Agenus Reports Updated NEST Phase 2 Results Supporting Neoadjuvant BOT+BAL in Colon Cancer
Agenus Inc. (Nasdaq: AGEN), a biotechnology company focused on immuno-oncology innovation, has announced the peer-reviewed publication of updated results from the investigator-sponsored Phase 2 NEST clinical trial evaluating neoadjuvant botensilimab (BOT) in combination with balstilimab (BAL) in patients with resectable colon cancer.
The findings, published in Clinical Cancer Research, provide longer-term clinical and biological follow-up from the NEST study and offer additional evidence supporting the investigation of the combination as a pre-surgical treatment for colon cancer. The manuscript, titled “Neoadjuvant botensilimab/balstilimab for localized mismatch repair proficient and deficient colon cancer: Results of the NEST phase 2 clinical trial,” expands on earlier findings presented at the 2025 ASCO Gastrointestinal Cancers Symposium.
Botensilimab is Agenus’ multifunctional, Fc-enhanced anti-CTLA-4 antibody, while balstilimab is the company’s anti-PD-1 antibody. The combination is being investigated for its ability to stimulate anti-tumor immune responses before surgical removal of localized colorectal tumors.
The updated NEST analysis includes longer follow-up of tumor responses, circulating tumor DNA (ctDNA) clearance, disease-free outcomes and changes within the tumor microenvironment. According to Agenus, the data provide additional support for advancing botensilimab plus balstilimab into larger clinical studies in earlier-stage, curative-intent mismatch repair proficient (pMMR) and microsatellite stable (MSS) colon cancer.
No Colorectal Cancer Recurrences Observed at Data Cutoff
At the March 31, 2026 data cutoff, no colorectal cancer recurrences had been observed among patients participating in the NEST study. Median follow-up reached 32.2 months in the NEST-1 cohort and 23.5 months in NEST-2.
The absence of observed recurrences during the available follow-up is an encouraging finding, although the study’s relatively small size and single-arm design mean that the results require confirmation in larger randomized clinical trials.
The findings are particularly notable for patients with pMMR/MSS tumors, which account for approximately 85% of early-stage colorectal cancers. Historically, this group has derived limited benefit from conventional immunotherapy approaches, especially in metastatic disease.
For localized colon cancer, treatment has traditionally centered on surgical resection, often combined with chemotherapy depending on disease stage and risk characteristics. Consequently, there remains a significant need for treatment strategies that can produce deeper tumor responses before surgery and potentially reduce the risk of disease recurrence.
Investigating Immunotherapy Before Surgery
The NEST trial explores the concept of administering immunotherapy before surgical removal of the tumor, known as neoadjuvant therapy.
This treatment setting may provide an important biological advantage because the primary tumor, tumor-draining lymph nodes and surrounding immune microenvironment remain present while treatment is administered. These components can potentially interact with the immune system and help generate a broader anti-tumor response.
Agenus’ approach is designed to use the combination of BOT and BAL to stimulate immune activity while also addressing immunosuppressive mechanisms within the tumor microenvironment.
The updated NEST findings suggest that this strategy can generate measurable tumor regression and immune changes before surgery in patients with pMMR/MSS disease, a population that has historically presented challenges for immunotherapy.
Phase 2 NEST Study Design
NEST was a single-center, open-label, single-arm Phase 2 study. The trial enrolled 24 eligible patients with a total of 26 resectable colorectal tumors.
Among the tumors included in the analysis, 22 were pMMR/MSS and four were deficient mismatch repair (dMMR)/microsatellite instability-high (MSI-H).
Patients received botensilimab and balstilimab during one of two pre-surgical treatment intervals. The NEST-1 cohort received treatment over approximately four weeks, while patients in NEST-2 were treated over approximately eight weeks.
An important finding was that patients proceeded to their planned surgical resections without treatment-related delays. This observation is relevant because any neoadjuvant treatment strategy must ultimately be compatible with definitive surgery, particularly when treatment is being considered with curative intent.
The study evaluated not only pathological tumor responses but also molecular and immunological changes, providing researchers with several complementary measures of treatment activity.
Strong Pathologic Responses in pMMR/MSS Tumors
Among the 22 pMMR/MSS tumors evaluated, 59% achieved a pathologic response following neoadjuvant BOT+BAL treatment.
The reported pathologic response rate included patients achieving a pathologic complete response, major pathologic response or partial response.
