Harnessing Negative B Cell Selection to Overcome Drug-Resistance in Acute Lymphoblastic Leukemia
Bibliographic record
Abstract
Abstract Background: B cells are selected for an intermediate level of (pre-) B cell receptor (BCR) signaling strength: attenuation below minimum (e.g. non-functional BCR) or hyperactivation above maximum (e.g. autoreactive BCR) thresholds of signaling strength causes negative selection and cell death. About 25% of B cell acute lymphoblastic leukemia (ALL) is driven by oncogenic tyrosine kinases (e.g. BCR-ABL1 in Ph+ ALL), which mimics constitutively active pre-BCR signaling and defines the ALL subgroup with the worst clinical outcome. Currently more potent tyrosine kinase inhibitors (TKI) are developed for Ph+ ALL to suppress oncogenic signaling below a minimum threshold for survival. However Ph+ ALL cells invariably develop resistance against TKI. Here, we tested the hypothesis that targeted hyperactivation of oncogenic signaling above a maximum threshold will trigger B cell-inherent mechanisms of negative selection and selectively kill Ph+ALL cells. Results: The Ph+ ALL cells don not express a functional pre-BCR and BCR-ABL1 oncogene mimics a constitutively active pre-BCR by phosphorylating SYK, LYN, BTK and PLCg2. An incremental increase of pre-BCR downstream signaling (ITAM or SYK overexpression) was indeed sufficient to induce cell death in Ph+ ALL. TKI-treatment, while designed to kill leukemia cells, seemingly paradoxically rescued Ph+ALL cells in this experimental setting. Ph + ALL cells differ from normal pre-B cells by expression of high levels of ITIM containing inhibitory receptors including PECAM1 (CD31), CD300A and LAIR1. Importantly, high expression levels of ITIM-receptors are predictive of poor outcome in two clinical trials. In the COG trial (P9906; n=207) for children high-risk ALL, mRNA levels of PECAM1, CD300A and LAIR1at diagnosis positively correlated with early minimal residual disease (MRD) findings on day 29 (p<0.0005), and negatively correlated with overall survival (OS) rate (p<0.02) or relapse free survival (RFS) rate (p<0.05). In the ECOG trial (E2993; n=215) for adults ALL, PECAM1 mRNA level negatively correlated with OS rate (p=0.0285). Genetic studies revealed that Pecam1, Cd300a and Lair1 receptors are critical to calibrate pre-BCR signaling strength through recruitment of the inhibitory phosphatases Ptpn6 (SHP1) and Inpp5d (SHIP1). Deletion of Pecam1, Cd300a or Lair1 in Ph+ ALL cells caused increased ROS levels, G0/G1cell cycle arrest, decreased colony formation capacity and cellular senescence. Phosphorylation of pre-BCR downstream molecules (SYK, LYN, BTK and PLCg2) was increased after Lair1 deletion and this hyper-signaling could not be tolerated by Ph+ ALL cells. Lair1 deletion resulted in rapid leukemia regression and prolonged survival of recipient mice in a transplant experiment. Leukemia cell death caused by Lair1-deletion could be rescued by overexpression of the active inhibitory phosphatase Ptpn6 (CD8-SHP1) or Inpp5d (CD8-SHIP1). Genetic deletion of Ptpn6 and Inpp5d caused increased pre-BCR signaling and cell death in BCR-ABL1 ALL cells but not myeloid cells (normal and BCR-ABL1-transformed), which -unlike B cells- are not subject to negative selection of auto-reactive clones. Decreasing pre-BCR signaling by SYK inhibition rescued cell death after Ptpn6- or Inpp5d- deletion. Blocking inhibitory receptors by using chimeric PECAM1, CD300A and LAIR1 receptor decoys inhibited proliferation and caused cell death in Ph+ ALL xenograft cells. More potently, a novel small molecule inhibitor of INPP5D (SHIP1) selectively killed Ph+ ALL xenograft cells through inducing hyper pre-BCR signaling, regardless of TKI resistance. We demonstrate that inhibitory phosphatase signaling represents a potential novel class of therapeutic targets for Ph+ALL. Conclusions: These results indicated that inhibitory receptors and downstream phosphatases are critical regulators of pre-BCR signaling strength in Ph+ ALL, and identified ITIM-receptors and phosphatases as members of a potential novel class of therapeutic targets. The concept of pharmacological perturbance of oncogenic signaling equilibrium in leukemia cells by inhibition (e.g. TKI-treatment) or exaggeration of signaling strength (e.g. blockade of ITIM-receptors) may lead to the discovery of multiple additional therapeutic targets and broaden our repertoire of currently available therapeutic intervention. Disclosures No relevant conflicts of interest to declare.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".