Extranodal dissemination of non-Hodgkin lymphoma requires CD47 and is inhibited by anti-CD47 antibody therapy

Abstract

Non-Hodgkin lymphoma (NHL) presents as both localized and disseminated disease with spread to secondary sites carrying a worse prognosis. Although pathways driving NHL dissemination have been identified, there are few therapies capable of inhibiting them. Here, we report a novel role for the immunomodulatory protein CD47 in NHL dissemination, and we demonstrate that therapeutic targeting of CD47 can prevent such spread. We developed 2 in vivo lymphoma metastasis models using Raji cells, a human NHL cell line, and primary cells from a lymphoma patient. CD47 expression was required for Raji cell dissemination to the liver in mouse xenotransplants. Targeting of CD47 with a blocking antibody inhibited Raji cell dissemination to major organs, including the central nervous system, and inhibited hematogenous dissemination of primary lymphoma cells. We hypothesized that anti-CD47 antibody-mediated elimination of circulating tumor cells occurred through phagocytosis, a previously described mechanism for blocking anti-CD47 antibodies. As predicted, inhibition of dissemination by anti-CD47 antibodies was dependent on blockade of phagocyte SIRPα and required macrophage effector cells. These results demonstrate that CD47 is required for NHL dissemination, which can be therapeutically targeted with a blocking anti-CD47 antibody. Ultimately, these findings are potentially applicable to the dissemination and metastasis of other solid tumors.

Figure 1

Dissemination of NHL is dependent on CD47. (A) Raji cells were transduced with lentiviruses encoding shRNA CD47 knockdown constructs (shCD47) or a GFP control, and CD47 protein expression was determined by flow cytometry. (B) Relative CD47 expression levels were quantified by comparing mean fluorescence intensity with wild-type Raji cells. (C) Raji cells from panels A and B were transplanted subcutaneously into the right flank of adult NSG mice and monitored weekly for tumor growth. Representative mice are shown 28 days after transplantation with flank tumors demarcated (red box). (D) Tumor volume was quantified for all mice (n = 5 per cohort), demonstrating reduced growth from shCD47-1,2–transduced cells compared with GFP control. Statistical comparison was performed using a 2-way ANOVA. Data are mean ± SD. (E) Posttransplantation day 28, these mice were killed and analyzed for the number of gross liver metastases with representative mice shown (livers are shown in right panels). Direct invasion from the primary tumor (black arrows) to adjacent organs was not observed. (F) Number of liver metastases was quantified for all mice, with each data point representing an individual mouse. P values were calculated by Student t test: **P < .005. ***P < .0005.

Figure 2

A blocking anti-CD47 antibody inhibits formation of extranodal disease in Raji-engrafted mice. (A) Luciferase-labeled Raji cells were transplanted subcutaneously into the right flank of NSG mice. One week later, mice were administered daily therapy with 200 μg anti-CD47 antibody or mouse IgG control. Tumor volume was measured until end of treatment (posttransplantation day 28). Anti-CD47 antibody treatment reduced tumor volume compared with IgG control. ***P < .0001 (2-way ANOVA). (B) These mice were analyzed in parallel for the presence of luciferase-positive disease to assess tumor dissemination. Spread of disease to secondary sites (red arrows) was detected in IgG control-treated mice 3 weeks after transplantation, whereas no dissemination was observed in anti-CD47 antibody-treated mice. Representative mice are shown (n = 6 per treatment group). (C) Analysis of tumor lesions was performed by MRI at 3 weeks after transplantation, demonstrating tumor nodules (red circles) in controls, but not in mice treated with anti-CD47 antibody. The table reports the number of tumor nodules observed for each mouse, as assessed by a blinded-clinically trained radiation oncologist. (D) Mice were then killed and assessed for gross lesions, which demonstrated diffuse liver involvement in representative mice treated with control IgG, but not with anti-CD47 antibody.

Figure 3

A blocking anti-CD47 antibody inhibits dissemination of Raji cells to multiple major organs. Mice engrafted subcutaneously with Raji cells and treated with either IgG control (A) or anti-CD47 antibody (B; from Figure 2) were killed after 1 month, and major organs were analyzed for dissemination of human lymphoma by H&E staining. Lymphoma dissemination was observed in several major organs of IgG control-treated mice as demonstrated by invasion of monomorphic lymphoma cells and disruption of normal cellular architecture. (A) Red asterisks indicate areas of lymphoma invasion. (B) No evidence of human lymphoma was observed in anti-CD47 antibody-treated mice. (C) Human lymphoma organ invasion was assessed by a blinded pathologist. The number of mice with disseminated lymphoma in each organ is indicated.

