Why Immutep (IMMP) Is Crashing 95% Today

Immutep Limited (NASDAQ: IMMP) shares are down roughly 95% during Wednesday's regular session, falling from a prior close of $5.68 to around $0.28 per share. The Australian biotech company is the session's biggest decliner by a wide margin.

What Drove the Move

The drop follows a September 21, 2026 announcement via GlobeNewswire titled "Change to American Depositary Share Ratio" and a corresponding 6-K filing with the SEC dated September 22, 2026.

Immutep is an Australia-based biotechnology firm listed on NASDAQ as an American Depositary Receipt (ADR). The company develops immunotherapeutic candidates, most notably eftilagimod alfa (efti), which is in multiple Phase II and Phase III clinical trials for various cancers including metastatic breast cancer, head and neck squamous cell carcinoma, and non-small cell lung cancer.

Understanding ADR Ratio Changes

When a company changes its ADR ratio, it alters how many underlying foreign shares each US depositary receipt represents. This type of corporate action can trigger significant trading adjustments, particularly when the change is large or unexpected. Trading volume in IMMP was approximately 46,000 shares as of mid-session, relatively light compared to the stock's average daily volume.

Recent Company Developments

The ADR ratio announcement comes amid an active period for Immutep. Earlier in September, the company outlined a focused development strategy for eftilagimod alfa. In July 2026, Immutep reported positive mature overall survival data from the INSIGHT-003 study in first-line NSCLC and provided an update from TACTI-004.

In April 2026, Immutep received FDA Orphan Drug Designation for eftilagimod alfa in soft tissue sarcoma, and its stock roughly doubled on the news. The company also disclosed in April 2026 that it received a Nasdaq notice of bid price deficiency, indicating the stock had fallen below the exchange's minimum bid price requirement.

Pipeline Highlights

Immutep's key programs include:

  • Eftilagimod alfa (efti): The lead candidate in multiple Phase II/III trials as a chemoimmunotherapy combination for metastatic breast cancer and as a combo with pembrolizumab for lung and head/neck cancers
  • TACTI-004 (KEYNOTE-F91): Phase III trial in first-line NSCLC, though the company reported in March 2026 that a futility analysis led to discontinuation of certain study arms
  • IMP761: A first-in-class LAG-3 agonist antibody for autoimmune diseases, with positive Phase I data presented at EULAR 2026

The company entered a strategic collaboration with India's Dr. Reddy's in December 2025 for commercialization of eftilagimod alfa in certain markets.

What Investors Should Know

The steep decline reflects the direct market reaction to the ADR ratio disclosure. Investors holding US-listed ADRs of foreign companies should understand how ratio changes affect their positions. Immutep's market capitalization has been reduced dramatically in this session, falling from approximately $837 million to roughly $41 million based on current share counts.

As with any biotech company, Immutep's valuation remains heavily tied to clinical trial outcomes and regulatory milestones for its pipeline candidates. The stock will likely remain volatile as the market digests today's corporate action and reassesses the company's development priorities.