More specifically, 41% of pMMR/MSS tumors achieved a major pathologic response (MPR), defined as 10% or less viable tumor remaining at the time of surgery.
A pathologic complete response (pCR) was observed in 32% of pMMR/MSS tumors. A pCR means that no viable tumor was identified in the surgical specimen or adjacent lymph nodes.
These findings are particularly notable because pMMR/MSS colorectal cancers have generally demonstrated lower sensitivity to immune checkpoint therapy than dMMR/MSI-H tumors.
The NEST publication references previously reported MPR rates of approximately 19% to 20%, with pCR rates of around 10%, for first-generation CTLA-4 and PD-1 combination approaches in pMMR colon cancer. However, Agenus emphasizes that cross-trial comparisons must be interpreted cautiously because clinical studies can differ substantially in patient populations, study design, treatment regimens and follow-up duration.
Encouraging Results in dMMR/MSI-H Tumors
The study also evaluated four tumors classified as dMMR/MSI-H.
All four tumors achieved a major pathologic response. Two patients achieved a pathologic complete response, while the remaining two tumors demonstrated near-complete tumor regression, with 98% and 99% regression reported.
Although the number of dMMR/MSI-H tumors in the NEST study was very small, the results add to the overall assessment of the combination’s biological activity across different molecular subgroups of colorectal cancer.
Because dMMR/MSI-H tumors are generally more responsive to immune checkpoint blockade than pMMR/MSS tumors, larger studies will be needed to determine the clinical significance of these observations.
ctDNA Clearance Provides Additional Evidence of Treatment Activity
Another important component of the NEST analysis was the evaluation of circulating tumor DNA.
ctDNA refers to fragments of tumor-derived genetic material that can be detected in a patient’s bloodstream. Monitoring ctDNA can provide researchers with a molecular measure of residual disease and treatment response.
Among patients who had detectable ctDNA at baseline and available pre-surgical samples, 88% cleared ctDNA before surgery.
In addition, ctDNA remained undetectable following surgical resection in all patients evaluated.
The company believes these findings provide another potential indicator of deep treatment response. However, the clinical significance of ctDNA clearance and its ability to predict long-term outcomes will require further validation in larger prospective studies.
Immune Remodeling in the Tumor Microenvironment
The NEST study also examined changes within the tumor microenvironment, providing insight into how BOT+BAL may be exerting its effects.
Analysis of paired tumor samples showed coordinated immune remodeling in responding tumors. This included increased infiltration of CD8-positive T cells, reductions in FOXP3-positive regulatory T cells and increased CD8-positive T-cell-to-Treg ratios.
Researchers also observed spatial reorganization of immune cells within the tumor.
These findings are potentially important because tumors can develop highly immunosuppressive environments that limit the ability of immune cells to recognize and eliminate malignant cells.
Agenus believes that the observed immune changes provide biological support for the multifunctional, Fc-enhanced design of botensilimab. According to the company, BOT is intended to extend beyond conventional checkpoint blockade by helping remodel the immunosuppressive tumor environment.
The immune findings may help explain why the combination showed activity in pMMR/MSS tumors, which have historically been less responsive to immunotherapy.
Surgery Remained Feasible
Maintaining the ability to perform surgery as planned is a critical consideration for neoadjuvant treatment.
In the NEST trial, patients proceeded to planned surgical resection without treatment-related delays. The study also reported no Grade 4 treatment-related adverse events, treatment-related deaths or treatment-related study discontinuations.
These safety and feasibility findings provide additional support for continued investigation of the combination in the pre-surgical setting.
Nevertheless, larger randomized trials will be necessary to establish the safety profile of BOT+BAL more comprehensively and determine whether the pathological and molecular responses translate into improved long-term outcomes.
ROBBIN Phase 3 Program Planned
The updated NEST publication supports Agenus’ decision to prioritize BOT+BAL for earlier-stage, curative-intent MSS colon cancer.
The company is advancing ROBBIN, a planned global randomized Phase 3 trial designed to compare neoadjuvant BOT+BAL followed by standard of care with standard of care alone in previously untreated patients with high-risk Stage II or Stage III MSS colon cancer.
Event-free survival is planned as the primary endpoint.
The objective of the ROBBIN program is to determine whether the deep tumor responses and molecular changes observed in NEST can translate into better long-term outcomes for patients.
