Hunting the immune system's hidden off switches - and building the antibodies to flip them back on.
The Apeximmune wordmark. A five-person team in the Bay Area's biotech corridor, backing a first-in-class swing at cancer's most stubborn tumors.
Most cancer immunotherapy circles the same short list of targets. Apeximmune Therapeutics went looking somewhere else. The company mines thousands of tumor RNA-sequencing transcriptomes across more than twenty cancer types, searching for the molecular factors that quietly switch off the immune cells sent to fight a tumor. That search has produced more than thirty novel immune targets - and a pipeline of antibodies designed to turn those switches back on.
Founded in 2020 and based in the Bay Area's biotech corridor, Apeximmune describes its purpose plainly: to pioneer a new generation of therapeutic antibodies and biologics that harness the immune system to treat cancer and autoimmune disease. It is a lean operation - roughly five employees - but the ambition is first-in-class, meaning it aims for medicines that hit targets no existing drug addresses.
The company's lead program, AI-306, is an antagonist monoclonal antibody aimed at AIM-103, a checkpoint the company says is highly expressed in some of oncology's hardest cases: pancreatic, liver, colon and esophageal cancers. In parallel, its MEBA platform takes a contrarian route through the immune system - recruiting macrophages, the cells that literally engulf and digest tumor cells, rather than the T cells most rivals rely on.
In March 2025 the strategy drew a vote of confidence: a $21.3 million Series A, oversubscribed past its $20 million goal, led by publicly traded PharmaEssentia. It brought the company's total funding to roughly $27.3 million and set a clear next milestone - an IND filing that would move AI-306 toward first-in-human trials.
Solid tumors survive by suppressing the immune response inside their own microenvironment. Checkpoint inhibitors like anti-PD-1 changed oncology by releasing one of those brakes, but they leave many patients - and many tumor types - untouched. Cancers with few infiltrating lymphocytes, like several gastrointestinal tumors, are especially resistant.
Apeximmune's thesis is that the map of immune brakes is incomplete. Its discovery platform hunts for the immune-attenuating factors that suppress tumor-infiltrating T cells and that no one has yet turned into a drug. AIM-103, its lead find, is unusual: the company reports it controls both the innate and adaptive arms of the immune system, and works through both enzyme-dependent and previously unknown enzyme-independent pathways.
A first-in-class antagonist monoclonal antibody targeting the novel checkpoint AIM-103. Designed to reverse the tumor's immune suppression and reinvigorate anti-tumor T-cell immunity, with a focus on gastrointestinal cancers. Advancing toward IND.
Macrophage Engaging Bispecific Antibodies pair a class-leading activator of macrophage phagocytosis with tumor-associated antigen targets. Candidates AI-328, AI-201 and AI-614 aim to work even in low-lymphocyte tumors, with a safety profile the company positions above T-cell engagers.
A proprietary bioinformatics pipeline analyzing thousands of RNA-seq transcriptomes across 20+ tumor types to find novel immune-attenuating factors. It has already yielded more than 30 targets of interest for future programs.
Stage positions are approximate, based on public company disclosures.
The crowded field of immuno-oncology mostly builds on T cells - the checkpoint inhibitors and T-cell engagers that dominate headlines and clinics. Apeximmune's MEBA platform takes a different lane. By activating macrophage phagocytosis and pointing it at tumor-associated antigens, it aims to be effective in tumors where T cells are scarce, a setting where conventional approaches often stall.
The second differentiator is upstream: the discovery platform itself. Rather than licensing known targets, Apeximmune generates its own from raw transcriptomic data, which is what lets it credibly claim "first-in-class." AIM-103 is the proof point - a checkpoint the company says spans both innate and adaptive immunity.
The company operates near macrophage-checkpoint players working the CD47/SIRPa axis and a broad set of bispecific antibody developers, while positioning its programs as complements to - not replacements for - established PD-1 and LAG-3 checkpoint drugs. Its edge is less about a single molecule than about a repeatable engine for finding the next one.
Backing that engine is an advisory bench that outweighs the company's size: innate-immunity pioneer Jenny Ting, LAG-3 researcher Dario Vignali, and autoimmune-disease authority Lawrence Steinman among them - names that lend scientific credibility well beyond a five-person headcount.
The 2025 Series A was led by PharmaEssentia Corporation, with participation from DCI Partners, Taya Venture Capital, KDI Marketing, Huahai US, Hercules BioVenture LP and TTM 2025 LLC. It closed above its $20 million target. PharmaEssentia's chief scientific officer, Lih-Ling Lin, sits on Apeximmune's board of directors - aligning capital and science. The proceeds are earmarked to move AI-306 through IND-enabling work into clinical trials and to expand the company's R&D and leadership.
As a venture-backed clinical-stage developer, Apeximmune creates value by discovering and validating novel immune targets, then advancing first-in-class antibody candidates through preclinical and early clinical stages on equity capital. The likely path to return is partnering, licensing or acquisition by larger pharma - not near-term product revenue.
The ultimate beneficiaries are cancer and autoimmune-disease patients underserved by current therapies. Near-term stakeholders are pharmaceutical partners, biotech investors and the oncology research community watching AI-306's progress toward the clinic.
Founder Li-Fen Lee brings more than two decades in immunology and drug development, with prior roles at AbbVie, NGM and Pfizer and a former faculty position at Stanford University School of Medicine. The board includes former Amgen biologics leader Hsieng Lu and PharmaEssentia CSO Lih-Ling Lin.
Apeximmune is established to develop immune-harnessing antibody therapeutics for cancer and autoimmune disease.
An early round funds the build-out of the discovery platform.
Analysis across 20+ tumor types yields more than 30 novel immune targets, including AIM-103.
Macrophage-engaging bispecific candidates AI-328, AI-201 and AI-614 progress in preclinical work.
PharmaEssentia leads an oversubscribed round to push AI-306 toward the clinic.
It is a biotechnology company that discovers novel immune targets and develops first-in-class antibody therapeutics to treat cancer and autoimmune disease by harnessing the immune system.
AI-306 is Apeximmune's lead program - a first-in-class antagonist monoclonal antibody targeting the novel immune checkpoint AIM-103, aimed at gastrointestinal cancers such as pancreatic, liver, colon and esophageal cancer.
MEBA (Macrophage Engaging Bispecific Antibody) is Apeximmune's platform for building bispecific antibodies that activate macrophage phagocytosis against tumor-associated antigens, effective even in tumors with few lymphocytes.
About $27.3 million in total, including a $6 million Pre-A round in 2021 and a $21.3 million Series A in 2025 led by PharmaEssentia.
It was founded by Dr. Li-Fen (Lilian) Lee, its CEO and a former Stanford School of Medicine faculty member, together with co-founders Ching-Leou Teng and Hsieng Lu.
Video interviews and a product demo were not publicly available at publication. Check the company's LinkedIn and newsroom for future updates.