A Novel Approach to Achieve Long-Lasting Antitumor Immunity in Multiple Myeloma

Background: A dysfunctional innate and adaptive immune system plays a vital role in the evolution of multiple myeloma (MM). Immune checkpoints (ICs) inhibition is considered revolutionary antitumor immunotherapy; however, the toxicity of this approach, namely infections and autoimmune conditions, precluded its further development in MM (Usmani et al., 2018; Jelinek et al., 2018). The intricate immune suppressive microenvironment, including macrophage-suppressed "Don't eat me” signal with overexpression of CD47 on myeloma cells, adds challenges to IC therapy (Jiang et al., 2021). Mounting evidence has shown that the CD47-SIRPα immune checkpoint pathway plays an essential role in tumor immune evasion and innate immunotherapy (Li et al., 2021). However, targeting CD47 with a monospecific antibody approach is challenging due to hematological antigen sink and toxicity due to widespread expression of CD47, especially in red blood cells (Advani et al., 2018). The novel combination therapies using multi-target ICs blockades with better efficacy and less toxicity are unmet need to enhance innate and adaptive immunity in MM. CD84 is a self-adhesion immunoreceptor of the CD2 family and is expressed on myeloid cells, monocytes/macrophage populations, T-cells, and cancer cells (Sintes et al., 2010; Gunes et al., 2021).

Methods and Results: We found a significant elevation of CD84 expression on monocyte/macrophage populations in MM patients compared to that in healthy donors (HDs). According to a publicly available gene data set, CD84 expression positively correlates with monocyte/macrophage infiltration in bone marrow (BM) of monoclonal gammopathy of undetermined significance (MGUS) patients (n=131) and MM patients (n=354), suggesting that CD84 can be a potential target to enhance innate immunity via macrophages phagocytosis in MM. We also noted that CD47 expression was significantly upregulated in MGUS (n=44, **P < 0.01) and MM patients (n=12, **P < 0.01) compared to that in healthy individuals (n=22). We detected a profound CD84 expression on the surface of CD80+ M1- and CD163+ M2-like macrophages differentiated from isolated CD14+ monocytes derived from peripheral blood (PB) of HDs (n=3). We next assessed the impact of anti-CD84 (B4) monoclonal antibody (mAb) on the phagocytosis of myeloma cells by coculturing GFP+/Luc+ MM.1S cells with human CD80+ M1-like macrophages (n=3, ***P < 0.001) and CD11b+, F4/80+ mouse M0 BM-derived macrophages (BMDMs) (n=3, **P < 0.01). Strikingly, we found that CD84 regulates the signal regulatory protein α (SIRPα), which can contribute to the regulation of macrophage phagocytosis. While activation of CD84 with an agonist anti-CD84 mAb increased SIRPα surface expression on CD11b+, F4/80+ M0 BMDMs derived from healthy NSG mice (n=3, **P < 0.01), B4 treatment reduced SIRPα surface expression on the peritoneal CD11b+, F4/80+ M0 macrophages in CD45+ immune cells derived from the tumors of engrafted NSG mice with GFP+/Luc+ MM.1S (n=3, **P < 0.01). Moreover, our data showed that CD47-blocking mAb induced phagocytosis of MM cells in a coculturing setting with CD11b+, F4/80+ mouse M0 BMDMs and GFP+/Luc+ RPMI-8226 cells (n=3, *P < 0.05). To test the efficacy of the anti-CD47 mAb in vivo, we first performed a pilot study by engrafting GFP+/Luc+ RPMI-8226 cells subcutaneously (s.q.) into NOD-scid IL2rγ^null mice. With 4-week treatment, anti-CD47 mAb considerably decreased tumor growth compared to that in the control group (n=5). To assess the therapeutic potential of B4 mAb in combination with the anti-CD47 mAb in a small study, GFP+/Luc+ MM.1S were s.q. transplanted into NOD-scid IL2rγ^null mice. Two weeks after the engraftment, the mice were treated with a low dose of B4 mAb (1mg/kg) via intravenously (i.v.) injections, anti-CD47 mAb (5mg/kg) intraperitoneal (i.p.) injections, or a combination of B4 (1mg/kg, i.v.) and anti-CD47 (5mg/kg, i.p.) mAbs, twice a week. After a total of eight-dose treatment, the combination treatment showed significantly decreased tumor growth compared with the other treatment groups (n=3, **P < 0.01).

Conclusion: Overall, our preliminary data indicate innate and adaptive immunity can be concurrently enhanced by blocking the CD47-SIRPα axis with B4 and anti-CD47 mAbs combination and reducing T-cells exhaustion with B4 mAb treatment. This combination strategy can be an effective novel approach to achieving long-lasting antitumor immunity in MM.

Janakiram:Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Feng:Innovent Biologics: Consultancy. Rosen:January Biotech: Current holder of stock options in a privately-held company; Exicure: Current holder of stock options in a privately-held company; Pepromene Bio, Inc: Current holder of stock options in a privately-held company; Pepromene Bio, Inc: Membership on an entity's Board of Directors or advisory committees; NeoGenomics: Membership on an entity's Board of Directors or advisory committees; Verastem, Inc: Consultancy; Trillium Therapeutics, Inc: Consultancy; PharmaGene, LLC: Consultancy; Apobiologix/Apotex Inc: Consultancy; Exicure: Consultancy; Pheromone Bio, Inc: Consultancy; Trillium Therapeutics: Current holder of stock options in a privately-held company.