Biotechnology investing is a strange corner of the market.

A company can own a drug that may eventually produce billions of dollars in sales and still find itself scrambling to raise enough cash to survive another year.

A stock can double after a successful clinical trial and give the entire gain back when the FDA asks one unexpected question.

Patents, trial design, manufacturing, reimbursement, and management competence can all matter as much as the science.

Most investors have no business wandering around this part of the market without a guide.

Fortunately, SEC filings allow us to follow investors who have spent years learning how to navigate it.

One of the more interesting guides is David Johnson of Caligan Partners.

Johnson worked in principal investments at Morgan Stanley before spending seven years as a managing director at Carlyle Group. He established Caligan Partners in 2017 and has served as its managing partner and chief investment officer ever since.

Caligan is an SEC-registered investment firm focused on healthcare.

That description is accurate, but it leaves out the interesting part.

Johnson and his team do not simply buy a biotechnology stock, wait for a clinical result, and hope for the best.

They invest more like private equity owners.

Caligan takes concentrated positions, provides financing, seeks board seats, pushes for better capital allocation, and occasionally encourages a company to sell itself.

The firm tends to look for medical assets that are underfunded, misunderstood, or trapped inside a poorly managed company.

When Caligan finds one, it is willing to get involved.

That approach has produced some interesting results.

AMAG Pharmaceuticals was acquired by Covis Pharma. ANI Pharmaceuticals bought Alimera Sciences. Merck acquired Verona Pharma for approximately $10 billion. Liquidia has appreciated substantially and successfully launched its primary commercial product.

Public filings do not tell us exactly how much Caligan made on those investments.

They do tell us this is a firm worth watching when it starts buying.

Caligan’s latest filing gives us several new ideas to investigate.

A Portfolio Built Around Conviction

Caligan reported 28 Form 13F line items worth approximately $2.13 billion as of June 30, 2026.

That was up from $1.50 billion at the end of March and approximately $395 million at the end of 2024.

Do not mistake that increase for a reported investment return.

The change could include new investor capital, additional purchases, investment gains, option positions, and private securities becoming publicly reportable.

The filing also does not contain 28 separate companies. Caligan reported both common shares and call options in some names.

What stands out is the concentration.

The five largest investments accounted for approximately 69.7% of the reported portfolio.

Liquidia and Revolution Medicines alone represented half of the entire filing.

This is not a manager attempting to hug the biotechnology index.

When Caligan develops conviction, it puts real money behind the idea.

That can work beautifully when the science and strategy come together.

It can also cause a great deal of pain when a clinical trial fails or an FDA decision goes the wrong way.

Johnson clearly accepts that bargain.

Liquidia Corporation (LQDA)

Liquidia Corporation was Caligan’s largest position by a wide margin.

The firm reported approximately 8.1 million shares worth $647.3 million, equal to 30.5% of the portfolio.

Liquidia treats pulmonary hypertension. Its primary product is YUTREPIA, an inhaled dry-powder version of treprostinil.

The FDA approved YUTREPIA in May 2025 for adults with pulmonary arterial hypertension and pulmonary hypertension associated with interstitial lung disease. Liquidia began shipping the drug the following month.

The launch appears to be gaining traction.

By April 30, 2026, Liquidia had received more than 4,500 prescriptions and started approximately 3,750 patients on treatment. More than 980 physicians had prescribed the drug.

Caligan first disclosed a 19.2% stake in Liquidia in 2021, and Johnson joined the board.

That timing matters.

Caligan did not wait for YUTREPIA to receive final approval and begin generating prescriptions.

It invested while Liquidia was still dealing with regulatory questions, patent litigation, financing needs, and the enormous practical challenge of launching a new drug.

The investment has paid off handsomely on paper.

Caligan did not reduce its Liquidia position during the second quarter, even after the stock’s substantial advance.

Liquidia remains a risky investment. YUTREPIA has to compete for patients, earn reimbursement, survive continued patent challenges, and prove that its early commercial momentum is sustainable.

Caligan’s position leaves little doubt about its level of conviction as of June 30.

Revolution Medicines (RVMD)

Revolution Medicines was the second-largest investment.

