatory therapies, such as immune checkpoint inhibitors, in the cervical cancer population, aiming at restoring an effective anti-tumor immune response.

The treatment of cervical cancer has not changed greatly over the last decade. Early-stage disease may be cured by radical surgery with tailored adjuvant therapy. However, patients diagnosed with locally advanced disease (International Federation of Gynecology and Obstetrics (FIGO) 2009 stage IB2–IVA) despite radical chemoradiation therapy plus high-dose-rate brachytherapy experience a 5- year disease-free survival and overall survival of 47–80%.12 Finally, the management of women with persistent or recurrent disease, who are not candidates for radical-intent local therapies and those who present with metastatic (FIGO 2009 stage IVB) disease, has represented a high unmet clinical need. In the past years, the addition of the anti-vascular endothelial growth factor agent bevacizumab to platinum-based chemotherapy succeeded in extending median overall survival to nearly 17 months.13 More recently, the incorporation of immune checkpoint inhibitors in the therapeutic armamentarium of cervical cancer has represented a major breakthrough. Two pivotal trials, EMPOWER-Cervical 1 and KEYNOTE-826, demonstrated that cemiplimab (anti-PD-1) and pembrolizumab (anti-PD-1) provided a significant overall survival improvement in both post-platinum failure and front-line persistent, recurrent, or metastatic cervical cancer settings, respectively.14 15

The present review is focused on the most relevant published or presented data on clinical trials exploring immunotherapy in cervical cancer in different disease settings, from locally advanced to persistent, recurrent, or metastatic cervical cancer in both front-line and post-platinum progression. Additionally, emerging data coming from early-phase trials on novel immunotherapy approaches have been included in this review.

ROLE OF IMMUNE CHECKPOINT INHIBITORS FOR PERSISTENT, RECURRENT, AND METASTATIC DISEASE FOLLOWING PLATINUM FAILURE

In the persistent, recurrent, and metastatic disease setting, there has been a high unmet clinical need for active therapies to overcome this population’s dismal prognosis. In particular, for patients whose disease has progressed after first-line platinum-based therapy, multiple chemotherapeutic agents can still be an option in subsequent treatment lines. However, the efficacy outcomes were globally very poor, with an overall response rate of less than 20%, median progression-free survival of 3.3 months, and median overall survival of 6.7 months.16 In this adverse scenario arises the clinical development of immune checkpoint inhibitors in the cervical cancer population, based on the aforementioned biological rationale.

Immune Checkpoint Inhibitor Monotherapy Approaches

The first evidence for the clinical activity of an immune checkpoint inhibitor in patients with advanced cervical cancer was obtained from the phase Ib KEYNOTE-028 trial. Twenty-four PD-L1-positive pre-treated patients with advanced cervical cancer (96% squamous cell carcinoma) were enrolled in the trial and received pembrolizumab at a dose of 10 mg/kg every 2 weeks for up to 2 years. The confirmed overall response rate was 17% (95% CI 5% to 37%), with a median duration of response of 5.4 months (95% CI 4.1 to 7.5). No grade 4–5 adverse events occurred and only two patients discontinued pembrolizumab due to grade 3 adverse events—namely, colitis and Guillain-Barré syndrome.17

Subsequently, KEYNOTE-158 was a phase II basket trial that included a cohort of patients with pre-treated advanced cervical cancer, regardless of PDL-1 status. Ninety-eight patients (94% squamous cell carcinoma) were enrolled and received 3-weekly pembrolizumab at a flat dose of 200 mg for a maximum of 2 years. In an updated analysis, with a median follow-up of 36.9 months, the overall response rate of the cervical cancer cohort was 14.3% (95% CI 8.0% to 22.8%), only observing responses in the PDL-1-positive subgroup, with a confirmed overall response rate of 17.1% (95% CI 9.7% to 27.0%). Interestingly, the median duration of response was not reached (range 3.7+ to 35.2+) (Table 1). Treatment-related adverse events occurred in 65.3% of patients, and the most common were hypothyroidism (11.2%), fatigue (11.2%), and decreased appetite (9.2%).18 In 2018, following this efficacy and safety data, pembrolizumab gained Food and Drug Administration (FDA approval in PDL-1-positive (combined positive score ≥1%) advanced cervical cancer after platinum failure.

Table 1

Efficacy data of immune checkpoint inhibitors in the persistent, recurrent, and metastatic cervical cancer setting, according to programmed death-ligand 1 (PD-L1) status (if available)

The phase I/II CheckMate-358 trial evaluated the clinical activity and safety of nivolumab (anti-PD-1) at a flat dose of 240 mg every 2 weeks for a maximum of 24 months, in HPV-related squamous vulvar, vaginal, and cervical tumors, regardless of PDL-1 status. Nineteen patients with metastatic squamous cervical cancer previously treated with up to two prior lines of therapy were included in this trial. Interestingly, 21% of the enrolled patients received the study treatment in the first-line setting. On the latest update, with a minimum follow-up of 24 months, the primary endpoint overall response rate in the cervical cohort was 26% (95% CI 95% to 51%), and the median duration of response was not reached (range 35.3 months to not recorded). It should be underscored that responses were not limited to the PD-L1-positive tumors (Table 1). Regarding the safety profile, any-grade treatment-related adverse events were reported in 63% of the cervical cohort, with diarrhea being the most commonly reported adverse event.19 20

