While in vivo CAR-T therapies eliminate complex ex vivo manufacturing, they introduce a new critical variable: the patient's own immune system. The therapy's efficacy relies on modifying T-cells within the body, but each patient's immune status is different, especially after prior treatments. This makes optimizing and standardizing the dose a significant challenge compared to engineered cell therapies.

In the Cartitude 1 trial, the strongest predictor of long-term remission with Siltacel was a lower burden of disease (measured by bone marrow percentage and soluble BCMA levels), rather than the number of prior treatments. This implies using CAR-T therapy earlier in the disease course is more effective.

Data from J&J's Majestic 3 trial suggests its off-the-shelf bispecific combination could rival the efficacy of its own blockbuster CAR-T, Carvykti. This sets up an internal competition where a more accessible therapy could challenge a complex, personalized one in earlier lines of treatment.

Due to significant ocular toxicity affecting most patients, the approved starting dose for belantumab is likely not optimal long-term. Effective management requires clinicians to proactively hold, delay, and reduce doses at the first sign of side effects, meaning real-world application will differ from the initial protocol.

Despite exciting early efficacy data for in vivo CAR-T therapies, the modality's future hinges on the critical unanswered question of durability. How long the therapeutic effects last, for which there is little data, will ultimately determine its clinical viability and applications in cancer versus autoimmune diseases.

The future of medicine isn't about finding a single 'best' modality like CAR-T or gene therapy. Instead, it's about strategic convergence, choosing the right tool—be it a bispecific, ADC, or another biologic—based on the patient's specific disease stage and urgency of treatment.

Developers often test novel agents in late-line settings because the control arm is weaker, increasing the statistical chance of success. However, this strategy may doom effective immunotherapies by testing them in biologically hostile, resistant tumors, masking their true potential.

The DREAM-7 trial showed a belantumab combination had an overall survival benefit versus a daratumumab regimen, a "premier drug" that previously changed the myeloma treatment landscape. This surprising result establishes a new, higher standard of care and positions belantumab as a top-tier therapy, not merely another option.

Using a BCMA bispecific antibody first can exhaust a patient's T-cells or cause tumors to lose the BCMA target, rendering a subsequent BCMA-targeted CAR-T therapy ineffective. The optimal sequence is CAR-T first, which preserves T-cell function and BCMA expression, leaving bispecifics as a viable later-line option.