Caligan owned approximately 1.96 million common shares worth $367.4 million. It also held call options covering 251,800 shares, valued at approximately $47.2 million.

Combined, the common shares and call options were worth $414.6 million and accounted for 19.5% of the portfolio.

Revolution Medicines is attacking cancers driven by mutations in RAS proteins.

These mutations appear in some of the most difficult pancreatic, lung, and colorectal cancers.

For years, researchers considered RAS almost impossible to target effectively. Revolution Medicines has built a collection of drugs intended to prove that assumption wrong.

The company has already made the leap from clinical development to commercialization.

The FDA approved RASONQUE, also known as daraxonrasib, for previously treated metastatic pancreatic cancer.

Revolution Medicines is studying daraxonrasib in other settings while developing zoldonrasib, an experimental treatment aimed at RAS G12D mutations.

Zoldonrasib is being evaluated in pancreatic and lung cancers, both alone and in combination with other treatments.

Caligan added about 309,000 common shares during the second quarter and increased its call position.

This is clearly not a quick trade around one FDA decision.

Caligan appears to be investing in the entire RAS drug portfolio and the possibility that these treatments will eventually address several major cancer markets.

The expectations are high, and so is the valuation.

Revolution Medicines will have to deliver.

Caligan is betting that the approved drug and the pipeline can support a much larger business over time.

Abivax (ABVX)

Abivax was Caligan’s third-largest investment.

The firm owned approximately 1.56 million American depositary shares worth $207.6 million, or 9.8% of the portfolio.

Caligan added 96,000 shares during the quarter.

Abivax is a French biotechnology company developing obefazimod, an oral treatment for ulcerative colitis.

Anyone who has watched a friend or family member deal with ulcerative colitis knows how brutal the disease can be.

Patients can suffer from abdominal pain, bleeding, weight loss, and potentially serious complications. Existing drugs help many people, but patients frequently stop responding and must move to another therapy.

Obefazimod is an experimental oral miR-124 enhancer designed to stabilize the immune response.

In June 2026, Abivax reported positive results from its Phase 3 ABTECT maintenance trial in patients with moderately to severely active ulcerative colitis.

If obefazimod makes it through the regulatory process, Abivax could have a differentiated oral treatment for a large market with an ongoing need for new options.

The company still faces regulatory, manufacturing, and commercialization risks.

It may also attract interest from a larger pharmaceutical company looking to expand in immunology, although investors should never buy a stock solely because someone might acquire it.

Caligan’s position is large enough to tell us the firm sees something it likes.

Vaxcyte (PCVX)

Vaxcyte was worth approximately $127.2 million, or 6% of Caligan’s reported portfolio.

The company is developing pneumococcal vaccines that could protect against more bacterial strains than existing products.

Pneumococcal disease can cause pneumonia, meningitis, bloodstream infections, and other serious illnesses.

It is already a large commercial vaccine market, but established pharmaceutical companies dominate it.

Vaxcyte’s leading candidate is VAX-31, which is designed to protect against 31 pneumococcal serotypes.

The company is evaluating the vaccine in a Phase 3 adult development program and completed enrollment in two Phase 3 studies during 2026. One of the pivotal trials enrolled approximately 4,000 adults.

The opportunity is enormous if VAX-31 provides broader protection and reaches the market.

The obstacles are enormous as well.

Vaccines are difficult to manufacture. Regulators demand extensive evidence. Established competitors have deep pockets, longstanding physician relationships, and worldwide distribution networks.

Caligan owned approximately 2.19 million Vaxcyte shares and added about 128,000 during the quarter.

Johnson appears willing to accept the development and competitive risks in exchange for a shot at one of the world’s largest vaccine markets.

Exelixis (EXEL)

Exelixis gives Caligan something different from its clinical-stage holdings.

The company already has a profitable cancer franchise.

Cabozantinib, sold under the Cabometyx and Cometriq names, generates substantial revenue and cash flow.

Caligan became involved with Exelixis through an activist effort led by Farallon Capital. The investors argued that Exelixis was spreading its research dollars across too many programs while failing to return enough capital to shareholders.

Johnson joined the board in 2023 and is currently the chair.

That gives him a direct role in discussions involving research priorities, governance, and capital allocation.