The phase II C-700-01 trial evaluated the efficacy and safety of balstilimab (anti-PD-1), in patients with previously treated recurrent or metastatic cervical cancer, regardless of PD-L1 expression. A total of 161 patients were enrolled in the study (62.7% squamous cell carcinoma and 36.6% adenocarcinoma/adenosquamous) and received balstilimab at a dose of 3 mg/kg every 2 weeks, for a maximum of 2 years. The primary endpoint overall response rate in the overall population was 15% (95% CI 10.0% to 21.8%). The median duration of response was 15.4 months (95% CI 5.7 months to not reached). As a part of an exploratory analysis, investigators demonstrated that balstilimab was clinically active regardless of PD-L1 status (Table 1). Additionally, responses were not restricted to squamous histology (overall response rate of 17.6%), demonstrating an overall response rate of 12.5% in the adenocarcinoma subgroup. Regarding safety data, the most common grade 3 or higher treatment-related adverse events were colitis (3.1%) and diarrhea (1.9%).21 Following these encouraging results, the BRAVA trial (NCT04943627), a phase III randomized study, was designed to compare balstilimab with the investigator’s choice of chemotherapy, but unfortunately, the trial was withdrawn before enrolling its first participant, due to pembrolizumab approval by the FDA in this same disease setting, as specified above.

As the data on the activity of immune checkpoint inhibitors in cervical cancer were coming to light, the EMPOWER-Cervical 1/GOG-3061/ENGOT-cx9 was initiated. This was an open-label, randomized, multicenter, phase III study, comparing the efficacy of cemiplimab with single-agent chemotherapy in patients with recurrent or metastatic cervical cancer whose disease had progressed after front-line platinum doublet, regardless of PD-L1 status. A total of 304 patients received cemiplimab at a dose of 350 mg every 3 weeks, and 304 were treated either with pemetrexed, vinorelbine, gemcitabine, irinotecan, or topotecan, for a maximum of 96 weeks. Most of the enrolled patients (77.8%) had a squamous cell carcinoma, and only 22.2% had an adenocarcinoma/adenosquamous cell cancer. The primary endpoint was overall survival, which was tested hierarchically in the squamous cell carcinoma subgroup followed by the total population. Secondary endpoints included progression-free survival, overall response rate, quality of life, and safety.

Recently, the final overall survival analysis per protocol, with a median follow-up time of 30.2 months, confirmed the overall survival outcomes of the second interim analysis published by Tewari et al in the New England Journal of Medicine: median overall survival was 10.9 months in the squamous cell carcinoma subpopulation who received cemiplimab, compared with 8.8 months in those patients treated with chemotherapy (HR=0.69; 95% CI 0.56 to 0.85; p=0.0023). Median overall survival in the overall population was 11.7 months with cemiplimab compared with 8.5 months with chemotherapy (HR=0.65; 95% CI 0.54 to 0.79; p<0.001). In an exploratory analysis, efficacy data on the adenocarcinoma/adenosquamous subset was also reported, showing a median overall survival of 13.5 months in the cemiplimab arm compared with 7.0 months in the chemotherapy arm (HR=0.54; 95% CI 0.36 to 0.81). Cemiplimab also surpassed chemotherapy in progression-free survival, overall response rate, and duration of response, in the overall and squamous cell carcinoma populations. Additionally, cemiplimab demonstrated a statistically significant benefit in general health status/quality of life and physical functioning versus chemotherapy.14 22

Regarding the baseline PD-L1 status, it should be emphasized that it was neither an eligibility criteria nor a study stratification factor. However, it was retrospectively assessed as part of an exploratory analysis. In the latest update, only 371 of all randomized patients (61%) had valid baseline PD-L1 samples. In the PD-L1 tested population, cemiplimab yielded better overall survival outcomes than chemotherapy, reducing the risk of death by 38% and 35%, in the PD-L1 ≥1% and PD-L1 <1% subgroups. Additionally, responses to cemiplimab were observed regardless of PD-L1 status (Table 1). Regarding the toxicity profile, any treatment-related adverse events occurred in 57.3% of the patients receiving cemiplimab and in 81.7% of those receiving chemotherapy. Up to 5.7% of patients discontinued the treatment due to adverse events in the cemiplimab arm versus 3.4% in the chemotherapy arm.14 22 Based on the trial’s outcomes, cemiplimab was granted priority review by the FDA for women with previously treated recurrent or metastatic cervical cancer in September 2021. Nevertheless, after consulting with FDA, Regeneron ultimately decided to withdraw the biologics license application for cemiplimab in January 2022. Further on, in March 2022, Canada’s regulatory agency approved cemiplimab for patients with recurrent or metastatic cervical cancer progressing after front-line platinum-based chemotherapy. Recently, on October 13, 2022, the European Committee for Medicinal Products for Human Use adopted a positive opinion for cemiplimab in the treatment of patients with cervical cancer, regardless of PD-L1 status, and having progressed, on or after, platinum doublet.

Regarding the CTLA-4 blockade, the phase I/II dose-escalation trial investigated ipilimumab monotherapy in patients with recurrent or metastatic HPV-related cervical cancer having progressed on platinum chemotherapy. Unfortunately, the clinical activity of ipilimumab monotherapy was meager, with only 1 of 34 evaluable patients showing a partial response while the rest had stable or progressive disease.23 These efficacy data suggested that anti-CTLA-4 agents alone are probably ineffective for metastatic disease but could potentially be used as part of a combined regimen.

