Agenus Reports Promising Phase 2 UNICORN Trial Results for Neoadjuvant Botensilimab and Balstilimab in Resectable Colon Cancer Published in Nature Medicine
Agenus Inc., a biotechnology company focused on developing innovative immuno-oncology therapies, has announced the peer-reviewed publication of clinical results from the investigator-sponsored, multicenter Phase 2 UNICORN trial evaluating its investigational immunotherapy candidates botensilimab (BOT) and balstilimab (BAL) in patients with resectable, locally advanced colon cancer. The study investigated short-course preoperative, or neoadjuvant, treatment with botensilimab alone or in combination with balstilimab in patients with mismatch repair-proficient/microsatellite stable (pMMR/MSS) and mismatch repair-deficient/microsatellite instability-high (dMMR/MSI-H) colon cancer.
The findings have been published in the peer-reviewed journal Nature Medicine in a manuscript titled, “Preoperative botensilimab with or without balstilimab for patients with resectable, locally advanced pMMR or dMMR colon cancer: the UNICORN trial by GONO.” The publication is available under DOI: 10.1038/s41591-026-04710-1.
The UNICORN study evaluated whether a short course of immunotherapy administered before surgery could generate meaningful antitumor activity, improve pathological responses, and potentially reduce the risk of cancer recurrence. The findings are particularly relevant to patients with pMMR/MSS colon cancer, a population that has historically demonstrated limited benefit from conventional immunotherapy approaches.
Botensilimab is Agenus’ multifunctional, Fc-enhanced anti-CTLA-4 antibody designed to activate and enhance antitumor immune responses. Balstilimab is the company’s anti-PD-1 antibody, which is designed to block the programmed cell death protein 1 (PD-1) immune checkpoint and support the immune system’s ability to recognize and attack cancer cells.
The combination was evaluated across four non-randomized treatment cohorts involving 56 patients. Results demonstrated encouraging pathological response rates, including major pathological responses and complete pathological responses, particularly among patients receiving the combination therapy. In the pMMR/MSS population, 36% of patients treated with BOT+BAL achieved a major pathological response, while 29% achieved a pathological complete response. In the dMMR/MSI-H combination cohort, all patients achieved a major pathological response, including 93% who experienced a complete pathological response.
Importantly, no cancer recurrences had been observed among patients receiving the combination treatment at the February 9, 2026, data cutoff. Twelve-month event-free survival was 100% in both combination treatment cohorts, with median follow-up periods of 19.2 months in pMMR/MSS disease and 16.7 months in dMMR/MSI-H disease.
These results provide additional clinical evidence supporting the investigation of botensilimab and balstilimab earlier in the treatment course of colon cancer, particularly in patients with MSS disease, where new treatment strategies are needed to improve outcomes.
UNICORN Trial Design and Patient Population
The investigator-sponsored Phase 2 UNICORN trial was conducted as a multicenter study evaluating neoadjuvant botensilimab, either as a single agent or in combination with balstilimab, in patients with resectable, locally advanced colon cancer.
The study enrolled 56 patients across four non-randomized cohorts, with 14 patients assigned to each cohort. The trial included patients with two distinct molecular subtypes of colon cancer: pMMR/MSS and dMMR/MSI-H.
Mismatch repair status and microsatellite instability are important biological characteristics that influence how tumors respond to immunotherapy. Patients with dMMR/MSI-H tumors often demonstrate greater sensitivity to immune checkpoint inhibitors because these cancers can accumulate genetic mutations that generate abnormal proteins recognizable by the immune system.
In contrast, pMMR/MSS tumors generally demonstrate lower responsiveness to conventional checkpoint inhibitor treatments. This difference represents a significant challenge in colorectal cancer treatment, particularly because MSS disease accounts for approximately 85% of early-stage colorectal cancers.
The UNICORN study investigated whether combining an Fc-enhanced anti-CTLA-4 antibody with PD-1 inhibition could generate deeper antitumor responses in both molecular subtypes.
The four treatment cohorts evaluated were:
- Botensilimab monotherapy in patients with pMMR/MSS colon cancer.
- Botensilimab plus balstilimab in patients with pMMR/MSS colon cancer.