Figure 4

Anti-CD47 antibody inhibits hematogenous dissemination of primary human NHL. (A) NSG mice were transplanted subcutaneously with bulk cells from a primary human DLBCL patient (NHL7, supplemental Table 1). Mice with a palpable mass (3 weeks after transplantation) were treated with daily injections of control IgG or anti-CD47 antibody for 11 days. Anti-CD47 antibody treatment had no effect on decreasing tumor volume compared with control IgG (P = .49, 2-way ANOVA). Data are mean ± SD. The presence of human CD45⁺CD19⁺ lymphoma cells in the bone marrow (B-C) and peripheral blood (D) of these mice after treatment (treatment day 11, posttransplantation day 32) was analyzed by flow cytometry. (C-D) Statistical analysis was calculated by Fisher exact test measuring engraftment versus no engraftment. ***P < .0005.

Figure 5

CD47 expression is increased on disseminated lymphoma cells compared with primary lesions. (A) DLBCL cells from patient sample NHL7 were engrafted subcutaneously into NSG mice where they eventually disseminated to the bone marrow. Three weeks after transplantation, engrafted human lymphoma cells from the primary subcutaneous injection site and from secondary bone marrow disease were profiled for CD47 expression by flow cytometry (representative plot shown). CD47 expression was analyzed on human CD45⁺CD19⁺ cells. (B) CD47 expression was increased on lymphoma cells from the primary engraftment site compared with bone marrow metastases (P = .026, t test) when a panel of engrafted mice was profiled (n = 3 in each group). Data are mean ± SD. (C) When analyzing a panel of NHL patient samples, CD47 protein expression was increased on lymphoma cells from peripheral blood compared with lymph node. Normalized mean expression (and range) was determined for lymph node 584.0 (229.5-1142.0) and peripheral blood 1234.0 (745.0-1556). Each symbol represents a distinct NHL sample (supplemental Table 1). *P < .05. ***P < .0005.

Figure 6

Anti-CD47 antibody inhibits chemokine-mediated migration of lymphoma but does not affect integrin-mediated adhesion. (A) Raji cells engineered with reduced CD47 expression levels (as in Figure 1) were assessed in a transwell migration assay with chemokines, either human SDF-1α (10nM) or CXCL13 (1 μg/mL) for 3 hours at 37°C. (B) Wild-type Raji cells were preincubated with the indicated antibodies at 10 μg/mL for 20 minutes and then assessed in a transwell migration assay for 3.5 hours at 37°C with the indicated chemokine. (A-B) The percentage of migrating cells relative to input was determined. Experiments were performed in duplicate and repeated. (C) Raji cell subclones were incubated on plates coated with human VCAM at 1 μg/mL unless indicated (VCAM negative = BSA-coated plates). (D) Raji cells were incubated in similar conditions to panel C with the indicated antibodies at 10 μg/mL. Adhesion of cells was determined by measuring absorbance at 490 nm, and relative absorbance to BSA-coated plates is shown ± SEM. No differences in VCAM-coated conditions were observed in either panel C or D. *P < .05 (t test). **P < .01 (t test). ***P < .005 (t test). ****P < .0001 (t test).

Figure 7

Inhibition of lymphoma dissemination by anti-CD47 antibody requires macrophages and blockade of SIRPα. (A) Subcutaneously engrafted DLBCL mice with palpable flank tumors (3 weeks after transplantation) were treated with control IgG or anti-CD47 antibody for 11 days in the presence of liposomal clodronate or liposomal control. Tumor volume was assessed and indicated that clodronate administration partially abrogated anti-CD47 antibody-mediated reduction in tumor volume compared with control (P = .25). No difference was observed between clodronate and liposomal control administration in control IgG-treated mice (P = .62). In mice treated with liposomal control, anti-CD47 antibody partially reduced tumor volume compared with control IgG treatment, but this difference was not statistically significant (P = .49). Statistical analysis was conducted with a 2-way ANOVA test. (B-C) The presence of lymphoma in the bone marrow (B) and peripheral blood (C) of anti-CD47 antibody-treated mice was assessed in respective treatment cohorts. Lymphoma dissemination to the bone marrow and peripheral blood was observed in anti-CD47 antibody-treated mice receiving clodronate macrophage depletion, but not in controls. Statistical analysis was conducted with Fisher exact test. Each treatment group consisted of 3 or 4 mice. (D) Luciferase-labeled Raji cells were coated ex vivo with the indicated primary antibodies, labeled with a fluorescently conjugated secondary antibody, and analyzed for binding by flow cytometry. (E) Raji cells incubated ex vivo with the indicated antibodies were transplanted intravenously into adult NSG mice. One week later, mice were analyzed by bioluminescent imaging for engraftment, and representative mice are shown. (F) The luciferase signal was determined for a cohort of mice transplanted with ex vivo antibody-coated cells where each point represents a single mouse. Blocking anti-CD47 (B6H12.2) antibody inhibited tumor engraftment compared with the nonblocking anti-CD47 (2D3) antibody and antibody controls. Statistical analysis was conducted with Fisher exact test. Data are mean ± SD. *P < .05. **P < .005. ***P < .0005.