Immune Checkpoint Inhibitors Combination Approaches

Immune checkpoint inhibitor monotherapy has shown modest efficacy results, with significant primary resistance events in patients with advanced cervical cancer. Recently, increasing pre-clinical and clinical data support the use of immune checkpoint inhibitors combination approach in various tumor types, as a strategy to overcome resistance. Indeed, the dual checkpoint blockade anti-CTLA-4 (cytotoxic T-lymphocyte associated protein 4)/PD-(L)1 allows targeting of the T cell priming and effector phases, respectively, potentially leading to a more effective anti-tumor immune response.24

Several phase II studies evaluating this dual checkpoint inhibition targeting CTLA-4 and PD-(L)1 in patients with advanced cervical cancer are described below.

The CheckMate-358 trial also evaluated the combination of nivolumab plus ipilimumab in patients with recurrent or metastatic squamous cell carcinoma of the cervix who had received up to two prior therapies, regardless of PD-L1 status. Patients were randomly assigned to receive either of these two regimens: (A) nivolumab 3 mg/kg every 2 weeks plus ipilimumab 1 mg/kg every 6 weeks, or (B) nivolumab 1 mg/kg plus ipilimumab 3 mg/kg every 3 weeks for four doses followed by nivolumab maintenance 240 mg every 2 weeks, for up to 2 years. Following the initial efficacy signal, cohort B was expanded to enroll patients in both first- and second-line settings. According to the most recent data update, with a minimum follow-up of 24 months, the overall response rate (primary endpoint) seemed to be higher in combination B than in combination A: 38% and 31%, respectively. For key secondary endpoints, combination B also showed a trend for higher median progression-free survival and overall survival, in comparison with combination A: 5.8 and 20.9 months and 3.8 and 15.2 months, respectively. Interestingly, patients receiving the immune checkpoint inhibitors dual blockade as a chemo-free regimen in the first-line setting (40% of patients in arm A and 64% in arm B) showed globally better efficacy outcomes in overall response rate across both treatment regimens, as compared with those treated in second line or beyond: 39% vs 26% in arm A, and 41% vs 35% in arm B, respectively. Of note, despite having few patients in subgroups, responses were seen regardless of PD-L1 expression (Table 1). Concerning the toxicity profile, it should be underscored that the rate of adverse events, particularly hepatitis and diarrhea/colitis appeared to be higher in patients receiving combination B than with combination A.20

The phase II C-550-01 trial evaluated the combination of balstilimab and zalifrelimab (anti-CTLA-4) in patients with recurrent or metastatic cervical carcinoma with disease progression after first-line platinum-based chemotherapy, regardless of PD-L1 status. A total of 119 patients were finally included in the efficacy analysis of the trial, and received the combination of balstilimab 3 mg/kg every 2 weeks and zalifrelimab 1 mg/kg every 6 weeks, for up to 2 years. The primary endpoint overall response rate was 25.6% (95% CI 14% to 28%). At the time of the data cut-off point, the median duration of response was not reached (not reached; 95% CI 9.7 to not reached). Additionally, responses were seen across all histological subtypes (overall response rate of 32.6% in squamous cell carcinoma and 8.8% in adenocarcinoma/adenosquamous subgroups). Once again, responses were demonstrated regardless of combined positive score (Table 1).

Regarding the immune-related adverse events of any grade, the incidence of gastrointestinal disorders, laboratory abnormalities (creatinine, lipase, aminotransferases, electrolytes, and thyroid-stimulating hormone level abnormalities), and endocrine disorders was higher with the combination than with balstilimab monotherapy.25 Following these results, the RaPiDS study (NCT03894215) was launched. RaPiDS is a phase II randomized clinical trial aiming at assessing the efficacy and safety of balstilimab monotherapy and combined with zalifrelimab in women with recurrent or metastatic cervical cancer with relapse or progression after first-line platinum-based chemotherapy. This trial is already closed for enrollment and its read-out is enthusiastically awaited.

Cadonilimab (AK104) is a next-generation first-in-class anti-PD-1/CTLA-4 bispecific monoclonal antibody being evaluated as monotherapy for patients with recurrent or metastatic cervical cancer after failure of platinum-based chemotherapy. It has received FDA fast-track and orphan drug designation as well as China’s National Medical Products Administration breakthrough therapy designation. The pivotal trial was a multicenter, open-label, single-arm, phase II (NCT04380805) that assessed the efficacy and safety of cadonilimab monotherapy in patients with previously treated recurrent or metastatic cervical cancer. Results showed an overall response rate of 33.0% in 100 patients treated with cadonilimab, with a 12% complete-response rate, and a median duration of response not reached. Importantly, adonilimab yielded responses regardless of PD-L1 status (Table 1). Regarding the safety profile, grade 3 to 4 treatment-related adverse events occurred in 28.8%, and the most common were anemia (7.2%) and decreased appetite (2.7%).26

Beyond CTLA-4 and PD-(L)1, multiple other immune co-inhibitory molecules are also targeted with immune checkpoint blockade in the clinic. Specifically, T cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT) is a promising new target for cancer immunotherapy. TIGIT is a co-inhibitory receptor upregulated by immune cells, such as CD4+ and CD8+ T cells. TIGIT binds to two ligands, CD155 and CD112, that are expressed by tumor cells and antigen-presenting cells. There is now robust evidence that the TIGIT pathway limits anti-tumor and other CD8+ T cell-dependent immune responses. Therefore, the dual PD-(L)1/TIGIT blockade synergistically and specifically enhances CD8+ T cell effector functions.27 Preliminary clinical activity of this combination strategy is emerging in the cervical cancer population.

