823P - The bone marrow immune ecosystem shapes acquired resistance to daratumumab in plasma cell myeloma

Background

Daratumumab (dara) is an effective therapy of plasma cell myeloma (PCM). However, most initial responders relapse or progress. The potential impact of changes in the bone marrow immune ecosystem are poorly-defined.

Methods

The cellular composition of the bone marrow immune ecosystem associated with loss of response to dara was identified using scRNA-seq and digital signal processing (DSP) technology and validated with PrimeFlow and in vitro and in vivo experiments.

Results

Operating strategy is shown(A). 7 populations of T-cells were identified. Percentage of GZMK⁺CD8⁺T-cells increased in acquired resistance samples(B). Subjects with a higher GZMK MFI expression in CD8⁺T-cells correlated with resistance but decreased in CR samples(C). 3 of the CD8⁺T-cell subsets had higher transcriptional signatures for cytotoxicity and exhaustion. CD8⁺T-cells had an increased exhausted and cytotoxic signature and decreased naïve signature upon recurrence(D). Expression levels of most checkpoint markers increased after acquiring resistance(E). We also analyzed B-cell, myeloid cell and NK-/NKT-cell alteration (not shown). 7 populations of plasma cells were identified. Compared with pre-therapy numbers of neoplastic plasma cells increased paralleling acquired resistance(F). Clusters 2, 5, 7 and 8 increased in numbers after acquiring resistance(G). GO/KEGG enrichment analysis showed the variations in different clusters(H). AoIs marked with CD138⁺ and CD45⁺ were included in the DSP analysis, evaluated and adjusted based on H&E and IHC staining (I). ssGSEA algorithm showed changes in signature in the cancer centre and margin regions(J). Persons with a high resistance plasma cell cluster 8 signature had poor survival in coMMpass cohort(K). We hypothesized IFN-γ produced by cytotoxic immune cells activates MYC associated with acquired resistance(L). IFN-γ exposure stimulated MYC expression and increased phosphorylation of MYC in PCM cell lines(M). MYC inhibitor MYCi975 reversed the resistance to dara(N). Synergistic effect of MYCi975 and dara was suggested and further validated by in vivo experiments(O).

Conclusions

Increased activation of MYC following anti-cancer stress may be an important mechanism promoting acquired dara resistance.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Sun Yat-sen University Start-Up Funding.

Disclosure

All authors have declared no conflicts of interest.