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1883 Long-Term Follow-up and T Cell Characteristics of Patients with ASXL1-Mutated Relapsed or Refractory MDS or CMML Treated with Guadecitabine and Atezolizumab

Program: Oral and Poster Abstracts
Session: 637. Myelodysplastic Syndromes – Clinical and Epidemiological: Poster I
Hematology Disease Topics & Pathways:
MDS, Chronic Myeloid Malignancies, CMML, Diseases, Myeloid Malignancies
Saturday, December 9, 2023, 5:30 PM-7:30 PM

Casey L. O'Connell, MD1, Maria R. Baer, MD2,3, Vu H. Duong, MD, MS2,3, Andreas Due Ørskov, MD, PhD4,5,6,7*, Jakob Werner Hansen, MD, PhD4,5,6*, Sunil Kumar Saini, PhD8*, Denice Tsao-Wei, MS9*, Justin Cheng10*, Peter A. Jones, PhD, DSc11* and Kirsten Grønbæk, MD, DMSc4,5,6,7

1Jane Anne Nohl Division of Hematology, Department of Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA
2Department of Medicine, University of Maryland School of Medicine, Baltimore, MD
3University of Maryland Greenebaum Comprehensive Cancer Center, Baltimore, MD
4Department of Hematology, Rigshospitalet, Copenhagen, Denmark
5Biotech Research and Innovation Centre, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
6The Danish Stem Cell Center (Danstem), Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
7Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
8Department of Health Technology, Section of Experimental and Translational Immunology, Technical University of Denmark, Kgs. Lyngby, AL, DNK
9Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles
10Keck School of Medicine of USC, Los Angeles, CA
11Department of Epigenetics, Van Andel Institute, Grand Rapids, MI


Treatment of patients with myelodysplastic syndrome (MDS) or chronic myelomonocytic leukemia (CMML) after failure of a hypomethylating agent (HMA) remains an unmet need. We and others demonstrated a modest overall response rate (ORR) to the combination of immune checkpoint inhibition (ICI) and an HMA in such patients; a promising overall survival (OS) compared to historical data (5-6 months) was seen in some, but not all, studies. Our study and that of Daver et al. suggested that patients with ASXL1 mutations, in particular, may benefit from the addition of ICI.

We conducted a Phase I/II clinical trial evaluating the addition of a programmed death ligand 1 (PD-L1) inhibitor, atezolizumab, to a subcutaneous prodrug of the HMA decitabine, guadecitabine. We evaluated the presence of common driver mutations in CD3- bone marrow mononuclear cells (BMMC) and CD3+ T lymphocytes. Among 27 tested patients, 12 had the ASXL1 mutations in the myeloid compartment and, of those, 5 patients’ T cells carried the exact same mutation at a variant allele frequency (VAF) of >10%. Both patients with complete remission in the study (n=2) carried the mutation in both compartments (co-mutated) and median OS was significantly better for co-mutated patients (not reached) than for those with CD3- BMMC (myeloid) mutations (9.5 months) or wild type ASXL1 (16.5 months). Herein we report long-term follow-up of this cohort of patients, along with T cell programmed death-1 (PD-1) expression analyzed based on mutational status.


Details of the trial design and correlative plan are published. In the published study we used a VAF cutoff of 2% (1% for TP53) for BMMC and 10% for CD3+ T lymphocytes for the panel of 40 commonly mutated genes. In the current study we also evaluated patients with a T cell ASXL1 VAF of 5-10%. Patients have been followed for progression and survival every 6 months. Demographic and disease characteristics and outcome data were compared based on ASXL1 mutation status. Previously obtained T lymphocyte PD-1 expression data from samples obtained pre-treatment (PRE), during cycle 2 (EARLY) and after cycle 3 or 4 (LATE) were analyzed based on ASXL1 mutation status.


Among 27 patients from 4 centers with DNA available for genetic analysis, 15 had no ASXL1 mutation (ASXL1 WT), 5 had ASXL1 mutations restricted to the myeloid lineage, and 7 had ASXL1 mutations in both the myeloid and T-cell populations (ASXL1 co-mutated). Two co-mutated patients had T cell VAFs of 5-10% and 5 had VAFs>10% (Figure 1). No baseline characteristic by ASXL1 mutational status was significantly associated with response to study treatment, though 6 of 7 co-mutated patients (vs 3/5 myeloid-only patients) had not responded to first-line HMA (refractory).

With a median follow-up time of 64.9 months, median survival times were 48.9 months (15.1, 64.9+) for co-mutated patients with T cell VAF >10%, 34.9 months (8.5, NR) for co-mutated patients including those with T cell VAF of >5%, 16.4 months (3.3, 27.3) for ASXL1 WT patients, and 9.5 months (2.1, 35) for myeloid-only patients (Figure 2). This was statistically significant after adjusting for age and ECOG performance status at study entry, diagnosis, baseline bone marrow blast percentage, and number of prior chemotherapy regimens using the likelihood ratio test from multivariate analysis for overall survival (P = 0.008).

Early treatment-induced upregulation of CD8+ T cell PD1 was observed in the ASXL1 WT, before returning to baseline levels. This upregulation was more pronounced in the ASXL1 co-mutated group beginning at a lower baseline and peaking at a higher MFI and was statistically significant (P = 0.0098). No significant treatment-induced change in PD-1 expression was noted in the myeloid-only subset.


In patients with relapsed or refractory MDS or CMML, the presence of an ASXL1 mutation in both myeloid and T lymphocyte compartments, as compared to WT or myeloid-only mutations, was associated with a significantly longer median OS when treated with the combination of ICI and HMA. Significant upregulation of PD-1 was noted in T lymphocytes from both wild-type and co-mutated patients. The effect of mutant ASXL1 on T cell responsiveness to ICI deserves further investigation; patients with ASXL1-mutated HMA-refractory myeloid malignancies may benefit from ICI.

Disclosures: O'Connell: Astex Pharmaceuticals, Inc: Other: Prior research support. Provision of drug for the study ; Genentech: Other: Prior research support. Provision of drug for the study . Baer: Abbvie (Inst): Research Funding; Kite, a Gilead company (Inst): Research Funding; Ascentage Pharma (Inst): Research Funding; FORMA Therapeutics (Inst): Research Funding; Takeda (Inst): Research Funding; Kura Oncology (Inst): Research Funding. Hansen: Bristol-Meyer Squibb: Honoraria. Jones: Zymo Corporation: Consultancy. Grønbæk: Kirsten Grønbæk received research support from Janssen and is on the advisory board of Nanexa and GSK.: Consultancy, Research Funding.

*signifies non-member of ASH