The following table shows the activity within the liability account in the year ended December 31, 2024 and for the period from the inception of the royalty transactions to December 31, 2024 (in thousands):


	Year ended December 31, 2024			Period from inception to December 31, 2024
Liability related to sale of future royalties and milestones - beginning balance	$	257,296		$	—
Proceeds from sale of future royalties and milestones		63,879			268,879
Non-cash royalty and milestone revenue		(100,978	)		(400,468	)
Non-cash interest expense recognized		117,342			469,128
Liability related to sale of future royalties and milestones - ending balance		337,539			337,539
Less: unamortized transaction costs		(1,172	)		(1,172	)
Liability related to sale of future royalties and milestones, net	$	336,367		$	336,367

On January 6, 2018, we, through Antigenics, entered into the HCR Royalty Purchase Agreement with HCR, which closed on January 19, 2018. Pursuant to the terms of the HCR Royalty Purchase Agreement, we sold to HCR 100% of Antigenics’ worldwide rights to receive royalties on sales of GSK’s vaccines containing our QS-21 STIMULON adjuvant. At closing, we received gross proceeds of $190.0 million from HCR. As part of the transaction, we reimbursed HCR for transaction costs of $100,000 and incurred approximately $500,000 in transaction costs of our own, which are presented net of the liability in the consolidated balance sheet and will be amortized to interest expense over the estimated life of the HCR Royalty Purchase Agreement. Although we sold all of our rights to receive royalties on sales of GSK’s vaccines containing QS-21, as a result of our obligation to HCR, we are required to account for the $190.0 million in proceeds from this transaction as a liability on our consolidated balance sheets that will be relieved in proportion to the royalty payments from GSK to HCR over the estimated life of the HCR Royalty Purchase Agreement. The liability is classified between the current and non-current portion of liability related to sale of future royalties and milestones in the consolidated balance sheets based on the estimated royalty payments to be received by HCR in the next 12 months from the financial statement reporting date.

In the years ended December 31, 2024, 2023 and 2022, we recognized $101.0 million, $114.6 million and $45.3 million, respectively, of non-cash royalty revenue and we recorded $106.7, $100.3 million and $62.7 million, respectively, of related non-cash interest expense related to the HCR Royalty Purchase Agreement.

As royalties are remitted to HCR from GSK, the balance of the recorded liability will be effectively repaid over the life of the HCR Royalty Purchase Agreement. To determine the amortization of the recorded liability, we are required to estimate the total amount of future royalty payments to be received by HCR. The sum of these royalty amounts less the $190.0 million proceeds we received will be recorded as interest expense over the life of the HCR Royalty Purchase Agreement. Periodically, we assess the estimated royalty payments to be paid to HCR from GSK, and to the extent the amount or timing of the payments is materially different from our original estimates, we will prospectively adjust the amortization of the liability, and the related recognition of interest expense. Since the inception of the HCR Royalty Purchase Agreement our estimate of the effective annual interest rate over the life of the agreement decreased to 23.8%, which results in a retrospective interest rate of 24.6%.

There are a number of factors that could materially affect the amount and timing of royalty payments from GSK, all of which are not within our control. Such factors include, but are not limited to, changing standards of care, the introduction of competing products, manufacturing or other delays, biosimilar competition, patent protection, adverse events that result in governmental health authority imposed restrictions on the use of the drug products, significant changes in foreign exchange rates, and other events or circumstances that could result in reduced royalty payments from GSK, all of which would result in a reduction of non-cash royalty revenues and the non-cash interest expense over the life of the HCR Royalty Purchase Agreement. Conversely, if sales of GSK’s vaccines containing QS-21 are more than expected, the non-cash royalty revenues and the non-cash interest expense recorded by us would be greater over the life of the HCR Royalty Purchase Agreement.

Pursuant to the HCR Royalty Purchase Agreement, we were also entitled to receive up to $40.4 million in milestone payments from HCR (through the royalty payments from GSK) based on sales of GSK’s vaccines as follows: (i) $15.1 million upon reaching $2.0 billion last-twelve-months net sales any time prior to 2024 and (ii) $25.3 million upon reaching $2.75 billion last-twelve-months net sales any time prior to 2026. In the fourth quarter of 2019, the $15.1 million milestone was achieved, as sales for the year ended December 31, 2019 exceeded $2.0 billion. In the second quarter of 2022, the final milestone was achieved, as sales for the 12 months ended June 30, 2022 exceeded $2.75 billion. As such, we recognized royalty sales milestone revenue of $25.3 million during the year ended December 31, 2022. This milestone was paid through royalties received from GSK.

