4basebio PLC (4BB), the UK-listed genomic medicines company, has received a major shareholder notification confirming that Elevage Medical Technologies Holdings, LLC holds a combined 27.8% voting interest, down from a previously notified 29.9%. The disclosure, filed on 11 November 2026 following a threshold crossing on 10 November 2026, reveals a concert party arrangement between Fort Aggregator, LP and the Prudential Assurance Company Limited, the latter acting within M&G plc's investment management structure. Investors in 4basebio may be watching closely, given that the two entities together now control 5,350,075 voting rights in the company.

Key Points

  • 4basebio PLC (4BB) — UK-listed genomic medicines company with ordinary shares of €1.00 each (ISIN: GB00BMCLYF79)
  • Elevage Medical Technologies Holdings, LLC disclosed a combined 27.8% voting stake via a TR-1 major holdings notification
  • Threshold crossed on 10 November 2026; total voting rights held stand at 5,350,075, compared with 4,627,741 at the previous notification
  • Investors should watch for the separate M&G plc notification covering the Prudential Assurance Company Limited's 12.6% shareholding

Fort Aggregator and Prudential Assurance Act in Concert Across Two Ownership Chains

The notification states that Fort Aggregator, LP and the Prudential Assurance Company Limited are acting in concert pursuant to DTR 5.2.1(a), requiring their positions to be aggregated and disclosed together. Fort Aggregator, LP, registered in Wilmington, Delaware, holds 2,923,171 voting rights indirectly, equating to 15.2% of 4basebio's voting share capital. The Prudential Assurance Company Limited, registered in London, contributes a further 2,426,904 voting rights indirectly, representing 12.6%. The combined total of 5,350,075 voting rights produces the reported 27.8% aggregate stake.

Voting Rights Fall from 29.9% to 27.8% Despite Increase in Absolute Share Count

Whilst the percentage holding has decreased from 29.9% to 27.8% since the previous notification, the absolute number of voting rights held has actually risen — from 4,627,741 to 5,350,075. The announcement does not explicitly explain this apparent divergence, though it is consistent with an increase in 4basebio's total issued share capital diluting the percentage even as the concert party's absolute holding grew. The company did not disclose further detail on this point in the announcement. No financial instruments, warrants, or convertible instruments form part of this notification, with both the B1 and B2 subtotals recorded as nil.

M&G plc's Multi-Entity Chain Underpins Prudential's 12.6% Indirect Interest in 4basebio

The disclosure sets out a detailed ownership chain behind the Prudential Assurance Company Limited's 12.6% indirect interest. The chain runs through M&G plc, M&G Group Regulated Entity Holding Company Limited, M&G Group Limited, M&G FA Limited, and ultimately M&G Investment Management Limited. The announcement confirms that a separate TR-1 notification will be filed on behalf of M&G plc in respect of this shareholding. Elevage Medical Technologies GP, LLC sits atop the Fort Aggregator chain, with Elevage Medical Technologies Holdings, LLC acting as the indirect parent shareholder under DTR 5.1.2 and 5.2.1(e).