- Botensilimab monotherapy in patients with dMMR/MSI-H colon cancer.
- Botensilimab plus balstilimab in patients with dMMR/MSI-H colon cancer.
The primary focus included evaluating pathological responses following preoperative treatment. Researchers also assessed event-free survival, circulating tumor DNA (ctDNA) clearance, and biological changes within tumor tissue collected before treatment and at the time of surgery.
This translational research component enabled investigators to examine not only whether tumors responded to treatment but also how the immune environment changed during the short treatment period before surgical resection.
Combination Therapy Demonstrates Encouraging Results in MSS Colon Cancer
One of the most important findings from UNICORN involved the 14 patients with pMMR/MSS colon cancer who received botensilimab in combination with balstilimab.
Within this cohort, 36% of patients achieved a major pathological response (MPR), defined as 10% or less viable tumor remaining at the time of surgery. Additionally, 29% achieved a pathological complete response (pCR), indicating that no viable tumor remained in the primary tumor or lymph nodes.
Overall, 71% of patients in the combination cohort demonstrated a pathological response, defined in the study as at least a 50% reduction in tumor burden.
These findings are particularly notable because MSS colon cancer has historically been considered resistant to conventional immunotherapy. The observed responses suggest that combining CTLA-4 and PD-1 inhibition through botensilimab and balstilimab may offer a different therapeutic approach for this patient population.
For historical comparison, previously reported studies of first-generation CTLA-4/PD-1 combination immunotherapy demonstrated a major pathological response rate of approximately 20% in pMMR colon cancer. Neoadjuvant chemotherapy demonstrated an MPR rate of approximately 8% in previously reported studies.
Although these historical comparisons are not based on a randomized head-to-head evaluation, the response rates observed in UNICORN provide encouraging evidence supporting further clinical investigation of the combination.
The study also evaluated botensilimab as a single agent in a separate cohort of 14 patients with pMMR/MSS colon cancer.
In this group, 43% of patients experienced partial tumor regression. However, none achieved a major pathological response or pathological complete response.
These findings suggest that botensilimab monotherapy can initiate antitumor activity in a subset of patients with MSS colon cancer. However, the deeper pathological responses observed in the combination cohort indicate that adding balstilimab and PD-1 blockade may contribute to stronger treatment activity.
The results support continued investigation of the complementary mechanisms of CTLA-4 and PD-1 inhibition in tumors that have historically shown limited responsiveness to immunotherapy.
High Pathological Response Rates in dMMR/MSI-H Colon Cancer
The UNICORN trial also demonstrated substantial pathological responses among patients with dMMR/MSI-H colon cancer receiving the combination of botensilimab and balstilimab.
All 14 patients in the dMMR/MSI-H combination treatment cohort achieved a major pathological response, representing a 100% response rate. Among these patients, 13 achieved a pathological complete response, corresponding to a rate of 93%.
These findings demonstrate a high level of pathological tumor clearance following short-course neoadjuvant combination immunotherapy.
For comparison, the dMMR/MSI-H cohort receiving botensilimab monotherapy achieved an MPR rate of 36% and a pCR rate of 29%.
The difference between the monotherapy and combination cohorts suggests that the addition of balstilimab may enhance the depth of pathological response in this molecular subtype.
The findings also highlight the potential clinical relevance of evaluating combination immunotherapy before surgery, when the primary tumor and its surrounding immune environment remain intact.
UNICORN Phase 2: Key pathological response findings
| Treatment group | Major pathological response | Complete pathological response |
|---|---|---|
| pMMR/MSS BOT+BAL | 36% | 29% |
| pMMR/MSS BOT alone | 0% | 0% |
| dMMR/MSI-H BOT+BAL | 100% | 93% |
| dMMR/MSI-H BOT alone | 36% | 29% |
MPR: 10% or less viable tumor remaining. pCR: no viable tumor in the primary tumor or lymph nodes.
Durable Responses and Preservation of Surgical Feasibility
In addition to pathological response rates, the investigators evaluated the durability of treatment responses and the ability of patients to proceed with planned surgical procedures.
At the February 9, 2026, data cutoff, no patients treated with botensilimab plus balstilimab had experienced cancer recurrence.