On September 20, 2018, we, through our wholly-owned subsidiary, Agenus Royalty Fund, LLC, entered into a Royalty Purchase Agreement (the “XOMA Royalty Purchase Agreement”) with XOMA (US) LLC (“XOMA US”). Pursuant to the terms of the XOMA Royalty Purchase Agreement, XOMA US paid us $15.0 million at closing in exchange for the right to receive 33% of the future royalties and 10% of the future milestones that we were then entitled to receive from Incyte and Merck Sharp & Dohme (“Merck”) under our agreements with each party (see Note 13), net of certain of our obligations to a third party and excluding the $5.0 million milestone from Incyte that we recognized in the quarter ended September 30, 2018. We retained 90% of the future milestones and 67% of the future royalties under our agreements with Incyte and Merck. Although we sold our rights to receive 33% of future royalties and 10% of future milestones, as a result of our significant continued involvement in the generation of the potential royalties and milestones, we are required to account for the full amount of these royalties and milestones as revenue when earned, and we recorded the $15.0 million in proceeds from this transaction as a liability on our consolidated balance sheet. Under the terms of the XOMA Royalty Purchase Agreement, should the percentage of milestones and royalties ultimately received by XOMA US fail to repay the amount received by us at closing we would have no further obligation to XOMA US. No royalty or milestone revenue was recognized under this agreement in the years ended December 31, 2024, 2023 or 2022.

In May 2024, we and certain wholly-owned subsidiaries, entered into a Purchase and Sale Agreement (the "Ligand Purchase Agreement") with Ligand Pharmaceuticals Incorporated ("Ligand"). Pursuant to the terms of the Ligand Purchase Agreement, Ligand

will receive (i) 31.875% of the development, regulatory and commercial milestone payments we were then eligible to receive under our agreements with BMS, UroGen, Gilead, Merck and Incyte, (the “Covered License Agreements”) (ii) 18.75% of the royalties the Company receives under the Covered License Agreements; and (iii) a 2.625% synthetic royalty on worldwide net sales of botensilimab and balstilimab (collectively the “Purchased Assets”). In the event that we relicense the programs in the Covered License Agreements, Ligand would retain its economic interest in any new agreement.

The total amounts payable to Ligand are subject to a 50% reduction in the event total payments to Ligand exceed a specified return hurdle. The synthetic royalty is subject to a reduction if annual worldwide net sales exceed a specified level, and a cap on annual worldwide net sales if annual worldwide net sales exceed a higher specified level. The synthetic royalty can increase by 1% based on the occurrence of certain future events.

In consideration for the sale of the Purchased Assets, we received gross proceeds of $75.0 million, less $0.9 million in reimbursable expenses, on the closing date. In addition, Ligand has a time-based option to invest an additional $25.0 million on a pro rata basis ("Purchaser Upsize Option"), which expires on June 30, 2025.

In connection with the sale of the Purchased Assets, we issued to Ligand a warrant (the "Ligand Warrant") to purchase 867,052 shares of our common stock, at an exercise price equal to $17.30 per share. See Note 9 - Equity for further detail.

The $75.0 million in gross proceeds was allocated to the identified components as follows (in thousands):


Liability related to sale of future royalties and milestones	$	63,879
Ligand Warrant		7,098
Purchaser Upsize Option		4,023
Total Ligand Purchase Agreement gross proceeds	$	75,000

As a result of our significant continuing involvement in the generation of the cash flows of the Purchased Assets, we are required to account for $63.9 million of the proceeds from this transaction as a liability on our condensed consolidated balance sheet that will be recognized into revenue in proportion to the royalty and milestone payments paid to Ligand over the estimated life of the Ligand Purchase Agreement.

The Purchaser Upsize Option is considered a freestanding financial instrument as it is separately exercisable and can be legally transferred from the Ligand Purchase Agreement. As such, it is accounted for as a written option which is accounted for as a liability at fair value and remeasured at each balance sheet date with changes in fair value recorded in earnings. The fair value of the Purchaser Upsize Option at December 31, 2024 was $69,200.

The Ligand Warrant is considered a freestanding financial instrument as it is separately exercisable and can be legally transferred from the Ligand Purchase Agreement, which was determined to be equity-classified under ASC 815.

To allocate the proceeds, the Purchaser Upsize Option liability and equity-classified Ligand Warrants were recognized based on their fair values and the residual was allocated to a liability related to the sale of future royalties and milestones on our consolidated balance sheets.

During the year ended December 31, 2024, we recorded $10.6 million of non-cash interest expense related to the Ligand Purchase Agreement.

As royalties are remitted to us and milestone and sales are earned from the Purchased Assets, the balance of the recorded liability will be effectively repaid over the life of the Ligand Purchase Agreement. To determine the amortization of the recorded liability, we are required to estimate the total amount of future payments that Ligand is entitled to under the Ligand Purchase Agreement. The sum of these amounts less the $63.9 million proceeds allocated to the liability related to sale of future royalties and milestones will be recorded as interest expense over the life of the Ligand Purchase Agreement. Periodically, we assess the estimated royalty and milestone payments to be received and sales to be earned under the Ligand Purchase Agreement, and to the extent the amount or timing of the payments is materially different from our original estimates, we will prospectively adjust the amortization of the liability, and the related recognition of interest expense. As of December 31, 2024, our estimate of the effective annual interest rate over the life of the agreement was 24.3%.