November 20, 2025 /

B Cell Depletion Therapy (BCDT) directly targets the root cause of immune dysregulation, restoring immune homeostasis through precise intervention, thereby emerging as a revolutionary approach for autoimmune diseases. Since most BCDT agents originate from oncology applications, while autoimmune diseases and malignancies differ significantly in therapeutic objectives and mechanisms, the complex interplay among dosage, efficacy, and side effects remains a critical research focus.

Recent findings presented at the December 2024 ACR Conference highlight the  substantial impact of these differences on the correlation between B cell depletion depth and clinical outcomes. In previous two articles, we explored the fundamental principles and applications of BCDT in autoimmune diseases, introduced major B cell-driven autoimmune disorders, and summarized BCDT applications in these conditions. This article will briefly synthesize key clinical data disclosed at the conference and discuss distinctions between autoimmune and oncological treatments.

 

1. Correlation Between B Cell Depletion Depth and Efficacy

For autoimmune diseases, the primary goal of BCDT is to eliminate pathogenic B cell populations to achieve “immune reset.” Consequently, the depth of B-cell depletion critically influences therapeutic efficacy. Clinical trial data show that deep B cell depletion sustained for months or longer often results in disease remission exceeding two years, whereas insufficient depletion shortens the duration of effective response. Below is a summary of recent findings in CAR-T and T-Cell Engager (TCE) therapies.

CAR-T Cell Therapy

• Dr. Georg Schett’s Research

As a pioneer in BCDT for autoimmune diseases, Dr. Schett has accumulated data from 30 patients across three indications: systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and idiopathic inflammatory myopathy (IIM). The study demonstrated:

• Peripheral B cell reconstitution occurred approximately 30–90 days after CD19 CAR-T treatment.
• Most patients maintained low autoantibody levels and drug-free remission during at least 6 months of follow-up, with only 1 IIM patient relapsing at 15 months post-treatment.
  

Notably, no cytokine release syndrome (CRS) of grade 3 or higher occurred during the entire treatment course, and immune effector cell-associated neurotoxicity syndrome (ICANS) was not observed, demonstrating favorable safety and tolerability.

• iCell Gene Therapeutics

iCell conducted studiesat Zhongshan Hospital and Peking University Shenzhen Hospital, enrolling 12 patients with SLE and lupus nephritis (LN). Participants received dual-targeting BCMA/CD19 CAR-T therapy with a median follow-up of 20 months. B cells typically re-emerged in peripheral blood within 2–6 months post-treatment. Complete remission was achieved in 11 of 12 patients, with normalization of autoantibodies and complement levels. In the single non-responding patient, residual proteinuria was attributable to pre-existing cumulative renal damage rather than active disease.

Among 10 LN patients, 7 achieved complete renal recovery. Analysis of 9 patients with SLEDAI-2K scores of 0 showed an average 85% reduction in proteinuria compared to prior therapies. Furthermore, no CRS or ICANS was observed throughout the treatment course, indicating favorable tolerability.

• BMS

BMS-986353 is a CD19-targeted CAR-T therapy evaluated in patients with SLE, SSc, and IIM. Most patients exhibited peripheral B-cell reconstitution approximately two months post-infusion. Throughout the follow-up period (maximum 253 days), all 7 SLE patients maintained drug-free remission.

Notably, treatment-emergent adverse events included 8 cases of grade 1/2 CRS, 1 grade 1 ICANS, and 1 grade 3 ICANS. These observations indicate the need for further safety evaluation in larger clinical trials.

T-Cell Engager (TCE) Therapy

• Cullinan Therapeutics

CLN-978 is a CD3/CD19-targeting T-cell engager (TCE) bispecific antibody incorporating an anti-human serum albumin VHH domain for half-life extension.

In vitro studies demonstrate that CLN-978 induces comparable levels of B-cell killing, T-cell activation, and cytokine production in peripheral blood mononuclear cells (PBMC) from both healthy donors and SLE patients.

In cynomolgus monkey models, 4 weekly subcutaneous doses of CLN-978 achieved profound B-cell depletion across peripheral blood, bone marrow, spleen, and lymphoid tissues, with favorable tolerability. Although the ACR presentation did not disclose specific therapeutic efficacy data in autoimmune diseases, the B-cell depletion depth observed in B-cell non-Hodgkin lymphoma (B-NHL) patients was less comprehensive than CAR-T-mediated clearance—a finding consistent with results from both in vitro and animal studies.

At the ACR presentation, Cullinan Therapeutics did not disclose specific efficacy data for autoimmune indications; however, available results in B-cell non-Hodgkin lymphoma (B-NHL) patients demonstrated that the extent of B-cell depletion achieved by their therapeutic approach was less profound compared to CAR-T-mediated clearance.

 

 

• ITabMed

A-319 is a CD3-CD19 TCE evaluated in 6 patients with refractory SLE. 1 patient presented with concurrent LN and encephalopathy, while 2 patients had comorbid SSc or rheumatoid arthritis(RA).

During the first week (W1), patients received continuous 24-hour intravenous infusions at 0.05 μg/kg/day on days 1, 3, and 5. From weeks 2–4, the dosing regimen was adjusted to 6-hour intravenous infusions at 0.3 μg/kg/day on the same schedule (days 1, 3, and 5).

Follow-up data extending to maximum 1 year demonstrated significant B-cell depletion post-treatment. However, B cells began to gradually recover starting from the second week, while autoantibody levels continued to decline for at least 8 weeks. Although the B-cell depletion capability of this TCE was slightly less pronounced than that achieved with CAR-T therapy, no CRS or ICANS was observed during treatment, indicating a favorable safety profile.

