GSK Bets Up to $750M on Chimagen Trispecific T Cell Engager

T cell engagers have become some of the most effective drugs in multiple myeloma, and some of the most demanding to give. GSK is now betting up to $750 million on a Chimagen trispecific T cell engager designed to keep that efficacy while easing the burden.

GSK plc (LSE/NYSE: GSK) announced on September 15, 2026, that it has agreed to acquire the program from Chimagen Biosciences, a privately held, China-based biotech. GSK calls the molecule a potential best-in-class T cell engager (TCE) and plans to develop it in multiple myeloma, with Phase 1 trials expected to begin in 2027. It is the second asset GSK has agreed to buy from Chimagen in under two years.

Deal Terms

GSK will pay an undisclosed upfront fee for full global rights to the program, and Chimagen is eligible for success-based development and commercial milestone payments. The total potential value is up to $750 million, and the deal is subject to customary closing conditions.

GSK has not named the molecule or its two tumor targets. Its shares edged higher in early London trading, on a morning when Berenberg also upgraded the stock to buy.

The price reflects that stage. In July 2025, AbbVie agreed to pay $700 million upfront, plus up to $1.225 billion in milestones, to license ISB 2001, a CD38×BCMA×CD3 trispecific that already had Phase 1 data. GSK’s entire deal is worth only slightly more than AbbVie’s upfront payment alone.

Why Myeloma Needs a Better T Cell Engager

Multiple myeloma is the third most common blood cancer worldwide, with approximately 196,000 new cases each year (IARC 2026). It is treatable but not yet curable, and because it commonly becomes refractory to available drugs, patients often need several options over time (Malard et al. 2024).

T cell engagers bind CD3 on a patient’s T cells and a target on myeloma cells, bringing the two together so the T cell can kill the tumor (Devasia et al. 2024). Their efficacy is no longer in question. In March 2026, the FDA approved J&J’s Tecvayli (teclistamab) with Darzalex Faspro for patients with at least one prior line of therapy, including a proteasome inhibitor and an immunomodulatory agent. In the MajesTEC-3 trial, the combination cut the risk of progression or death by 83% (HR 0.17) versus daratumumab-based triplets (Costa et al. 2026).

The trade-off is the treatment experience. In the US, Tecvayli and J&J’s GPRC5D-targeted Talvey (talquetamab) carry boxed warnings for cytokine release syndrome (CRS) and neurologic toxicity, including immune effector cell-associated neurotoxicity syndrome (ICANS). Both are available only through a restricted REMS program and require 48-hour hospital stays during step-up dosing. BCMA-directed therapy also depletes the normal plasma cells that make antibodies, leaving patients vulnerable to infections (Mazahreh et al. 2023; Devasia et al. 2024). GPRC5D targeting adds oral toxicity such as taste changes, weight loss, and skin and nail changes (Chari et al. 2022; Janssen Biotech 2025).

GSK frames the problem plainly: TCEs have shown “transformational efficacy” in myeloma but have been associated with “difficult tolerability profiles.” The Chimagen molecule is designed to address this by binding T cells while simultaneously targeting two “strategically selected and validated” tumor-associated antigens. The goal is deeper, more durable responses with better tolerability, which GSK says could enable broader adoption and earlier use. Citing market forecasts, GSK says the US TCE market in multiple myeloma is expected to exceed $10 billion by 2032.

The Case for Hitting Two Targets

A second tumor-binding arm is meant to address two weaknesses of current bispecifics. Myeloma cells can lose or reduce expression of a single antigen under treatment pressure (Lee et al. 2023; Lee et al. 2026), and expression varies from cell to cell (Pillarisetti et al. 2026). Hitting two antigens should, in theory, close off escape routes and, through higher avidity, help the drug bind cancer cells tightly even when either target is expressed at low levels (Carretero-Iglesia et al. 2024; Pillarisetti et al. 2026).

Chimagen’s antigen choice remains undisclosed. Among the best-validated myeloma targets are BCMA and GPRC5D, both hit by approved bispecifics (Devasia et al. 2024), and CD38, the target of daratumumab and isatuximab. The most advanced trispecifics pair BCMA with one of the other two.

The earlier GSK–Chimagen deal hints at the company’s engineering approach, although GSK has not said whether the new asset shares it. In 2024, GSK described that first molecule, CMG1A46, as IgG-like, with high affinity for its B-cell targets and low affinity for CD3, a design it said could mitigate the toxicities typically associated with TCEs.

A Race Already Underway

GSK’s molecule will not reach patients before 2027, and the next wave of myeloma immune engagers is moving fast.

• J&J’s ramantamig (JNJ-79635322) targets BCMA, GPRC5D and CD3 (Pillarisetti et al. 2026). In Phase 1 data presented at ASCO 2025, it achieved an 86.1% response rate at the recommended Phase 2 dose, and 100% in patients naive to BCMA- and GPRC5D-directed therapy. CRS occurred in 59% of patients, with no events of grade 3 or higher, though 28% had grade 3 or higher infections. Ramantamig is now in Phase 3 head-to-head trials against BCMA-directed bispecifics, including Tecvayli (NCT07258511; NCT07518186). J&J will present updated data, including on outpatient dosing, at the International Myeloma Society meeting later this month.
• Innovent’s IBI3003, a GPRC5D×BCMA×CD3 trispecific, dosed its first patient in the pivotal Phase 3 TriadicMM-1 trial, the company announced in June. It had reported an 83.3% response rate in 24 patients at doses of at least 120 μg/kg (Innovent Biologics 2026).
• AbbVie’s ABBV-2001 (ISB 2001), a CD38×BCMA×CD3 trispecific, had shown a 79% response rate in 35 heavily pretreated patients when AbbVie licensed it.

