# Re-designing anti-CD20 monoclonal antibody therapy using novel insights into limitations of innate immune cytotoxicity

> **NIH NIH R21** · UNIVERSITY OF ROCHESTER · 2022 · $215,985

## Abstract

Project Summary
 Unconjugated monoclonal antibodies (mAbs) are highly effective but non-curative targeted therapies for
B cell malignancies. The Bruton tyrosine kinase inhibitor (BTKi) ibrutinib improved outcomes but does not cure
chronic lymphocytic leukemia (CLL), the most prevalent lymphoid malignancy in the USA. Ibrutinib mobilizes
CLL cells into the circulation where they are highly sensitive to mAb targeting CD20 (αCD20 mAb). However,
addition of standard doses of the αCD20 mAb rituximab (RTX) to ibrutinib showed no benefit in clinical trials.
Studies by us and others suggest that limited innate immune cytotoxic capacity, decreased CLL cell CD20 after
standard dose αCD20 mAb therapy, and inhibition of RTX induced cytotoxicity by off-target effects of ibrutinib
are largely responsible for this negative outcome. We propose that these data on the mechanisms of action of
αCD20 mAb and BTKi can be used to improve combination targeted therapy.
 We and others have shown that activating antibody dependent cellular phagocytosis (ADCP) by fixed
macrophages is the primary mechanism of action of αCD20 mAb. We then showed that initially rapid
engulfment of target lymphocytes during ADCP (< 1h) is followed by a prolonged pause of ~ 24h (hypophagia)
which limits innate immune cytotoxic capacity. In addition, standard dose αCD20 mAb therapy induces
sufficient non-lethal removal of B-cell membrane CD20-αCD20 mAb immune complexes from circulating CLL
cells by immune effector cells (trogocytosis) to cause drug resistance. mAb activity against malignant B cells in
lymphoid tissue is limited by slow tissue penetration by these large molecules, limited innate immune cytotoxic
capacity, and microenvironment support. Ibrutinib can mobilize lymphoid tissue resident CLL cells into the
circulation where they are sensitive to αCD20 mAb mediated cytotoxicity. Unfortunately, ibrutinib also inhibits
mAb mediated cellular cytotoxicity including ADCP by off-target effects. In contrast the more specific BTKi
acalabrutinib mobilizes CLL cells into the circulation without inhibiting macrophage mediated ADCP.
 Using these data, we have repurposed RTX in a novel high frequency low dose regimen with
acalabrutinib for initial treatment of patients with CLL. The regimen is being tested in a fully enrolled (n=38)
clinical trial funded by Acerta/AstraZeneca (ClinicalTrials.gov NCT03788291). We are requesting funding to
perform the correlative studies required to determine if this design is achieving the stated goals: 1) Determine
if sequential low dose RTX can achieve maximum clearance of circulating CLL cells and 2) Determine
the effect of acalabrutinib on sensitivity of CLL cells to RTX induced cytotoxicity. Data generated by
these studies are essential for designing future clinical trials to test strategies to optimize treatment efficacy,
tolerance, convenience and accessibility at lower cost. A potential triplicate therapy of HFLD αCD20 mAb, BTK
and BCL2 inhibitors could result ...

## Key facts

- **NIH application ID:** 10511323
- **Project number:** 1R21CA267040-01A1
- **Recipient organization:** UNIVERSITY OF ROCHESTER
- **Principal Investigator:** Clive Steven Zent
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $215,985
- **Award type:** 1
- **Project period:** 2022-07-01 → 2024-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10511323

## Citation

> US National Institutes of Health, RePORTER application 10511323, Re-designing anti-CD20 monoclonal antibody therapy using novel insights into limitations of innate immune cytotoxicity (1R21CA267040-01A1). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10511323. Licensed CC0.

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