C4 Therapeutics cemsidomide shows T-cell data at IMS 2026
C4 Therapeutics has presented new biomarker data from its Phase 1 and Phase 1b clinical programmes for cemsidomide in relapsed/refractory multiple myeloma at the 23rd International Myeloma Society Annual Meeting in late September 2026. The data reinforce the company's thesis that the oral cereblon-modulating protein degrader can serve as a backbone combination partner for immune-based therapies by sustaining T-cell activity in heavily pre-treated patients.
In the fully enrolled Phase 1 trial of cemsidomide plus dexamethasone, analysis across 62 patients showed coordinated activation of CD8+ T cells and functional reprogramming of natural killer cells. The company noted that enhanced immune cell function was most pronounced at the highest dose levels studied, 75 µg and 100 µg, which also produced what it described as compelling overall response rates. Full efficacy data from the Phase 1 study have been previously reported; the new poster focused on the immunological correlates that may explain those results.
Phase 1b safety milestone
Preliminary biomarker data from the first two patients enrolled in the ongoing Phase 1b trial, which pairs cemsidomide with elranatamab (Pfizer's FDA-approved BCMAxCD3 bispecific antibody), showed expansion and activation of CD8+ effector memory T cells, measured via elevated HLA-DR expression, alongside suppressed markers of T-cell exhaustion including PD-1, TIM-3 and LAG3. The safety data review committee has now declared the 75 µg starting dose level safe after evaluating six patients, allowing the trial to advance simultaneously into a 100 µg dose escalation cohort and a 75 µg expansion cohort. Consolidated data from all cohorts are expected in mid-2027.
Len Reyno, chief medical officer at C4 Therapeutics, said: "T-cell exhaustion is associated with both primary resistance and relapse in these patients. Maintaining T-cell fitness is an important component of achieving deep and durable responses."
Cemsidomide degrades the IKZF1 and IKZF3 transcription factors, which are central to myeloma cell survival. The cereblon-modulating mechanism places it in the same broad class as the immunomodulatory drugs lenalidomide and pomalidomide, but its protein degrader profile is intended to offer a differentiated potency and tolerability window.
Competitive and market context
Multiple myeloma is the second most common blood cancer in the United States, with roughly 36,000 new diagnoses annually and more than 175,000 people living with or in remission from the disease. The treatment landscape has been reshaped over the past several years by CD38-directed antibodies, BCMA-directed antibody-drug conjugates such as belantamab mafodotin, and bispecific T-cell engagers including elranatamab and teclistamab. CAR-T therapies targeting BCMA have also entered routine practice at specialist centres.
The overarching clinical challenge is that responses to these immune-redirecting approaches can be short-lived, in part because T-cell exhaustion limits sustained tumour control. C4 Therapeutics is positioning cemsidomide as a solution to that problem, on the hypothesis that cereblon-mediated IKZF1/3 degradation maintains the T-cell repertoire needed to support bispecific and CAR-T activity. Several academic groups and companies are exploring analogous immunomodulatory combination strategies, making the mid-2027 Phase 1b readout a meaningful data point for the field as a whole.
The company has not yet initiated a pivotal trial for cemsidomide, and regulatory timelines remain dependent on the dose optimisation work now underway. Investors will focus on whether the 100 µg level in the Phase 1b programme achieves a similar safety clearance and, eventually, whether response depth in combination exceeds what either agent achieves alone.