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2050 The DNA Sensor AIM2 Determines B Cell Fate after BCR Activation in Chronic Graft-Vs-Host Disease

Program: Oral and Poster Abstracts
Session: 701. Experimental Transplantation: Basic and Translational: Poster I
Hematology Disease Topics & Pathways:
Research, Translational Research, GVHD, Immune Disorders, immune mechanism, Diseases, immunology, Biological Processes
Saturday, December 9, 2023, 5:30 PM-7:30 PM

Fahmin Basher, MD, PhD1, Jonathan Visentin, PharmD, PhD2*, Wei Jia, MD, PhD1*, Jonathan C Poe, PhD1*, Christina Sofian1*, Hsuan Su1*, Sonali Bracken, MD, PhD3*, Rachel Dicioccio4*, Itaevia Curry-Chisolm4*, Vincent T. Ho, MD5,6*, Vanja Sisirak, PhD7*, Mitchell Horwitz, MD8, Nelson J. Chao, MD1 and Stefanie Sarantopoulos, MD, PhD1

1Division of Hematologic Malignancies and Cellular Therapy, Department of Medicine, Duke University, Durham, NC
2Bordeaux University, Bordeaux, FRA
3Division of Rheumatology and Immunology, Department of Medicine, Duke University Medical Center, Durham, NC
4Division of Hematologic Malignancies and Cellular Therapy, Department of Medicine, Duke University Medical Center, Durham, NC
5Harvard Medical School, Boston, MA
6Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA
7ImmunoConcEpT, Bordeaux, FRA
8Adult Stem Cell Transplant Program, Division of Cellular Therapy, Department of Medicine, Duke University Medical Center, Durham, NC

Prevention and treatment of chronic graft-vs-host disease (cGVHD), a debilitating late immune toxicity in patients after allogeneic hematopoietic stem cell transplantation (allo-HCT), who are otherwise cured of hematological malignancies, remains a major challenge. T cells incite and promote cGVHD through coordinated T-B cell responses. Alloantibody production (Srinivasan et al, Blood 2012, Jin et al, Blood 2016) and aberrant B Cell Receptor (BCR) signaling (Allen et al, Blood 2014, Flynn et al, Blood 2015) play fundamental roles in the pathology of cGVHD. B cell-intrinsic pathways in cGVHD remain incompletely understood, limiting our therapeutic capacity for patients.

In a single cell RNA sequencing study, we found that transcript levels of the DNA sensor Absent in Melanoma 2 (AIM2) were significantly increased in CD27+ BCR-activated B cell clusters in circulating as well as in tissue-resident cGVHD B cells (Poe et al, JCI Insight 2023). After confirming AIM2 expression is restricted to the nucleus, we also previously showed that AIM2-expressing B cells were augmented after BCR and interferon-gamma (IFNγ) and/or Toll-like receptor (TLR)-7 or 9 stimulation (Visentin J, Blood 2022;140 Supp 1), suggesting a context-dependent role for AIM2 after allo-HCT.

Our new findings now afford the hypothesis that an AIM2-BCR signaling axis determines B cell fate after allo-HCT. To address this hypothesis, we first examined whether AIM2 modulates the promotion of antibody-secreting cells (ASCs) after BCR activation using a hapten-carrier immunization model. We compared numbers of hapten-specific ASCs from immunized WT and AIM2-KO mouse splenocytes using enzyme-linked immunosorbent spot (ELISPOT). We compared numbers of ASCs on day 3 post-immunization, when early germinal center (GC) formation is known to occur. We found that hapten-specific IgM ASCs were significantly increased in WT splenocytes compared to AIM2-KO (p=0.002). By contrast, when we looked at day 8, when mature GC formation and rapid ASC proliferation is known to occur, we found that AIM2-KO immunized mice had significantly lower numbers of hapten-specific IgM (p=0.005) and IgG (p=0.004) ASCs in AIM2-expressing mice (Figure 1a). Our results suggest a role for AIM2 in regulating the survival of short-lived plasmablast-like ASCs after high affinity antigen encounter and maturation of germinal centers.

To further investigate whether AIM2 affects expansion of GC-derived (GL7+CD95+) ASCs, we stimulated B cells purified from wildtype (WT) or global AIM2-deficient (AIM2-KO) mice in vitro with lipopolysaccharide (LPS) and IL-4 +/- BCR stimulation. We found that AIM2-deficient B cells, especially GC-like cell populations, expanded significantly in an anti-IgM concentration-dependent manner up to 12-fold (p=0.03) after 72 hr (Figure 1b). By contrast, B cell expansion was constrained in AIM2-sufficient B cells. This expansion was unlikely to be due to differences in proliferation alone, as we did not detect differential Ki67 expression in stimulated B cells with or without AIM2. Together, these data suggest a role for AIM2 in modulating BCR signaling.

Finally, we examined the role of AIM2 in BCR-mediated cell death after chronic antigen exposure using our previously described bone marrow transplant (BMT) model, where recipients of bone marrow and splenocytes (BM+Spl) exhibit cGVHD manifestations (Poe et al, JCI Insight 2018, Jia et al, Blood 2021). We have previously generated C57BL/6J mice with conditional deficiency of AIM2 only in B cells (AIM2fl/flMb1Cre/+, CKO), and used these in our BMT model as donors. At day 58 post BMT, we performed ex vivo stimulation of splenic B cells from BMT recipients. While B cells from CKO BM+Spl recipients expanded ex vivo in an anti-IgM concentration-dependent manner, B cells from AIM2-sufficient BM+Spl recipients demonstrated limited responsiveness ex vivo to BCR stimulation. This extends our in vitro observations by suggesting a role for AIM2 in B cell tolerance after chronic antigen exposure. Ongoing experiments will determine if B cell-intrinsic AIM2 contributes to cGVHD pathogenesis.

Thus far, our data reveal a novel role for AIM2 as a B cell survival checkpoint after BCR activation. Further delineation of context-dependent and synergistic AIM2-BCR signaling after allo-HCT will lead to strategies that block the development of cGVHD without adversely affecting anti-tumor activity.

Disclosures: Ho: Alexion: Consultancy; Omeros: Consultancy; Jazz: Consultancy, Research Funding; Allovir: Consultancy; CareDx: Research Funding. Horwitz: AbbVie: Consultancy; CareDx: Consultancy; Kadmon: Consultancy; Magenta: Consultancy; GamidaCell: Research Funding. Sarantopoulos: Incyte: Consultancy.

*signifies non-member of ASH