KEYVIBE-001 trial (NCT02964013) was launched to investigate vibostolimab (anti-TIGIT) alone and in combination with pembrolizumab in patients with advanced solid tumors. The dose-expansion phase of the trial included patients with histologically confirmed, locally advanced, or metastatic PD-1/PD-L1 inhibitor-naïve cervical cancer who had experienced treatment failure with prior platinum-based chemotherapy. Enrolled patients were randomized 1:1 to receive either 200 mg of vibostolimab or 700 mg of vibostolimab in combination with 200 mg of pembrolizumab every 3 weeks, for up to 35 cycles. Among all evaluable patients (n=80), the confirmed overall response rate was 19%, being slightly higher in the 700 mg cohort. As opposed to pembrolizumab monotherapy, the combination was clinically active regardless of PD-L1 status (Table 1). Regarding the safety profile, patients in the 700 mg cohort experienced a higher incidence of treatment-related adverse events of any grade (69% vs 66%) and adverse events leading to discontinuation (13% vs 7%) compared with the 200 mg cohort. Among the most common adverse events were pruritus, fatigue, and fever; hypothyroidism was also higher in the 700 mg cohort.28 Based on these data, the ongoing KEYVIBE-005 (NCT05007106), an all-solid tumor basket study, is evaluating the vibostolimab/pembrolizumab co-formulation, at the recommended phase II dose for vibostolimab (200 mg every 3 weeks), for all patients.

Moreover, the SKYSCRAPER-04 (NCT04300647) is a randomized, open-label phase II trial, evaluating the efficacy and safety of tiragolumab (anti-TIGIT) plus atezolizumab and atezolizumab monotherapy in patients with metastatic or recurrent PD-L1-positive cervical cancer, and its results are still awaited.

IMMUNE CHECKPOINT INHIBITORS FOR PERSISTENT, RECURRENT, DISEASE IN THE FRONT-LINE SETTING

The introduction of bevacizumab to front-line platinum-based chemotherapy has extended median overall survival from 12 to 17 months, since becoming the standard of care for this population, based on the results of the GOG-240 trial.13 Beyond this historical approval back in 2014, no further targeted therapy has demonstrated a survival benefit in the front-line setting, until the recent advent of immune checkpoint inhibitors.

The biological rationale for the introduction of immune checkpoint inhibitors and the encouraging results in previously treated patients with advanced cervical cancer led the investigators to assess immunotherapy early on in the disease course when the host immune system is more robust. Interestingly, chemo-naïve patients seemed to show better efficacy outcomes when treated with immune checkpoint inhibitors according to the results of the CheckMate-358 trial, shown above. Additionally, new combination approaches with immune checkpoint inhibitors and other agents have been proposed to enlarge the population benefiting from immunotherapy. In this sense, both platinum agents and bevacizumab can modulate the immune tumor microenvironment favoring the synergism with anti-PD-1/PD-L1 monoclonal antibodies.29 30

Currently, three phase III trials are investigating the combination of immune checkpoint inhibitors and front-line standard of care based on platinum doublet, with or without bevacizumab, for patients with recurrent, persistent, or metastatic cervical cancer: KEYNOTE-826 (NCT03635567), BEATcc (NCT03556839), and FERMATA (NCT03912415) trials. So far, KEYNOTE-826 is the only one of these with published results.

MK-3475–826/KEYNOTE-826 is a phase III randomized, double-blind, placebo-controlled trial, evaluating the efficacy and safety of adding pembrolizumab to front-line chemotherapy with or without bevacizumab, in patients with persistent, recurrent, or metastatic cervical cancer. Six hundred and seventeen patients (72% squamous cell carcinoma and 28% adenocarcinoma/adenosquamous) were randomly assigned to receive pembrolizumab at a fixed dose of 200 mg or placebo every 3 weeks for up to 35 cycles plus platinum doublet for up to six cycles and bevacizumab at the discretion of investigators. Stratification factors were metastatic status at diagnosis, bevacizumab use, and baseline PD-L1 status. PD-L1 expression was assessed by PD-L1 22C3 assay at a central laboratory and was scored using combined positive score. The co-primary endpoints were progression-free and overall survival, assessed sequentially in patients with combined positive score ≥1%, in the intention-to-treat population, and finally in patients with combined positive score ≥10%.

After a median follow-up of 22.0 months, 548 patients with combined positive score ≥1% (89% of the total population), demonstrated a median progression-free survival of 10.4 months in the pembrolizumab arm versus 8.2 months in the placebo arm (HR=0.62; 95% CI 0.50 to 0.77; p<0.001). Among 617 patients in the intention-to-treat population, median progression-free survival was 10.4 months and 8.2 months, respectively (HR=0.65; 95% CI 0.53 to 0.79; p<0.001). Lastly, among 317 patients with combined positive score ≥10%, median progression-free survival was 10.4 months and 8.1 months, respectively (HR=0.58; 95% CI 0.44 to 0.77; p<0.001).

