SIRPγ-CD47 Interaction Positively Regulates the Activation of Human T Cells in Situation of Chronic Stimulation.

A numerous number of positive and negative signals via various molecules modulate T-cell activation. Within the various transmembrane proteins, SIRPγ is of interest since it is not expressed in rodents. SIRPγ interaction with CD47 is reevaluated in this study. Indeed, we show that the anti-SIRPγ mAb clone LSB2.20 previously used by others has not been appropriately characterized. We reveal that the anti-SIRPα clone KWAR23 is a Pan anti-SIRP mAb which efficiently blocks SIRPα and SIRPγ interactions with CD47. We show that SIRPγ expression on T cells varies with their differentiation and while being expressed on Tregs, is not implicated in their suppressive functions. SIRPγ spatial reorganization at the immune synapse is independent of its interaction with CD47. In vitro SIRPα-γ/CD47 blockade with KWAR23 impairs IFN-γ secretion by chronically activated T cells. In vivo in a xeno-GvHD model in NSG mice, the SIRPγ/CD47 blockade with the KWAR23 significantly delays the onset of the xeno-GvHD and deeply impairs human chimerism. In conclusion, we have shown that T-cell interaction with CD47 is of importance notably in chronic stimulation.

Selective SIRPα blockade reverses tumor T cell exclusion and overcomes cancer immunotherapy resistance.

T cell exclusion causes resistance to cancer immunotherapies via immune checkpoint blockade (ICB). Myeloid cells contribute to resistance by expressing signal regulatory protein-α (SIRPα), an inhibitory membrane receptor that interacts with ubiquitous receptor CD47 to control macrophage phagocytosis in the tumor microenvironment. Although CD47/SIRPα-targeting drugs have been assessed in preclinical models, the therapeutic benefit of selectively blocking SIRPα, and not SIRPγ/CD47, in humans remains unknown. We report a potent synergy between selective SIRPα blockade and ICB in increasing memory T cell responses and reverting exclusion in syngeneic and orthotopic tumor models. Selective SIRPα blockade stimulated tumor nest T cell recruitment by restoring murine and human macrophage chemokine secretion and increased anti-tumor T cell responses by promoting tumor-antigen crosspresentation by dendritic cells. However, nonselective SIRPα/SIRPγ blockade targeting CD47 impaired human T cell activation, proliferation, and endothelial transmigration. Selective SIRPα inhibition opens an attractive avenue to overcoming ICB resistance in patients with elevated myeloid cell infiltration in solid tumors.

Subretinal Injection of HY Peptides Induces Systemic Antigen-Specific Inhibition of Effector CD4+ and CD8+ T-Cell Responses.

Purpose: Injection of an antigen into the anterior chamber of the eye induces a peripheral antigen-specific immune modulation mechanism, known as anterior chamber-associated immune deviation (ACAID). Delayed-type hypersensitivity experiments argue that the subretinal space (SR) of the eye displays properties similar to ACAID. However, no investigation was performed regarding the differential impact of a subretinal antigen injection on peripheral CD4+ versus CD8+ T cells, on the potential immune deviation regarding Th profiles, and on the antigen-specificity of the inhibition. A better understanding of these mechanisms is crucial to improve safety and immunomonitoring of ongoing therapeutic approaches targeting the SR. The aim of this study is to characterize the proliferative capacities and cytokine patterns of antigen-specific CD4+ and CD8+ T cells after a subretinal injection of antigen in mice. Methods: Ubiquitously Transcribed tetratricopeptide repeat gene Y-linked (UTY) and DEAD Box polypeptide 3 Y-linked (DBY) peptides which respectively include MHCI- and MHCII-restricted T-cell epitopes of the mouse HY male antigen, were injected into the subretinal space of C57BL/6 female mice. 2 weeks later, these mice were immunized subcutaneously with these peptides and compared to control mice. A week later, T-cell immune responses were analyzed by IFNγ ELISpot assays and cytokine measurements (IL-2, IL-4, IL-6, IL-10, IL-13, IL-17a, IFNγ, TNFα, GM-CSF, and MCP-1) in the spleen and with proliferation assays in draining lymph nodes. Results: Immune cells from mice that received HY peptides in the SR before immunization, compared with those from control immunized mice, secreted significantly smaller quantities of Th1/Tc1, Th2/Tc2, and Th17/Tc17 cytokines, and HY-specific CD4+ T cells proliferated less in response to HY peptides. Conclusion: Taken together, our data clearly demonstrate that the subretinal injection of HY peptides induces a systemic HY-specific inhibition of conventional Th profiles and CD8+ T cells. We propose to call this phenomenon SRAII, for subretinal-associated immune inhibition.