 

• Roche

Analysis of the phase II NOBILITY trial (NCT02550652) of Obinutuzumab in LN, alongside the primary clinical endpoints (such as proteinuria reduction) used in the ongoing phase III REGENCY study (NCT04221477) and the BLISS-LN trial (NCT01639339), demonstrates that Obinutuzumab in combination with standard therapy significantly reduces proteinuria compared to placebo plus standard therapy, with superior clinical benefits observed at both Weeks 76 and 104.

Compared to Rituximab, Obinutuzumab achieved faster, deeper, and longer-lasting peripheral B cell depletion. Although all dosing was completed within 6 months, clinical benefits continued to improve throughout the 24-month observation period. These findings suggest a positive correlation between the duration of B-cell depletion and clinical outcomes, providing a broader therapeutic window for renal repair and ultimately promoting complete remission.

 

• Roche/Genentech

RO7507062 is currently undergoing Phase I clinical trials in SLE patients, with no publicly available human data yet. However, preliminary studies demonstrate that：

In vitro, RO7507062 induces dose-dependent B-cell depletion in human PBMCs.

In humanized immune system mouse models, a single intravenous injection rapidly and profoundly depleted B cells in peripheral blood, lymph nodes, spleen, and bone marrow, accompanied by only modest increases in serum cytokine levels without significant clinical symptoms.

In cynomolgus monkey studies, intravenous administration of RO7507062 also resulted in dose-dependent B-cell depletion and cytokine release. At the highest dose, mild and transient CRS was observed, with cytokine peaks occurring 2–6 hours post-dosing and returning to baseline within 72 hours. Subcutaneous injection demonstrated improved tolerability compared to intravenous administration while maintaining comparable B-cell clearance efficacy.

 

2. Comparison of Dosage and Efficacy

BCDT dosage and ultimate efficacy are closely tied to therapeutic goals. In autoimmune diseases, the aim is to eliminate pathogenic B cells while preserving normal immune function; thus, low to moderate doses are often employed to achieve the “minimal immune reset threshold,” thereby minimizing side effects. In contrast, the treatment of hematologic malignancies requires deeper depletion of malignant B cells to prevent recurrence, typically requiring higher dosage intensities.

• CAR-T

For autoimmune diseases, typical CAR-T dosing ranges from 0.5×10^6 – 5×10^6 cells/kg, with immune reset effects often achievable at 1×10^6 cells/kg, sustaining remission for 3–6 months.

For B-cell lymphoma regimens—typically 2×10^6 – 5×10^6 cells/kg or even up to 200×10^8 cells per patient—to achieve profound depletion of malignant B cells in bone marrow and systemic tissues.

• Rituximab

For RA, the standard regimen contains 2 doses of 1000 mg administered 2 weeks apart, with clinical follow-up every 24 weeks to determine the need for retreatment based on disease activity.

For diffuse large B-cell lymphoma(DLBCL) or non-Hodgkin lymphoma(NHL), dosing is standardized at 375 mg/m² per week (approximately 600–700 mg weekly) for 4–8 weeks.

• TCE

No TCE has been formally approved for autoimmune diseases, though several clinical trials offer preliminary insights. For example, Blinatumomab was tested in RA patients at cumulative doses of 77 μg or 198 μg, with no significant safety concerns identified. For B-cell lymphoma, the typical regimen involves continuous infusion of 28 μg per day for 28 days, followed by a 14-day treatment-free interval, repeated for 4–9 cycles depending on disease subtype and clinical response.

CLN-978 achieved sustained peripheral B-cell depletion in cynomolgus monkeys with a single dose as low as 0.1 mg/kg. While in trials with B-cell lymphoma patients, dosing ranged from 30 μg weekly for 7–24 weeks.

These observations indicate that BCDT for autoimmune diseases typically requires only a fraction of the dose used in oncology, accompanied by a significantly lower incidence of adverse events—including CRS and ICANS. However, this also underscores the need to define the minimal depletion depth required for effective “immune reset” based on target specificity and drug characteristics, and to optimize dosing regimens accordingly. Inadequate dosing may lead to inadequate efficacy and disease relapse.

 

 

3. Data Highlights

Through studies in cynomolgus monkeys, humanized immune system mice, and other translational research, the relationships between dosing, clinical efficacy, and side effects of BCDT in autoimmune diseases are becoming increasingly clear. These investigations enable researchers to define dosing and administration regimens with greater precision, utilizing tools including flow cytometry, BCR sequencing, and autoantibody analysis to assess the depth of B-cell depletion and determine whether the goal of immune reset has been achieved. Furthermore, they help elucidate the relationship between depletion depth and adverse effects, providing critical data to inform the design of clinical trials.

PharmaLegacy has established robust platforms for immunophenotyping panels in humans and cynomolgus monkeys, in vitro functional assays, biomarker analysis, and pharmacokinetic evaluation, with flexible customization to support BCDT efficacy and PK/PD studies across species. Selected data are presented below:

• B cell subset depletion in cynomolgus monkeys

• Antigen recall response post-B cell depletion
  
• Human peripheral B cell subset and Killing assays

4. Conclusion

Looking ahead, through technological innovation, personalized medicine, and the application of combination therapies, BCDT holds promise for enhancing efficacy while further optimizing safety. As animal models and translational medical research continue to advance, the design of clinical trials for BCDT will become more scientifically robust, offering hope for sustained remission and cure for a greater number of patients.

PharmaLegacy has accumulated extensive experience in this field, leveraging advanced experimental platforms and a specialized team to drive innovation and development in BCDT. We warmly welcome collaborators across the industry to engage in related experimental and partnership opportunities, working together to deliver superior treatment options for patients.