The overall survival at 24 months was 53.0% in the pembrolizumab arm versus 41.7% in the placebo arm (HR=0.64; 95% CI 0.50 to 0.81; p<0.001), 50.4% vs 40.4% (HR=0.67; 95% CI 0.54 to 0.84; p<0.001), and 54.4% vs 44.6% (HR=0.61; 95% CI 0.44 to 0.84; p=0.001), in the combined positive score ≥1%, intention-to-treat, and combined positive score ≥10% subpopulations, respectively. The overall survival benefit of adding pembrolizumab was generally consistent across all subgroups. Nevertheless, the combined positive score <1% subgroup had no significant overall survival benefit (HR=1.00; 95% CI 0.53 to 1.89).15

In a post hoc analysis, patients receiving bevacizumab, 63% seemed to have better overall survival outcomes (HR=0.63; 95% CI 0.47 to 0.87), as did those treated with cisplatin versus carboplatin (HR=0.59 vs 0.69).31 Although the trial met its primary endpoint in the intention-to-treat population, the regulatory agencies, FDA and European Medicines Agency (EMA), approved the use of pembrolizumab added to platinum-based chemotherapy plus or minus bevacizumab exclusively for patients whose tumors had a combined positive score ≥1%. Further studies are warranted to analyze the performance of pembrolizumab in the subpopulation with combined positive score <1%, which represented only 11% of the total population of the trial (Table 1).

Regarding the toxicity profile, the most common grade 3 to 5 adverse events were anemia (30.3% in the pembrolizumab arm and 26.9% in the placebo arm) and neutropenia (12.4% and 9.7%, respectively). The most common immune-related adverse events of any grade were hypothyroidism and hyperthyroidism (18.2% and 7.5%, respectively), colitis (5.2%), and skin reactions (4.6%). It is important to underscore that 5.2% of patients treated with pembrolizumab discontinued any of the treatments due to adverse events versus 0.3% of patients in the placebo arm.15

Another clinical study worth mentioning is the BEATcc trial (ENGOT-Cx10/GEICO 68-C/JGOG1084/GOG-3030). The BEATcc trial is a randomized, open-label, phase III study investigating the addition of atezolizumab (anti-PD-L1) to platinum doublet plus bevacizumab (mandatory for all enrolled patients) in women with metastatic, persistent, or recurrent cervical cancer, regardless of PD-L1 status. Both overall survival and progression-free survival will be assessed as co-primary endpoints of the study. The BEATcc trial has been carried out under the ENGOT umbrella alongside GOG-F and JGOG, with GEICO as the lead group on behalf of ENGOT. The trial began in the third quarter of 2018 and met its enrollment goal in August 2021. The first read-out date is expected to be reported in early 2023.32

ENGOT-cx13/AGO/FERMATA is a multicenter, randomized, double-blind, placebo-controlled trial, designed to evaluate the efficacy and safety of incorporating BCD-100 (anti-PD-1) to the front-line platinum doublet, with or without bevacizumab, in patients with advanced squamous cell carcinoma of the cervix, regardless of PD-L1 status. The primary endpoint of the study is overall survival exclusively. A total of 316 subjects, from sites in Russia, China, Georgia, and Turkey, will be enrolled in the study. The expected duration of the clinical trial is approximately 60 months (Q4 2019 to Q4 2024), including approximately 24 months for recruitment and 36 months for final efficacy assessment.

Interestingly, the dual blockade anti-CTLA4/PD-L1 has also been investigated in combination with front-line standard therapy. Following the promising efficacy results of cadonilimab monotherapy as second or third line, a phase II clinical trial conducted in China (NCT04868708), reported an overall response rate of 79.3% regardless of PD-L1 expression in a cohort of 45 patients with persistent, recurrent, or metastatic cervical cancer treated with cadonilimab in combination with platinum-based chemotherapy with or without bevacizumab.33 Therefore, a phase III trial of cadonilimab versus placebo combined with platinum-based chemotherapy with or without bevacizumab for first-line persistent, recurrent or metastatic cervical cancer was launched in July 2021 (NCT04982237).

ROLE OF IMMUNE CHECKPOINT INHIBITORS IN THE LOCALLY ADVANCED SETTING

Approximately 40–50% of cervical cancer cases are diagnosed in the locally advanced stage. Following current standard-of-care treatment, concurrent chemoradiotherapy, the recurrence rate remains as high as 40% within the first 2 years after initial diagnosis. Particularly, women diagnosed with high-risk locally advanced cervical cancer—namely, those with stage III and IV (FIGO staging 2018), are at the greatest risk for recurrence, reaching up to 70%34–36; however, the standard-of-care treatment for these patients has not changed in over two decades.

Over the last years, several strategies have been investigated to improve the poor prognosis of patients with locally advanced cervical cancer, especially those at higher risk, with little success. In this regard, adjuvant chemotherapy after concurrent chemoradiotherapy yielded no consistent benefit in overall survival and progression-free survival, with an unfavorable toxicity profile leading to suboptimal compliance with the treatment.37 As a result, this approach has not been widely accepted by the scientific community.

The robust biological rationale and the fast-growing clinical evidence for the use of immunotherapy in patients with advanced cervical cancer have supported the clinical development of immune checkpoint inhibitors in the locally advanced setting. Indeed, incorporating immunotherapy during and/or after concomitant chemoradiotherapy seems to be one of the best scenarios since it takes advantage of a more favorable immune tumor microenvironment induced by radiation and cytotoxic agents.38

Supporting this approach, the PACIFIC trial reported positive results of durvalumab (anti-PD-L1) maintenance treatment in patients with unresectable, stage III, non-small cell lung cancer without disease progression after concomitant chemoradiotherapy. Consolidative durvalumab was associated with significant and durable improvements in both overall survival and progression-free survival.39 40 Pembrolizumab has also been explored in the locally advanced setting of head and neck squamous cell carcinoma in combination with and following concurrent chemoradiotherapy. The addition of pembrolizumab was associated with a favorable trend toward improved event-free survival versus placebo plus chemoradiotherapy, but the difference did not reach statistical significance in the intention-to-treat population.41

In recent years, several phase II/III clinical trials have been launched to evaluate the role of PD-(L)1 antibodies, given concomitantly with chemoradiotherapy and/or as adjuvant treatment, in the locally advanced cervical cancer setting: durvalumab in the CALLA trial (NCT03830866),42 pembrolizumab in KEYNOTE-A18/ENGOT-cx11/GOG-3047 (NCT04221945),43 atezolizumab in ATEZOLACC (NCT03612791), and dostarlimab (anti-PD-1) in the ATOMICC trial44 (NCT03833479).

