Summary: Anti-CD20 is the monoclonal antibody class targeting B-cell surface antigen CD20 to selectively deplete B cells. Since the first drug rituximab (Rituxan) entered lymphoma treatment in 1997, it evolved through next-gen obinutuzumab (Gazyva·~4x stronger B-cell depletion). Indications expanded from lymphoma → rheumatoid arthritis → multiple sclerosis → lupus (2026 FDA decision pending). With expanded recognition that B-cell-produced autoantibodies are central to autoimmunity mechanism, anti-CD20 targeted drugs are settling as the new standard for broad autoimmune diseases.

What Is CD20

CD20 (Cluster of Differentiation 20) is a membrane protein expressed on B-cell surfaces. Expressed mid-B-cell differentiation (pre-B to immediately before plasma cell), with these features:

Regulates B-cell calcium signaling
Involved in B-cell activation·proliferation
NOT expressed in plasma cells (antibody-producing cells)
NOT expressed in stem cells·precursor B cells

This expression pattern enables anti-CD20 drug safety — plasma cells already producing antibodies survive, only B cells that would produce new autoantibodies are depleted.

Mechanism — 4 Circuits

After binding to B cells, anti-CD20 antibodies deplete via 4 circuits:

1. ADCC (Antibody-Dependent Cellular Cytotoxicity):

NK cells·macrophages recognize antibody-tagged B cells → kill
Enhanced in next-gen anti-CD20 (obinutuzumab)

2. CDC (Complement-Dependent Cytotoxicity):

Complement system activation → membrane attack complex → B-cell lysis
Dominant in 1st gen (rituximab)

3. ADCP (Antibody-Dependent Cellular Phagocytosis):

Macrophages engulf tagged B cells
Gradual depletion effect

4. Direct Cell Death:

CD20 binding triggers B-cell apoptosis signaling
Enhanced in next-gen (obinutuzumab)

Evolution — From 1st-Gen to Next-Gen

1st-gen (Type I, chimeric or humanized):

Rituximab (Rituxan·1997): first anti-CD20, chimeric antibody
Ofatumumab (Arzerra·2009): humanized, binds different CD20 epitope
Ocrelizumab (Ocrevus·2017): multiple sclerosis

Next-gen (Type II, glycoengineered):

Obinutuzumab (Gazyva·2013): glycoengineered for ↑↑ ADCC
B-cell depletion efficiency: ~4x rituximab
Enhanced direct cell death effect

Aspect	1st gen (rituximab)	Next gen (obinutuzumab)
Class	Type I	Type II
ADCC	Moderate	Strong
CDC	Strong	Weak
Direct cell death	Weak	Strong
B-cell depletion	Baseline	~4x
Indications	Lymphoma·RA·MS	CLL·SLE (2026 FDA decision)

Indication Expansion — 30-Year Ladder

How anti-CD20 drug indications expanded:

1997 — Lymphoma (B-cell lymphoma)

Rituximab first approved for non-Hodgkin lymphoma
B cells themselves are the tumor → direct target

2006 — Rheumatoid Arthritis (RA)

First autoimmune indication
Methotrexate-insufficient patients
B cells produce rheumatoid factor (RF) → blockade

2010s — Multiple Sclerosis (MS)

Ocrelizumab approved for relapsing + primary progressive MS
B cells produce neural antigen antibodies → blockade
Paradigm shift in MS treatment

2026 — Lupus (SLE) Filing in Progress

Gazyva ALLEGORY phase 3 results (52-week 76.7% vs 53.5%)
FDA decision expected December 2026
First SLE B-cell targeted drug line in 30 years

Indications under research:

Autoimmune nephritis (anti-PLA2R-positive membranous nephropathy etc)
Neuromyelitis optica spectrum disorder (NMOSD)
Chronic inflammatory demyelinating polyneuropathy (CIDP)

Side Effects·Safety

Common side effects:

Infusion reactions: most common at first dose (managed with premedication)
↑ infection risk: respiratory·urinary
Hypogammaglobulinemia: immunoglobulin reduction with long-term use
Hepatitis B reactivation: chronic carrier pre-screening required
PML (progressive multifocal leukoencephalopathy): very rare but class warning

Female-specific considerations:

Women of childbearing potential: no use during pregnancy (B-cell depleted neonate risk)
Last dose recommended 6 months before pregnancy
Postpartum lactation safety still accumulating

Korean Status

Rituximab:

Lymphoma·CLL: standard 1st-line, insurance covered
RA·MS: specialty disease cost reimbursement
Autoimmune nephritis: off-label use

Obinutuzumab (Gazyva):

CLL: Korean MFDS approval, insurance covered
SLE indication under review for Korean introduction post-FDA approval

Pricing (Korea):

Rituximab (Mabthera): per cycle ₩24M (5% patient burden under specialty disease cost)
Obinutuzumab: per cycle ₩35M

FAQ

Q. Doesn’t depleting all B cells damage immunity? A. Plasma cells (already producing antibodies) are preserved, and new B cells continue to form in bone marrow. Recovery within 6~12 months after temporary B-cell depletion.

Q. Are autoantibodies really the cause in autoimmunity? A. Autoantibodies aren’t the direct cause in all autoimmune diseases, but in many (lupus·MS·RA·autoimmune nephritis), B cells play multiple roles including autoantibody production·antigen presentation·T-cell activation.

Q. Which is better, rituximab or obinutuzumab? A. Depends on indication. Lymphoma: both effective. Autoimmune: obinutuzumab expected to have stronger effect. Patient-specific decision.

Q. Does B-cell depletion affect vaccine immunity? A. Yes. Vaccines recommended 6 months before drug administration or after recovery. COVID·influenza·pneumococcal etc.

Q. If obinutuzumab is approved for SLE, can Korean patients use it? A. After FDA approval, Korean MFDS approval takes 1~~2 years. Insurance reimbursement another 1~~2 years. Meanwhile clinical trial or off-label use options.

Conclusion

Anti-CD20 B-cell depletion is the central class of autoimmune targeted therapy that expanded over 30 years from lymphoma → rheumatoid arthritis → multiple sclerosis → lupus. Next-gen obinutuzumab (Gazyva)‘s December 2026 FDA decision pending for SLE represents the first targeted drug line in 30 years for SLE treatment of women of reproductive age (90% of patients). B-cell autoantibody blockade is the molecular ladder of autoimmune precision medicine.

Anti-CD20 B-cell Depletion — The Central Circuit of Autoimmune·Lymphoma Targeting