Siglec-G represses DAMP-mediated effects on T cells
Tomomi Toubai, Corinne Rossi, Katherine Oravecz-Wilson, Cynthia Zajac, Chen Liu, Thomas Braun, Hideaki Fujiwara, Julia Wu, Yaping Sun, Stuart Brabbs, Hiroya Tamaki, John Magenau, Pang Zheng, Yang Liu, Pavan Reddy
Tomomi Toubai, Corinne Rossi, Katherine Oravecz-Wilson, Cynthia Zajac, Chen Liu, Thomas Braun, Hideaki Fujiwara, Julia Wu, Yaping Sun, Stuart Brabbs, Hiroya Tamaki, John Magenau, Pang Zheng, Yang Liu, Pavan Reddy
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Research Article Immunology Transplantation

Siglec-G represses DAMP-mediated effects on T cells

Abstract

The role of negative regulators or suppressors of the damage-associated molecular pattern–mediated (DAMP-mediated) stimulation of innate immune responses is being increasingly appreciated. However, the presence and function of suppressors of DAMP-mediated effects on T cells, and whether they can be targeted to mitigate T cell–dependent immunopathology remain unknown. Sialic acid–binding immunoglobulin-like lectin G (Siglec-G) is a negative regulator of DAMP-mediated responses in innate immune cells, but its T cell–autonomous role is unknown. Utilizing loss-of-function–based (genetic knockout) and gain-of-function–based (agonist) approaches, we demonstrate that in the presence of certain DAMPs, Siglec-G suppressed in vitro and in vivo T cell responses. We also demonstrate that its T cell–autonomous role is critical for modulating the severity of the T cell–mediated immunopathology, graft-versus-host disease (GVHD). Enhancing the Siglec-G signaling in donor T cells with its agonist, a CD24Fc fusion protein, ameliorated GVHD while preserving sufficient graft-versus-tumor (GVT) effects in vivo. Collectively, these data demonstrate that Siglec-G is a potentially novel negative regulator of T cell responses, which can be targeted to mitigate GVHD.

Authors

Tomomi Toubai, Corinne Rossi, Katherine Oravecz-Wilson, Cynthia Zajac, Chen Liu, Thomas Braun, Hideaki Fujiwara, Julia Wu, Yaping Sun, Stuart Brabbs, Hiroya Tamaki, John Magenau, Pang Zheng, Yang Liu, Pavan Reddy

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Figure 5

Siglec-G–CD24 interaction regulates DAMP-mediated donor T cell responses and enhancement of Siglec-G/CD24 axis mitigates GVHD.

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Siglec-G–CD24 interaction regulates DAMP-mediated donor T cell responses...
(A) Isolated CD90.2+ T cells from B6 WT were cultured with irradiated splenocytes from B6 WT, BALB/c WT or CD24–/– BALB/c animals for 72 hours in a mixed lymphocyte reaction (MLR) and analyzed for proliferation following 3H-thymidine incorporation during the last 6 hours of incubation. Unpaired t test. Data are shown as the mean ± SEM of quadruplicate cultures and are representative from 1 of 3 similar experiments. *P < 0.05 when B6 WT versus B6 CD24–/– antigen-presenting cells were compared. (B) Overall survival. Recipient BALB/c WT or BALB/c CD24–/– animals received 8.5 Gy on day –1 and were transplanted with splenic T cells along with T cell–depleted bone marrow (TCD-BM) cells from either syngeneic BALB/c or allogeneic MHC-mismatched B6 donors. n = 6–12 per group, pooled from 3 experiments. Kaplan-Meier method, *P < 0.05 when BALB/c WT versus BALB/c CD24–/– recipients were compared. (C) CD24Fc treatment increased phosphorylated (p) and total of SHP-1. Upper: A representative figure of immunoblot analysis of p-SHP-1 and total SHP-1 protein in lysates of donor T cells from untreated and treated animals at day 7 after allogeneic bone marrow transplantation (allo-BMT). Lower: The bar graph shows the ratio p-SHP-1/total SHP-1. Mann-Whitney U test, *P < 0.05. (D–F) BALB/c CD24–/– animals were lethally irradiated with 8.5 Gy and infused with 0.75 × 106 CD90.2+ T cells along with 5 × 106 TCD-BM cells from allogeneic MHC-mismatched B6 donors (D) or B6 Siglec-G–/– donors (E) or B6 CD24–/– donors (F). The recipients were injected with CD24Fc or diluent control on day 0 before allo-BMT. Kaplan-Meier method, *P < 0.05, when control diluent versus CD24Fc treatment animals were compared. n = 4–18 per group, pooled from 2 experiments. (G) Augmenting Siglec-G with CD24Fc improves tacrolimus-induced protection of experimental graft-versus-host disease (GVHD). BALB/c WT animals were lethally irradiated with 8.5 Gy and infused with 0.75 × 106 CD90+ T cells along with 5 × 106 TCD-BM cells from either syngeneic BALB/c WT or allogeneic MHC-mismatched B6 donors. The recipients were injected with CD24Fc (5 mg/kg) or diluent control on day 0 and treated with tacrolimus (0.005 mg/kg, i.p.) for 14 days. n = 6–15 per group, pooled from 3 experiments. Kaplan-Meier method, **P < 0.01, when control versus CD24Fc plus tacrolimus treatment group and *P < 0.05, when tacrolimus versus CD24Fc treatment groups were compared.