For GSK, the “best-in-class” label will have to be earned in the clinic, against molecules that are already years ahead.

A Second Bet on Chimagen’s Platform

The deal builds on GSK’s October 2024 agreement to acquire CMG1A46, a dual CD19- and CD20-targeted TCE, for $300 million upfront and up to $550 million in milestones. GSK took it on to pursue lupus and related autoimmune conditions, and it is now in Phase 1 trials for B-cell malignancies and B-cell-dependent autoimmune disorders. Coming back for a second asset signals confidence in Chimagen’s platforms, which generate multi-specific T cell and NK cell engagers for cancer and autoimmune disease.

Working with GSK combines our precision T-cell engager programme with their global development and commercial capabilities to redefine care for multiple myeloma patients

said Zhenhao Zhou, Chief Executive Officer of Chimagen Biosciences. He added that the agreement

marks another major milestone for our platforms as we continue to build an industry-leading pipeline of multi-specific antibody candidates.

The deal also fits a wider pattern of large drugmakers sourcing new antibodies from China. Out-licensing deals signed by companies in the greater China region hit a record $137.7 billion in 2025, nearly ten times the 2021 total, according to data provider Pharmcube, as reported by Reuters (Wu and Silver 2026).

Where It Fits in GSK’s Oncology Strategy

In multiple myeloma, GSK’s marketed product is Blenrep (belantamab mafodotin), a BCMA-targeted antibody-drug conjugate. The FDA approved Blenrep with bortezomib and dexamethasone in October 2025 for patients with at least two prior lines of therapy, including a proteasome inhibitor and an immunomodulatory agent. Blenrep combinations are also approved in the EU, UK, Japan and other markets, and the drug generated £59 million in sales in the first half of 2026. GSK is also testing it in newly diagnosed, transplant-ineligible patients in the Phase 3 DREAMM-10 trial.

The deal secures a promising T cell engager and advances GSK’s leadership goals in blood cancer

said Hesham Abdullah, Senior Vice President, Global Head Oncology, R&D, GSK.

The agreement complements our existing portfolio in multiple myeloma, adding a new potential option to address the different needs of patients facing this complex disease.

Hesham Abdullah/GSK

The deal fits the playbook CEO Luke Miels described when GSK agreed to buy Nuvalent for $10.6 billion in June: acquiring

assets that have clinically proven targets and meaningfully address an efficacy and/or tolerability gap.

Luke Miels/GSK

That acquisition closed in July  and has already delivered an FDA approval for Jideytro (zidesamtinib) in previously treated ROS1-positive non-small cell lung cancer.

GSK’s oncology sales rose 17% at constant exchange rates to £569 million in the second quarter of 2026. The company is expanding from blood and women’s cancers into lung, gastrointestinal and other solid tumors, with priority programs including the antibody-drug conjugates risvutatug rezetecan (B7-H3) and mocertatug rezetecan (B7-H4), and the KIT inhibitor velzatinib.

What Still Has to Land

The deal still has to close, and human data will not arrive before Phase 1 begins in 2027. Three questions will define the program:

• Which two antigens it targets, and how it will be positioned against BCMA- and GPRC5D-directed drugs already in use
• Whether first-in-human data show clearly lower rates of CRS, ICANS and serious infections than today’s bispecifics
• Whether responses are deep and durable enough to support earlier-line use, where a Tecvayli-based combination is already approved

Bottom Line

Takeaway: GSK is paying a preclinical price for a shot at the next generation of myeloma T cell engagers, betting that two tumor targets and careful engineering can match the power of today’s bispecifics with fewer of their burdens. The rationale is sound and the market is large, but with J&J and Innovent already in Phase 3, Chimagen’s molecule will need clearly differentiated data to live up to its best-in-class billing.

Read more biotech insights on OncoDaily Biotech.

Frequently Asked Questions

What is GSK acquiring from Chimagen Biosciences?

GSK is acquiring full global rights to a preclinical trispecific T cell engager for multiple myeloma. The molecule binds T cells and two undisclosed tumor-associated antigens and is expected to enter Phase 1 trials in 2027.

How much is the GSK–Chimagen deal worth?

The deal has a total potential value of up to $750 million, made up of an undisclosed upfront payment plus success-based development and commercial milestones.

What is a trispecific T cell engager?

A trispecific T cell engager is an engineered antibody that binds three different targets. In the myeloma trispecifics discussed here, one engages CD3 on T cells and two recognize targets on cancer cells. Targeting two antigens is intended to strengthen tumor binding and make it harder for cancer cells to escape by losing a single target.

Are any trispecific T cell engagers approved for multiple myeloma?

Not as of September 2026. Trispecifics remain investigational, with J&J’s ramantamig and Innovent’s IBI3003 the most advanced, both in Phase 3. Approved T cell engagers in the US include the BCMA-targeted Tecvayli, Elrexfio and Lynozyfic, and the GPRC5D-targeted Talvey.