It is important to underline that these four clinical trials partially differ in their design, target population, and study endpoints. Both CALLA and KEYNOTE-A18 are phase III randomized, double-blind, placebo-controlled clinical trials, whereas ATEZOLACC and ATOMICC are phase II, randomized, open-label trials. The three first trials are evaluating the use of immune checkpoint inhibitors both concomitantly with chemoradiotherapy and as adjuvant treatment, whereas the ATOMICC trial is exclusively assessing the introduction of dostarlimab as maintenance therapy after chemoradiotherapy.

Regarding the target study population, CALLA, KEYNOTE-A18, and ATOMICC trials are enrolling a very similar although not identical, population of women with high-risk locally advanced cervical cancer—namely, those with squamous cell carcinoma, adenocarcinoma, or adenosquamous carcinoma FIGO 2009 stages IB2–IIB node-positive and stage IIIA–IVA with any node stage. However, ATEZOLACC is run in a slightly different population, including FIGO 2009 stages IB1–IIA node-positive, stage IIB–IVA regardless of lymph node involvement, and stage IVB, only if the metastases are limited to the para-aortic lymph nodes, indeed no longer stage IVB according FIGO 2018.

Further, regarding the study endpoints, progression-free survival is the primary endpoint in CALLA, ATEZOLACC, and ATOMICC trials. In contrast, a dual co-primary endpoint, progression-free survival and overall survival, was set in the KEYNOTE-A18 study.

To date, CALLA is the only study evaluating immunotherapy in the locally advanced cervical cancer setting with reported results. CALLA is a phase III, double-blind, placebo-controlled trial, exploring the role of durvalumab with and following concurrent chemoradiotherapy in a population with newly diagnosed high-risk, locally advanced cervical cancer, as indicated above. Randomized patients with locally advanced cervical cancer received (in a 1:1 fashion) durvalumab 1500 mg IV or placebo every 4 weeks for 24 cycles. For concurrent chemotherapy, both weekly cisplatin 40 mg/m2 or carboplatin area under the curve 2 for 5–6 weeks were allowed. Stratification factors were disease stage (FIGO IB2–IIB and positive lymph nodes, FIGO >III and negative lymph nodes, and FIGO >III and positive lymph nodes) and world region. The primary endpoint was progression-free survival assessed by the investigator according to RECIST 1.1. or histopathological confirmation of local tumor progression or death. A total of 385 patients were assigned to each treatment arm. Demographics and baseline clinicopathological characteristics were globally well-balanced. Most patients had squamous histology (83% in each arm) and PD-L1-positive tumors (>90% in each arm) according to the tumor area positivity score (SP263). Pelvic lymph node involvement rate (patients with at least one positive lymph node were enrolled) was numerically lower in the durvalumab arm (63.9%) than in the placebo arm (69.6%). Conversely, stage IVA and para-aortic lymph node involvement was slightly greater in the experimental arm (6.5% vs 4.9% and 12.2% vs 9.9%, respectively). Regarding chemoradiotherapy compliance, the placebo arm seemed to have lower concurrent chemotherapy compliance, 87% vs 90.1%. Pelvic external radiotherapy and brachytherapy delivery and biological total dose did not differ substantially between arms, and 72% of patients in each arm completed radiotherapy in less than 60 days.

With a median follow-up of 18.5 months and 31% of data maturity, durvalumab in combination with and following chemoradiotherapy did not improve significantly progression-free survival versus placebo (HR=0.84; 95% CI 0.65 to 1.08; p=0.174). Additionally,no benefit in overall survival was observed; however, it is important to stress that data maturity at the data cut-off point was only 17%. While progression-free survival outcome was consistent across all analyzed subgroups, higher-risk patients, such as those with para-aortic lymph node involvement and stage III–IVA with positive lymph node, seemed to draw a greater benefit from the addition of durvalumab: HR=0.60 (95% CI 0.30 to 1.17) for para-aortic node-positive and HR=0.71 (95% CI 0.49 to 1.03) for stage III–IVA node positive. Regarding the safety profile, adverse events of grade 3–4 occurred in 51.7% and 51% of patients in the durvalumab and placebo arms, respectively so, it does not seem that durvalumab endangers the radiotherapy delivery.42

Despite a strong rationale, the CALLA trial did not meet its primary endpoint. Several factors may have influenced these disappointing results, such as the short follow-up with a low maturity of the survival data, patient selection and their risk of progression, or the adequacy of progression-free survival as a primary endpoint. The role of immune checkpoint inhibitors in this disease setting is still to be determined in the upcoming years and the ongoing clinical trials exploring similar or identical approaches to the CALLA trial will further corroborate or overcome these discouraging efficacy outcomes.