Caligan owned approximately 1.55 million Exelixis shares worth $84.5 million, equal to about 4% of the portfolio.

The firm did not change its share count during the second quarter.

Exelixis has less binary risk than many of Caligan’s other investments because Cabometyx is already an established commercial drug.

Continued cash generation, sensible research spending, pipeline success, and shareholder returns could all increase the value of the company.

These five holdings establish what Caligan looks like when it develops serious conviction.

Now we get to what interests me even more.

Where is Johnson putting new money?

Five New Positions

Caligan started five positions during the second quarter.

The largest was Immunocore Holdings (IMCR), a commercial-stage biotechnology company developing T-cell receptor therapies for cancer, infectious diseases, and autoimmune disorders.

Caligan reported approximately 1.38 million Immunocore depositary shares worth $43.9 million.

Immunocore deserves further research, but I want to spend more time on the four smaller and less widely followed additions.

Those are Sagimet Biosciences, Viridian Therapeutics, Artiva Biotherapeutics, and Cellectar Biosciences.

These are the types of stocks I love finding in a 13F filing.

They are not household names.

Most investors could not tell you what they do.

A specialist with a record of getting directly involved has started buying.

That is enough to get my attention.

Sagimet Biosciences (SGMT)

Sagimet Biosciences is developing drugs that inhibit fatty acid synthase, an enzyme involved in the production of fatty acids.

Its lead drug is denifanstat.

The company is developing it for metabolic dysfunction-associated steatohepatitis, usually called MASH, and moderate-to-severe acne.

MASH is a progressive liver disease involving fat accumulation, inflammation, and fibrosis.

Denifanstat produced positive Phase 2b results in MASH. Sagimet’s Chinese licensing partner also reported positive Phase 3 results for the drug in moderate-to-severe acne.

The acne program may offer Sagimet a more direct path toward the market.

In August 2026, the FDA cleared the company’s application to begin a U.S. Phase 3 acne trial. Sagimet expects patient screening to begin in October, with the first patient enrolled shortly afterward.

The study is expected to include approximately 800 patients, including about 450 adolescents.

Patients will receive denifanstat or a placebo for 12 weeks, followed by a longer safety evaluation.

A successful oral treatment could find a large audience.

Physicians and patients would welcome additional alternatives to antibiotics and isotretinoin.

Caligan bought 2.5 million shares worth approximately $19.3 million.

Sagimet is speculative, but denifanstat gives the company more than one way to win.

The drug is being investigated in two large markets, and the same fatty acid synthase platform could eventually support additional programs.

Viridian Therapeutics (VRDN)

Viridian Therapeutics is developing and commercializing drugs for autoimmune and rare diseases.

Its first target is thyroid eye disease, an autoimmune condition that causes inflammation and tissue expansion around the eyes.

Patients can suffer from pain, double vision, facial disfigurement, and vision problems.

The FDA approved Viridian’s intravenous treatment Lumvoa in June 2026. Patients receive five infusions over 12 weeks.

Viridian is also developing elegrobart as a subcutaneous treatment that could be more convenient and may eventually be administered outside an infusion center.

The clinical story is not perfectly clean.

Elegrobart met the primary endpoint in a Phase 3 study involving active thyroid eye disease, but some results fell short of what investors had expected. Later findings in chronic thyroid eye disease were more encouraging.

Viridian still has to prove it can compete against Amgen’s Tepezza.

Efficacy will matter, but so will safety, convenience, pricing, reimbursement, and the ability to convince physicians to use a new product.

Caligan purchased approximately 2.19 million shares worth $40.3 million.

Viridian was its second-largest new investment after Immunocore.

The timing is worth noting.

Caligan began buying as Viridian moved from developing drugs to selling one.

That transition is difficult, but it can also be when a biotechnology company begins creating substantial value.

Artiva Biotherapeutics (ARTV)

Artiva Biotherapeutics is developing natural killer cell therapies for autoimmune diseases.

Personalized cell therapies can produce remarkable responses, but they are expensive and difficult to manufacture.

Patients may also have to wait while a treatment is made specifically for them.

Artiva is working on a different approach.

Its treatments are allogeneic, meaning they are manufactured in advance from donor cells and can potentially be used across many patients.