The transition from a small investigator-sponsored Phase 2 study to a randomized Phase 3 program represents an important step in the development of the approach. A randomized trial will provide a more rigorous assessment of whether adding BOT+BAL to standard treatment can reduce recurrence and improve disease control compared with standard therapy alone.
Experts Highlight Potential of Earlier Immunotherapy
Steven O’Day, M.D., Chief Medical Officer of Agenus, said the updated NEST results provide important context for the company’s focus on neoadjuvant BOT+BAL in MSS colon cancer.
According to O’Day, the longer follow-up across both NEST cohorts demonstrates that BOT+BAL can produce deep tumor responses and immune activation before surgery without delaying surgical treatment. He said the findings strengthen the rationale for the ROBBIN Phase 3 trial and continued evaluation of the combination in curative-intent disease.
Pashtoon M. Kasi, M.D., M.S., Medical Director of GI Medical Oncology at City of Hope Orange County and Rad Family Chair in Gastrointestinal Oncology, who originated the NEST study, also emphasized the potential importance of administering immunotherapy before surgery.
Kasi noted that the NEST findings support the concept of using immunotherapy earlier in colorectal cancer, while the primary tumor and immune system remain positioned to generate a coordinated anti-tumor response.
He highlighted the combination of pathologic responses, ctDNA clearance, immune remodeling and the absence of observed colorectal cancer recurrences during longer follow-up as encouraging signals, particularly in pMMR/MSS disease.
Next Steps for BOT+BAL Development
The NEST findings represent an important milestone in Agenus’ efforts to develop immunotherapy strategies for earlier-stage colorectal cancer. The combination of BOT and BAL demonstrated substantial pathologic responses in pMMR/MSS tumors, molecular evidence of response through ctDNA clearance and measurable changes in the tumor immune microenvironment.
At the same time, the results should be interpreted within the context of the study’s limitations, including its small patient population, single-center setting and single-arm design. The absence of observed recurrences is encouraging but cannot establish comparative efficacy without a control group and longer follow-up.
The planned ROBBIN Phase 3 trial will therefore be critical in determining whether the promising signals observed in NEST can translate into a clinically meaningful reduction in recurrence and improvement in outcomes.
Agenus is also continuing development of the neoadjuvant strategy through NEST3, a multicenter Phase 2 investigator-sponsored study that is currently enrolling.
Overall, the updated peer-reviewed NEST data strengthen the scientific rationale for evaluating botensilimab plus balstilimab earlier in the treatment journey of colon cancer. By targeting the immune system before surgery, the approach seeks to generate deeper tumor regression and potentially eliminate microscopic disease that could otherwise contribute to recurrence. Future randomized clinical data will determine whether this strategy can ultimately improve long-term outcomes for patients with high-risk localized MSS colon cancer.
About the NEST and NEST 3 Studies
NEST (NCT05571293) was an investigator-initiated, single-center, open-label Phase 2 study evaluating neoadjuvant BOT+BAL in patients with resectable colorectal cancer. The study enrolled 24 eligible patients with 26 resectable colorectal tumors, including 22 with mismatch repair proficient/microsatellite stable and four mismatch repair deficient/microsatellite instability-high tumors. Patients received neoadjuvant BOT+BAL before planned surgical resection. The primary objectives were to assess safety, feasibility and anti-tumor activity, with exploratory analyses evaluating treatment-associated changes in the tumor immune microenvironment. Agenus supported the study and provided BOT and BAL.
NEST3 (NCT07595874) is an open and actively enrolling multicenter Phase 2 investigator-sponsored study evaluating neoadjuvant BOT+BAL in advanced resectable colorectal cancer. The study is sponsored by City of Hope Medical Center, led by Pashtoon M. Kasi, M.D., M.S., as overall principal investigator, and designed to enroll approximately 100 patients across 11 U.S. sites. The first patient was dosed in July 2026. NEST3 is being conducted through City of Hope’s National Clinical Trials Model, a centralized research framework designed to expand patient access to clinical trials across multiple City of Hope locations. More information is available at ClinicalTrials.gov.
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, research and discovery. 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. Botensilimab 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.
Approximately 1,300 patients have been treated with botensilimab and/or balstilimab in phase 1 and phase 2 clinical trials. Botensilimab alone, or in combination with Agenus’ investigational PD-1 antibody, balstilimab, has shown clinical responses across nine metastatic, late-line cancers. 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.