PD1 and PDL1 upregulation and survival after decitabine treatment in lower risk MDS

Immunodepletion of MDSC by AMV564, a novel bivalent, bispecific CD33/CD3 T cell engager, ex vivo in MDS and melanoma

We have reported previously that CD33hi myeloid-derived suppressor cells (MDSCs) play a direct role in the pathogenesis of myelodysplastic syndromes (MDSs) and that their sustained activation contributes to hematopoietic and immune impairment, including modulation of PD1/PDL1. MDSCs can also limit the clinical activity of immune checkpoint inhibition in solid malignancies. We hypothesized that depletion of MDSCs may ameliorate resistance to checkpoint inhibitors and, hence, targeted them with AMV564 combined with anti-PD1 in MDS bone marrow (BM) mononuclear cells (MNCs) enhanced activation of cytotoxic T cells. AMV564 was active in vivo in a leukemia xenograft model when co-administered with healthy donor peripheral blood MNCs (PBMCs). Our findings provide a strong rationale for clinical investigation of AMV564 as a single agent or in combination with an anti-PD1 antibody and in particular for treatment of cancers resistant to checkpoint inhibitors.

S100A9-induced overexpression of PD-1/PD-L1 contributes to ineffective hematopoiesis in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are characterized by dysplastic and ineffective hematopoiesis that can result from aberrant expansion and activation of myeloid-derived suppressor cells (MDSCs) within the bone marrow (BM) niche. MDSCs produce S100A9, which mediates premature death of hematopoietic stem and progenitor cells (HSPCs). The PD-1/PD-L1 immune checkpoint impairs immune responses by inducing T-cell exhaustion and apoptosis, but its role in MDS is uncharacterized. Here we report an increased expression of PD-1 on HSPCs and PD-L1 on MDSCs in MDS versus healthy donors, and that this checkpoint is also activated in S100A9 transgenic (S100A9Tg) mice, and by treatment of BM mononuclear cells (BM-MNC) with S100A9. Further, MDS BM-MNC treated with recombinant PD-L1 underwent cell death, suggesting that the PD-1/PD-L1 interaction contributes to HSPC death in MDS. In accordance with this notion, PD-1/PD-L1 blockade restores effective hematopoiesis and improves colony-forming capacity in BM-MNC from MDS patients. Similar findings were observed in aged S100A9Tg mice. Finally, we demonstrate that c-Myc is required for S100A9-induced upregulation of PD-1/PD-L1, and that treatment of MDS HSPCs with anti-PD-1 antibody suppresses the expression of Myc target genes and increases the expression of hematopoietic pathway genes. We conclude anti-PD-1/anti-PD-L1 blocking strategies offer therapeutic promise in MDS in restoring effective hematopoiesis.

Leveraging Hypomethylating Agents for Better MDS Therapy

PURPOSE OF REVIEW

Myelodysplastic syndrome (MDS) is a clinically and molecularly heterogeneous disease, which primarily occurs in older adults. Although hypomethylating agents have survival benefit and are the current standard of care, many MDS patients will not garner a response from therapy. For those who do respond, most responses are not durable, and the only hope for a cure is allogeneic stem cell transplant. New therapies to improve outcomes are urgently needed.

RECENT FINDINGS

Clinical trials combining standard hypomethylating agents with novel experimental agents are underway in an effort to improve clinical outcomes in MDS patients. Several of these small molecules have demonstrated the ability to augment the response rates of hypomethylating agents alone, including complete remission rates, in both the front line and refractory settings. Combination approaches utilizing hypomethylating agents and novel-targeted therapies have demonstrated the ability to improve response rates in MDS patients in both the front line and salvage settings, and thus may change the standard of care.