The median follow-up period was 19.2 months among patients with pMMR/MSS disease and 16.7 months among those with dMMR/MSI-H disease.
Furthermore, the 12-month event-free survival rate was 100% in both combination treatment cohorts.
Event-free survival is an important clinical endpoint in the curative-intent setting because it evaluates the period during which patients remain free from defined disease-related events following treatment. In colon cancer, reducing the likelihood of recurrence following surgery is a major objective of treatment.
The ability to administer immunotherapy before surgery without substantially disrupting planned surgical schedules is another important consideration.
In UNICORN, planned surgical timing was preserved in 98% of patients, and all 56 enrolled patients ultimately underwent surgical resection.
One patient experienced a 10-day surgical delay associated with Grade 3 hyperthyroidism. This finding highlights the importance of monitoring immune-related adverse events during neoadjuvant immunotherapy, particularly when treatment is administered before a planned surgical procedure.
Overall, the results indicate that short-course botensilimab-based treatment was feasible within the study setting, with most patients maintaining their planned surgical schedules.
Safety and Immune-Related Adverse Events
The study also assessed the safety and tolerability of botensilimab administered alone or in combination with balstilimab.
Grade 3 or Grade 4 immune-related adverse events occurred in 2% of patients.
Immune checkpoint inhibitors work by modifying immune system activity to improve the recognition and destruction of cancer cells. However, these treatments can sometimes cause the immune system to attack healthy tissues, resulting in inflammatory or autoimmune-like complications.
The reported incidence of severe immune-related adverse events provides an important safety observation for the neoadjuvant treatment approach.
The surgical findings are also relevant because treatment-related complications can potentially affect the timing and feasibility of curative-intent procedures.
Although all 56 patients underwent surgical resection, continued evaluation in larger randomized clinical studies will be important to further characterize the safety profile of the combination, identify potential risks, and assess its suitability across broader patient populations.
Translational Findings Highlight ctDNA Clearance and Immune Remodeling
Beyond clinical response measurements, UNICORN incorporated translational research designed to investigate the biological changes associated with treatment activity.
Two important areas of investigation included circulating tumor DNA clearance and changes in the tumor immune microenvironment.
Circulating tumor DNA clearance
Circulating tumor DNA consists of small fragments of tumor-derived genetic material that enter the bloodstream. Measuring ctDNA can provide information about the presence of residual cancer activity and may help researchers evaluate treatment response.
In the UNICORN trial, ctDNA clearance was associated with pathological response.
All five evaluable patients with pMMR/MSS colon cancer who achieved a major pathological response also cleared ctDNA before surgery.
Additionally, none of the patients who achieved ctDNA clearance had experienced cancer recurrence at the February 9, 2026, data cutoff.
These findings suggest that ctDNA clearance may provide a useful biological indicator of treatment response and could potentially contribute to future strategies for monitoring patients following neoadjuvant immunotherapy.
However, further research will be needed to establish the predictive and prognostic value of ctDNA measurements in larger patient populations.
Changes in the tumor immune environment
The researchers also examined paired tumor tissue samples collected before treatment and at surgery to understand how botensilimab-based treatment influenced the tumor microenvironment.
The analysis identified immune-related changes associated with treatment response that were consistent with botensilimab’s Fc-enhanced design.
These changes included reductions in immunosuppressive regulatory T-cell signatures and increased immune-cell infiltration within tumor tissue.
Regulatory T cells are an important component of the immune system, but certain regulatory T-cell populations within tumors can suppress antitumor immune responses and contribute to an immunosuppressive tumor environment.
Reducing these immunosuppressive signals while promoting immune-cell infiltration may help create conditions that support stronger immune-mediated tumor destruction.
The observed biological changes provide additional evidence supporting the scientific rationale behind botensilimab’s multifunctional, Fc-enhanced mechanism.
Together, pathological responses, ctDNA clearance, and immune remodeling provide multiple complementary indicators of treatment activity.
UNICORN and NEST Publications Strengthen the Clinical Evidence
The publication of the UNICORN findings follows the recent peer-reviewed publication of results from the independent Phase 2 NEST study, which also evaluated neoadjuvant botensilimab plus balstilimab.