The lead candidate, AlloNK, is a nonengineered, cryopreserved natural killer cell therapy designed to work alongside antibodies that target B cells.

Artiva is studying AlloNK in rheumatoid arthritis, Sjögren’s disease, and other autoimmune conditions driven by abnormal B-cell activity.

The therapy is also being tested with rituximab in certain blood cancers.

Cell therapy is one of the most intriguing areas in autoimmune medicine.

Early results across the industry suggest it may produce deep and lasting responses in some patients.

Artiva still has to prove that its treatment works, remains safe, and can be delivered economically.

Caligan established a position of approximately 1.74 million shares worth $16.8 million.

A position this size is not yet a massive Caligan commitment.

It is large enough to suggest the firm wants meaningful exposure if the clinical results begin moving in the right direction.

Cellectar Biosciences (CLRB)

Cellectar Biosciences is developing targeted radiotherapies for cancer.

The company’s phospholipid drug conjugate platform is designed to carry radioactive material into cancer cells while limiting exposure to healthy tissue.

Its lead drug, iopofosine I-131, combines a cancer-targeting molecule with radioactive iodine.

Cellectar has studied it in Waldenström macroglobulinemia, multiple myeloma, and pediatric brain cancers.

Waldenström macroglobulinemia is a rare blood cancer in which abnormal white blood cells produce excessive amounts of a protein that can thicken the blood and damage organs.

Caligan and Johnson reported beneficial ownership of 469,998 Cellectar shares, or approximately 5.9% of the company.

Cellectar is the smallest and probably the most speculative of these new ideas.

The company still must prove that its radiotherapy is effective, tolerable, and commercially practical in relatively small patient populations.

The low valuation creates room for a substantial move if the company produces good clinical data or finds a workable regulatory path.

The same low valuation tells us the market has serious doubts.

That combination of high uncertainty and potentially large upside is exactly why a specialist investor’s involvement matters.

What I See in the Filing

Caligan is not sitting around waiting for financing conditions to improve or for the biotechnology indexes to break out.

Johnson is buying companies with specific drugs, defined clinical programs, and visible events that could change how the market values them.

There is also a pattern to the purchases.

Sagimet has its fatty acid synthase platform.

Artiva is developing natural killer cell technology.

Cellectar has a targeted radiotherapy delivery system.

Viridian has antibody-engineering capabilities that could extend beyond thyroid eye disease.

Immunocore is working with T-cell receptor therapies across several disease categories.

Caligan wants more than one roll of the dice.

A drug that can treat several diseases is more interesting than one limited to a tiny indication. A scientific platform that produces several drug candidates may eventually become attractive to a larger pharmaceutical company.

Financing is part of the equation as well.

Great science does not help shareholders if the company runs out of cash halfway through a clinical trial.

Caligan has participated in private placements and other transactions that helped companies reach their next milestone.

Johnson is also willing to get involved when he believes management is wasting money. Caligan has sought board representation or pressed for changes at AMAG Pharmaceuticals, Anika Therapeutics, Liquidia, and Exelixis.

That makes these filings more useful than the average hedge fund shopping list.

Caligan is often investing in the science, the capital structure, and the possibility of changing how the company is run.

The Alpha Buying Takeaway

None of these stocks is safe.

A failed clinical trial can cut a biotechnology stock in half before breakfast.

FDA delays, manufacturing problems, patent disputes, weak launches, and desperate capital raises can do almost as much damage.

The 13F is also an old snapshot by the time we see it.

We do not know Caligan’s exact cost basis, hedges, private investments, or plans. A new purchase could become a much larger commitment, or Caligan could decide the original thesis was wrong and leave.

We should not blindly copy the portfolio.

We should investigate it.

Sagimet Biosciences, Viridian Therapeutics, Artiva Biotherapeutics, and Cellectar Biosciences are underfollowed healthcare companies with identifiable clinical and commercial catalysts.

They carry serious risk, but each has a credible path to becoming far more valuable if the science works.

Caligan’s involvement does not guarantee success.

It tells us that an experienced healthcare investor has looked closely enough to put money on the line.

For me, that is more than enough reason to start digging.