NOVEL IMMUNOTHERAPY APPROACHES IN CERVICAL CANCER

Beyond immune checkpoint inhibitors, there are several other immunotherapy approaches under investigation for advanced cervical cancer. Cancer therapeutic vaccines and cell-based therapy are among the most promising strategies.

The well-established pathogenic implication of HPV in cervical cancer makes HPV E6 and E7 oncoproteins attractive target antigens for vaccine-based therapies in the setting of pre-invasive or invasive disease. These cancer vaccines can facilitate T cell priming, generating both new antigen-specific T cell responses and amplifying existing responses against tumor cells. Therapeutic HPV vaccines used in the clinic have different technologies to deliver HPV-related antigens as well as various adjuvants to stimulate an immune response.8 Below, we discuss the vaccination strategies for the platforms most frequently tested in the clinic—namely, peptide-based, vector-based (bacterial or viral), and DNA-based. For the purpose of the present review, we will focus on invasive disease and those clinical trials exploring this strategy, alone or combined with immune checkpoint inhibitors, with published or presented data.

Vector-based vaccines are genetically engineered live attenuated or inactive, either viral or bacterial vectors modified to express an antigen of interest. The phase III AIM2CERV trial was launched to evaluate the efficacy of ADXS11-001 (live attenuated Listeria monocytogenes immunotherapy bioengineered to secrete an HPV16 E7 fusion protein) administered in the adjuvant setting after completion of chemoradiotherapy in patients with high-risk locally advanced cervical cancer. Unfortunately, the study was put on hold by the FDA due to an inquiry into manufacturing procedures and it was finally closed in 2019 based on the funding company priorities and before full accrual was reached.

Peptide-based vaccines directly deliver short or long peptides encoding HPV oncoproteins. These have been shown, however, to be weakly immunogenic and need to be delivered with adjuvants to improve the potency of both cellular and humoral immune responses.8

ISA101 consists of 12 synthetic long peptides from the E6/E7 HPV-16 capable of inducing HPV-specific T cells. A single-arm phase II trial (NCT02426892) explored the combination of ISA101 and nivolumab in patients with recurrent or metastatic HPV-16-positive cancer. Of the 24 patients enrolled in this study (among the enrolled patients, only one had advanced cervical cancer), the overall response rate was 33%, with a median duration of response of 11.2 months. Interestingly, 3 out of 8 (38%) patients with objective response were without progression at 3 years. The median overall survival and progression-free survival were 15.3 months and 2.66 months, respectively.45 Following these preliminary results, two trials exploring ISA101 in different settings and combinations have been launched: (1) phase II, single-arm, open-label study (NCT04646005) assessing the efficacy and safety of ISA101b in combination with cemiplimab in patients with recurrent or metastatic HPV-16-positive cervical cancer in the post-platinum progression setting; and, (2) phase I/II (NCT02128126) investigating the safety, tolerability, and the HPV-specific immune responses of different doses of ISA101 vaccine with or without pegylated interferon α as combination therapy with carboplatin and paclitaxel+/−bevacizumab.

PDS0101 is another HPV therapeutic peptide vaccine consisting of the immune-activating cationic lipid R-DOTAP and HLA-unrestricted HPV-16 E6 and E7 peptides that have shown in vivo CD8+ T cell induction and tolerable safety profile in a phase I study.46 The IMMUNOCERV (NCT04580771) study is a single-arm, phase II trial currently evaluating the safety and efficacy of chemoradiotherapy combined with the PDS0101 vaccine in treating patients with locally advanced cervical cancer (stages IB3–IVA FIGO 2018). Moreover, an ongoing phase I/II trial (NCT04287868) is evaluating PDS0101 in combination with anti-PD-L1/ransforming growth factor β trap (M7824), interleukin-12 in recurrent or metastatic HPV-positive tumors, including cervical cancer.

Finally, DNA vaccination is an approach that incorporates an antigen-encoding gene into a backbone of a bacterial plasmid. Its main advantage is its ability to activate both innate and adaptive immune responses.8

GX-188E is a DNA vaccine encoding the E6/E7 fusion protein of HPV subtypes 16 and 18, plus the immune-enhancer, Fms-like tyrosine kinase-3 ligand (FLT3L), with potential immunostimulating and antineoplastic activities. A phase Ib/II, open-label trial has been launched to evaluate the combination of GX-188E and pembrolizumab (NCT03444376) in patients previously treated with HPV-16/18-positive recurrent/advanced cervical cancer. A total of 60 patients were analyzed in the phase II treatment group. Results showed an overall response rate of 31.7%, with a median duration of response of 12.3 months. Interestingly, responses were observed regardless of PD-L1 status. Regarding the safety data, the combination therapy was found to be safe and tolerable with a safety profile similar to that of pembrolizumab monotherapy.47

VB10.16 is a therapeutic DNA vaccine composed of three parts, one encodes the E6/E7 fusion protein of HPV16, the second is a dimerization entity, and the third part encodes a protein that specifically binds to antigen-presenting cells, with potential immunostimulating and antineoplastic effects. A multicenter, open-label, phase IIa trial (NCT04405349) evaluated the safety and efficacy of VB10.16 in combination with atezolizumab in patients with advanced or recurrent non-resectable HPV16-positive cervical cancer. In an interim analysis, with a median follow-up of 6 months, the combination therapy yielded an overall response rate of 21% in the heavily pre-treated population (minimum two prior lines of therapy), and a disease control rate of 64%. It is important to underscore that responses were observed in both PD-L1-positive and PD-L1-negative patients.48