With both NEST and UNICORN now peer reviewed, Agenus points to complementary clinical evidence generated across single-center and multicenter research settings.
Although the two studies differed in their designs, both reported findings supporting the potential of botensilimab and balstilimab in earlier-stage colon cancer.
The results provide additional clinical support for the investigation of combination immunotherapy in patients with MSS colon cancer, a population that has historically derived limited benefit from conventional immune checkpoint inhibitors.
The consistency of the reported findings across independently conducted studies is particularly relevant because it supports further evaluation of the combination in a larger, randomized clinical trial.
In the curative-intent setting, administering immunotherapy before surgery may provide an opportunity to stimulate immune responses while the primary tumor and its surrounding immune environment remain present.
The objective is not limited to reducing tumor size before surgical removal. Researchers are also investigating whether early immune activation can eliminate residual cancer cells, reduce recurrence risk, and potentially increase the number of patients who achieve long-term disease control or cure.
Company Leadership Highlights Potential to Transform MSS Colon Cancer Treatment
Steven O’Day, M.D., Chief Medical Officer of Agenus, emphasized the significance of the UNICORN findings and their potential implications for the development of neoadjuvant immunotherapy.
“UNICORN delivers compelling, independent evidence that BOT+BAL can produce deep responses in MSS colon cancer, a disease historically resistant to conventional immunotherapy,” said O’Day. “With no recurrences observed to date, these findings reinforce the promise of treating earlier. Together with NEST, they provide a strong foundation for our planned Phase 3 ROBBIN trial and our ambition to change how MSS colon cancer is treated in the curative-intent setting.”
Filippo Ghelardi, M.D., first author of the publication and Medical Oncology Fellow in the Department of Medical Oncology at Fondazione IRCCS Istituto Nazionale dei Tumori in Milan, Italy, highlighted the importance of the translational findings.
“UNICORN gave us a rare opportunity to look beyond whether a tumor responded and examine what was changing biologically during a very short period before surgery,” said Ghelardi. He noted that the relationship between deep pathological responses, ctDNA clearance, and changes in the tumor immune environment provided multiple indicators of treatment activity.
He also emphasized the importance of these findings for MSS colon cancer, where conventional immunotherapy has historically had limited impact.
Filippo Pietrantonio, M.D., senior author, study principal investigator, and Head of the Gastrointestinal Oncology Unit at Fondazione IRCCS Istituto Nazionale dei Tumori in Milan, Italy, highlighted the potential significance of moving immunotherapy earlier in the treatment pathway.
“For many years, MSS colon cancer has largely been considered resistant to immunotherapy. The UNICORN study challenges that assumption in the curative-intent setting,” said Pietrantonio.
He explained that the objective of neoadjuvant treatment is not simply to shrink tumors before surgery but also to prevent disease recurrence and ultimately increase the number of patients who may be cured.
The observation of deep pathological responses following a short treatment course, combined with preserved surgical feasibility and no reported recurrences in the combination cohorts at the data cutoff, provides a rationale for further investigation in a larger randomized study.
Agenus Advances Planned Phase 3 ROBBIN Trial
Building on the findings from UNICORN and NEST, Agenus is advancing plans for ROBBIN, a global randomized Phase 3 clinical trial evaluating neoadjuvant botensilimab plus balstilimab in patients with high-risk Stage II or Stage III pMMR/MSS colon cancer.
The planned study will compare botensilimab and balstilimab administered before surgery, followed by standard-of-care treatment, against standard-of-care treatment alone.
The trial is intended to enroll previously untreated patients with high-risk Stage II or Stage III MSS/pMMR colon cancer.
Event-free survival has been selected as the planned primary endpoint, reflecting the importance of preventing recurrence and improving long-term outcomes in patients receiving curative-intent treatment.
The planned randomized study represents an important next step in determining whether the encouraging pathological response findings observed in the earlier Phase 2 studies can translate into improved clinical outcomes in a larger patient population.
A randomized Phase 3 evaluation will also provide an opportunity to compare the combination directly with standard-of-care treatment under a controlled clinical trial design.
Advancing Immunotherapy for Earlier-Stage Colon Cancer
The publication of the UNICORN trial results in Nature Medicine represents an important clinical development for Agenus and its botensilimab and balstilimab programs.
The findings highlight the potential of short-course neoadjuvant immunotherapy to generate deep pathological responses in patients with both pMMR/MSS and dMMR/MSI-H colon cancer.
The results are particularly encouraging in MSS disease, which represents approximately 85% of early-stage colorectal cancers and has historically been difficult to treat with conventional immunotherapy.
With major pathological responses, complete pathological responses, ctDNA clearance, immune-environment changes, and encouraging early event-free survival observations, the study provides a scientific and clinical foundation for further investigation of the combination.
The company’s planned Phase 3 ROBBIN trial will be an important next milestone in determining whether these findings can be translated into improved outcomes for patients with high-risk, resectable MSS colon cancer.
As Agenus continues advancing its immuno-oncology pipeline, the broader objective remains to develop treatment strategies capable of overcoming tumor immune resistance and bringing the potential benefits of immunotherapy to patients earlier in their disease journey.
About the UNICORN Study
UNICORN (NCT05845450) is an ongoing multicenter, non-randomized, open-label Phase 2 window-of-opportunity platform trial sponsored by Fondazione GONO. The study evaluates short-course preoperative therapies in molecularly selected patients with resectable colorectal cancer.
The analysis reported in Nature Medicine evaluated Cohorts 4 through 7, comprising 56 patients with pMMR/MSS or dMMR/MSI-H colon cancer treated with BOT alone or BOT+BAL prior to curative-intent surgery. Patients receiving BOT monotherapy received botensilimab 1 mg/kg on Day 1. Patients receiving BOT+BAL received botensilimab 1 mg/kg on Day 1 and balstilimab 3 mg/kg on Days 1 and 15. Surgery was planned for Day 35 ± 5 days.
The primary endpoint was centrally assessed major pathologic response, defined as 10% or less residual viable tumor. Secondary and exploratory analyses included safety, quality of life, longitudinal ctDNA, spatial transcriptomics, peripheral immune-cell dynamics, genomic correlates and microbiome analyses. The study was supported by GONO and other research funding sources. Agenus supplied BOT and BAL.
About Agenus
Agenus is a leading immuno-oncology company targeting cancer with a comprehensive pipeline of immunological agents. The company was founded in 1994 with a mission to expand patient populations benefiting from cancer immunotherapy through combination approaches, using a broad repertoire of antibody therapeutics, adoptive cell therapies (through MiNK Therapeutics) and adjuvants.
Agenus has robust end-to-end development capabilities, across commercial and clinical cGMP manufacturing facilities, research and discovery, and a global clinical operations footprint. Agenus is headquartered in Lexington, MA. For more information, visit www.agenusbio.com or @agenus_bio. Information that may be important to investors will be routinely posted on our website and social media channels.
About Botensilimab (BOT)
Botensilimab (BOT) is a human multifunctional, Fc-enhanced anti-CTLA-4 antibody designed to boost both innate and adaptive anti-tumor immune responses. Its novel design leverages mechanisms of action to extend immunotherapy benefits to “cold” tumors which generally respond poorly to standard of care or are refractory to conventional PD-1/CTLA-4 therapies and investigational therapies. BOT augments immune responses across a wide range of tumor types by priming and activating T cells, reducing intratumoral regulatory T cells, activating myeloid cells and inducing durable memory responses.
BOT+ balstilimab (BAL) has been studied in over 1,500 patients across more than nine tumor types, spanning late-line refractory disease and early-stage neoadjuvant settings. The combination is being developed to expand immunotherapy benefit to more patients, including those with microsatellite stable (MSS) disease and tumors considered immunologically “cold” or resistant to existing immunotherapies.
For more information about botensilimab trials, visit www.clinicaltrials.gov.
About Balstilimab (BAL)
Balstilimab is a novel, fully human monoclonal immunoglobulin G4 (IgG4) designed to block PD-1 (programmed cell death protein 1) from interacting with its ligands PD-L1 and PD-L2. It has been evaluated in more than 900 patients to date and has demonstrated clinical activity and a favorable tolerability profile in several tumor types.