One of the main advances in the immunotherapy field is the adoptive cell transfer based on autologous T cells, which showed encouraging responses in patients with advanced/recurrent cervical cancer. C-145-04 (NCT03108495) is an open-label, multicenter phase II trial assessing the safety and efficacy of LN-145 tumor-infiltrating lymphocyte therapy in patients with recurrent, metastatic, or persistent cervical carcinoma. This study contains five arms as follows: arm 1: LN-145 monotherapy in patients with cervical cancer who had undergone at least one prior line of chemotherapy for advanced disease; arm 2: LN-145 monotherapy in patients who had also received treatment with an immune checkpoint inhibitor in the setting of recurrent, metastatic, or persistent disease, either as monotherapy or in combination; arm 3 (USA only): LN-145 plus pembrolizumab in a cervical population who had not received prior lines of therapy in the advanced setting; arm 4: LN-145 monotherapy in a patient population not meeting the inclusion criteria of arms 1 and 2; and, arm 5: patients who have been previously treated with LN-145 may be given a second treatment with tumor-infiltrating lymphocytes.

Tumors surgically harvested at local institutions were shipped to central facilities for generation of tumor-infiltrating lymphocytes in a 22-day manufacturing process. The final LN-145 tumor-infiltrating lymphocyte product was then cryopreserved and shipped to sites. Patients receive 1 week of pre-conditioning lymphodepletion (cyclophosphamide and fludarabine) and a single LN-145 infusion, followed by up to six doses of interleukin-2 (600 000 IU/kg). For arm 3, patients were administered pembrolizumab, followed by lymphodepletion chemotherapy, then infused with their autologous tumor-infiltrating lymphocyte (LN-145) followed by pembrolizumab every 3 or 6 weeks post-interleukin-2 administration up to 24 months. In arm 1, a total of 27 evaluable patients were finally included in the efficacy analysis. Preliminary efficacy results of this cohort were impressive, with an OR of 44% (12/27) and a disease control rate of 89%, with 11/12 patients maintaining their response at a median follow-up of 3.5 months.49 Following these promising results, in 2019, FDA granted LN-145 breakthrough therapy designation for the treatment of pre-treated patients with advanced cervical cancer. Additionally, 14 treatment-naïve recurrent patients with metastatic or persistent cervical cancer were enrolled in arm 3, receiving the combination of LN-145 and pembrolizumab, as previously indicated. The reported overall response rate was 57.1% with a disease control rate of 92.9% (median study follow-up of 7.6 months), and a manageable toxicity profile.50

Genetically engineered T cell therapy—namely, T cell receptor-modified T cells and chimeric antigen receptor T cells, has been a therapeutic breakthrough for hematologic malignancies and is now being investigated for the treatment of HPV-associated carcinomas.51

T cell receptor-engineered T cells are generated by transduction of T cells, with a single T cell receptor demonstrated to recognize a specific tumor antigen in an HLA-dependent manner. Given the reliance of this technology on T cell receptor–major histocompatibility complex pairing, HLA matching of patients is required for this approach and it is also an important limitation. Several early-phase trials showed preliminary data of T cell receptor-modified T cells targeting different tumor-specific antigens, such as proteins E6 (NCT02280811, NCT03578406), and E7 (NCT02858310) of high-risk HPV and MAGE-A3 (NCT02153905, NCT02111850).52

Chimeric antigen receptor-T cell therapy in HPV-mediated cancers is a promising strategy, as it targets surface antigens directly and thus avoids the need to target major histocompatibility complex-bound antigens, overcoming defects in the antigen presentation pathway seen in HPV-related malignancies. Nevertheless, the identification of recurrent and unique cell-surface antigens outside of major histocompatibility complex-bound viral antigens in HPV-related malignancies presents a major challenge to this approach. Chimeric antigen receptor-T cell therapies targeting antigens such as mesothelin (NCT01583686), CD22 (NCT04556669), or others (NCT03356795) are still underway in the cervical cancer population.

CONCLUSIONS

The incorporation of immunotherapy—namely, immune checkpoint inhibitors, in the therapeutic armamentarium of recurrent, persistent, and metastatic cervical cancer, has represented a major breakthrough for this population with poor prognosis. Two pivotal trials have demonstrated a clinically and statistically significant survival benefit of adding immune checkpoint inhibitors in both post-platinum progression and front-line settings, respectively. Furthermore, several ongoing clinical trials will define the role of immunotherapy in the high-risk locally advanced setting in the near future, although preliminary results from the CALLA trial seem to be disappointing. This incorporation of immunotherapy opens a very optimistic scenario for patients with recurrent, persistent, and metastatic cervical cancer; however, it also raises the question of what will be the best therapeutic approach for those patients whose disease has progressed under immune checkpoint inhibitors. The next step in our clinical research should be how to overcome the resistance. In addition, a significant proportion of patients do not benefit from immune checkpoint inhibitors, revealing the presence of primary mechanisms of resistance, which have not yet been well identified. Indeed, patient selection for immunotherapy approaches remains challenging, and further research on predictive biomarkers beyond PD-L1 status appears to be critical in the upcoming years. Translational research aiming at analyzing the immune tumor microenvironment and its dynamics may be essential to uncover potential resistance, better stratify our patients, and develop novel therapeutic strategies.

Finally, promising clinical efficacy data are now emerging from early-phase clinical trials investigating novel approaches of immunotherapy in cervical cancer, such as therapeutic HPV vaccination and adoptive cell therapy.

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